In recent years,many studies have focused on the effects of global climate warming and increased nitrogen deposition on the structure and function of grassland ecosystem.However,there are still significant uncertainti...In recent years,many studies have focused on the effects of global climate warming and increased nitrogen deposition on the structure and function of grassland ecosystem.However,there are still significant uncertainties in the response mechanism of stability of plant community biomass in alpine meadows of the Qinghai-Xizang Plateau,China to these two major climate factors.Given this,based on field control experiments,this study systematically evaluated the effects of different levels of climate warming(W0(no warming),W1(air temperature increased by 0.47℃ or soil temperature increased by 0.61℃),W2(air temperature increased by 0.92℃ or soil temperature increased by 1.09℃),W3(air temperature increased by 1.44℃ or soil temperature increased by 1.95℃)),nitrogen deposition(N0(0 kg N/(hm^(2)·a)),N16(16 kg N/(hm^(2)·a)),and N32(32 kg N/(hm^(2)·a))),and their interactions on plant community biomass and its temporal stability,and explored its potential regulatory mechanisms.The results showed that the biomass of total community,Gramineae,and dominant species increased significantly with increasing temperature,but the biomass of common and rare species decreased significantly.Nitrogen deposition also significantly promoted the biomass accumulation of community and gramineous plants.Under the treatment of W3N32,the biomass of plant community,Gramineae,and dominant species reached the highest values,indicating that there was a synergistic effect under this treatment.Structural equation model showed that increasing temperature significantly decreased the stability of plant community biomass by reducing the stability of grass and dominant species biomass and weakening species asynchronism.Interaction of increased nitrogen deposition and temperature increased the biomass fluctuation of grass functional group,thus amplifying its negative influence on community stability.More attention should be paid to the response and regulatory mechanisms of dominant species and functional groups under global climate change.This study provides a theoretical basis for revealing the stability maintenance mechanism of alpine grassland and also provides scientific support for the development of future grassland ecosystem management and assessment.展开更多
In recent decades, global climate change and overgrazing have led to severe degradation of alpine meadows. Understanding the changes in soil characteristics and vegetation communities in alpine meadows with different ...In recent decades, global climate change and overgrazing have led to severe degradation of alpine meadows. Understanding the changes in soil characteristics and vegetation communities in alpine meadows with different degrees of degradation is helpful to reveal the mechanism of degradation process and take the remediation measures effectively. This study analyzed the changes in vegetation types and soil characteristics and their interrelationships under three degradation degrees, i.e., non-degradation(ND),moderate degradation(MD), and severe degradation(SD) in the alpine meadows of northeastern Qinghai-Xizang Plateau, China through the long-term observation. Results showed that the aggressive degradation changed the plant species, with the vegetation altering from leguminous and gramineous to forbs and harmful grasses. The Pielou evenness and Simpson index increased by 24.58% and 7.01%,respectively, the Shannon-Wiener index decreased by 17.52%, and the species richness index remained constant. Soil conductivity, soil organic matter, total potassium, available potassium, and porosity declined.However, the number of vegetation species increased in MD. Compared with ND, the plant diversity in MD enhanced by 8.33%, 8.69%, and 7.41% at family, genus, and species levels, respectively. In conclusion,changes in soil properties due to degradation can significantly influence the condition of above-ground vegetation. Plant diversity increases, which improves the structure of belowground network. These findings may contribute to designing better protection measures of alpine meadows against global climate change and overgrazing.展开更多
Climate warming profoundly affects plant biodiversity, community productivity, and soil properties in alpine and subalpine grassland ecosystems. However, these effects are poorly understood across elevational gradient...Climate warming profoundly affects plant biodiversity, community productivity, and soil properties in alpine and subalpine grassland ecosystems. However, these effects are poorly understood across elevational gradients in subalpine meadow ecosystems. To reveal the elevational patterns of warming effects on plant biodiversity, community structure, productivity, and soil properties, we conducted a warming experiment using open-top chambers from August 2019 to August 2022 at high(2764 m a. s. l.), medium(2631 m a. s. l.), and low(2544 m a. s. l.) elevational gradients on a subalpine meadow slope of Mount Wutai, Northern China. Our results showed that three years of warming significantly increased topsoil temperature but significantly decreased topsoil moisture at all elevations(P<0.05), and the percentage of increasing temperature and decreasing moisture both gradually raised with elevation lifting. Warming-induced decreasing proportions of soil organic carbon(SOC, by 19.24%), and total nitrogen(TN, by 24.56%) were the greatest at high elevational gradients. Experimental warming did not affect topsoil C: N, p H, NO_(3)^(-)-N, or NH_(4)^(+)-N at the three elevational gradients. Warming significantly increased species richness(P<0.01) and Shannon-Weiner index(P<0.05) at low elevational gradients but significantly decreased belowground biomass(P<0.05) at a depth of 0–10 cm at three elevational gradients. Warming caused significant increases in the aboveground biomass in the three elevational plots. Warming significantly increased the aboveground biomass of graminoids in medium(by 92.47%) and low(by 98.25%) elevational gradients, that of sedges in high(by 72.44%) and medium(by 57.16%) elevational plots, and that of forbs in high(by 75.88%), medium(by 34.38%), and low(by 74.95%) elevational plots. Species richness had significant linear correlations with SOC, TN, and C: N(P<0.05), but significant nonlinear responses to soil temperature and soil moisture in the warmed treatment(P<0.05). The warmed aboveground biomass had a significant nonlinear response to soil temperature and significant linear responses to soil moisture(P<0.05). This study provided evidence that altitude is a factor in sensitivity to climate warming, and these different parameters(e.g., plant species richness, Shannon-Weiner index, soil temperature, soil moisture, SOC, and TN) can be used to measure this sensitivity.展开更多
Grazing exclusion is widely adopted in restoring degraded alpine grasslands on the Qinghai-Tibetan Plateau. However, its effectiveness remains poorly understood. In this study, we investigated the effects of grazing e...Grazing exclusion is widely adopted in restoring degraded alpine grasslands on the Qinghai-Tibetan Plateau. However, its effectiveness remains poorly understood. In this study, we investigated the effects of grazing exclusion on plant productivity, species diversity and soil organic carbon （SOC） and soil total nitrogen （STN） storage along a transect spanning from east to west of alpine meadows in northern Tibet, China. After six years of grazing exclusion, plant cover, aboveground biomass （AGB）, belowground biomass （BGB）, SOC and STN were increased, but species diversity indices declined. The enhancement of AGB and SOC caused by grazing exclusion was correlated positively with mean annual precipitation （MAP）. Grazing exclusion led to remarkable biomass increase of sedge species, especially Kobresia pygmaea, whereas decrease of biomass in forbs and no obvious change in grass, leguminous and noxious species. Root biomass was concentrated in the near surface layer （10 cm） after grazing exclusion. The effects of grazing exclusion on SOC storage were confined to shallow soil layer in sites with lower MAP. It is indicated that grazing exclusion is an effective measure to increase forage production and enhance soil carbon sequestration in the studied region. The effect is more efficient in sites with higher precipitation. However, the results revealed a tradeoff between vegetation restoration and ecological biodiversity. Therefore, carbon pools recover more quickly than plant biodiversity in the alpine meadows. We suggest that grazing exclusion should be combined with other measures to reconcile grassland restoration and biodiversitv conservation.展开更多
Potentilla fruticosascrub, Kobresia humilismeadow and Kobresia tibeticameadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-...Potentilla fruticosascrub, Kobresia humilismeadow and Kobresia tibeticameadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-GC method, a study on CO 2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO 2 emission rates from various treatments were 672.09±152.37 mgm -2 h -1 for FC (grass treatment); 425.41±191.99 mgm -2 h -1 for FJ (grass exclusion treatment); 280.36±174.83 mgm -2 h -1 for FL (grass and roots exclusion treatment); 838.95±237.02 mgm -2 h -1 for GG (scrub+grass treatment); 528.48±205.67 mgm -2 h -1 for GC (grass treatment); 268.97±99.72 mgm -2 h -1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm -2 h -1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilismeadow, Potentilla fruticosascrub meadow and Kobresia tibeticameadow differed greatly in average CO 2 emission rate of soil-plant system, in the order of GG>FC>LC>GC. Moreover, in Kobresia humilismeadow, heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosascrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from GG; 49% and 51% from GC. In addition, root respiration from Kobresia humilismeadow approximated 145 mgCO 2 m -2 h -1 , contributed 34% to soil respiration. During the experiment period, Kobresia humilismeadow and Potentilla fruticosascrub meadow had a net carbon fixation of 111.11 gm -2 and 243.89 gm -2 , respectively. Results also showed that soil temperature was the main factor which influenced CO 2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO 2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture may be the inhibitory factor of CO 2 emission from Kobresia tibeticameadow, and more detailed analyses should be done in further research.展开更多
