Temperature and freeze-thaw events are two key factors controlling litter decomposition in cold biomes.Predicted global warming and changes in freeze-thaw cycles therefore may directly or indirectly impact litter deco...Temperature and freeze-thaw events are two key factors controlling litter decomposition in cold biomes.Predicted global warming and changes in freeze-thaw cycles therefore may directly or indirectly impact litter decomposition in those ecosystems. Here, we conducted a2-year-long litter decomposition experiment along an elevational gradient from 3000 to 3600 m to determine the potential effects of litter quality, climate warming and freeze-thaw on the mass losses of three litter types [dragon spruce（Picea asperata Mast.）, red birch（Betula albosinensis Burk.）, and minjiang fir（Abies faxoniana Rehd. et Wild）]. Marked differences in mass loss were observed among the litter types and sampling dates. Decay constant（k） values of red birch were significantly higher than those of the needle litters. However, mass losses between elevations did not differ significantly for any litter type.During the winter, lost mass contributed 18.3-28.8 % of the net loss rates of the first year. Statistical analysis showed that the relationships between mass loss and litter chemistry or their ratios varied with decomposition periods. Our results indicated that short-term field incubations could overestimate the k value of litter decomposition.Considerable mass was lost from subalpine forest litters during the wintertime. Potential future warming may not affect the litter decomposition in the subalpine forest ecosystems of eastern Tibetan Plateau.展开更多
Background:Insect pests are a significant threat to natural resources and social development.Modeling species assemblages of insect pests can predict spatiotemporal pest dynamics.However,research gaps remain regarding...Background:Insect pests are a significant threat to natural resources and social development.Modeling species assemblages of insect pests can predict spatiotemporal pest dynamics.However,research gaps remain regarding the mechanism for determining species assemblages of insect pests in alpine forest ecosystems.Here,we explored these determinants using a field investigation conducted for insect pests in a region of the Qinghai-Tibet Plateau.We assessed the species assemblages of insect pests in alpine forest ecosystems based on species co-occurrence patterns and species diversity(i.e.,observed diversity,dark diversity,community completeness,and species pool).A probabilistic model was used to test for statistically significant pairwise patterns of species co-occurrence using the presence-absence matrix of pest species based on species interactions.We used ordinary least squares regression modeling to explore relationships between abiotic factors(i.e.,climate factors and human influence)and species diversity.Results:Positive pest species interactions and many association links can occur widely across different investigation sites and parts of plant hosts in alpine forest ecosystems.We detected high dark diversity and low community completeness of insect pests in alpine forest ecosystems.High temperature and precipitation could promote pest species diversity,particularly dark diversity and species pools.Human influence could drive high levels of pest species diversity and lead to dark diversity and species pools.Community completeness could be an effective indicator for insect pest risk assessment.Conclusions:Our study provides new evidence for the determinants of insect pest species assemblages in alpine forest ecosystems from the perspectives of pest species interactions and abiotic factors.The findings of our study could reveal the mechanism for shaping species assemblages and support the prevention and control of insect pests in alpine forest ecosystems.展开更多
Aims Alpine forest gaps can control understory ecosystem processes by manipulating hydrothermal dynamics.Here,we aimed to test the role of alpine forest gap disturbance on total phenol loss(TPL)from the decomposing li...Aims Alpine forest gaps can control understory ecosystem processes by manipulating hydrothermal dynamics.Here,we aimed to test the role of alpine forest gap disturbance on total phenol loss(TPL)from the decomposing litter of two typical shrub species(willow,Salix paraplesia Schneid.,and bamboo,Fargesia nitida(Mitford)Keng f.).Methods We conducted a field litterbag experiment within a representative fir(Abies faxoniana Rehd.)forest based on‘gap openness treatments’(plot positions in the gap included the gap center south,gap center north,canopy edge,expanded edge and closed canopy).The TPL rate and litter surface microbial abundance(fungi and bacteria)of the two shrub species were measured during the following periods over 2 years:snow formation(SF),snow cover(SC),snow melting(ST),the early growing season(EG)and the late growing season(LG).Important Findings At the end of the study,we found that snow cover depth,freeze–thaw cycle frequency and the fungal copies g−1 to bacterial copies g−1 ratio had significant effects on litter TPL.The abundances of