Alpine Steppe Ecosystem Research Articles

Alpine meadow and alpine steppe plant-soil network in Qinghai-Tibet Plateau, China

Alpine meadow and alpine steppe are crucial ecosystem types in the Qinghai-Tibet Plateau. However, due to ecosystem fragility and human disturbance, the nutrient imbalance between plant and soil leads to grassland degradation. From a systematic perspective, there needs to be a comprehensive understanding of the plant and soil traits within these two ecosystem types. This study addressed this gap by constructing plant-soil trait networks for alpine meadow and alpine steppe, identifying bridge traits, and comparing the stability and distinctions of the two trait networks. The results demonstrated a significant difference in the distribution of network structure edge weights between the alpine meadow and steppe. In the network of alpine meadow, the soil organic carbon was responsible for linking plant and soil traits, exhibiting the highest impact. Conversely, the network of alpine steppe revealed an increasing negative correlation between plant and soil traits. The results of bridge traits agreed with the optimal distribution hypothesis. The bridge traits of the alpine meadow were aboveground traits (AGB or PlantC), while those of the alpine steppe were belowground traits (BGB and RootN). Based on our findings, different management measures could be taken. The alpine meadow could be primarily restored through natural processes, and climate warming would enhance its carbon sequestration capacity. The alpine steppe ecosystem exhibits low nitrogen availability, which could be augmented through fertilisation or the return of yak manure.

Soil Moisture Rather Than Atmospheric Dryness Dominates CO2 Uptake in an Alpine Steppe

AbstractThe Tibetan Plateau (TP) has the largest area of alpine grasslands in the world. Among the various grassland types, alpine steppe covers 72 million hectares in the central–western TP, where the climate is even drier than in other alpine ecosystems. Rapid climate warming (0.34°C per decade) since the 1970s has caused significant atmospheric dryness—that is, an increase in the vapor pressure deficit—despite increases in both precipitation and soil moisture on the TP. However, it remains controversial whether the availability of atmospheric or soil moisture has a stronger role in the growth of vegetation. We used eddy covariance to measure the CO2 fluxes in a grazed alpine steppe over three consecutive years. Our results showed that the alpine steppe acted as a net CO2 sink of 47.9–72.7 g C m−2 yr−1 despite significant grazing. The CO2 fluxes showed a clear seasonal pattern, largely regulated by climate factors, although human activities were also documented. The soil moisture content dominated the seasonal variation in the net ecosystem productivity: the importance of soil moisture to the net ecosystem productivity was 49.0%, whereas the importance of the vapor pressure deficit was 36.5%. We found that the surface soil moisture, rather than the water content of soil layers deeper than 10 cm, affected the net CO2 uptake more strongly, although its role may have been affected by intense rainfall. This study emphasizes that the availability of surface soil water rather than atmospheric dryness regulates CO2 uptake in alpine steppe ecosystems, suggesting that a warming–wetting climate will favor the net uptake of CO2 by alpine steppes.

The Relative Effects of Climate Change and Phenological Change on Net Primary Productivity Vary with Grassland Types on the Tibetan Plateau

Quantifying the impact of climate change and vegetation phenology on ecosystem productivity in the alpine grasslands of the Tibetan Plateau (TP) is essential for assessing carbon balance dynamics at regional and global scales. However, the relative contributions of climate change and phenological change to vegetation productivity across various grassland types remain indistinguishable. This study examined the effects of climate change and phenological change on net primary productivity (NPP) in the alpine meadow and alpine steppe ecosystems of the TP from 2001 to 2020. The results revealed that (1) NPP exhibited a positive correlation with vegetation phenology, particularly with an extended growing season length and an earlier start of the growing season. Among the phenological variables studied, changes in the start of the growing season had the strongest influence on NPP variations in both alpine meadows and alpine steppes. (2) NPP displayed a positive correlation with annual precipitation and annual temperature, with changes in annual precipitation playing a dominant role in shaping NPP variations in alpine steppes. (3) NPP showed a negative correlation with annual radiation, and the impact of radiation changes on NPP variations was comparable to that of precipitation or temperature in both alpine meadows and alpine steppes. (4) Climate change exerted a stronger impact on NPP than phenological change in alpine steppes, while NPP was jointly affected by climate change and phenological change in alpine meadows. Our findings indicated that the relative effects of climate change and phenological change on vegetation productivity vary across different grassland types on the TP.