Steller chamaejasme L. （S. chamaejasme for short） is one of the most noxious unpalatable weeds in China, which has been frequently reported its negative interaction （i.e. competition and allelopathy） with other he...Steller chamaejasme L. （S. chamaejasme for short） is one of the most noxious unpalatable weeds in China, which has been frequently reported its negative interaction （i.e. competition and allelopathy） with other herbaceous species in grasslands. This study compared species diversity, biomass and sexual reproduction of herbaceous plants in meadows with S. chamaejasme and in open meadows without S. ehamaejasme in overgrazing meadows on the Tibetan Plateau in China to determine whether positive facilitation exist between S. chamaejasme and other herbaceous species under livestock＇s overgrazing. The results showed that there are more herbaceous species in meadows with S. chamaejasme than those in open meadows （35s and30s, respectively）. Diversity index and above-ground biomass were also significantly higher in meadows with S. charnaejasme. There were 39% （11/28） of all species with sexual reproduction found in meadows with S. charnaejasme, which was 7 times more than those in open meadows. Our study showed that S. charnaejasme could provide biotic refuge for neighboring plants and preserve plant diversity from livestock＇s overgrazing in alpine meadows on the Tibetan Plateau. It also suggested that inter-specific facilitation between S. charnaejasme and other herbaceous species may play a key role in overgrazing alpine meadows.展开更多
[ Objective ] The paper was to understand the characteristics of plant communities in three kinds of typical alpine meadows in Haibei Region, Qinghai Province. [ Method] The characteristics and diversity of plant comm...[ Objective ] The paper was to understand the characteristics of plant communities in three kinds of typical alpine meadows in Haibei Region, Qinghai Province. [ Method] The characteristics and diversity of plant communities in typical alpine meadow, including Kobresia humilis, PotentiUafruticose and Kobresia menyuanica, were studied, with Menyuan studfarm in Haibei region of Qinghai Province as an example. [ Result] Results showed that the three kinds of plant communities in alpine meadows presented complex structure; the diversity index had close relationship with the evenness index; there were fewer common species and higher species replacement rate among different alpine meadow communities ; the aboveground biomass of K. humilis alpine meadow was 1.62 and 1.69 times of P. fruticose and K. menyuanica meadows, respectively; the underground biomass mainly distributed in the 0 - 10 cm soil layer, and the vertical spatial distribution structure was ＂T＂ type; the aboveground and underground biomass were negatively correlated. [ Conclusion] The paper will provide basis for protection and further use of different grassland plant communities in Haibei Region, Qinghai Province.展开更多
Alpine meadows of the Qinghai-Tibetan Plateau(QTP)are experiencing severe degradation due to intensified human activity and climate changes.However,there has been litle attention paid to the effects of different grazi...Alpine meadows of the Qinghai-Tibetan Plateau(QTP)are experiencing severe degradation due to intensified human activity and climate changes.However,there has been litle attention paid to the effects of different grazing practices on the soil hydrological properties of alpine meadows.In this study,three grazing practices were established in an alpine Kobresia meadow:free grazing,reduced grazing and grazing exclusion.We found that the 0-10 cm soil water retention capacity(SWR)and plant available water content(AWC)in grazing exclusion treatment were higher than that in reduced or free grazing treatments,whereas the 20-40 cm SWR and AWC display the opposite pattern.The AWC and SWR variations were closely related to soil properties,and the redundancy analysis showed that SWR and AWC were positive related to soil organic matter(SOM),total porosity(TP)and capillary porosity(CP),but were negative correlated with soil bulk density(BD),clay and silt content.Structural equation modeling found that SOM was identified as the most important factor affecting SWR,and CP was the key factor influencing AWC.Therefore,the higher O-10 cm SWR and AWC in grazing exclusion treatment may be attributed to its higher SOM and CP,respectively.Furthermore,root biomass can affect SWR and AWC through altering BD and SOM.Our study suggests that the response of soil hydrological properties to grazing practices was different,grazing exclusion only increase topsoil water retention capacity but not favor deep soil water retention capacity.展开更多
Global climate change is expected to have a signifcant impact on ecosystems worldwide,especially for alpine meadows which are considered as one of the most vulnerable components.However,the effects of global warming o...Global climate change is expected to have a signifcant impact on ecosystems worldwide,especially for alpine meadows which are considered as one of the most vulnerable components.However,the effects of global warming on the plant nitrogen-phosphorus stoichiometry and resorption in alpine meadows remain unclear.Therefore,to investigate the plant nitrogen-phosphorus stoichiometry and resorption in alpine meadows on the Qinghai-Tibet Plateau,we conducted an artifcial warming study using open-top chambers(OTCs)over the 3 years of warming period.We selected three dominant species,four height types of OTCs(0.4,0.6,0.8 and 1 m)and four warming methods(year-round warming,winter warming,summer-autumn-winter warming and spring-summer-autumn warming in the experiment)in this experiment.In our study,soil temperature signifcantly increased with increasing the height of OCTs under the different warming methods.Kobresia pygmaea presented an increase in nitrogen(N)limitation and Kobresia humilis presented an increase in phosphorus(P)limitation with increasing temperature,while Potentilla saundersiana was insensitive to temperature changes in terms of nitrogen and phosphorus limitations.Both nitrogen resorption effciency:phosphorus resorption effciency and N:P trends in response to rising temperatures were in the same direction.The differential responses of the chemical stoichiometry of the three species to warming were observed,refecting that the responses of nitrogen and phosphorus limitations to warming are multifaceted,and the grassland ecosystems may exhibit a certain degree of self-regulatory capability.Our results show that using chemical dosage indicators of a single dominant species to represent the nitrogen and phosphorus limitations of the entire ecosystem is inaccurate,and using N:P to refect the nutritional limitations might have been somewhat misjudged in the context of global warming.展开更多
Global climate change and overgrazing are driving shifts in the plant composition of grassland com-munities,which may profoundly affect the function of grassland ecosystems in regulating runoff and soil erosion.Here,w...Global climate change and overgrazing are driving shifts in the plant composition of grassland com-munities,which may profoundly affect the function of grassland ecosystems in regulating runoff and soil erosion.Here,we examined the shift effects of normal hillslope alpine meadow to shrub and severely degraded meadow states on runoff and sediment generation under natural rainfall conditions,and determined the contributions of plant and soil properties changes to soil erodibility,runoff and sediment generation by in situ rainfall experiment and monitoring on the hillslope of Qinghai-Tibetan Plateau.The results showed that normal meadow shift into severely degraded meadow state,mean weight diameter,soil saturated hydraulic conductivity,soil cohesion and soil erodibility K-factor at the topsoil decreased by 70.3%,73.1%,80.3%and-13.1%,respectively,and when normal meadows shift into shrub meadow state,they reduced by 49.1%,-1.3%,49.4%,and-8.3%,respectively.Runoff and soil loss significantly changed by-40.0%and 177.8%when normal meadow shifted into a severely degraded meadow state,while runoff and soil loss significantly changed by+65.0%and+77.8%when normal meadow shifted into a shrub meadow state.Our findings highlight that the two divergent shifts both increased soil loss compared to the normal hillslope alpine meadows.Overall,our results indicate that the divergent shifts of normal alpine meadows exacerbated soil erodibility and soil loss of hillslope alpine meadows.These results obtained here offer a novel perspective on the regulation of runoff and soil erosion in the alpine meadow ecosystem.展开更多