fungi and bacteria decreased from the gap center to the closed canopy during the SF,SC,ST and LG periods and showed the opposite trend during the EG periods.The rate of TPL among plot positions closely followed the same trend as microbial abundance during the first year of incubation.In addition,both species had higher rates of TPL in the gap center than at other positions during the first winter,first year and entire 2-year period.These findings suggest that alpine forest gap formation accelerates litter TPL,although litter TPL exhibits dual responses to gap disturbance during specific critical periods.In conclusion,reduced snow cover depth and duration during winter warming under projected climate change scenarios or as gaps vanish may slow litter TPL in alpine biomes.展开更多
Alpine forests in the eastern Tibetan Plateau are important ecological barriers in the upper reaches of the Yangtze River.However,due to continuous high-intensity harvesting,a large number of plantings,and the complet...Alpine forests in the eastern Tibetan Plateau are important ecological barriers in the upper reaches of the Yangtze River.However,due to continuous high-intensity harvesting,a large number of plantings,and the complete harvesting ban measures in recent decades,the forest tree species and age cohorts have become relatively homogenous,and the biodiversity and ecological functions have been reduced.To design effective forest management options to optimize forest structure and increase carbon sequestration capacity,Mao County in Sichuan Province was selected as the study site and six forest management options(harvesting,planting)of different intensities were tested using the LANDIS-II model to simulate and compare the differences in forest aboveground carbon sequestration rate(ACSR)between these options and the current management option over the next 100 years.Our results showed that(i)the different harvesting and planting intensities significantly changed the ACSR compared with the current management options;(ii)different communities responded differently to the management options,with the ACSR differing significantly in cold temperate conifers and temperate conifers but not in broad-leaved trees(P<0.05);and(iii)a comprehensive consideration of forest management options at the species,community and landscape levels was necessary.Our results suggest that implementing a longer harvesting and planting interval(20 years)at the study site can maximize forest ACSR.This study provides an important reference for evaluating the ability of forest management options to restore forest ecological functions and increase carbon sequestration capacity and for selecting effective forest management programs in the eastern Tibetan Plateau.展开更多
Background:Alpine coniferous forest ecosystems dominated by ectomycorrhizal(ECM)tree species are generally characterized by low soil nitrogen(N)availability but stabilized plant productivity.Thus,elucidating potential...Background:Alpine coniferous forest ecosystems dominated by ectomycorrhizal(ECM)tree species are generally characterized by low soil nitrogen(N)availability but stabilized plant productivity.Thus,elucidating potential mechanisms by which plants maintain efficient N acquisition is crucial for formulating optimized management practices in these ecosystems.Methods:We summarize empirical studies conducted at a long-term field monitoring station in the alpine coniferous forests on the eastern Tibetan Plateau,China.We propose a root-soil interaction-based framework encompassing key components including soil N supply,microbial N transformation,and root N uptake in the rhizosphere.Results:We highlight that,(i)a considerable size of soil dissolved organic N pool mitigates plant dependence on inorganic N supply;(ii)ectomycorrhizal roots regulate soil N transformations through both rhizosphere and hyphosphere effects,providing a driving force for scavenging soil N;(iii)a complementary pattern of plant uptake of different soil N forms via root-and mycorrhizal mycelium-pathways enables efficient N acquisitions in response to changing soil N availability.Conclusions:Multiple rhizosphere processes abovementioned collaboratively contribute to efficient plant N acquisition in alpine coniferous forests.Finally,we identify several research outlooks and directions to improve the understanding and prediction of ecosystem functions in alpine coniferous forests under on-going global changes.展开更多
