Understanding livestock performance in typical steppe ecosystems is essential for optimizing grassland-livestock interactions and minimizing environmental impact.To assess the effects of different stocking rates on th...Understanding livestock performance in typical steppe ecosystems is essential for optimizing grassland-livestock interactions and minimizing environmental impact.To assess the effects of different stocking rates on the growth performance,energy and nitrogen utilization,methane(CH_(4))emissions,and grazing behavior of Tan sheep,a 2-year grazing experiment in the typical steppe was conducted.The grazing area was divided into 9 paddocks,each 0.5 ha,with 3 spatial replicates for each stocking rate treatment(4,8,and 13 sheep per paddock),corresponding to 2.7,5.3,and 8.7 sheep ha^(–1).The results showed that the neutral detergent fiber(NDF)and acid detergent fiber(ADF)contents of herbage varied between grazing years(P<0.05),with a positive correlation between stocking rate and crude fiber content in the herbage(P<0.05).Dry matter intake(DMI)decreased with increasing stocking rate(P<0.05),and the average daily gain(ADG)was highest at 2.7 sheep ha^(–1)(P<0.05).Compared to 2.7 and 8.7 sheep ha^(–1),the5.3 sheep ha^(–1)treatment exhibited the lowest nutrient digestibility for dry matter,nitrogen,and ether extract(P<0.05).Fecal nitrogen was lowest at 8.7 sheep ha^(–1)(P<0.05),while retained nitrogen as a proportion of nitrogen intake was highest.Digestive energy(DE),metabolic energy(ME),and the ratios of DE to gross energy(GE)and ME to GE were highest at 8.7 sheep ha^(–1)(P<0.05).In contrast,CH_4 emissions,CH_4 per DMI,and CH_(4)E as a proportion of GE were highest at 2.7 sheep ha^(–1)(P<0.05).Stocking rate and grazing year did not significantly affect rumen fermentation parameters,including volatile fatty acids,acetate,propionate,and the acetate/propionate ratio.At 8.7sheep ha^(–1),daily grazing time and inter-individual distance increased,while time allocated to grazing,walking,and ruminating/resting decreased as stocking rates increased(P<0.05).This study highlights the importance of adjusting stocking rates based on the nutritional value of forage and grazing year to optimize grazing management.展开更多
Remote sensing(RS) technologies provide robust techniques for quantifying net primary productivity(NPP) which is a key component of ecosystem production management. Applying RS, the confounding effects of carbon consu...Remote sensing(RS) technologies provide robust techniques for quantifying net primary productivity(NPP) which is a key component of ecosystem production management. Applying RS, the confounding effects of carbon consumed by livestock grazing were neglected by previous studies, which created uncertainties and underestimation of NPP for the grazed lands. The grasslands in Xinjiang were selected as a case study to improve the RS based NPP estimation. A defoliation formulation model(DFM) based on RS is developed to evaluate the extent of underestimated NPP between 1982 and 2011. The estimates were then used to examine the spatiotemporal patterns of the calculated NPP. Results show that average annual underestimated NPP was 55.74 gC·m^(-2)yr^(-1) over the time period understudied, accounting for 29.06% of the total NPP for the Xinjiang grasslands. The spatial distribution of underestimated NPP is related to both grazing intensity and time. Data for the Xinjiang grasslands show that the average annual NPP was 179.41 gC·m^(-2)yr^(-1), the annual NPP with an increasing trend was observed at a rate of 1.04 gC·m^(-2)yr^(-1) between 1982 and 2011. The spatial distribution of NPP reveals distinct variations from high to low encompassing the geolocations of the Tianshan Mountains, northern and southern Xinjiang Province and corresponding with mid-mountain meadow, typical grassland, desert grassland, alpine meadow, and saline meadow grassland types. This study contributes to improving RS-based NPP estimations for grazed land and provides a more accurate data to support the scientific management of fragile grassland ecosystems in Xinjiang.展开更多
＂Ryegrass, orchard grass, Festuca arundinacea and Trifolium repens＂ were researched in Dushan County, Guizhou Province, in order explore grass characteristics by different grazing methods in seasons. The results sho...＂Ryegrass, orchard grass, Festuca arundinacea and Trifolium repens＂ were researched in Dushan County, Guizhou Province, in order explore grass characteristics by different grazing methods in seasons. The results show that grass community height in different groups was of little differences（P0.05）; the group of moderate grazing in spring, summer and autumn dominated in grass cover; grass density showed insignificant variations among different treatment groups（P0.05） and in the groups of heavy grazing in spring and autumn and moderate grazing in summer and of moderate grazing in spring, summer and autumn, grass community density was higher compared with the other groups（P0.05）; as for above-ground biomass, the group of moderate grazing in spring and autumn and heavy grazing in summer and of moderate grazing in spring, summer and autumn dominated.展开更多
Animals excrete feces during grazing. The uneven distribution of feces causes a spatial heterogeneity in grassland communities. In this study, we attempted to clarify the effects of feces on spatial distribution patte...Animals excrete feces during grazing. The uneven distribution of feces causes a spatial heterogeneity in grassland communities. In this study, we attempted to clarify the effects of feces on spatial distribution patterns of plant species. A field study was conducted on four grasslands each grazed by a single cow. These four grasslands were defined as Poa pratensis （Kentucky bluegrass） dominated grassland without feces （PoF-）, Poa pratensis dominated grassland with feces （PoF＋）, Zoysia japonica Steud. （Japanese lawngrass） dominated grassland without feces （ZyF-）, and Zoysia japonica Steud. dominated grassland with feces （ZyF＋）. A 50 m line that transects 100 equally spaced quadrats （L-quadrats） was drawn on each of the four grasslands. Each quadrat was 0.50 m × 0.50 m in size and consisted of four equal-area cells of 0.25 m ×0.25 m （S-quadrats）. The occurrences of all plant species were recorded in each S-quadrat. The binomial distribution （BD） and beta-binomial distribution （BBD） were used to represent the variation in spatial patterns. The BBD provided a significant description of the frequency distribution of plants per quadrat. A power law was used to calculate the spatial heterogeneity of each species together with the community heterogeneity. The results revealed that the plants on each of the four grasslands were aggregatively distributed. The ZyF＋ exhibited greater spatial heterogeneity than the ZyF-due to the uneven deposition of feces by cows grazing on the grasslands. Additionally we also found that the feces had effect on the heterogeneity inZyF＋ and did not have effect in PoF＋.展开更多
In semi-arid lands,vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix.Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation ...In semi-arid lands,vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix.Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation and soil compaction.Nevertheless,some species with anchorage mechanisms in their seeds might overcome this,such as Nassella tenuis(Phil.)Barkworth.This is an important species in grazing paddocks because it has an intermediate palatability and its relatively tolerant to grazing.These characteristics allow N.tenuis to increase its abundance in grazed sites.Our objective was to assess how grazing affects the key palatable species from seeds to seedlings:i.e.,seed rain,soil seed bank,and seedling recruitment in different microsites along a windward-leeward transect across shrub canopy.We hypothesized that:(1)the negative effects of grazing on N.tenuis fructification are reflected in its seed rain,soil seed bank,and seedling recruitment,especially in interpatches;(2)Nassella tenuis seed rain reduction,soil compaction by cattle in grazed sites,and removal of seeds by wind decrease its soil seed bank,especially in microsites exposed to the predominant wind;and(3)the decrease in N.tenuis soil seed bank and cover increase in annual species in grazed sites have negative effects on its seedling recruitment,especially in microsites exposed to predominant wind.We placed seed traps,collected soil samples,and monitored seedling recruitment in different locations around shrub canopy to address our hypotheses.Also,we established a manipulative experiment in which we sow N.tenuis seeds and followed its recruitment in different microsites.We compared the seed rain,soil seed bank,natural seedling recruitment,and sown seeds recruitment of N.tenuis between grazed and ungrazed sites.We analyzed differences between microsites along a windward-leeward transect across shrubs patches.Seed rain and soil seed bank had the same density in patches and interpatches both in ungrazed and grazed sites.But seed rain was higher,and soil seed bank was lower in ungrazed sites than in grazed sites.Almost all under-canopy microsites showed greater soil seed bank abundance and natural seedling recruitment in ungrazed sites.Sown seeds recruitment was the same between grazed and ungrazed sites,but it showed protective effects of shrubs in leeward microsites under grazed sites.As a conclusion,seed rain and soil seed bank are complementary under grazed sites.展开更多