Surface soil cracking in alpine meadows signifies the transition of degradation from quantitative accumulation to qualitative deterioration.Quantitative research remains insufficient regarding changes in the mechanica...Surface soil cracking in alpine meadows signifies the transition of degradation from quantitative accumulation to qualitative deterioration.Quantitative research remains insufficient regarding changes in the mechanical properties of degraded meadow soils and the mechanical thresholds for cracking initiation.This study explored the relationships between surface cracking and the physical properties,tensile strength,and matrix suction of root-soil composites in alpine meadow sites with different stages of degradation(undegraded(UD),lightly degraded(LD),moderately degraded(MD),and heavily degraded(HD))under different water gradients(high water content(HWC),medium water content(MWC),and low water content(LWC))corresponding to different drying durations at a constant temperature of 40.0°C.The Huangcheng Mongolian Township in Menyuan Hui Autonomous County,Qinghai Province,China was chosen as the study area.The results indicated that as the degradation degree of alpine meadow intensified,both water content of rootsoil composite and the fine grain content of soil decreased.In contrast,the root-soil mass ratio and root area ratio initially increased and then decreased with progressive degradation.Under a consistent water content,the tensile strength of root-soil composite followed a pattern of MD>HD>LD>UD.The peak displacement of tensile strength also decreased as the degradation degree of alpine meadow increased.Both the tensile strength and matrix suction of root-soil composite increased as root-soil water content decreased.A root-soil water content of 30.00%-40.00%was found to be the critical threshold for soil cracking in alpine meadows.Within this range,the matrix suction of root-soil composite ranged from 50.00 to 100.00 kPa,resulting in the formation of linear cracks in the surface soil.As the root-soil water content continued to decrease,liner cracks evolved into branch-like and polygonal patterns.The findings of this study provide essential data for improving the mechanical understanding of grassland cracking and its development process.展开更多
Global warming leads to snow cover loss in the alpine ecosystem,exposing seeds to extreme diurnal temperature fluctuations during the growing season.The risk of freezing increases as seeds have increased moisture cont...Global warming leads to snow cover loss in the alpine ecosystem,exposing seeds to extreme diurnal temperature fluctuations during the growing season.The risk of freezing increases as seeds have increased moisture content.Studying the survival mechanisms of seeds at low temperatures can help analyze changes in alpine meadow populations and target conservation efforts.Here,we used three species of Poaceae as a model to understand freezing stress.Fully imbibed Elymus dahuricus,Festuca elata,and Lolium multiflorum seeds were subjected to programmed cooling at fast and slow rates(-1.0/0.05℃/min)and then assessed for survival.Differential Scanning Calorimetry was used to analyze thermal transitions during cooling.HE-stained paraffin sections and a Transmission Electron Microscope were employed to observe internal morphology and ultrastructural changes.E.dahuricus seeds exhibited greater tolerance to low temperatures than those of the other two species,with an LT_(50)of approximately-20℃for both cooling rates and maintained relatively intact ultrastructure.The observed the low-temperature exotherm(LTE)correlated with seed survival,with viability decreasing extensively below LTE.Fast cooling caused fewer changes to seed morphology and ultrastructure than slow cooling,suggesting that the primary survival mechanism during fast cooling is freezing avoidance through supercooling.Seeds exhibited greater freeze tolerance under slow than fast cooling,primarily by migrating intracellular water to extracellular spaces where it froze,causing considerable damage to cell ultrastructure and forming apparent cavities in some seeds.展开更多
Alpine meadows,alpine wetlands,and alpine desert steppes are the three typical vegetation types on the Qinghai-Tibet Plateau.The complex terrain and harsh climatic conditions across this region lead to considerable di...Alpine meadows,alpine wetlands,and alpine desert steppes are the three typical vegetation types on the Qinghai-Tibet Plateau.The complex terrain and harsh climatic conditions across this region lead to considerable diversification in the vegetation growth environment,resulting in substantial spatial heterogeneity in ecosystem carbon flux and its controlling mechanisms.Using eddy covariance data collected from March to August 2019,this study examined the responses of carbon and water fluxes in different ecosystems on the Tibetan Plateau to typical hydrometeorological factors,focusing on Net Ecosystem CO□Exchange(NEE)and Evapotranspiration(ET).The results indicate that:1)The Longbao alpine wetland primarily acted as a carbon sink from May to August,while serving as a carbon source from March to April.In the Maqin alpine meadow,it functioned as a carbon sink during June and July but acted as a carbon source in March,April,May,and August.The Tuotuohe alpine desert strppe was predominantly a net carbon sink from March to August.Overall,after the entire growing season(March to August),the Longbao alpine wetlands,Maqin alpine meadow,and Tuotuohe alpine desert steppe all showed net carbon sink properties,with net CO_(2)uptakes of 236.12 g/m^(2),291.45 g/m^(2),and 290.28 g/m^(2),respectively.2)The importance of meteorological factors to NEE varies with scale and ecosystem type,with global radiation(Rg)being the most critical factor influencing NEE variation.Volumetric soil water content(Soil_VWC)and soil temperature(Soil_T)had a positive effect on NEE at Maqin alpine meadow and Tuotuohe alpine desert steppe,while higher values of these variables showed a negative contribution.Furthermore,the sensitivity of NEE to Soil_T at Longbao alpine wetland and Tuotuohe alpine desert steppe was greater than its sensitivity to air temperature(Tair).3)The effect of Gross Primary Productivity(GPP)on NEE in alpine desert steppes is significantly greater than in alpine meadows.Both Ecosystem Respiration(Reco)and NEE were substantially limited by GPP,with 84%of GPP in alpine wetlands contributing to Reco and 16%to NEE;92%of GPP in alpine meadows contributing to Reco and 8%to NEE;and 40%of GPP in high-altitude desert grasslands contributing to Reco and 60%to NEE.4)The strong correlation between NEE and evapotranspiration suggests that water availability is the primary factor controlling changes in the carbon and water budgets of alpine ecosystems.展开更多
Aims Variations in vegetation spring phenology are widely attributed to temperature in temperate and cold regions.However,temperature effect on phenology remains elusive in cold and arid/semiarid ecosystems because so...Aims Variations in vegetation spring phenology are widely attributed to temperature in temperate and cold regions.However,temperature effect on phenology remains elusive in cold and arid/semiarid ecosystems because soil water condition also plays an important role in mediating phenology.Methods We used growing degree day(GDD)model and growing season index(GSI)model,coupling minimum temperature(T_(min))with soil moisture(SM)to explore the influence of heat requirement and hydroclimatic interaction on the start of carbon uptake period(SCUP)and net ecosystem productivity(NEP)in two alpine meadows with different precipitation regimes on the Qinghai-Tibet Plateau(QTP).One is the water-limited alpine steppe-meadow,and the other is the temperature-limited alpine shrub-meadow.Important Findings We observed two clear patterns linking GDD and GSI to SCUP:SCUP was similarly sensitive to variations in preseason GDD and GSI in the humid alpine shrub-meadow,while SCUP was more sensitive to the variability in preseason GSI than GDD in the semiarid alpine steppe-meadow.The divergent patterns indicated a balance of the limiting climatic factors between temperature and water availability.In the humid meadow,higher temperature sensitivity of SCUP could maximize thermal benefit without drought stress,as evidenced by the stronger linear correlation coefficient(R2)and Akaike’s information criterion(AIC)between observed SCUPs and those of simulated by GDD model.However,greater water sensitivity of SCUP could maximize the benefit of water in semiarid steppe-meadow,which is indicated by the stronger R2 and AIC between observed SCUPs and those of simulated by GSI model.Additionally,although SCUPs were determined by GDD in the alpine shrub-meadow ecosystem,NEP was both controlled by accumulative GSI in two alpine meadows.Our study highlights the impacts of hydroclimatic interaction on spring carbon flux phenology and vegetation productivity in the humid and semiarid alpine ecosystems.The results also suggest that water,together with temperature should be included in the models of phenology and carbon budget for alpine ecosystems in semiarid regions.These fi ndings have important implications for improving vegetation phenology models,thus advancing our understanding of the interplay between vegetation phenology,productivity and climate change in future.展开更多
From 30 June to 24 September in 2003 ecosystem respiration （Re） in two alpine meadows on the Tibetan Plateau were measured using static chamber- and gas chromatography- （GC） based techniques. Simultaneously, plant...From 30 June to 24 September in 2003 ecosystem respiration （Re） in two alpine meadows on the Tibetan Plateau were measured using static chamber- and gas chromatography- （GC） based techniques. Simultaneously, plant removal treatments were set to partition Re into plant autotrophic respiration （Ra） and microbial heterotrophic respiration （Rh）. Results indicated that Re had clear diurnal and seasonal variation patterns in both of the meadows. The seasonal variability of Re at both meadow sites was caused mainly by changes in Ra, rather than Rh. Moreover, atthe Kobresia humilis meadow site （K_site）, Ra and Rh accounted for 54% and 46% of Re, respectively. While at the Potentilla fruticosa scrub meadow （P_site）, the counterparts accounted for 61% and 39%, respectively. T test showed that there was significant difference in Re rates between the two meadows （t = 2.387, P = 0.022）. However, no significant difference was found in Rh rates, whereas a significant difference was observed in Ra rates between the two meadows. Thus, the difference in Re rate between the two meadows was mainly attributed to plant autotrophic respirations. During the growing season, the two meadows showed relatively low Q10 values, suggesting that Re, especially Rh was not sensitive to temperature variation in the growing season. Additionally, Re and Rh at the K_site, as well as Rh at the Psite was negatively correlated with soil moisture, indicating that soil moisture would also play an important role in respirations.展开更多