Central Asia,located in the innermost part of the Eurasian continent,has experienced“warming and humidification”in recent decades,with potentially important implications for tree growth in alpine forests,which are c...Central Asia,located in the innermost part of the Eurasian continent,has experienced“warming and humidification”in recent decades,with potentially important implications for tree growth in alpine forests,which are critical for regional water reserves.We use nested principal component analysis to assess tree radial growth patterns and reveal significant positive trends since the 20th century across Central Asian alpine forests(0.076 per decade during 1900-2021,p=0.003).Regional hydroclimatic variations affect the greening of these alpine forests,especially with extreme droughts being the most damaging.Growth acceleration is driven by low-latitude warming,which enhances regional temperatures and precipitation.The warming ocean centers alter atmospheric circulation patterns,leading to more moisture being transported to the Central Asian alpine forests,thereby increasing regional precipitation and promoting tree growth.Our model projections indicate that growth rates will continue to rise in the future.However,unprecedented warming may eventually lead to growth deterioration if negative effects,such as insufficient precipitation,occur due to breakdown signs of positive feedback mechanisms,such as moisture transport driven by low-latitude warming.Our study highlights the beneficial,but not unlimited,influences of climate warming on tree growth in Central Asian alpine forests,with implications for the sustainability of water resources.However,as urban and agricultural demands escalate,a holistic,long-term perspective is recommended to mitigate the adverse effects of temperature increases.展开更多
Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence...Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence,climate change has been assumed to be the main driver behind this treeline movement.The latest review of treeline studies was published in 2009 by Harsch et al.Since then,a plethora of papers have been published studying local treeline migration.Here we bring together this knowledge through a review of 142 treeline related publications,including 477 study locations.We summarize the information known about factors limiting tree-growth at and near treelines.Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline.These conditions appear to have become favorable at many locations,particularly so in recent years.The review revealed that at 66%of these treeline sites forest cover had increased in elevational or latitudinal extent.The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements.Our analysis also revealed that while a greater percentage of elevational treelines are moving,the latitudinal treelines are capable of moving at greater horizontal speed.This can potentially have substantial impacts on ecosystem carbon storage.To conclude the review,we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced,increased or remain the same due to treeline migration.While the answer still remains under debate,we believe that all three hypotheses are likely to apply depending on the encroached ecosystem.Concerningly,evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future.展开更多
Alpine forest soil in the southeastern Qinghai–Xizang Plateau plays a crucial role in regional and global climate and biogeochemical cycles,yet the elevational distribution of soil nitrogen(N)availability and losing ...Alpine forest soil in the southeastern Qinghai–Xizang Plateau plays a crucial role in regional and global climate and biogeochemical cycles,yet the elevational distribution of soil nitrogen(N)availability and losing risk is unresolved.In this study,we characterized soil N composition and key N transformation processes across different elevations in 3 typical mounts of the Qinghai–Xizang Plateau.In contrast to previous suggestions,soil total N and ammonium are found to accumulate in high elevation zones.This accumulation of N at higher altitudes is due to a consistent soil net N mineralization rate coupled with an extremely low net nitrification rate,which is suppressed by low p H and high soil moisture in high elevation zones.Moreover,the elevated rates of biological N fixation along the elevation further contribute to N accumulation in high elevation regions in which the acid-tolerant Bradyrhizobium,plant-associated Herbaspirillum,and Klebsiella are identified as the key diazotrophic microbial taxa responsible for active N fixation.Collectively,our results suggest that total N and NH_(4)^(+)-N accumulation in higher altitude zone is a ubiquitous phenomenon in the southeast Qinghai–Xizang Plateau,with lower nitrification rates and higher biological nitrogen fixation being key processes enabling this occurrence.展开更多
Soil dissolved organic matter (DOM) is vital in terrestrial ecosystem carbon (C) cycling;however,the regulatory effects of forest types and elevations on soil DOM dynamics in mountain ecosystems remain incompletely un...Soil dissolved organic matter (DOM) is vital in terrestrial ecosystem carbon (C) cycling;however,the regulatory effects of forest types and elevations on soil DOM dynamics in mountain ecosystems remain incompletely understood.Here,we investigated DOM content,spectroscopic characteristics,molecular traits and their potential drivers along an elevational gradient (2600-3500 m) in the Hengduan Mountains.Our results showed that soil dissolved organic C (DOC) content was higher in broad-leaf forest soil (at 2900 m and 3500 m) than in coniferous forest soil (at 2600 m and 3200 m) irrespective of elevation,with a greater amount in wet season than in dry season.Humification index (HIX) trends aligned with the DOC content,while