The Flooding Pampa grasslands are the last remnant of the Rio de la Plata grasslands in Argentina.Anthropo-genic interventions have led to severe degradation and,as a result,the ecosystem services provided by the gras...The Flooding Pampa grasslands are the last remnant of the Rio de la Plata grasslands in Argentina.Anthropo-genic interventions have led to severe degradation and,as a result,the ecosystem services provided by the grass-lands are declining,in terms of provisioning,regulating,and supporting services.We synthesized the existing literature on the ecosystem goods and services provided by these grasslands under grazing in different conditions and conservation status.We found that plant and animal diversity and primary production are the most studied ecosystem services,while climate regulation,water supply,nutrient cycling,meat production and erosion control,in that order,are less studied.Cultural services are under-researched.Continuous grazing and glyphosate spraying are the main drivers of grassland degradation.Controlled grazing and conservative stocking rates have been shown to reverse degradation and demonstrate that livestock production is compatible with ecosystem conserva-tion by maintaining regulating and provisioning services.As these management strategies are poorly integrated,improving their implementation will require important changes in farmers’decisions and the development of policies that create the economic conditions for this to happen.Research is needed to understand the conditions that prevent the knowledge generated from being transferred to producers and translated into practices that would improve the provision of ecosystem services.展开更多
Based on the work of Mumby et al.[Thresholds and the resilience of Caribbean coral reefs,Nature 450(2007)98-101],this study is devoted to investigate the deterministic and stochastic features of a coral reef ecosystem...Based on the work of Mumby et al.[Thresholds and the resilience of Caribbean coral reefs,Nature 450(2007)98-101],this study is devoted to investigate the deterministic and stochastic features of a coral reef ecosystem in which macroalgae and coral compete to occupy algae turfs,and the macroalgae are grazed by parrotfish.By taking the grazing rate as the focused parameter,we completely analyze the global dynamics of the deterministic coral reef ecosystem,including bistable phenomenon,linear equilibria and degenerate attractor.It is found that for different grazing rates,the coral reef system may exhibit rich dynamics which are closely dependent on the initial values.Furthermore,we derive a stochastic coral reef model in the form of continuous-time Markov chain(CTMC),and estimate the extinction probabilities of macroalgae and coral by using the branching process theory.Analytical results reveal that the macroalgae or coral species will go to extinction in a positive probability,even if it can survive in the deterministic environment.展开更多
Global grassland degradation necessitates the identification of sustainable grazing management strategies.In semi-arid regions,grazing exclusion(GE),cold-season grazing(CG),and free grazing(FG)represent common practic...Global grassland degradation necessitates the identification of sustainable grazing management strategies.In semi-arid regions,grazing exclusion(GE),cold-season grazing(CG),and free grazing(FG)represent common practices in grassland ecosystems,yet the long-term ecological consequences of these patterns on plant community structure and soil aggregate stability remain inadequately elucidated.In this study,we evaluated the effects of GE,CG,and FG on soil organic carbon,soil water content,soil bulk density,soil aggregates,and vegetation indicators in Xilamuren steppe,a semi-arid grassland in northern China through field sampling and laboratory analyses in 2024.Our findings revealed that,compared to CG and FG,GE significantly enhanced aboveground and belowground biomass,species diversity,and soil physical-chemical properties in the 0–30 cm layer.The dominant plant species in GE and CG sites were Stipa krylovii,Leymus chinensis,and Agropyron cristatum,whereas Stipa krylovii,Artemisia frigida,and Leymus chinensis were predominant in FG site.Different grazing patterns led to distinct soil aggregate distributions,with>2.00 and<0.25 mm aggregates exhibiting the highest content in different soil layers depending on the grazing patterns.All grazing management strategies significantly improved soil aggregate stability,with the overall stability following the order:GE>CG>FG.Furthermore,random forest modeling identified plant species diversity,plant growth traits,and grazing patterns as the primary determinants of soil aggregate stability.Collectively,these results offer valuable insights into the sustainable management and ecological restoration of semi-arid grasslands under different grazing pressures.展开更多
The alpine grassland vegetation on the Qinghai-Tibet Plateau is composed of plant patches in varied sizes.It remains uncertain whether vegetation recovery following grazing exclusion(GE)in degraded grasslands is drive...The alpine grassland vegetation on the Qinghai-Tibet Plateau is composed of plant patches in varied sizes.It remains uncertain whether vegetation recovery following grazing exclusion(GE)in degraded grasslands is driven by increases in patches number(NP),patch size(PS),or both.We based our predictions on two hypotheses:GE intensifies plant competition,and facilitation prevails near patches while competition prevails in interpatch spaces.We predicted that the NP would remain stable or decrease and PS would increase under GE treatment.To evaluate these predictions,we conducted a study in six lightly degraded alpine grasslands under free grazing(FG)conditions in Bangor County,Xizang Autonomous Region,China,with corresponding GE treatments using transects in 2017 and 2018.Results revealed that four sites in 2017 and five sites in 2018 had reduced NP and increased PS,with probabilities of 0.033(2017)and 0.004(2018),respectively,and a joint probability of 0.0001 under the null hypothesis that GE does not affect NP or PS.The NP reduction was solely due to the decrease in small patch sizes.An increase in PS was common across species,and a predominant tendency for NP reduction was observed among species across the sites.The overall changes in NP and PS were primarily driven by the three most abundant species(contributing more than 60%in both years),rather than by shifts in floristic composition.Our findings highlight that vegetation recovery in Bangor alpine steppes following GE relies solely on the expansion of existing patches rather than the recruitment of new ones in interpatch gaps.We recommend prioritizing growth-promoting measures,such as nutrient or water management,over seed addition when assisting with GE for restoring lightly degraded grasslands.展开更多
The connection between climatic factors and grazing is essential for maintaining ecosystem function and vegetation productivity.This study examined the impact of grazing intensity on vegetation across a broad climatic...The connection between climatic factors and grazing is essential for maintaining ecosystem function and vegetation productivity.This study examined the impact of grazing intensity on vegetation across a broad climatic gradient spanning the Espinal,Argentine Low Monte,and Patagonian Steppe ecoregions of Argentina.The research was carried out at eight sampling sites with radial grazing gradients generated around artificial water sources(piospheres),exhibiting two contrasting response patterns of vegetation to grazing pressure.One of the response patterns shows a typical vegetation response to grazing that the vegetation productivity increases with the distance to the water sources(decreasing grazing intensity).The second pattern is found in drier regions,where vegetation presents an inverse productivity response that vegetation productivity is higher near water sources(high grazing intensity)due to increased shrub cover.Vegetation productivity was measured using the Normalized Difference Vegetation Index(NDVI).Vegetation patch structure and cover were determined for each site with high,medium,and low grazing intensities.Results indicated that shrub cover is the primary driver of vegetation productivity,showing contrasting responses to grazing intensity between the two identified patterns.While NDVI proved to be a reliable proxy for shrub cover and total vegetation cover(R2>0.70),it failed to reflect grass cover dynamics.Furthermore,mean annual temperature was more strongly correlated with vegetation cover changes,while grazing intensity significantly altered vegetation patch structure and soil cover distribution.Specifically,in drier regions,high grazing intensity led to larger patches while,in wetter regions,it led to smaller patches(fragmentation).Shrubs,with their deeper roots and drought tolerance,were less preferred and more resistant to grazing in arid environments and thrived under grazing pressure in these arid conditions.Our results underscored the need for adaptive management strategies in grazing systems.Traditional approaches may require significant adjustments,as the efficacy of management hinges on the interplay of specific climatic conditions and the varied responses of vegetation.Furthermore,effective conservation efforts should prioritize the recognition and protection of shrubs given their critical contribution to ecosystem function and biodiversity.Ultimately,this research provides a valuable framework to understand the complex dynamics between grazing and vegetation in arid and semi-arid environments,highlighting that sustainable grazing practices should be tailored to account for both climatic variables and the unique characteristics of different plant communities.展开更多
Pine and oak forests have great relevance worldwide since they are recognized for the benefits and services they provide.Grazing can affect nitrogen reserves in forest trees in complex ways,the effects manifest throug...Pine and oak forests have great relevance worldwide since they are recognized for the benefits and services they provide.Grazing can affect nitrogen reserves in forest trees in complex ways,the effects manifest through changes in the soil,vegetation,and the nitrogen cycle.Nature tourism can have negative impacts on tree physiology.These impacts affect vital processes such as photosynthesis,respiration,water relations,and metabolism.This study was developed in order to determine whether natural populations of pine(Pinus cembroides Zucc.)and oak(Quercus grisea Liebm.)are affected physiologically by grazing and tourism during the stages of development and dormancy,specifically in nitrogenous compounds(Total Soluble Proteins[TSP]and Total Amino Acids[TAA])stocked in perennial organs(stem and roots)and leaves.The results showed that grazing and tourism have both negative and favorable effects on the concentrations of nitrogen compounds.The highest concentration of nitrogenous compounds was found in oak compared to pine.The root,trunk,and leaves in the grazed and non-impacted sites showed the highest concentrations of nitrogen compounds compared to the tourism-impacted site.Pine is the species most affected by anthropogenic processes(grazing and tourism)in the stages of development and dormancy,since the concentrations of nitrogenous compounds were lower compared to oak.展开更多