Aims Grasslands used for animal husbandry are chosen depending on the nutritive values of dominant herbage species.However,the influence of grazing in combination with precipitation and growing season on the nutritive...Aims Grasslands used for animal husbandry are chosen depending on the nutritive values of dominant herbage species.However,the influence of grazing in combination with precipitation and growing season on the nutritive values of dominant species has not been explicated.Methods To unveil the influence of the different grazing intensities on the nutritional values,an ecological study was formulated,namely fencing(G0),light grazing(G1),moderate grazing(G2)and high grazing(G3).This ambitious study was undertaken on the nutritive values of the four dominant species of herbage in an alpine meadow on the Qinghai-Tibet Plateau(QTP)during growing season(June–September)for two successive years,namely 2015(rainy year)and 2016(droughty year).Important Findings We found that(i)the nutritive value of Kobresia capillifolia,Polygonum viviparum and Caragana sinica was noticeably increased by grazing,but negligible effect on Potentilla fruticosa nutritive value was recorded.(ii)During the rainy year(2015),compared with G0,Polygonum viviparum and Potentilla fruticosa displayed 5.4 and 1.5%increases in the crude protein(CP)content and 8.5 and 2.4%increases in vitro true digestibility(IVTD),respectively,while the neutral detergent fibre(NDF)decreased by 13.5 and 0.9%,respectively.During the droughty year(2016),compared with G0,C.sinica and Potentilla fruticosa showed increases in the CP content by 4.3 and 1.3%and increases in the IVTD by 10.7 and 0.4%,respectively,during G3,while the NDF decreased by 6.0 and 1.0%,respectively.(iii)The nutritive values of all species were higher in the years when the rains were good.However,the nutritive values suffered heavily during drought conditions.Besides,the highest and lowest values of nutrition were detected in June and in September,respectively.The inter-seasonal and the inter-annual changes in the nutritional values of species were higher for K.capillifolia and Polygonum viviparum than for Potentilla fruticosa and C.sinica,suggesting that Potentilla fruticosa and C.sinica had higher water-use efficiency.(iv)Grazing clearly reduced the drought tolerance of three species and showed no effects on Potentilla fruticosa.(v)Grazing clearly increased the inter-month variation in the nutritional value of K.capillifolia and Polygonum viviparum but showed no effects on Potentilla fruticosa or C.sinica.Evidently,the grazing effects impacting the nutritional value of the dominant species of herbage exhibited conspicuous inter-annual and seasonal variations with species-specific influences and responses.Our findings are expected to have far-reaching implications enabling the authorities to arrive at strategic decisions and designing of relevant policies for the efficient management of the ecosystems ensuring the speed restoration of the QTP under severe grazing and extreme climatic circumstances.展开更多
Land surface process modeling of high and cold area with vegetation cover has not yielded satisfactory results in previous applications. In this study, land surface energy budget is simulated using a land surface mode...Land surface process modeling of high and cold area with vegetation cover has not yielded satisfactory results in previous applications. In this study, land surface energy budget is simulated using a land surface model for the A'rou meadow in the upper-reach area of the Heihe River Basin in the eastern Tibetan Plateau. The model performance is evaluated using the in-situ observations and remotely sensed data. Sensible and soil heat fluxes are overestimated while latent heat flux is underestimated when the default parameter setting is used. By analyzing physical and physiological processes and the sensitivities of key parameters, the inappropriate default setting of optimum growth and inhibition temperatures is identified as an important reason for the bias. The average daytime temperature during the period of fastest vegetation growth(June and July) is adopted as the optimum growth temperature, and the inhibition temperatures were adjusted using the same increment as the optimum temperature based on the temperature acclimation. These adjustments significantly reduced the biases in sensible, latent, and soil heat fluxes.展开更多
Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development.Crack characterization indices are crucial for the quantitative characterization of complex c...Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development.Crack characterization indices are crucial for the quantitative characterization of complex cracks,serving as vital factors in assessing the degree of cracking and the development morphology.So far,research on evaluating the degree of grassland degradation through crack characterization indices is rare,especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce.Therefore,based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau,we selected the alpine meadow in the Huangcheng Mongolian Township,Menyuan Hui Autonomous County,Qinghai Province,China as the study area,used unmanned aerial vehicle(UAV)sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation(light,medium,and heavy degradation),and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length,length density,branch angle,and burrow(rat hole)distribution density and combining them with in situ crack width and depth measurements.Finally,the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis.The results revealed that with the increase of degradation,the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly,the vegetation coverage reduced,and the root system aggregated in the surface layer of alpine meadow.As the degree of degradation increased,the fracture morphology developed from"linear"to"dendritic",and eventually to a complex and irregular"polygonal"pattern.The crack length,width,depth,and length density were identified as the crack characterization indices via analysis of variance.The results of grey relation analysis also revealed that the crack length,width,depth,and length density were all highly correlated with root length density,and as the degradation of alpine meadows intensified,the underground biomass increased dramatically,forming a dense layer of grass felt,which has a significant impact on the formation and expansion of cracks.展开更多
The alpine meadow ecosystem accounts for 27%of the total area of the Tibetan Plateau and is also one of the most important vegetation types.The Dangxiong alpine meadow ecosystem,located in the south-central part of th...The alpine meadow ecosystem accounts for 27%of the total area of the Tibetan Plateau and is also one of the most important vegetation types.The Dangxiong alpine meadow ecosystem,located in the south-central part of the Tibetan Plateau,is a typical example.To understand the carbon and water fluxes,water use efficiency(WUE),and their responses to future climate change for the alpine meadow ecosystem in the Dangxiong area,two parameter estimation methods,the Model-independent Parameter Estimation(PEST)and the Dynamic Dimensions Search(DDS),were used to optimize the Biome-BGC model.Then,the gross primary productivity(GPP)and evapotranspiration(ET)were simulated.The results show that the DDS parameter calibration method has a better performance.The annual GPP and ET show an increasing trend,while the WUE shows a decreasing trend.Meanwhile,ET and GPP reach their peaks in July and August,respectively,and WUE shows a“dual-peak”pattern,reaching peaks in May and November.Furthermore,according to the simulation results for the next nearly 100 years,the ensemble average GPP and ET exhibit a significant increasing trend,and the growth rate under the SSP5–8.5 scenario is greater than that under the SSP2–4.5 scenario.WUE shows an increasing trend under the SSP2–4.5 scenario and a significant increasing trend under the SSP5–8.5 scenario.This study has important scientific significance for carbon and water cycle prediction and vegetation ecological protection on the Tibetan Plateau.展开更多
[Objective] To investigate the relationship between the grassland caterpillar with different grades and the structure of alpine Kobresia meadow or soil feature. [Method] A total of 10 plots （20.00 m × 20.00 m） ...[Objective] To investigate the relationship between the grassland caterpillar with different grades and the structure of alpine Kobresia meadow or soil feature. [Method] A total of 10 plots （20.00 m × 20.00 m） were chosen. In each plot, five smaller plots （5.00 m × 5.00 m） were randomly selected and six sample plots （0.25 m × 0.25 m） were then selected in each smaller plot. The biomass, vegetation height, grasslayer thickness, bare land area, soil moisture and total vegetation cover degree were determined. Data were analyzed statistically by Excel 2003 and SPSS 13.0 software. [ Result] There was a significant difference （P 〈 0.05） between the grassland caterpillars at different hazard grades and the structure of alpine Kobresia meadow or soil properties. [ Conclusion] With the increase of grassland caterpillar density, the plant community structure of alpine Kobresia meadows changes from sedge family-dominant community to the forbs-dominant community.展开更多
基金supported by the Key Research and Development and Transformation Plan of Qinghai Provincial Science and Technology Department(2024-NK-137)the Qinghai Province Science and Technology Commissioner Special Project(2024-NK-P28).