the aromaticity index (AI) showed an inverse relationship.These patterns were linked to the quality of litter carbon sources.Molecular-level analysis of DOM suggested that lignins/CRAM-like structure compounds and tannins predominated in soil DOM,indicating that the molecular composition of soil DOM was typical of plant-derived sources in our study region.Additionally,the relative abundance of lignin compounds decreased gradually with increasing elevation during the dry season.We detected that soil properties (especially,NH_(4)^(+)-N content) predominantly mediated DOM dynamics in dry season,whereas litter traits (i.e.,leaf-DOC content) were the key factors across elevations in wet season.Overall,our results revealed litter traits and soil properties predominantly regulated soil DOM mechanism along elevational gradient,indicating that soil DOM dynamics associated with tree species in alpine mountain ecosystems may differentially influence soil C sequestration under future climate change scenarios.展开更多
The alpine treeline ecotone is characterized as the upper limit of the forest in the high-mountain ecosystem.Due to the freeze-thaw cycles,the soil organism community,such as microbial communities are expected to chan...The alpine treeline ecotone is characterized as the upper limit of the forest in the high-mountain ecosystem.Due to the freeze-thaw cycles,the soil organism community,such as microbial communities are expected to change between seasons.However,there are limited microbialcommunity studies focused on the high altitude alpine ecosystem.We conducted a study in the alpine treeline ecotone on the eastern Qinghai-Tibet Plateau,China,and investigated the seasonal variability of the soil microbial community.We collected all soil samples within the alpine treeline ecotone,between the treeline and timberline in the high-mountain region.The 16S rRNA genes of the microbial communities(bacterial and archaeal)were analyzed by highthroughput sequencing to the genus level.The results showed that soil microbial community in the alpine treeline ecotone was consistently dominated by eight phyla which consisted of 95% of the total microbial community,including Proteobacteria,Actinobacteria,Acidobacteria,Firmicutes,Planctomycetes,Chloroflexi,Bacteroidetes,and Verrucomicrobia.The overall diversity and evenness of the community were relatively stable,with an average of 0.5% difference between seasons.The highest seasonal variability occurred at the upper boundary of the alpine treeline ecotone,and few or almost no seasonal change was observed at lower elevations,indicating dense forest cover and litter deposition might have created a local microclimate that reduced seasonal variation among the surrounding environmental conditions.Our study was one of the first group that documented the microbial community assemblage in the treeline ecotone on the Qinghai-Tibet Plateau.展开更多
The diversity and cold adaptation of endophytic fungi associated with five dominant plant species collected from the Baima Snow Mountain(altitude 4,000–4,300 m),Southwest China,were investigated.A total of 604 cultur...The diversity and cold adaptation of endophytic fungi associated with five dominant plant species collected from the Baima Snow Mountain(altitude 4,000–4,300 m),Southwest China,were investigated.A total of 604 culturable endophytic fungi were isolated from 800 stems and leaf segments.The colonization rate of endophytic fungi in the five plant species ranged from 54%to 91%,and the colonization rate of endophytic fungi in the stems was significantly higher(87%)than that in the leaves(67%)(X∼2045.172,P<0.001,chi-squared test).Based on the morphological characteristics and the ITS sequence analysis,the isolates were identified to 43 taxa,of which Cephalosporium,Sirococcus,Penicillium and Aspergillus were the dominant genera,and their relative frequencies were 14.06%,12.58%,9.44%and 7.95%,respectively.The Shannon-Weiner diversity indices and the Sorenson’s coefficient similarity indices of the endophytic fungi from the five plant species ranged from 1.25 to 2.70 and 0.53 to 0.67,respectively.Growth temperature tests indicated that 75%of the isolates from the Baima Snow Mountain were psychrotrophs and 14%were the transitional type between psychrotrophs and mesophiles,whereas all of the isolates from the Yuanjiang Dry-hot Valley were mesophiles,which suggested that the endophytes from the Baima Snow Mountain possess a remarkable ability to adapt to cold environments.展开更多
基金supported by the National Natural Science Foundation of China(3157044531570601+2 种基金31500509 and31570605)Postdoctoral Science Foundation of China(2013M540714 and 2014T70880)Collaborative Innovation Center of Ecological Security in the Upper Reaches of Yangze River