Developing advanced acoustic treatments,such as the Multi-Degree-of-Freedom(MDOF)septum liner,to realize the broadband noise reduction is critical for silent aeroengines.This study investigates experimentally the MDOF...Developing advanced acoustic treatments,such as the Multi-Degree-of-Freedom(MDOF)septum liner,to realize the broadband noise reduction is critical for silent aeroengines.This study investigates experimentally the MDOF septum liner and its impedance model on the Beihang Grazing Flow Duct(BGFD)setup,over a wide frequency range under grazing flows up to 0.5 Mach number and Sound Pressure Level(SPL)up to 150 dB,typically encountered in aeroengine nacelles.Several specimens varying in the numbers,types,and depths of septa among units are designed,fabricated,and measured.Their impedances and Transmission Losses(TL)are obtained using the mirror-based multimodal straightforward method and the mode decomposition technique,respectively.Generally,the model predictions show good agreement with the educed impedances in all cases,and such liners with a large-porosity facesheet exhibit low acoustic nonlinearities in the presence of high SPL,especially under high-velocity grazing flows.Moreover,a MDOF liner we delicately designed,compared with a conventional broadband three-layer perforated liner as the reference,is close to the resonant state at more frequencies and thus has higher and wider measured TL spectra almost from 1 kHz up to 10 kHz at studied Mach numbers,under the premise of saving 22.7 mm in the thickness.These show that,the MDOF septum liner,if well designed,can achieve an ultra-broadband efficient sound attenuation using more limited spaces in complex aeroacoustic environments.展开更多
Aim Grasslands are dominant vegetation of China,support outstanding biodiversity and sequester bulk amount of atmospheric CO_(2).These grasslands are highly degraded and fragmented due to remarkable anthropogenic and ...Aim Grasslands are dominant vegetation of China,support outstanding biodiversity and sequester bulk amount of atmospheric CO_(2).These grasslands are highly degraded and fragmented due to remarkable anthropogenic and grazing loads.Chinese Government has made great attempt to restore by grazing exclusion.The relations of carbon fluxes with species composition and diversity in the communities sensitive to grazing by large herbivores are needed to be analysed under the global climate change scenario.The objective of present study was to comprehend the effects of grazing and fencing on the ecosystem structure and function of the typical steppe grassland.Methods To meet the objectives,overgrazed and fenced(since year 2001)sys-tems were selected in typical steppe grassland at the Duolun Restoration Ecology Research Station,Inner Mogolia,China.Within each system,three dominant communities with three replicates were selected.In each replicate community,three 1×1 m plots,were randomly located.Each plot was divided into four 50×50 cm quadrats.A total of 216,50×50 cm quadrats were sampled.From each quadrat,number of individuals and above-ground herbaceous biomass for each species,soil respiration(SR),ecosystem respira-tion(ER),net(NEE)as well as gross(GEE)ecosystem CO_(2) exchanges were recorded in June 2015.Data were well analysed using statistical software.Canonical correspondence analysis showed dif-ferential responses of communities to the structure and function of the typical steppe grassland.Important Findings Across the communities,fencing reduced the soil tempera-ture by 12%and at the same time increased the soil moisture by 44.30%,thus,increased the species richness by 28%,evenness by 21%,above-ground biomass by 19%and plant carbon by 20%.Interestingly,fencing increased NEE by 128%,GEE by 77%,SR by 65%and ER by 39%.Under fencing,species composition partially governed the CO_(2) exchange processes.Conclusions Fencing reduces soil temperature and thereby improves species diversity and more efficient CO_(2) sequestration and long-term and in-depth study is desirable for a better understanding of the relation-ship between species diversity and ecosystem carbon uptake.展开更多
Background:Individual plants can identify their neighbors and adjust their biomass investment to avoid competing with their relatives or jointly cope with external stresses.Maternal effects can improve their offspring...Background:Individual plants can identify their neighbors and adjust their biomass investment to avoid competing with their relatives or jointly cope with external stresses.Maternal effects can improve their offspring adaptability under external stresses.However,how grazing-induced maternal effects influence plant kin interactions remain unknown.Methods:Clonal offspring of Leymus chinensis grown under multi-year grazing and non-grazing conditions were used for this study.A greenhouse experiment was conducted to evaluate the performance of focal plants in the presence of kin and stranger neighbors,with the aim of analyzing the interaction between maternal effect and kin relatedness.Results:Kin relatedness of neighboring plants affected the biomass production and allocation of focal plants,demonstrating the presence of kin recognition in L.chinensis.Moreover,grazing-induced maternal effects significantly enhanced kin recognition in the species.Consequently,the presence of stranger neighbors significantly improved the growth potential of grazed offspring.Specifically,the total biomass of clonal offspring increased by 73.1%compared to the kin group,potentially buffering grazing-induced plant productivity declines.Conclusions:This study shows that historical grazing enhances kin recognition in L.chinensis.Thus,introducing multi-genotypic plants can increase the productivity of grasslands.The findings of this study enhance our understanding of intraspecific plant–plant interactions in clonal species and provide new insights into sustainable grassland management.展开更多
Background:Native warm-season grass(NWSG)mixtures may provide a lownitrogen(N)-input summer perennial forage option to extensively managed forage-livestock systems.Methods:Mixed pastures of big bluestem(Andropogon ger...Background:Native warm-season grass(NWSG)mixtures may provide a lownitrogen(N)-input summer perennial forage option to extensively managed forage-livestock systems.Methods:Mixed pastures of big bluestem(Andropogon gerardii Vitman),little bluestem(Schizachyrium scoparium Michx.),and indiangrass(Sorghastrum nutans L.)fertilized with 0 or 67 kgNha−1 were continuously stocked with beef heifers and cows.Forage mass,nutritive value,and canopy heights were determined every 2 weeks during the grazing season.Stand persistence measures included the canopy cover and leaf area index(LAI)and plant crown density at spring emergence following 3 years of grazing management.Results:Forage mass,canopy height,and stocking densities were greater for N-fertilized NWSG than unfertilized NWSG for the first 30 days of the growing season across the 3-year study.Forage NWSG fertilized with N had a greater decrease in LAI during the growing season(51%decrease)than unfertilized NWSG.Spring NWSG plant density estimates following 3 years of grazing did not differ across N management strategies.Conclusions:Forage NWSG mixtures supported superior forage attributes and greater stocking densities early in the grazing season under low-level N than zero-N-input systems and may provide a low-N-input alternative for improved species use in southeastern US forage-livestock systems.展开更多
Fencing for grazing exclusion is regarded as a traditional and effective method for the natural restoration of degraded alpine steppe,and it effectively promotes plant growth and enhances soil carbon stocks.Arbuscular...Fencing for grazing exclusion is regarded as a traditional and effective method for the natural restoration of degraded alpine steppe,and it effectively promotes plant growth and enhances soil carbon stocks.Arbuscular mycorrhizal fungi(AMF)are essential microorganisms in grassland that play a major role in plant-derived C translocation into the soil.However,the effects of fencing on AMF communities and their contributions to soil carbon sequestration are still unclear.In this study,alpine steppe areas with three different fencing durations(free grazing,medium-term fencing for 5-6 years and long-term fencing for more than 10 years)in the northern Tibetan Plateau were selected to explore the effects of grazing exclusion on AMF communities and their roles in soil carbon sequestration.The results showed that medium-and long-term fencing significantly increased both plant aboveground biomass and soil organic carbon(SOC)content.The AMF community composition varied significantly during different fencing durations,with a dramatic increase in the relative abundance of Glomus but a significant reduction in the relative abundance of Diversispora with longer fencing time.Medium-term fencing significantly increased AMF richness and the ShannonWiener index.Meanwhile,fencing significantly increased hyphal length density(HLD),glomalin-related soil protein(GRSP)and the proportion of macroaggregates(250-2,000μm),all of which contribute positively to SOC.Structural equation modeling revealed that fencing time positively influenced HLD and the AMF community composition,subsequently affecting T-GRSP,which was tightly correlated with SOC.Our findings suggest the potentially important contribution of AMF to SOC sequestration,so more attention should be paid to AMF during alpine steppe fencing,particularly for enhancing the efficiency of degraded grassland restoration efforts.展开更多