文摘In recent years,many studies have focused on the effects of global climate warming and increased nitrogen deposition on the structure and function of grassland ecosystem.However,there are still significant uncertainties in the response mechanism of stability of plant community biomass in alpine meadows of the Qinghai-Xizang Plateau,China to these two major climate factors.Given this,based on field control experiments,this study systematically evaluated the effects of different levels of climate warming(W0(no warming),W1(air temperature increased by 0.47℃ or soil temperature increased by 0.61℃),W2(air temperature increased by 0.92℃ or soil temperature increased by 1.09℃),W3(air temperature increased by 1.44℃ or soil temperature increased by 1.95℃)),nitrogen deposition(N0(0 kg N/(hm^(2)·a)),N16(16 kg N/(hm^(2)·a)),and N32(32 kg N/(hm^(2)·a))),and their interactions on plant community biomass and its temporal stability,and explored its potential regulatory mechanisms.The results showed that the biomass of total community,Gramineae,and dominant species increased significantly with increasing temperature,but the biomass of common and rare species decreased significantly.Nitrogen deposition also significantly promoted the biomass accumulation of community and gramineous plants.Under the treatment of W3N32,the biomass of plant community,Gramineae,and dominant species reached the highest values,indicating that there was a synergistic effect under this treatment.Structural equation model showed that increasing temperature significantly decreased the stability of plant community biomass by reducing the stability of grass and dominant species biomass and weakening species asynchronism.Interaction of increased nitrogen deposition and temperature increased the biomass fluctuation of grass functional group,thus amplifying its negative influence on community stability.More attention should be paid to the response and regulatory mechanisms of dominant species and functional groups under global climate change.This study provides a theoretical basis for revealing the stability maintenance mechanism of alpine grassland and also provides scientific support for the development of future grassland ecosystem management and assessment.
基金supported by the National Forage Industry Technology System Program (CARS-34)Grassland Ecological Restoration and Management Science and Technology Support Project of Gansu Forestry and Grassland Bureau (GSAU-TSYF-2021-011)。
文摘In recent decades, global climate change and overgrazing have led to severe degradation of alpine meadows. Understanding the changes in soil characteristics and vegetation communities in alpine meadows with different degrees of degradation is helpful to reveal the mechanism of degradation process and take the remediation measures effectively. This study analyzed the changes in vegetation types and soil characteristics and their interrelationships under three degradation degrees, i.e., non-degradation(ND),moderate degradation(MD), and severe degradation(SD) in the alpine meadows of northeastern Qinghai-Xizang Plateau, China through the long-term observation. Results showed that the aggressive degradation changed the plant species, with the vegetation altering from leguminous and gramineous to forbs and harmful grasses. The Pielou evenness and Simpson index increased by 24.58% and 7.01%,respectively, the Shannon-Wiener index decreased by 17.52%, and the species richness index remained constant. Soil conductivity, soil organic matter, total potassium, available potassium, and porosity declined.However, the number of vegetation species increased in MD. Compared with ND, the plant diversity in MD enhanced by 8.33%, 8.69%, and 7.41% at family, genus, and species levels, respectively. In conclusion,changes in soil properties due to degradation can significantly influence the condition of above-ground vegetation. Plant diversity increases, which improves the structure of belowground network. These findings may contribute to designing better protection measures of alpine meadows against global climate change and overgrazing.
基金carried out in the framework of the 1331 Project of Cultural Ecology Collaborative Innovation Center in Wutai Mountain (00000342)co-financed by Program for the Philosophy and Social Sciences Research of Higher Learning Institutions of Shanxi (2022J027)+1 种基金Applied Basic Research Project of Shanxi Province (202203021221225)Basic Research Project of Xinzhou Science and Technology Bureau (20230501)。
文摘Climate warming profoundly affects plant biodiversity, community productivity, and soil properties in alpine and subalpine grassland ecosystems. However, these effects are poorly understood across elevational gradients in subalpine meadow ecosystems. To reveal the elevational patterns of warming effects on plant biodiversity, community structure, productivity, and soil properties, we conducted a warming experiment using open-top chambers from August 2019 to August 2022 at high(2764 m a. s. l.), medium(2631 m a. s. l.), and low(2544 m a. s. l.) elevational gradients on a subalpine meadow slope of Mount Wutai, Northern China. Our results showed that three years of warming significantly increased topsoil temperature but significantly decreased topsoil moisture at all elevations(P<0.05), and the percentage of increasing temperature and decreasing moisture both gradually raised with elevation lifting. Warming-induced decreasing proportions of soil organic carbon(SOC, by 19.24%), and total nitrogen(TN, by 24.56%) were the greatest at high elevational gradients. Experimental warming did not affect topsoil C: N, p H, NO_(3)^(-)-N, or NH_(4)^(+)-N at the three elevational gradients. Warming significantly increased species richness(P<0.01) and Shannon-Weiner index(P<0.05) at low elevational gradients but significantly decreased belowground biomass(P<0.05) at a depth of 0–10 cm at three elevational gradients. Warming caused significant increases in the aboveground biomass in the three elevational plots. Warming significantly increased the aboveground biomass of graminoids in medium(by 92.47%) and low(by 98.25%) elevational gradients, that of sedges in high(by 72.44%) and medium(by 57.16%) elevational plots, and that of forbs in high(by 75.88%), medium(by 34.38%), and low(by 74.95%) elevational plots. Species richness had significant linear correlations with SOC, TN, and C: N(P<0.05), but significant nonlinear responses to soil temperature and soil moisture in the warmed treatment(P<0.05). The warmed aboveground biomass had a significant nonlinear response to soil temperature and significant linear responses to soil moisture(P<0.05). This study provided evidence that altitude is a factor in sensitivity to climate warming, and these different parameters(e.g., plant species richness, Shannon-Weiner index, soil temperature, soil moisture, SOC, and TN) can be used to measure this sensitivity.
基金Under the auspices of Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA05060700)Postdoctoral Science Foundation of China(No.2013M530716)
文摘Grazing exclusion is widely adopted in restoring degraded alpine grasslands on the Qinghai-Tibetan Plateau. However, its effectiveness remains poorly understood. In this study, we investigated the effects of grazing exclusion on plant productivity, species diversity and soil organic carbon （SOC） and soil total nitrogen （STN） storage along a transect spanning from east to west of alpine meadows in northern Tibet, China. After six years of grazing exclusion, plant cover, aboveground biomass （AGB）, belowground biomass （BGB）, SOC and STN were increased, but species diversity indices declined. The enhancement of AGB and SOC caused by grazing exclusion was correlated positively with mean annual precipitation （MAP）. Grazing exclusion led to remarkable biomass increase of sedge species, especially Kobresia pygmaea, whereas decrease of biomass in forbs and no obvious change in grass, leguminous and noxious species. Root biomass was concentrated in the near surface layer （10 cm） after grazing exclusion. The effects of grazing exclusion on SOC storage were confined to shallow soil layer in sites with lower MAP. It is indicated that grazing exclusion is an effective measure to increase forage production and enhance soil carbon sequestration in the studied region. The effect is more efficient in sites with higher precipitation. However, the results revealed a tradeoff between vegetation restoration and ecological biodiversity. Therefore, carbon pools recover more quickly than plant biodiversity in the alpine meadows. We suggest that grazing exclusion should be combined with other measures to reconcile grassland restoration and biodiversitv conservation.
文摘Potentilla fruticosascrub, Kobresia humilismeadow and Kobresia tibeticameadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-GC method, a study on CO 2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO 2 emission rates from various treatments were 672.09±152.37 mgm -2 h -1 for FC (grass treatment); 425.41±191.99 mgm -2 h -1 for FJ (grass exclusion treatment); 280.36±174.83 mgm -2 h -1 for FL (grass and roots exclusion treatment); 838.95±237.02 mgm -2 h -1 for GG (scrub+grass treatment); 528.48±205.67 mgm -2 h -1 for GC (grass treatment); 268.97±99.72 mgm -2 h -1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm -2 h -1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilismeadow, Potentilla fruticosascrub meadow and Kobresia tibeticameadow differed greatly in average CO 2 emission rate of soil-plant system, in the order of GG>FC>LC>GC. Moreover, in Kobresia humilismeadow, heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosascrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from GG; 49% and 51% from GC. In addition, root respiration from Kobresia humilismeadow approximated 145 mgCO 2 m -2 h -1 , contributed 34% to soil respiration. During the experiment period, Kobresia humilismeadow and Potentilla fruticosascrub meadow had a net carbon fixation of 111.11 gm -2 and 243.89 gm -2 , respectively. Results also showed that soil temperature was the main factor which influenced CO 2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO 2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture may be the inhibitory factor of CO 2 emission from Kobresia tibeticameadow, and more detailed analyses should be done in further research.