文摘Temperature and freeze-thaw events are two key factors controlling litter decomposition in cold biomes.Predicted global warming and changes in freeze-thaw cycles therefore may directly or indirectly impact litter decomposition in those ecosystems. Here, we conducted a2-year-long litter decomposition experiment along an elevational gradient from 3000 to 3600 m to determine the potential effects of litter quality, climate warming and freeze-thaw on the mass losses of three litter types [dragon spruce（Picea asperata Mast.）, red birch（Betula albosinensis Burk.）, and minjiang fir（Abies faxoniana Rehd. et Wild）]. Marked differences in mass loss were observed among the litter types and sampling dates. Decay constant（k） values of red birch were significantly higher than those of the needle litters. However, mass losses between elevations did not differ significantly for any litter type.During the winter, lost mass contributed 18.3-28.8 % of the net loss rates of the first year. Statistical analysis showed that the relationships between mass loss and litter chemistry or their ratios varied with decomposition periods. Our results indicated that short-term field incubations could overestimate the k value of litter decomposition.Considerable mass was lost from subalpine forest litters during the wintertime. Potential future warming may not affect the litter decomposition in the subalpine forest ecosystems of eastern Tibetan Plateau.
基金supported by the National Natural Science Foundation of China(Nos.31800449 and 31800464)the project of the third forestry pest survey of Qinghai Province,China.
文摘Background:Insect pests are a significant threat to natural resources and social development.Modeling species assemblages of insect pests can predict spatiotemporal pest dynamics.However,research gaps remain regarding the mechanism for determining species assemblages of insect pests in alpine forest ecosystems.Here,we explored these determinants using a field investigation conducted for insect pests in a region of the Qinghai-Tibet Plateau.We assessed the species assemblages of insect pests in alpine forest ecosystems based on species co-occurrence patterns and species diversity(i.e.,observed diversity,dark diversity,community completeness,and species pool).A probabilistic model was used to test for statistically significant pairwise patterns of species co-occurrence using the presence-absence matrix of pest species based on species interactions.We used ordinary least squares regression modeling to explore relationships between abiotic factors(i.e.,climate factors and human influence)and species diversity.Results:Positive pest species interactions and many association links can occur widely across different investigation sites and parts of plant hosts in alpine forest ecosystems.We detected high dark diversity and low community completeness of insect pests in alpine forest ecosystems.High temperature and precipitation could promote pest species diversity,particularly dark diversity and species pools.Human influence could drive high levels of pest species diversity and lead to dark diversity and species pools.Community completeness could be an effective indicator for insect pest risk assessment.Conclusions:Our study provides new evidence for the determinants of insect pest species assemblages in alpine forest ecosystems from the perspectives of pest species interactions and abiotic factors.The findings of our study could reveal the mechanism for shaping species assemblages and support the prevention and control of insect pests in alpine forest ecosystems.
基金supported by the National Natural Science Foundation of China(no.31570445 and 31800518).
文摘Aims Alpine forest gaps can control understory ecosystem processes by manipulating hydrothermal dynamics.Here,we aimed to test the role of alpine forest gap disturbance on total phenol loss(TPL)from the decomposing litter of two typical shrub species(willow,Salix paraplesia Schneid.,and bamboo,Fargesia nitida(Mitford)Keng f.).Methods We conducted a field litterbag experiment within a representative fir(Abies faxoniana Rehd.)forest based on‘gap openness treatments’(plot positions in the gap included the gap center south,gap center north,canopy edge,expanded edge and closed canopy).The TPL rate and litter surface microbial abundance(fungi and bacteria)of the two shrub species were measured during the following periods over 2 years:snow formation(SF),snow cover(SC),snow melting(ST),the early growing season(EG)and the late growing season(LG).Important Findings At the end of the study,we found that snow cover depth,freeze–thaw cycle frequency and the fungal copies g−1 to bacterial copies g−1 ratio had significant effects on litter TPL.The abundances of fungi and bacteria decreased from the gap center to the closed canopy during the SF,SC,ST and LG periods and showed the opposite trend during the EG periods.The rate of TPL among plot positions closely followed the same trend as microbial abundance during the first year of incubation.In addition,both species had higher rates of TPL in the gap center than at other positions during the first winter,first year and entire 2-year period.These findings suggest that alpine forest gap formation accelerates litter TPL,although litter TPL exhibits dual responses to gap disturbance during specific critical periods.In conclusion,reduced snow cover depth and duration during winter warming under projected climate change scenarios or as gaps vanish may slow litter TPL in alpine biomes.