High-altitude peatlands(HAPs;defined as>1,500 m)provide important ecosystem services including soil carbon(C)storage.However,temperatures in high-altitude regions have been rising rapidly in recent decades,while HA...High-altitude peatlands(HAPs;defined as>1,500 m)provide important ecosystem services including soil carbon(C)storage.However,temperatures in high-altitude regions have been rising rapidly in recent decades,while HAPs are increasingly affected by human activities such as intensive drainage and grazing.Collectively,climate change and land management may strongly affect the HAP C cycle.Here,we synthesise current global progress on the HAP C cycle,focussing on the impacts of climate change and land management.Warming increased both ecosystem respiration(ER)and methane(CH_(4))emissions(26%–86%),while impacts on net ecosystem exchange(NEE)of CO_(2)were still unclear.However,short-term drought decreased ER and CH_(4)emissions(7%–96%),along with NEE(12%–52%).Snow,permafrost,and glacier decline may also impact the C cycle in HAPs,although a limited number of studies have been conducted.Grazing and vegetation degradation impacts on HAP C cycling were related to grazing and degradation intensity,while generally decreasing soil organic C stocks(3%–51%).Moving from shallower to deeper WTLs stimulated ER(9%–812%),while reducing CH_(4)emissions(13%–100%),with variable effects on NEE(-53%–700%).Restoration by rewetting began to reverse the trend of drainage.We highlight several knowledge gaps,including limited understanding of climate change and land-management effects on gross primary productivity and dissolved organic carbon,while there is still limited knowledge of regional differences in HAP C cycling.Future research should focus on the interaction of land-use and climate change in HAPs,including HAP restoration,which may help future conservation of these valuable ecosystems.展开更多
When the dominant species in a plant community are palatable,many believe that large herbivores will reduce the dominant species and promote the proportion of previously suppressed species.However,this view may not al...When the dominant species in a plant community are palatable,many believe that large herbivores will reduce the dominant species and promote the proportion of previously suppressed species.However,this view may not always hold true.We conducted a 4-year yak grazing experiment on the Qinghai-Tibet Plateau and tracked the plant compositions of the rotational grazing(RG)and grazing exclusion(GE)grasslands during the four years.The results showed that in the absence of yaks under GE,the plant community was dominated by two palatable species,Kobresia pygmaea and Stipa capillata,due to their small leaf area and rapid growth strategy.The presence of yaks under RG significantly inhibited S.capillata and over half of the forbs,while the proportion of K.pygmaea increased and it became the absolute dominant species,contradicting the view that large herbivores inhibit palatable species.Interannually,the dominance of K.pygmaea under RG decreased in the dry year,leading to an increase in the dominance of the other eight species.Under GE,the dominance of K.pygmaea declined notably in the dry year,while S.capillata and seven other forbs increased substantially.Overall,these results suggest that K.pygmaea is grazing-tolerant but not drought-tolerant,whereas the other eight species are drought-tolerant but not grazingtolerant.At the community level,community composition shifts resulting from succession after grazing exclusion exceeded those caused by drought,drought tends to induce community species turnover while grazing tends to induce species abundance variations.In summary,our conclusions remind ranch managers that when considering the impact of livestock on plant community composition,they should factor in local conditions and climate change rather than simply assuming that livestock will suppress the palatable species.展开更多
Invasive species are increasingly spreading,particularly in rangeland ecosystems.It is essential to evaluate the effectiveness of different methods for controlling invasive plants in these ecosystems.This study aimed ...Invasive species are increasingly spreading,particularly in rangeland ecosystems.It is essential to evaluate the effectiveness of different methods for controlling invasive plants in these ecosystems.This study aimed to investigate the effects of three strategies-21-year grazing exclusion(21-YES),mowing-grazing in rotation in alternate years(MGRS),and moderate grazing(MGS)-on the change in cover,density,and biomass of Leucanthemum vulgare Lam.(Ox-eye Daisy=OED)and the plant community.To accomplish this,three sites selected for each treatment.In 2021,270 vegetation plots were sampled using a random systematic method.Subsequently,we recorded the density and canopy cover of all growth forms(forbs,grasses,and ferns),the OED biomass,and the ground cover.The results indicated that MGS reduced OED density,OED canopy,and OED biomass.Furthermore,this strategy demonstrated the highest density and canopy cover of the plant community(including total,forbs,grasses,and ferns).Additionally,the strongest correlation was observed between the total canopy and the OED density(R2=-0.91,-0.95,-0.94 in 21-YES,MGRS,and MGS,respectively),as well as between the total canopy and the OED canopy(R2=-0.51,-0.98,-0.97 in 21-YES,MGRS,and MGS,respectively).The MGS led to an increase in diversity indices.In general,the grazing strategy has proven to be effective in controlling the spread of invasive OED and has also resulted in an increase in canopy cover,density,and diversity indices of the plant community.The study highlights the importance of ongoing management efforts to control invasive species,with moderate grazing potentially serving as a more practical,culturally accepted,and costeffective short-term control strategy for widespread rangeland weed infestations.展开更多
Climate and grazing have a significant effect on vegetation structure and soil organic carbon(SOC)distribution,particularly in mountain ecosystems that are highly susceptible to climate change.However,we lack a system...Climate and grazing have a significant effect on vegetation structure and soil organic carbon(SOC)distribution,particularly in mountain ecosystems that are highly susceptible to climate change.However,we lack a systematic understanding of how vegetation structure reacts to long-term grazing disturbances,as well as the processes that influence SOC distribution.This study uses multiple sets of data spanning 20 years from a typical alpine grassland in the Qilian Mountains to investigate the effects of climate and grazing on various root-type grasses as well as the mechanisms that drive SOC distribution.We found that grazing increases the biomass of annual,biennial and perennial taproots while decreasing that of perennial rhizomes.We also found that various root-type grasses have different responses to climate and grazing.Multiple factors jointly control the variation of SOC content(SOCc),and the variation of SOC stock(SOCs)is mainly explained by the interaction between climate and grazing years.Climate and grazing can directly or indirectly affect SOCc through vegetation,and SOCs are mainly dominated by the direct effects of grazing years and grazing gradients.Grazing gradients and root-type grass biomass have a significant effect on SOC,with little effect from climate factors.Therefore,long-term grazing may affect the root-type grass and further affect SOC distribution through differences in nutrient acquisition ability and reproductive pathways.These findings provide important guidance for regulating soil carbon sequestration potential by varying the proportion of different root-type grass in the community via sowing,livestock configuration,or grazing time.展开更多
基金supported by the National Natural Science Foundation of China(32161143028)the Key Technology of Grassland Ecological Civilization Demonstration Area in Ningxia Hui Autonomous Region,China(20210239)the Northwest Shelterbelt Construction Bureau of the National Forestry and Grassland Administration,China。
文摘Understanding livestock performance in typical steppe ecosystems is essential for optimizing grassland-livestock interactions and minimizing environmental impact.To assess the effects of different stocking rates on the growth performance,energy and nitrogen utilization,methane(CH_(4))emissions,and grazing behavior of Tan sheep,a 2-year grazing experiment in the typical steppe was conducted.The grazing area was divided into 9 paddocks,each 0.5 ha,with 3 spatial replicates for each stocking rate treatment(4,8,and 13 sheep per paddock),corresponding to 2.7,5.3,and 8.7 sheep ha^(–1).The results showed that the neutral detergent fiber(NDF)and acid detergent fiber(ADF)contents of herbage varied between grazing years(P<0.05),with a positive correlation between stocking rate and crude fiber content in the herbage(P<0.05).Dry matter intake(DMI)decreased with increasing stocking rate(P<0.05),and the average daily gain(ADG)was highest at 2.7 sheep ha^(–1)(P<0.05).Compared to 2.7 and 8.7 sheep ha^(–1),the5.3 sheep ha^(–1)treatment exhibited the lowest nutrient digestibility for dry matter,nitrogen,and ether extract(P<0.05).Fecal nitrogen was lowest at 8.7 sheep ha^(–1)(P<0.05),while retained nitrogen as a proportion of nitrogen intake was highest.Digestive energy(DE),metabolic energy(ME),and the ratios of DE to gross energy(GE)and ME to GE were highest at 8.7 sheep ha^(–1)(P<0.05).In contrast,CH_4 emissions,CH_4 per DMI,and CH_(4)E as a proportion of GE were highest at 2.7 sheep ha^(–1)(P<0.05).Stocking rate and grazing year did not significantly affect rumen fermentation parameters,including volatile fatty acids,acetate,propionate,and the acetate/propionate ratio.At 8.7sheep ha^(–1),daily grazing time and inter-individual distance increased,while time allocated to grazing,walking,and ruminating/resting decreased as stocking rates increased(P<0.05).This study highlights the importance of adjusting stocking rates based on the nutritional value of forage and grazing year to optimize grazing management.