基金funded by the National Natural Science Foundation of China (Grant Nos. 31100360, 31200378, 31000233)
文摘Steller chamaejasme L. （S. chamaejasme for short） is one of the most noxious unpalatable weeds in China, which has been frequently reported its negative interaction （i.e. competition and allelopathy） with other herbaceous species in grasslands. This study compared species diversity, biomass and sexual reproduction of herbaceous plants in meadows with S. chamaejasme and in open meadows without S. ehamaejasme in overgrazing meadows on the Tibetan Plateau in China to determine whether positive facilitation exist between S. chamaejasme and other herbaceous species under livestock＇s overgrazing. The results showed that there are more herbaceous species in meadows with S. chamaejasme than those in open meadows （35s and30s, respectively）. Diversity index and above-ground biomass were also significantly higher in meadows with S. charnaejasme. There were 39% （11/28） of all species with sexual reproduction found in meadows with S. charnaejasme, which was 7 times more than those in open meadows. Our study showed that S. charnaejasme could provide biotic refuge for neighboring plants and preserve plant diversity from livestock＇s overgrazing in alpine meadows on the Tibetan Plateau. It also suggested that inter-specific facilitation between S. charnaejasme and other herbaceous species may play a key role in overgrazing alpine meadows.
基金Supported by Technology R&D Program"Research and Demonstration of Fragile Ecological Restoration Technology for the Tibetan Plateau"(2013BAC04B02)Sub Project of National Key Technology R&D Program"Health Assessment Technology for Typical Fragile Ecosystem in the Tibetan Plateau"(2013BAC04B02-05)National Natural Science Foundation of China(31160120)
文摘[ Objective ] The paper was to understand the characteristics of plant communities in three kinds of typical alpine meadows in Haibei Region, Qinghai Province. [ Method] The characteristics and diversity of plant communities in typical alpine meadow, including Kobresia humilis, PotentiUafruticose and Kobresia menyuanica, were studied, with Menyuan studfarm in Haibei region of Qinghai Province as an example. [ Result] Results showed that the three kinds of plant communities in alpine meadows presented complex structure; the diversity index had close relationship with the evenness index; there were fewer common species and higher species replacement rate among different alpine meadow communities ; the aboveground biomass of K. humilis alpine meadow was 1.62 and 1.69 times of P. fruticose and K. menyuanica meadows, respectively; the underground biomass mainly distributed in the 0 - 10 cm soil layer, and the vertical spatial distribution structure was ＂T＂ type; the aboveground and underground biomass were negatively correlated. [ Conclusion] The paper will provide basis for protection and further use of different grassland plant communities in Haibei Region, Qinghai Province.
基金supported by the CAS"Light of West China"Program(grant no.xbzglzb2022031)the National Natural Science Foundation of China(grant no.U23A2002,42207524 and 32171650)+3 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(grant no.2019QzKK0405)Collaborative Innovation Center for ecological civilization from Hainan University(XTCX2022STC01 and XTCX2022STB07)Independent Initiated Project from Environment and Plant Protection Institute,Chinese Academy of Tropical Agriculture Sciences(hzs2024003)start-up funding from Hainan University[KYQD(ZR)-22085].
文摘Alpine meadows of the Qinghai-Tibetan Plateau(QTP)are experiencing severe degradation due to intensified human activity and climate changes.However,there has been litle attention paid to the effects of different grazing practices on the soil hydrological properties of alpine meadows.In this study,three grazing practices were established in an alpine Kobresia meadow:free grazing,reduced grazing and grazing exclusion.We found that the 0-10 cm soil water retention capacity(SWR)and plant available water content(AWC)in grazing exclusion treatment were higher than that in reduced or free grazing treatments,whereas the 20-40 cm SWR and AWC display the opposite pattern.The AWC and SWR variations were closely related to soil properties,and the redundancy analysis showed that SWR and AWC were positive related to soil organic matter(SOM),total porosity(TP)and capillary porosity(CP),but were negative correlated with soil bulk density(BD),clay and silt content.Structural equation modeling found that SOM was identified as the most important factor affecting SWR,and CP was the key factor influencing AWC.Therefore,the higher O-10 cm SWR and AWC in grazing exclusion treatment may be attributed to its higher SOM and CP,respectively.Furthermore,root biomass can affect SWR and AWC through altering BD and SOM.Our study suggests that the response of soil hydrological properties to grazing practices was different,grazing exclusion only increase topsoil water retention capacity but not favor deep soil water retention capacity.
基金the National Natural Science Foundation of China(31770501)the Science and Technology Innovation Base Free Research Program of Tibetan Autonomous Region of China(to Zhiyong,Yang).
文摘Global climate change is expected to have a signifcant impact on ecosystems worldwide,especially for alpine meadows which are considered as one of the most vulnerable components.However,the effects of global warming on the plant nitrogen-phosphorus stoichiometry and resorption in alpine meadows remain unclear.Therefore,to investigate the plant nitrogen-phosphorus stoichiometry and resorption in alpine meadows on the Qinghai-Tibet Plateau,we conducted an artifcial warming study using open-top chambers(OTCs)over the 3 years of warming period.We selected three dominant species,four height types of OTCs(0.4,0.6,0.8 and 1 m)and four warming methods(year-round warming,winter warming,summer-autumn-winter warming and spring-summer-autumn warming in the experiment)in this experiment.In our study,soil temperature signifcantly increased with increasing the height of OCTs under the different warming methods.Kobresia pygmaea presented an increase in nitrogen(N)limitation and Kobresia humilis presented an increase in phosphorus(P)limitation with increasing temperature,while Potentilla saundersiana was insensitive to temperature changes in terms of nitrogen and phosphorus limitations.Both nitrogen resorption effciency:phosphorus resorption effciency and N:P trends in response to rising temperatures were in the same direction.The differential responses of the chemical stoichiometry of the three species to warming were observed,refecting that the responses of nitrogen and phosphorus limitations to warming are multifaceted,and the grassland ecosystems may exhibit a certain degree of self-regulatory capability.Our results show that using chemical dosage indicators of a single dominant species to represent the nitrogen and phosphorus limitations of the entire ecosystem is inaccurate,and using N:P to refect the nutritional limitations might have been somewhat misjudged in the context of global warming.
基金funded by the National Natural Science Foundation of China(NSFC41930755,NSFC32230068)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB40000000)the Opening Project of State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau(A314021402-202105).
文摘Global climate change and overgrazing are driving shifts in the plant composition of grassland com-munities,which may profoundly affect the function of grassland ecosystems in regulating runoff and soil erosion.Here,we examined the shift effects of normal hillslope alpine meadow to shrub and severely degraded meadow states on runoff and sediment generation under natural rainfall conditions,and determined the contributions of plant and soil properties changes to soil erodibility,runoff and sediment generation by in situ rainfall experiment and monitoring on the hillslope of Qinghai-Tibetan Plateau.The results showed that normal meadow shift into severely degraded meadow state,mean weight diameter,soil saturated hydraulic conductivity,soil cohesion and soil erodibility K-factor at the topsoil decreased by 70.3%,73.1%,80.3%and-13.1%,respectively,and when normal meadows shift into shrub meadow state,they reduced by 49.1%,-1.3%,49.4%,and-8.3%,respectively.Runoff and soil loss significantly changed by-40.0%and 177.8%when normal meadow shifted into a severely degraded meadow state,while runoff and soil loss significantly changed by+65.0%and+77.8%when normal meadow shifted into a shrub meadow state.Our findings highlight that the two divergent shifts both increased soil loss compared to the normal hillslope alpine meadows.Overall,our results indicate that the divergent shifts of normal alpine meadows exacerbated soil erodibility and soil loss of hillslope alpine meadows.These results obtained here offer a novel perspective on the regulation of runoff and soil erosion in the alpine meadow ecosystem.