基金funded by the National Natural Science Foundation of China(41801185,32171550)the Natural Science Foundation of Sichuan Province(2023NSFSC0191)+1 种基金the Strategic Priority Research Program(category A)of Chinese Academy of Sciences(XDA20020302)the Youth Innovation Promotion Association of Chinese Academy of Sciences(2021371).
文摘Alpine forests in the eastern Tibetan Plateau are important ecological barriers in the upper reaches of the Yangtze River.However,due to continuous high-intensity harvesting,a large number of plantings,and the complete harvesting ban measures in recent decades,the forest tree species and age cohorts have become relatively homogenous,and the biodiversity and ecological functions have been reduced.To design effective forest management options to optimize forest structure and increase carbon sequestration capacity,Mao County in Sichuan Province was selected as the study site and six forest management options(harvesting,planting)of different intensities were tested using the LANDIS-II model to simulate and compare the differences in forest aboveground carbon sequestration rate(ACSR)between these options and the current management option over the next 100 years.Our results showed that(i)the different harvesting and planting intensities significantly changed the ACSR compared with the current management options;(ii)different communities responded differently to the management options,with the ACSR differing significantly in cold temperate conifers and temperate conifers but not in broad-leaved trees(P<0.05);and(iii)a comprehensive consideration of forest management options at the species,community and landscape levels was necessary.Our results suggest that implementing a longer harvesting and planting interval(20 years)at the study site can maximize forest ACSR.This study provides an important reference for evaluating the ability of forest management options to restore forest ecological functions and increase carbon sequestration capacity and for selecting effective forest management programs in the eastern Tibetan Plateau.
基金supported jointly by the Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(No.2019QZKK0301)the Chinese Academy of Sciences(CAS)Interdisciplinary Innovation Team(No.xbzg-zysys-202112)+1 种基金the National Natural Science Foundation of China(Nos.32171757,31872700)Bartosz Adamczyk acknowledges the Academy of Finland(No.330136)。
文摘Background:Alpine coniferous forest ecosystems dominated by ectomycorrhizal(ECM)tree species are generally characterized by low soil nitrogen(N)availability but stabilized plant productivity.Thus,elucidating potential mechanisms by which plants maintain efficient N acquisition is crucial for formulating optimized management practices in these ecosystems.Methods:We summarize empirical studies conducted at a long-term field monitoring station in the alpine coniferous forests on the eastern Tibetan Plateau,China.We propose a root-soil interaction-based framework encompassing key components including soil N supply,microbial N transformation,and root N uptake in the rhizosphere.Results:We highlight that,(i)a considerable size of soil dissolved organic N pool mitigates plant dependence on inorganic N supply;(ii)ectomycorrhizal roots regulate soil N transformations through both rhizosphere and hyphosphere effects,providing a driving force for scavenging soil N;(iii)a complementary pattern of plant uptake of different soil N forms via root-and mycorrhizal mycelium-pathways enables efficient N acquisitions in response to changing soil N availability.Conclusions:Multiple rhizosphere processes abovementioned collaboratively contribute to efficient plant N acquisition in alpine coniferous forests.Finally,we identify several research outlooks and directions to improve the understanding and prediction of ecosystem functions in alpine coniferous forests under on-going global changes.
基金supported by Excellent Research Group Program for Tibetan Plateau Earth System(continuation grant NSFC project No.41988101)the National Natural Science Foundation of China(Nos.U1803341 and 32061123008)+1 种基金the National Key R&D Program of China(No.2018YFA0606401)the National Youth Talent Support Program.