基金supported by the international Partnership Program of the Chinese Academy of Science(Grant No.131965KYSB20160004)the National Natural Science Foundation of China(Grant No.U1803243)+1 种基金the Network Plan of the Science and Technology Service,Chinese Academy of Sciences(STS Plan)Qinghai innovation platform construction project(2017-ZJ-Y20)
文摘Remote sensing(RS) technologies provide robust techniques for quantifying net primary productivity(NPP) which is a key component of ecosystem production management. Applying RS, the confounding effects of carbon consumed by livestock grazing were neglected by previous studies, which created uncertainties and underestimation of NPP for the grazed lands. The grasslands in Xinjiang were selected as a case study to improve the RS based NPP estimation. A defoliation formulation model(DFM) based on RS is developed to evaluate the extent of underestimated NPP between 1982 and 2011. The estimates were then used to examine the spatiotemporal patterns of the calculated NPP. Results show that average annual underestimated NPP was 55.74 gC·m^(-2)yr^(-1) over the time period understudied, accounting for 29.06% of the total NPP for the Xinjiang grasslands. The spatial distribution of underestimated NPP is related to both grazing intensity and time. Data for the Xinjiang grasslands show that the average annual NPP was 179.41 gC·m^(-2)yr^(-1), the annual NPP with an increasing trend was observed at a rate of 1.04 gC·m^(-2)yr^(-1) between 1982 and 2011. The spatial distribution of NPP reveals distinct variations from high to low encompassing the geolocations of the Tianshan Mountains, northern and southern Xinjiang Province and corresponding with mid-mountain meadow, typical grassland, desert grassland, alpine meadow, and saline meadow grassland types. This study contributes to improving RS-based NPP estimations for grazed land and provides a more accurate data to support the scientific management of fragile grassland ecosystems in Xinjiang.
基金Supported by Guizhou Academy of Agricultural Sciences Foundation(2010023)Guizhou Academy of Agricultural Sciences Special Funds([2011]021)Guizhou Academy of Agricultural Sciences Foundation for the Talents([2011]01)~~
文摘＂Ryegrass, orchard grass, Festuca arundinacea and Trifolium repens＂ were researched in Dushan County, Guizhou Province, in order explore grass characteristics by different grazing methods in seasons. The results show that grass community height in different groups was of little differences（P0.05）; the group of moderate grazing in spring, summer and autumn dominated in grass cover; grass density showed insignificant variations among different treatment groups（P0.05） and in the groups of heavy grazing in spring and autumn and moderate grazing in summer and of moderate grazing in spring, summer and autumn, grass community density was higher compared with the other groups（P0.05）; as for above-ground biomass, the group of moderate grazing in spring and autumn and heavy grazing in summer and of moderate grazing in spring, summer and autumn dominated.
文摘Animals excrete feces during grazing. The uneven distribution of feces causes a spatial heterogeneity in grassland communities. In this study, we attempted to clarify the effects of feces on spatial distribution patterns of plant species. A field study was conducted on four grasslands each grazed by a single cow. These four grasslands were defined as Poa pratensis （Kentucky bluegrass） dominated grassland without feces （PoF-）, Poa pratensis dominated grassland with feces （PoF＋）, Zoysia japonica Steud. （Japanese lawngrass） dominated grassland without feces （ZyF-）, and Zoysia japonica Steud. dominated grassland with feces （ZyF＋）. A 50 m line that transects 100 equally spaced quadrats （L-quadrats） was drawn on each of the four grasslands. Each quadrat was 0.50 m × 0.50 m in size and consisted of four equal-area cells of 0.25 m ×0.25 m （S-quadrats）. The occurrences of all plant species were recorded in each S-quadrat. The binomial distribution （BD） and beta-binomial distribution （BBD） were used to represent the variation in spatial patterns. The BBD provided a significant description of the frequency distribution of plants per quadrat. A power law was used to calculate the spatial heterogeneity of each species together with the community heterogeneity. The results revealed that the plants on each of the four grasslands were aggregatively distributed. The ZyF＋ exhibited greater spatial heterogeneity than the ZyF-due to the uneven deposition of feces by cows grazing on the grasslands. Additionally we also found that the feces had effect on the heterogeneity inZyF＋ and did not have effect in PoF＋.
基金supported by the National University of Río Negro(PI 40-C-654,PI 40-C-873)。
文摘In semi-arid lands,vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix.Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation and soil compaction.Nevertheless,some species with anchorage mechanisms in their seeds might overcome this,such as Nassella tenuis(Phil.)Barkworth.This is an important species in grazing paddocks because it has an intermediate palatability and its relatively tolerant to grazing.These characteristics allow N.tenuis to increase its abundance in grazed sites.Our objective was to assess how grazing affects the key palatable species from seeds to seedlings:i.e.,seed rain,soil seed bank,and seedling recruitment in different microsites along a windward-leeward transect across shrub canopy.We hypothesized that:(1)the negative effects of grazing on N.tenuis fructification are reflected in its seed rain,soil seed bank,and seedling recruitment,especially in interpatches;(2)Nassella tenuis seed rain reduction,soil compaction by cattle in grazed sites,and removal of seeds by wind decrease its soil seed bank,especially in microsites exposed to the predominant wind;and(3)the decrease in N.tenuis soil seed bank and cover increase in annual species in grazed sites have negative effects on its seedling recruitment,especially in microsites exposed to predominant wind.We placed seed traps,collected soil samples,and monitored seedling recruitment in different locations around shrub canopy to address our hypotheses.Also,we established a manipulative experiment in which we sow N.tenuis seeds and followed its recruitment in different microsites.We compared the seed rain,soil seed bank,natural seedling recruitment,and sown seeds recruitment of N.tenuis between grazed and ungrazed sites.We analyzed differences between microsites along a windward-leeward transect across shrubs patches.Seed rain and soil seed bank had the same density in patches and interpatches both in ungrazed and grazed sites.But seed rain was higher,and soil seed bank was lower in ungrazed sites than in grazed sites.Almost all under-canopy microsites showed greater soil seed bank abundance and natural seedling recruitment in ungrazed sites.Sown seeds recruitment was the same between grazed and ungrazed sites,but it showed protective effects of shrubs in leeward microsites under grazed sites.As a conclusion,seed rain and soil seed bank are complementary under grazed sites.