基金funded by the National Natural Science Foundation of China(42062019,42002283)。
文摘Surface soil cracking in alpine meadows signifies the transition of degradation from quantitative accumulation to qualitative deterioration.Quantitative research remains insufficient regarding changes in the mechanical properties of degraded meadow soils and the mechanical thresholds for cracking initiation.This study explored the relationships between surface cracking and the physical properties,tensile strength,and matrix suction of root-soil composites in alpine meadow sites with different stages of degradation(undegraded(UD),lightly degraded(LD),moderately degraded(MD),and heavily degraded(HD))under different water gradients(high water content(HWC),medium water content(MWC),and low water content(LWC))corresponding to different drying durations at a constant temperature of 40.0°C.The Huangcheng Mongolian Township in Menyuan Hui Autonomous County,Qinghai Province,China was chosen as the study area.The results indicated that as the degradation degree of alpine meadow intensified,both water content of rootsoil composite and the fine grain content of soil decreased.In contrast,the root-soil mass ratio and root area ratio initially increased and then decreased with progressive degradation.Under a consistent water content,the tensile strength of root-soil composite followed a pattern of MD>HD>LD>UD.The peak displacement of tensile strength also decreased as the degradation degree of alpine meadow increased.Both the tensile strength and matrix suction of root-soil composite increased as root-soil water content decreased.A root-soil water content of 30.00%-40.00%was found to be the critical threshold for soil cracking in alpine meadows.Within this range,the matrix suction of root-soil composite ranged from 50.00 to 100.00 kPa,resulting in the formation of linear cracks in the surface soil.As the root-soil water content continued to decrease,liner cracks evolved into branch-like and polygonal patterns.The findings of this study provide essential data for improving the mechanical understanding of grassland cracking and its development process.
基金supported by National Science Foundation of China(NSFC)[No.32001119].
文摘Global warming leads to snow cover loss in the alpine ecosystem,exposing seeds to extreme diurnal temperature fluctuations during the growing season.The risk of freezing increases as seeds have increased moisture content.Studying the survival mechanisms of seeds at low temperatures can help analyze changes in alpine meadow populations and target conservation efforts.Here,we used three species of Poaceae as a model to understand freezing stress.Fully imbibed Elymus dahuricus,Festuca elata,and Lolium multiflorum seeds were subjected to programmed cooling at fast and slow rates(-1.0/0.05℃/min)and then assessed for survival.Differential Scanning Calorimetry was used to analyze thermal transitions during cooling.HE-stained paraffin sections and a Transmission Electron Microscope were employed to observe internal morphology and ultrastructural changes.E.dahuricus seeds exhibited greater tolerance to low temperatures than those of the other two species,with an LT_(50)of approximately-20℃for both cooling rates and maintained relatively intact ultrastructure.The observed the low-temperature exotherm(LTE)correlated with seed survival,with viability decreasing extensively below LTE.Fast cooling caused fewer changes to seed morphology and ultrastructure than slow cooling,suggesting that the primary survival mechanism during fast cooling is freezing avoidance through supercooling.Seeds exhibited greater freeze tolerance under slow than fast cooling,primarily by migrating intracellular water to extracellular spaces where it froze,causing considerable damage to cell ultrastructure and forming apparent cavities in some seeds.
基金supported in part by the Fundamental Research Project of the Science and Technology Department of the Qinghai Province(Grant No.2025-ZJ-739)the National Natural Science Foundation of China(Grant No.U21A2021)+1 种基金the Open Fund of Greenhouse Gas and Carbon Neutral Key Laboratory of Qinghai Province(Grant No.ZDXM-2023-3)the Key Projects of Qinghai Meteorological Bureau(Grant No.QXZD2024-08)。
文摘Alpine meadows,alpine wetlands,and alpine desert steppes are the three typical vegetation types on the Qinghai-Tibet Plateau.The complex terrain and harsh climatic conditions across this region lead to considerable diversification in the vegetation growth environment,resulting in substantial spatial heterogeneity in ecosystem carbon flux and its controlling mechanisms.Using eddy covariance data collected from March to August 2019,this study examined the responses of carbon and water fluxes in different ecosystems on the Tibetan Plateau to typical hydrometeorological factors,focusing on Net Ecosystem CO□Exchange(NEE)and Evapotranspiration(ET).The results indicate that:1)The Longbao alpine wetland primarily acted as a carbon sink from May to August,while serving as a carbon source from March to April.In the Maqin alpine meadow,it functioned as a carbon sink during June and July but acted as a carbon source in March,April,May,and August.The Tuotuohe alpine desert strppe was predominantly a net carbon sink from March to August.Overall,after the entire growing season(March to August),the Longbao alpine wetlands,Maqin alpine meadow,and Tuotuohe alpine desert steppe all showed net carbon sink properties,with net CO_(2)uptakes of 236.12 g/m^(2),291.45 g/m^(2),and 290.28 g/m^(2),respectively.2)The importance of meteorological factors to NEE varies with scale and ecosystem type,with global radiation(Rg)being the most critical factor influencing NEE variation.Volumetric soil water content(Soil_VWC)and soil temperature(Soil_T)had a positive effect on NEE at Maqin alpine meadow and Tuotuohe alpine desert steppe,while higher values of these variables showed a negative contribution.Furthermore,the sensitivity of NEE to Soil_T at Longbao alpine wetland and Tuotuohe alpine desert steppe was greater than its sensitivity to air temperature(Tair).3)The effect of Gross Primary Productivity(GPP)on NEE in alpine desert steppes is significantly greater than in alpine meadows.Both Ecosystem Respiration(Reco)and NEE were substantially limited by GPP,with 84%of GPP in alpine wetlands contributing to Reco and 16%to NEE;92%of GPP in alpine meadows contributing to Reco and 8%to NEE;and 40%of GPP in high-altitude desert grasslands contributing to Reco and 60%to NEE.4)The strong correlation between NEE and evapotranspiration suggests that water availability is the primary factor controlling changes in the carbon and water budgets of alpine ecosystems.
基金supported by the National Natural Science Foundation of China(31870406,41661144045)the State Key Research and Development Program(2016YFC0502001,2017YFA0604801).
文摘Aims Variations in vegetation spring phenology are widely attributed to temperature in temperate and cold regions.However,temperature effect on phenology remains elusive in cold and arid/semiarid ecosystems because soil water condition also plays an important role in mediating phenology.Methods We used growing degree day(GDD)model and growing season index(GSI)model,coupling minimum temperature(T_(min))with soil moisture(SM)to explore the influence of heat requirement and hydroclimatic interaction on the start of carbon uptake period(SCUP)and net ecosystem productivity(NEP)in two alpine meadows with different precipitation regimes on the Qinghai-Tibet Plateau(QTP).One is the water-limited alpine steppe-meadow,and the other is the temperature-limited alpine shrub-meadow.Important Findings We observed two clear patterns linking GDD and GSI to SCUP:SCUP was similarly sensitive to variations in preseason GDD and GSI in the humid alpine shrub-meadow,while SCUP was more sensitive to the variability in preseason GSI than GDD in the semiarid alpine steppe-meadow.The divergent patterns indicated a balance of the limiting climatic factors between temperature and water availability.In the humid meadow,higher temperature sensitivity of SCUP could maximize thermal benefit without drought stress,as evidenced by the stronger linear correlation coefficient(R2)and Akaike’s information criterion(AIC)between observed SCUPs and those of simulated by GDD model.However,greater water sensitivity of SCUP could maximize the benefit of water in semiarid steppe-meadow,which is indicated by the stronger R2 and AIC between observed SCUPs and those of simulated by GSI model.Additionally,although SCUPs were determined by GDD in the alpine shrub-meadow ecosystem,NEP was both controlled by accumulative GSI in two alpine meadows.Our study highlights the impacts of hydroclimatic interaction on spring carbon flux phenology and vegetation productivity in the humid and semiarid alpine ecosystems.The results also suggest that water,together with temperature should be included in the models of phenology and carbon budget for alpine ecosystems in semiarid regions.These fi ndings have important implications for improving vegetation phenology models,thus advancing our understanding of the interplay between vegetation phenology,productivity and climate change in future.
基金Field Station Foundation In the Domain of Resource and Environment, CAS and GEF program (052456 and CHA-GS-Y-4)
文摘From 30 June to 24 September in 2003 ecosystem respiration （Re） in two alpine meadows on the Tibetan Plateau were measured using static chamber- and gas chromatography- （GC） based techniques. Simultaneously, plant removal treatments were set to partition Re into plant autotrophic respiration （Ra） and microbial heterotrophic respiration （Rh）. Results indicated that Re had clear diurnal and seasonal variation patterns in both of the meadows. The seasonal variability of Re at both meadow sites was caused mainly by changes in Ra, rather than Rh. Moreover, atthe Kobresia humilis meadow site （K_site）, Ra and Rh accounted for 54% and 46% of Re, respectively. While at the Potentilla fruticosa scrub meadow （P_site）, the counterparts accounted for 61% and 39%, respectively. T test showed that there was significant difference in Re rates between the two meadows （t = 2.387, P = 0.022）. However, no significant difference was found in Rh rates, whereas a significant difference was observed in Ra rates between the two meadows. Thus, the difference in Re rate between the two meadows was mainly attributed to plant autotrophic respirations. During the growing season, the two meadows showed relatively low Q10 values, suggesting that Re, especially Rh was not sensitive to temperature variation in the growing season. Additionally, Re and Rh at the K_site, as well as Rh at the Psite was negatively correlated with soil moisture, indicating that soil moisture would also play an important role in respirations.