文摘Central Asia,located in the innermost part of the Eurasian continent,has experienced“warming and humidification”in recent decades,with potentially important implications for tree growth in alpine forests,which are critical for regional water reserves.We use nested principal component analysis to assess tree radial growth patterns and reveal significant positive trends since the 20th century across Central Asian alpine forests(0.076 per decade during 1900-2021,p=0.003).Regional hydroclimatic variations affect the greening of these alpine forests,especially with extreme droughts being the most damaging.Growth acceleration is driven by low-latitude warming,which enhances regional temperatures and precipitation.The warming ocean centers alter atmospheric circulation patterns,leading to more moisture being transported to the Central Asian alpine forests,thereby increasing regional precipitation and promoting tree growth.Our model projections indicate that growth rates will continue to rise in the future.However,unprecedented warming may eventually lead to growth deterioration if negative effects,such as insufficient precipitation,occur due to breakdown signs of positive feedback mechanisms,such as moisture transport driven by low-latitude warming.Our study highlights the beneficial,but not unlimited,influences of climate warming on tree growth in Central Asian alpine forests,with implications for the sustainability of water resources.However,as urban and agricultural demands escalate,a holistic,long-term perspective is recommended to mitigate the adverse effects of temperature increases.
文摘Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence,climate change has been assumed to be the main driver behind this treeline movement.The latest review of treeline studies was published in 2009 by Harsch et al.Since then,a plethora of papers have been published studying local treeline migration.Here we bring together this knowledge through a review of 142 treeline related publications,including 477 study locations.We summarize the information known about factors limiting tree-growth at and near treelines.Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline.These conditions appear to have become favorable at many locations,particularly so in recent years.The review revealed that at 66%of these treeline sites forest cover had increased in elevational or latitudinal extent.The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements.Our analysis also revealed that while a greater percentage of elevational treelines are moving,the latitudinal treelines are capable of moving at greater horizontal speed.This can potentially have substantial impacts on ecosystem carbon storage.To conclude the review,we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced,increased or remain the same due to treeline migration.While the answer still remains under debate,we believe that all three hypotheses are likely to apply depending on the encroached ecosystem.Concerningly,evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future.
基金supported by the Second Qinghai-Xizang Plateau Scientific Expedition and Research Program(2019QZKK0306 and 2019QZKK0308)
文摘Alpine forest soil in the southeastern Qinghai–Xizang Plateau plays a crucial role in regional and global climate and biogeochemical cycles,yet the elevational distribution of soil nitrogen(N)availability and losing risk is unresolved.In this study,we characterized soil N composition and key N transformation processes across different elevations in 3 typical mounts of the Qinghai–Xizang Plateau.In contrast to previous suggestions,soil total N and ammonium are found to accumulate in high elevation zones.This accumulation of N at higher altitudes is due to a consistent soil net N mineralization rate coupled with an extremely low net nitrification rate,which is suppressed by low p H and high soil moisture in high elevation zones.Moreover,the elevated rates of biological N fixation along the elevation further contribute to N accumulation in high elevation regions in which the acid-tolerant Bradyrhizobium,plant-associated Herbaspirillum,and Klebsiella are identified as the key diazotrophic microbial taxa responsible for active N fixation.Collectively,our results suggest that total N and NH_(4)^(+)-N accumulation in higher altitude zone is a ubiquitous phenomenon in the southeast Qinghai–Xizang Plateau,with lower nitrification rates and higher biological nitrogen fixation being key processes enabling this occurrence.