文摘The Flooding Pampa grasslands are the last remnant of the Rio de la Plata grasslands in Argentina.Anthropo-genic interventions have led to severe degradation and,as a result,the ecosystem services provided by the grass-lands are declining,in terms of provisioning,regulating,and supporting services.We synthesized the existing literature on the ecosystem goods and services provided by these grasslands under grazing in different conditions and conservation status.We found that plant and animal diversity and primary production are the most studied ecosystem services,while climate regulation,water supply,nutrient cycling,meat production and erosion control,in that order,are less studied.Cultural services are under-researched.Continuous grazing and glyphosate spraying are the main drivers of grassland degradation.Controlled grazing and conservative stocking rates have been shown to reverse degradation and demonstrate that livestock production is compatible with ecosystem conserva-tion by maintaining regulating and provisioning services.As these management strategies are poorly integrated,improving their implementation will require important changes in farmers’decisions and the development of policies that create the economic conditions for this to happen.Research is needed to understand the conditions that prevent the knowledge generated from being transferred to producers and translated into practices that would improve the provision of ecosystem services.
基金supported by the grants from National Natural Science Foundation of China(12231012,12161005,62173161).
文摘Based on the work of Mumby et al.[Thresholds and the resilience of Caribbean coral reefs,Nature 450(2007)98-101],this study is devoted to investigate the deterministic and stochastic features of a coral reef ecosystem in which macroalgae and coral compete to occupy algae turfs,and the macroalgae are grazed by parrotfish.By taking the grazing rate as the focused parameter,we completely analyze the global dynamics of the deterministic coral reef ecosystem,including bistable phenomenon,linear equilibria and degenerate attractor.It is found that for different grazing rates,the coral reef system may exhibit rich dynamics which are closely dependent on the initial values.Furthermore,we derive a stochastic coral reef model in the form of continuous-time Markov chain(CTMC),and estimate the extinction probabilities of macroalgae and coral by using the branching process theory.Analytical results reveal that the macroalgae or coral species will go to extinction in a positive probability,even if it can survive in the deterministic environment.
基金supported by the National Key Research and Development Program of China(2024YFF1306305)the Inner Mongolia Autonomous Region Natural Science Foundation Project(2025QN03106)+1 种基金the Research Start-up Project for the Introduction of High-level and Outstanding Doctoral Talent at Inner Mongolia Agricultural University(NDYB2024-42)the National Natural Science Foundation of China(42201012).
文摘Global grassland degradation necessitates the identification of sustainable grazing management strategies.In semi-arid regions,grazing exclusion(GE),cold-season grazing(CG),and free grazing(FG)represent common practices in grassland ecosystems,yet the long-term ecological consequences of these patterns on plant community structure and soil aggregate stability remain inadequately elucidated.In this study,we evaluated the effects of GE,CG,and FG on soil organic carbon,soil water content,soil bulk density,soil aggregates,and vegetation indicators in Xilamuren steppe,a semi-arid grassland in northern China through field sampling and laboratory analyses in 2024.Our findings revealed that,compared to CG and FG,GE significantly enhanced aboveground and belowground biomass,species diversity,and soil physical-chemical properties in the 0–30 cm layer.The dominant plant species in GE and CG sites were Stipa krylovii,Leymus chinensis,and Agropyron cristatum,whereas Stipa krylovii,Artemisia frigida,and Leymus chinensis were predominant in FG site.Different grazing patterns led to distinct soil aggregate distributions,with>2.00 and<0.25 mm aggregates exhibiting the highest content in different soil layers depending on the grazing patterns.All grazing management strategies significantly improved soil aggregate stability,with the overall stability following the order:GE>CG>FG.Furthermore,random forest modeling identified plant species diversity,plant growth traits,and grazing patterns as the primary determinants of soil aggregate stability.Collectively,these results offer valuable insights into the sustainable management and ecological restoration of semi-arid grasslands under different grazing pressures.
基金financially supported by the Science and Technology Bureau of Ali Prefecture,project named“Assessing the Carbon Sequestration and Carbon Sink Enhancement Potential of Natural Ecosystems in Ali Region(QYXTZX-AL2022-05)”。
文摘The alpine grassland vegetation on the Qinghai-Tibet Plateau is composed of plant patches in varied sizes.It remains uncertain whether vegetation recovery following grazing exclusion(GE)in degraded grasslands is driven by increases in patches number(NP),patch size(PS),or both.We based our predictions on two hypotheses:GE intensifies plant competition,and facilitation prevails near patches while competition prevails in interpatch spaces.We predicted that the NP would remain stable or decrease and PS would increase under GE treatment.To evaluate these predictions,we conducted a study in six lightly degraded alpine grasslands under free grazing(FG)conditions in Bangor County,Xizang Autonomous Region,China,with corresponding GE treatments using transects in 2017 and 2018.Results revealed that four sites in 2017 and five sites in 2018 had reduced NP and increased PS,with probabilities of 0.033(2017)and 0.004(2018),respectively,and a joint probability of 0.0001 under the null hypothesis that GE does not affect NP or PS.The NP reduction was solely due to the decrease in small patch sizes.An increase in PS was common across species,and a predominant tendency for NP reduction was observed among species across the sites.The overall changes in NP and PS were primarily driven by the three most abundant species(contributing more than 60%in both years),rather than by shifts in floristic composition.Our findings highlight that vegetation recovery in Bangor alpine steppes following GE relies solely on the expansion of existing patches rather than the recruitment of new ones in interpatch gaps.We recommend prioritizing growth-promoting measures,such as nutrient or water management,over seed addition when assisting with GE for restoring lightly degraded grasslands.
基金supported by the Universidad Nacional de Río Negro(PI-UNRN 40C-1088)the Consejo Nacional de Investigaciones Científicas y Técnicas(PIP-CONICET 2023-402).
文摘The connection between climatic factors and grazing is essential for maintaining ecosystem function and vegetation productivity.This study examined the impact of grazing intensity on vegetation across a broad climatic gradient spanning the Espinal,Argentine Low Monte,and Patagonian Steppe ecoregions of Argentina.The research was carried out at eight sampling sites with radial grazing gradients generated around artificial water sources(piospheres),exhibiting two contrasting response patterns of vegetation to grazing pressure.One of the response patterns shows a typical vegetation response to grazing that the vegetation productivity increases with the distance to the water sources(decreasing grazing intensity).The second pattern is found in drier regions,where vegetation presents an inverse productivity response that vegetation productivity is higher near water sources(high grazing intensity)due to increased shrub cover.Vegetation productivity was measured using the Normalized Difference Vegetation Index(NDVI).Vegetation patch structure and cover were determined for each site with high,medium,and low grazing intensities.Results indicated that shrub cover is the primary driver of vegetation productivity,showing contrasting responses to grazing intensity between the two identified patterns.While NDVI proved to be a reliable proxy for shrub cover and total vegetation cover(R2>0.70),it failed to reflect grass cover dynamics.Furthermore,mean annual temperature was more strongly correlated with vegetation cover changes,while grazing intensity significantly altered vegetation patch structure and soil cover distribution.Specifically,in drier regions,high grazing intensity led to larger patches while,in wetter regions,it led to smaller patches(fragmentation).Shrubs,with their deeper roots and drought tolerance,were less preferred and more resistant to grazing in arid environments and thrived under grazing pressure in these arid conditions.Our results underscored the need for adaptive management strategies in grazing systems.Traditional approaches may require significant adjustments,as the efficacy of management hinges on the interplay of specific climatic conditions and the varied responses of vegetation.Furthermore,effective conservation efforts should prioritize the recognition and protection of shrubs given their critical contribution to ecosystem function and biodiversity.Ultimately,this research provides a valuable framework to understand the complex dynamics between grazing and vegetation in arid and semi-arid environments,highlighting that sustainable grazing practices should be tailored to account for both climatic variables and the unique characteristics of different plant communities.