基金Our research was funded by China’s Agricultural Research system(CARS-39-18).
文摘Aims Grasslands used for animal husbandry are chosen depending on the nutritive values of dominant herbage species.However,the influence of grazing in combination with precipitation and growing season on the nutritive values of dominant species has not been explicated.Methods To unveil the influence of the different grazing intensities on the nutritional values,an ecological study was formulated,namely fencing(G0),light grazing(G1),moderate grazing(G2)and high grazing(G3).This ambitious study was undertaken on the nutritive values of the four dominant species of herbage in an alpine meadow on the Qinghai-Tibet Plateau(QTP)during growing season(June–September)for two successive years,namely 2015(rainy year)and 2016(droughty year).Important Findings We found that(i)the nutritive value of Kobresia capillifolia,Polygonum viviparum and Caragana sinica was noticeably increased by grazing,but negligible effect on Potentilla fruticosa nutritive value was recorded.(ii)During the rainy year(2015),compared with G0,Polygonum viviparum and Potentilla fruticosa displayed 5.4 and 1.5%increases in the crude protein(CP)content and 8.5 and 2.4%increases in vitro true digestibility(IVTD),respectively,while the neutral detergent fibre(NDF)decreased by 13.5 and 0.9%,respectively.During the droughty year(2016),compared with G0,C.sinica and Potentilla fruticosa showed increases in the CP content by 4.3 and 1.3%and increases in the IVTD by 10.7 and 0.4%,respectively,during G3,while the NDF decreased by 6.0 and 1.0%,respectively.(iii)The nutritive values of all species were higher in the years when the rains were good.However,the nutritive values suffered heavily during drought conditions.Besides,the highest and lowest values of nutrition were detected in June and in September,respectively.The inter-seasonal and the inter-annual changes in the nutritional values of species were higher for K.capillifolia and Polygonum viviparum than for Potentilla fruticosa and C.sinica,suggesting that Potentilla fruticosa and C.sinica had higher water-use efficiency.(iv)Grazing clearly reduced the drought tolerance of three species and showed no effects on Potentilla fruticosa.(v)Grazing clearly increased the inter-month variation in the nutritional value of K.capillifolia and Polygonum viviparum but showed no effects on Potentilla fruticosa or C.sinica.Evidently,the grazing effects impacting the nutritional value of the dominant species of herbage exhibited conspicuous inter-annual and seasonal variations with species-specific influences and responses.Our findings are expected to have far-reaching implications enabling the authorities to arrive at strategic decisions and designing of relevant policies for the efficient management of the ecosystems ensuring the speed restoration of the QTP under severe grazing and extreme climatic circumstances.
基金supported by the National Natural Science Foundation of China(Grant Nos.91125002,40971221)FP7 CEOP-AEGI(Coordinated Asia European Long-Term Observing System of the Qinhai Tibet Plateau Hydro-meteorological Processes and the Asian Monsoon System with Ground Satellite Image data and numerical simulation)project
文摘Land surface process modeling of high and cold area with vegetation cover has not yielded satisfactory results in previous applications. In this study, land surface energy budget is simulated using a land surface model for the A'rou meadow in the upper-reach area of the Heihe River Basin in the eastern Tibetan Plateau. The model performance is evaluated using the in-situ observations and remotely sensed data. Sensible and soil heat fluxes are overestimated while latent heat flux is underestimated when the default parameter setting is used. By analyzing physical and physiological processes and the sensitivities of key parameters, the inappropriate default setting of optimum growth and inhibition temperatures is identified as an important reason for the bias. The average daytime temperature during the period of fastest vegetation growth(June and July) is adopted as the optimum growth temperature, and the inhibition temperatures were adjusted using the same increment as the optimum temperature based on the temperature acclimation. These adjustments significantly reduced the biases in sensible, latent, and soil heat fluxes.
基金This study was funded by the National Natural Science Foundation of China(42062019,42002283)the Project of Qinghai Science&Technology Department(2021-ZJ-927).
文摘Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development.Crack characterization indices are crucial for the quantitative characterization of complex cracks,serving as vital factors in assessing the degree of cracking and the development morphology.So far,research on evaluating the degree of grassland degradation through crack characterization indices is rare,especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce.Therefore,based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau,we selected the alpine meadow in the Huangcheng Mongolian Township,Menyuan Hui Autonomous County,Qinghai Province,China as the study area,used unmanned aerial vehicle(UAV)sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation(light,medium,and heavy degradation),and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length,length density,branch angle,and burrow(rat hole)distribution density and combining them with in situ crack width and depth measurements.Finally,the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis.The results revealed that with the increase of degradation,the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly,the vegetation coverage reduced,and the root system aggregated in the surface layer of alpine meadow.As the degree of degradation increased,the fracture morphology developed from"linear"to"dendritic",and eventually to a complex and irregular"polygonal"pattern.The crack length,width,depth,and length density were identified as the crack characterization indices via analysis of variance.The results of grey relation analysis also revealed that the crack length,width,depth,and length density were all highly correlated with root length density,and as the degradation of alpine meadows intensified,the underground biomass increased dramatically,forming a dense layer of grass felt,which has a significant impact on the formation and expansion of cracks.
基金supported by the Second Comprehensive Scientific Research Survey on the Tibetan Plateau[grant number 2019QZKK0103]the National Natural Science Foundation of China[grant numbers 42375071 and 42230610].
文摘The alpine meadow ecosystem accounts for 27%of the total area of the Tibetan Plateau and is also one of the most important vegetation types.The Dangxiong alpine meadow ecosystem,located in the south-central part of the Tibetan Plateau,is a typical example.To understand the carbon and water fluxes,water use efficiency(WUE),and their responses to future climate change for the alpine meadow ecosystem in the Dangxiong area,two parameter estimation methods,the Model-independent Parameter Estimation(PEST)and the Dynamic Dimensions Search(DDS),were used to optimize the Biome-BGC model.Then,the gross primary productivity(GPP)and evapotranspiration(ET)were simulated.The results show that the DDS parameter calibration method has a better performance.The annual GPP and ET show an increasing trend,while the WUE shows a decreasing trend.Meanwhile,ET and GPP reach their peaks in July and August,respectively,and WUE shows a“dual-peak”pattern,reaching peaks in May and November.Furthermore,according to the simulation results for the next nearly 100 years,the ensemble average GPP and ET exhibit a significant increasing trend,and the growth rate under the SSP5–8.5 scenario is greater than that under the SSP2–4.5 scenario.WUE shows an increasing trend under the SSP2–4.5 scenario and a significant increasing trend under the SSP5–8.5 scenario.This study has important scientific significance for carbon and water cycle prediction and vegetation ecological protection on the Tibetan Plateau.
基金funded by the grants from Basic Science and Research Special Fund for the State Level and Public Scientific Research Institute (Grassland Research Institute,Chinese Academy of Agricultural Sciences) and Wild Science Observation Testing Station of Alpine Meadow Grassland Resource and Ecotope of the Ministry of Agriculture
文摘[Objective] To investigate the relationship between the grassland caterpillar with different grades and the structure of alpine Kobresia meadow or soil feature. [Method] A total of 10 plots （20.00 m × 20.00 m） were chosen. In each plot, five smaller plots （5.00 m × 5.00 m） were randomly selected and six sample plots （0.25 m × 0.25 m） were then selected in each smaller plot. The biomass, vegetation height, grasslayer thickness, bare land area, soil moisture and total vegetation cover degree were determined. Data were analyzed statistically by Excel 2003 and SPSS 13.0 software. [ Result] There was a significant difference （P 〈 0.05） between the grassland caterpillars at different hazard grades and the structure of alpine Kobresia meadow or soil properties. [ Conclusion] With the increase of grassland caterpillar density, the plant community structure of alpine Kobresia meadows changes from sedge family-dominant community to the forbs-dominant community.