基金financially supported by the National Natural Science Foundation of China (32130069)the Special Project for Social Development of Yunnan Province (202103AC100001)+1 种基金the Major Program for Basic Research Project of Yunnan Province (202101BC070002)the Scientific Research Foundation of Education Department of Yunnan Province (2024Y004)。
文摘Soil dissolved organic matter (DOM) is vital in terrestrial ecosystem carbon (C) cycling;however,the regulatory effects of forest types and elevations on soil DOM dynamics in mountain ecosystems remain incompletely understood.Here,we investigated DOM content,spectroscopic characteristics,molecular traits and their potential drivers along an elevational gradient (2600-3500 m) in the Hengduan Mountains.Our results showed that soil dissolved organic C (DOC) content was higher in broad-leaf forest soil (at 2900 m and 3500 m) than in coniferous forest soil (at 2600 m and 3200 m) irrespective of elevation,with a greater amount in wet season than in dry season.Humification index (HIX) trends aligned with the DOC content,while the aromaticity index (AI) showed an inverse relationship.These patterns were linked to the quality of litter carbon sources.Molecular-level analysis of DOM suggested that lignins/CRAM-like structure compounds and tannins predominated in soil DOM,indicating that the molecular composition of soil DOM was typical of plant-derived sources in our study region.Additionally,the relative abundance of lignin compounds decreased gradually with increasing elevation during the dry season.We detected that soil properties (especially,NH_(4)^(+)-N content) predominantly mediated DOM dynamics in dry season,whereas litter traits (i.e.,leaf-DOC content) were the key factors across elevations in wet season.Overall,our results revealed litter traits and soil properties predominantly regulated soil DOM mechanism along elevational gradient,indicating that soil DOM dynamics associated with tree species in alpine mountain ecosystems may differentially influence soil C sequestration under future climate change scenarios.
基金funded by the National Natural Science Foundation of China(NSFC,No.41271094 and No.40871124).
文摘The alpine treeline ecotone is characterized as the upper limit of the forest in the high-mountain ecosystem.Due to the freeze-thaw cycles,the soil organism community,such as microbial communities are expected to change between seasons.However,there are limited microbialcommunity studies focused on the high altitude alpine ecosystem.We conducted a study in the alpine treeline ecotone on the eastern Qinghai-Tibet Plateau,China,and investigated the seasonal variability of the soil microbial community.We collected all soil samples within the alpine treeline ecotone,between the treeline and timberline in the high-mountain region.The 16S rRNA genes of the microbial communities(bacterial and archaeal)were analyzed by highthroughput sequencing to the genus level.The results showed that soil microbial community in the alpine treeline ecotone was consistently dominated by eight phyla which consisted of 95% of the total microbial community,including Proteobacteria,Actinobacteria,Acidobacteria,Firmicutes,Planctomycetes,Chloroflexi,Bacteroidetes,and Verrucomicrobia.The overall diversity and evenness of the community were relatively stable,with an average of 0.5% difference between seasons.The highest seasonal variability occurred at the upper boundary of the alpine treeline ecotone,and few or almost no seasonal change was observed at lower elevations,indicating dense forest cover and litter deposition might have created a local microclimate that reduced seasonal variation among the surrounding environmental conditions.Our study was one of the first group that documented the microbial community assemblage in the treeline ecotone on the Qinghai-Tibet Plateau.
基金supported by the Natural Science Foundation of Yunnan Province and the Science Foundation of Yunnan Educational Committee(2011Y381).
文摘The diversity and cold adaptation of endophytic fungi associated with five dominant plant species collected from the Baima Snow Mountain(altitude 4,000–4,300 m),Southwest China,were investigated.A total of 604 culturable endophytic fungi were isolated from 800 stems and leaf segments.The colonization rate of endophytic fungi in the five plant species ranged from 54%to 91%,and the colonization rate of endophytic fungi in the stems was significantly higher(87%)than that in the leaves(67%)(X∼2045.172,P<0.001,chi-squared test).Based on the morphological characteristics and the ITS sequence analysis,the isolates were identified to 43 taxa,of which Cephalosporium,Sirococcus,Penicillium and Aspergillus were the dominant genera,and their relative frequencies were 14.06%,12.58%,9.44%and 7.95%,respectively.The Shannon-Weiner diversity indices and the Sorenson’s coefficient similarity indices of the endophytic fungi from the five plant species ranged from 1.25 to 2.70 and 0.53 to 0.67,respectively.Growth temperature tests indicated that 75%of the isolates from the Baima Snow Mountain were psychrotrophs and 14%were the transitional type between psychrotrophs and mesophiles,whereas all of the isolates from the Yuanjiang Dry-hot Valley were mesophiles,which suggested that the endophytes from the Baima Snow Mountain possess a remarkable ability to adapt to cold environments.