基金funded by the National Council of Science and Technology(postgraduate scholarship awarded to Antonio Gallegos-Islas)the“Antonio Narro”Autonomous Agrarian University.
文摘Pine and oak forests have great relevance worldwide since they are recognized for the benefits and services they provide.Grazing can affect nitrogen reserves in forest trees in complex ways,the effects manifest through changes in the soil,vegetation,and the nitrogen cycle.Nature tourism can have negative impacts on tree physiology.These impacts affect vital processes such as photosynthesis,respiration,water relations,and metabolism.This study was developed in order to determine whether natural populations of pine(Pinus cembroides Zucc.)and oak(Quercus grisea Liebm.)are affected physiologically by grazing and tourism during the stages of development and dormancy,specifically in nitrogenous compounds(Total Soluble Proteins[TSP]and Total Amino Acids[TAA])stocked in perennial organs(stem and roots)and leaves.The results showed that grazing and tourism have both negative and favorable effects on the concentrations of nitrogen compounds.The highest concentration of nitrogenous compounds was found in oak compared to pine.The root,trunk,and leaves in the grazed and non-impacted sites showed the highest concentrations of nitrogen compounds compared to the tourism-impacted site.Pine is the species most affected by anthropogenic processes(grazing and tourism)in the stages of development and dormancy,since the concentrations of nitrogenous compounds were lower compared to oak.
基金co-supported by the National Natural Science Foundation of China(No.52206039)the Taihang Laboratory of China(No.A2053)+1 种基金the Aeronautical Science Foundation of China(No.20240011051001)the National Key R&D Program of China(No.2021YFB3703900)。
文摘Developing advanced acoustic treatments,such as the Multi-Degree-of-Freedom(MDOF)septum liner,to realize the broadband noise reduction is critical for silent aeroengines.This study investigates experimentally the MDOF septum liner and its impedance model on the Beihang Grazing Flow Duct(BGFD)setup,over a wide frequency range under grazing flows up to 0.5 Mach number and Sound Pressure Level(SPL)up to 150 dB,typically encountered in aeroengine nacelles.Several specimens varying in the numbers,types,and depths of septa among units are designed,fabricated,and measured.Their impedances and Transmission Losses(TL)are obtained using the mirror-based multimodal straightforward method and the mode decomposition technique,respectively.Generally,the model predictions show good agreement with the educed impedances in all cases,and such liners with a large-porosity facesheet exhibit low acoustic nonlinearities in the presence of high SPL,especially under high-velocity grazing flows.Moreover,a MDOF liner we delicately designed,compared with a conventional broadband three-layer perforated liner as the reference,is close to the resonant state at more frequencies and thus has higher and wider measured TL spectra almost from 1 kHz up to 10 kHz at studied Mach numbers,under the premise of saving 22.7 mm in the thickness.These show that,the MDOF septum liner,if well designed,can achieve an ultra-broadband efficient sound attenuation using more limited spaces in complex aeroacoustic environments.
基金This study was supported by TWAS Fellowships for Research and Advanced Training,Italy to R.S.(FR number 3240281997)the National Natural Science Foundation of China(31430015,31270564).
文摘Aim Grasslands are dominant vegetation of China,support outstanding biodiversity and sequester bulk amount of atmospheric CO_(2).These grasslands are highly degraded and fragmented due to remarkable anthropogenic and grazing loads.Chinese Government has made great attempt to restore by grazing exclusion.The relations of carbon fluxes with species composition and diversity in the communities sensitive to grazing by large herbivores are needed to be analysed under the global climate change scenario.The objective of present study was to comprehend the effects of grazing and fencing on the ecosystem structure and function of the typical steppe grassland.Methods To meet the objectives,overgrazed and fenced(since year 2001)sys-tems were selected in typical steppe grassland at the Duolun Restoration Ecology Research Station,Inner Mogolia,China.Within each system,three dominant communities with three replicates were selected.In each replicate community,three 1×1 m plots,were randomly located.Each plot was divided into four 50×50 cm quadrats.A total of 216,50×50 cm quadrats were sampled.From each quadrat,number of individuals and above-ground herbaceous biomass for each species,soil respiration(SR),ecosystem respira-tion(ER),net(NEE)as well as gross(GEE)ecosystem CO_(2) exchanges were recorded in June 2015.Data were well analysed using statistical software.Canonical correspondence analysis showed dif-ferential responses of communities to the structure and function of the typical steppe grassland.Important Findings Across the communities,fencing reduced the soil tempera-ture by 12%and at the same time increased the soil moisture by 44.30%,thus,increased the species richness by 28%,evenness by 21%,above-ground biomass by 19%and plant carbon by 20%.Interestingly,fencing increased NEE by 128%,GEE by 77%,SR by 65%and ER by 39%.Under fencing,species composition partially governed the CO_(2) exchange processes.Conclusions Fencing reduces soil temperature and thereby improves species diversity and more efficient CO_(2) sequestration and long-term and in-depth study is desirable for a better understanding of the relation-ship between species diversity and ecosystem carbon uptake.
基金supported by the National Natural Science Foundation of China(32071882),Xiliang Li.
文摘Background:Individual plants can identify their neighbors and adjust their biomass investment to avoid competing with their relatives or jointly cope with external stresses.Maternal effects can improve their offspring adaptability under external stresses.However,how grazing-induced maternal effects influence plant kin interactions remain unknown.Methods:Clonal offspring of Leymus chinensis grown under multi-year grazing and non-grazing conditions were used for this study.A greenhouse experiment was conducted to evaluate the performance of focal plants in the presence of kin and stranger neighbors,with the aim of analyzing the interaction between maternal effect and kin relatedness.Results:Kin relatedness of neighboring plants affected the biomass production and allocation of focal plants,demonstrating the presence of kin recognition in L.chinensis.Moreover,grazing-induced maternal effects significantly enhanced kin recognition in the species.Consequently,the presence of stranger neighbors significantly improved the growth potential of grazed offspring.Specifically,the total biomass of clonal offspring increased by 73.1%compared to the kin group,potentially buffering grazing-induced plant productivity declines.Conclusions:This study shows that historical grazing enhances kin recognition in L.chinensis.Thus,introducing multi-genotypic plants can increase the productivity of grasslands.The findings of this study enhance our understanding of intraspecific plant–plant interactions in clonal species and provide new insights into sustainable grassland management.
文摘Background:Native warm-season grass(NWSG)mixtures may provide a lownitrogen(N)-input summer perennial forage option to extensively managed forage-livestock systems.Methods:Mixed pastures of big bluestem(Andropogon gerardii Vitman),little bluestem(Schizachyrium scoparium Michx.),and indiangrass(Sorghastrum nutans L.)fertilized with 0 or 67 kgNha−1 were continuously stocked with beef heifers and cows.Forage mass,nutritive value,and canopy heights were determined every 2 weeks during the grazing season.Stand persistence measures included the canopy cover and leaf area index(LAI)and plant crown density at spring emergence following 3 years of grazing management.Results:Forage mass,canopy height,and stocking densities were greater for N-fertilized NWSG than unfertilized NWSG for the first 30 days of the growing season across the 3-year study.Forage NWSG fertilized with N had a greater decrease in LAI during the growing season(51%decrease)than unfertilized NWSG.Spring NWSG plant density estimates following 3 years of grazing did not differ across N management strategies.Conclusions:Forage NWSG mixtures supported superior forage attributes and greater stocking densities early in the grazing season under low-level N than zero-N-input systems and may provide a low-N-input alternative for improved species use in southeastern US forage-livestock systems.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program,China(2019QZKK0304)the National Natural Science Foundation of China(31800380 and 31761123001-1)。
文摘Fencing for grazing exclusion is regarded as a traditional and effective method for the natural restoration of degraded alpine steppe,and it effectively promotes plant growth and enhances soil carbon stocks.Arbuscular mycorrhizal fungi(AMF)are essential microorganisms in grassland that play a major role in plant-derived C translocation into the soil.However,the effects of fencing on AMF communities and their contributions to soil carbon sequestration are still unclear.In this study,alpine steppe areas with three different fencing durations(free grazing,medium-term fencing for 5-6 years and long-term fencing for more than 10 years)in the northern Tibetan Plateau were selected to explore the effects of grazing exclusion on AMF communities and their roles in soil carbon sequestration.The results showed that medium-and long-term fencing significantly increased both plant aboveground biomass and soil organic carbon(SOC)content.The AMF community composition varied significantly during different fencing durations,with a dramatic increase in the relative abundance of Glomus but a significant reduction in the relative abundance of Diversispora with longer fencing time.Medium-term fencing significantly increased AMF richness and the ShannonWiener index.Meanwhile,fencing significantly increased hyphal length density(HLD),glomalin-related soil protein(GRSP)and the proportion of macroaggregates(250-2,000μm),all of which contribute positively to SOC.Structural equation modeling revealed that fencing time positively influenced HLD and the AMF community composition,subsequently affecting T-GRSP,which was tightly correlated with SOC.Our findings suggest the potentially important contribution of AMF to SOC sequestration,so more attention should be paid to AMF during alpine steppe fencing,particularly for enhancing the efficiency of degraded grassland restoration efforts.
基金supported by the National Natural Science Foundation of China(Grants No.U2243226 and 42250410326)the Research Start-up Fund of the Institute of Geographic Sciences and Natural Resources Research(Chinese Academy of Sciences)。
文摘High-altitude peatlands(HAPs;defined as>1,500 m)provide important ecosystem services including soil carbon(C)storage.However,temperatures in high-altitude regions have been rising rapidly in recent decades,while HAPs are increasingly affected by human activities such as intensive drainage and grazing.Collectively,climate change and land management may strongly affect the HAP C cycle.Here,we synthesise current global progress on the HAP C cycle,focussing on the impacts of climate change and land management.Warming increased both ecosystem respiration(ER)and methane(CH_(4))emissions(26%–86%),while impacts on net ecosystem exchange(NEE)of CO_(2)were still unclear.However,short-term drought decreased ER and CH_(4)emissions(7%–96%),along with NEE(12%–52%).Snow,permafrost,and glacier decline may also impact the C cycle in HAPs,although a limited number of studies have been conducted.Grazing and vegetation degradation impacts on HAP C cycling were related to grazing and degradation intensity,while generally decreasing soil organic C stocks(3%–51%).Moving from shallower to deeper WTLs stimulated ER(9%–812%),while reducing CH_(4)emissions(13%–100%),with variable effects on NEE(-53%–700%).Restoration by rewetting began to reverse the trend of drainage.We highlight several knowledge gaps,including limited understanding of climate change and land-management effects on gross primary productivity and dissolved organic carbon,while there is still limited knowledge of regional differences in HAP C cycling.Future research should focus on the interaction of land-use and climate change in HAPs,including HAP restoration,which may help future conservation of these valuable ecosystems.
基金financially supported by grants from the National Natural Science Foundation of China(32101315 and 32101326)the National Key R&D Program of China(2021YFE0112400)+2 种基金the Second Tibetan Plateau Scientific Expedition and Research Program,China(2019QZKK0307)the HighLevel Talent Research Start-Up Project of Chongqing Technology and Business University,China(950319097)the Scientific and Technological Research Program of Chongqing Municipal Education Commission,China(KJQN202100827)。
文摘When the dominant species in a plant community are palatable,many believe that large herbivores will reduce the dominant species and promote the proportion of previously suppressed species.However,this view may not always hold true.We conducted a 4-year yak grazing experiment on the Qinghai-Tibet Plateau and tracked the plant compositions of the rotational grazing(RG)and grazing exclusion(GE)grasslands during the four years.The results showed that in the absence of yaks under GE,the plant community was dominated by two palatable species,Kobresia pygmaea and Stipa capillata,due to their small leaf area and rapid growth strategy.The presence of yaks under RG significantly inhibited S.capillata and over half of the forbs,while the proportion of K.pygmaea increased and it became the absolute dominant species,contradicting the view that large herbivores inhibit palatable species.Interannually,the dominance of K.pygmaea under RG decreased in the dry year,leading to an increase in the dominance of the other eight species.Under GE,the dominance of K.pygmaea declined notably in the dry year,while S.capillata and seven other forbs increased substantially.Overall,these results suggest that K.pygmaea is grazing-tolerant but not drought-tolerant,whereas the other eight species are drought-tolerant but not grazingtolerant.At the community level,community composition shifts resulting from succession after grazing exclusion exceeded those caused by drought,drought tends to induce community species turnover while grazing tends to induce species abundance variations.In summary,our conclusions remind ranch managers that when considering the impact of livestock on plant community composition,they should factor in local conditions and climate change rather than simply assuming that livestock will suppress the palatable species.
基金the University of Mohaghegh Ardabili,Department of Natural Resources,Iran for financial support。
文摘Invasive species are increasingly spreading,particularly in rangeland ecosystems.It is essential to evaluate the effectiveness of different methods for controlling invasive plants in these ecosystems.This study aimed to investigate the effects of three strategies-21-year grazing exclusion(21-YES),mowing-grazing in rotation in alternate years(MGRS),and moderate grazing(MGS)-on the change in cover,density,and biomass of Leucanthemum vulgare Lam.(Ox-eye Daisy=OED)and the plant community.To accomplish this,three sites selected for each treatment.In 2021,270 vegetation plots were sampled using a random systematic method.Subsequently,we recorded the density and canopy cover of all growth forms(forbs,grasses,and ferns),the OED biomass,and the ground cover.The results indicated that MGS reduced OED density,OED canopy,and OED biomass.Furthermore,this strategy demonstrated the highest density and canopy cover of the plant community(including total,forbs,grasses,and ferns).Additionally,the strongest correlation was observed between the total canopy and the OED density(R2=-0.91,-0.95,-0.94 in 21-YES,MGRS,and MGS,respectively),as well as between the total canopy and the OED canopy(R2=-0.51,-0.98,-0.97 in 21-YES,MGRS,and MGS,respectively).The MGS led to an increase in diversity indices.In general,the grazing strategy has proven to be effective in controlling the spread of invasive OED and has also resulted in an increase in canopy cover,density,and diversity indices of the plant community.The study highlights the importance of ongoing management efforts to control invasive species,with moderate grazing potentially serving as a more practical,culturally accepted,and costeffective short-term control strategy for widespread rangeland weed infestations.
基金funded by the China National Natural Science Foundation(32161143028)National Science and Technology Assistance(KY202002011)the Innovative Research Team of the Ministry of Education(IRT_17R50).
文摘Climate and grazing have a significant effect on vegetation structure and soil organic carbon(SOC)distribution,particularly in mountain ecosystems that are highly susceptible to climate change.However,we lack a systematic understanding of how vegetation structure reacts to long-term grazing disturbances,as well as the processes that influence SOC distribution.This study uses multiple sets of data spanning 20 years from a typical alpine grassland in the Qilian Mountains to investigate the effects of climate and grazing on various root-type grasses as well as the mechanisms that drive SOC distribution.We found that grazing increases the biomass of annual,biennial and perennial taproots while decreasing that of perennial rhizomes.We also found that various root-type grasses have different responses to climate and grazing.Multiple factors jointly control the variation of SOC content(SOCc),and the variation of SOC stock(SOCs)is mainly explained by the interaction between climate and grazing years.Climate and grazing can directly or indirectly affect SOCc through vegetation,and SOCs are mainly dominated by the direct effects of grazing years and grazing gradients.Grazing gradients and root-type grass biomass have a significant effect on SOC,with little effect from climate factors.Therefore,long-term grazing may affect the root-type grass and further affect SOC distribution through differences in nutrient acquisition ability and reproductive pathways.These findings provide important guidance for regulating soil carbon sequestration potential by varying the proportion of different root-type grass in the community via sowing,livestock configuration,or grazing time.