Dynamics and controls of ecosystem multiserviceability across the Qingzang Plateau

Ecosystem multiserviceability (EMS), a comprehensive and significant ecological indicator, reflects the capacity of ecosystems to offer multiple services concurrently. Intensified climate change and human activity are continuously altering ecosystem functions, services, and EMSs. However, numerous studies have only focused on one or a few ecosystem services, rarely taking into account spatial-temporal distribution and drivers of EMS on behalf of different agencies. We calculated EMS including pastoralist (PA), environmental protection agency (EPA), biodiversity conservation agency (BCA), and climate change mitigation agency (CCMA) using grassland production, habitat quality, water conservation, and carbon sequestration. Then, the effects of geographical features, climate factors, and human activities on spatial-temporal patterns of EMS were explored. The result indicated that EMS showed a decreasing tendency from the southeast to northwest on the Qingzang Plateau (QZP). Meanwhile, there were no obvious fluctuations in four simulated scenarios (PA, EPA, BCA and CCMA) among different vegetation types during 2000 to 2015. Notably, EMS of all simulated scenarios decreased in the alpine steppe ecosystem, but negligible changes were found in other ecosystems from 2015 to 2020. Moreover, the relative importance of precipitation in annual mean value (from 2000 to 2020) of PA, EPA, BCA and CCMA were 0.13, 0.11, 0.30 and 0.19, respectively. Overall, precipitation played the dominant role on the dynamics of EMS, followed by elevation and human footprint. Our findings highlighted that understanding the patterns and drivers of EMS could provide a reference for the regional management and maintenance of ecosystem stability on QZP.

Impacts of human pressure and climate on biodiversity-multifunctionality relationships on the Qinghai-Tibetan Plateau.

Many studies have investigated the effects of environmental context on biodiversity or multifunctionality in alpine regions, but it is uncertain how human pressure and climate may affect their relationships. Here, we combined the comparative map profile method with multivariate datasets to assess the spatial pattern of ecosystem multifunctionality and further identify the effects of human pressure and climate on the spatial distribution of biodiversity-multifunctionality relationships in alpine ecosystems of the Qinghai-Tibetan Plateau (QTP). Our results indicate that at least 93% of the areas in the study region show a positive correlation between biodiversity and ecosystem multifunctionality across the QTP. Biodiversity-multifunctionality relationships with increasing human pressure show a decreasing trend in the forest, alpine meadow, and alpine steppe ecosystems, while an opposite pattern was found in the alpine desert steppe ecosystem. More importantly, aridity significantly strengthened the synergistic relationship between biodiversity and ecosystem multifunctionality in forest and alpine meadow ecosystems. Taken together, our results provide insights into the importance of protecting and maintaining biodiversity and ecosystem multifunctionality in response to climate change and human pressure in the alpine region.

Carbon budgets and environmental controls in alpine ecosystems on the Qinghai-Tibet Plateau

Rapid warming in alpine regions exerts important effects on carbon cycling in alpine ecosystem, which are sensitive to environmental changes. So far, little is known about the spatial and temporal variation in carbon budgets and the main influencing factors over different ecosystems. Here, we examined the monthly and annual gross primary production (GPP), net ecosystem CO2 exchange (NEE) and ecosystem respiration (ER) during 2004–2017 in four types of ecosystems (i.e., alpine meadow, steppe, forest and cropland) on the Tibetan Plateau. We explored the relationships between carbon fluxes and environmental factors. The results show that forest, cropland and alpine meadow ecosystems acted as carbon sinks, with NEE values ranging from −21.25 ± 3.54 to −308.75 ± 21.65 g C m-2a-1, while alpine steppe and overmature forest ecosystems serve as carbon sources (mean annual NEE: 23.12 ± 15.88 g C m-2a-1). The temperature sensitivity values (Q10) of ER in the forest (9.39) and alpine steppe (7.47) ecosystems were greater than those in the alpine meadow ecosystems (Q10 = 4.20), indicating that the carbon emissions in the forest and alpine steppe ecosystems were more sensitive to warming. Multiple linear regression analysis indicated that the carbon fluxes (GPP, NEE, ER) of alpine steppe and alpine meadow in the permafrost regions were more sensitive to water forcing (precipitation, soil water content), while in the forest and cropland ecosystems temperature forcing (air and soil temperature) were strong predictors of all the carbon flux indices. Our results showed differential responses of carbon budgets among ecosystems, which could be considered in the future modeling of carbon cycle in alpine regions.

Shrub encroachment increases soil carbon and nitrogen stocks in alpine grassland ecosystems of the central Tibetan Plateau

Shrub encroachment can significantly affect the ecosystem structure and functioning of alpine grasslands. However, little is known about how this phenomenon alters soil organic carbon stocks (SOCS) and soil nitrogen stocks (STNS) in different alpine grassland ecosystems within the same region. Here we addressed this research gap by investigating the SOCS and STNS of encroached and non-encroached plots in alpine meadow and alpine steppe ecosystems on the central Tibetan Plateau. We found that, in both ecosystems, shrub encroachment significantly increased herbaceous plant richness, diversity, and aboveground biomass, but more notably in alpine meadow. Conversely, shrub encroachment increased belowground plant biomass in alpine steppe but had the opposite effect in alpine meadow, where belowground biomass was four times lower at encroached than at non-encroached plots. Importantly, encroaching shrubs resulted in significantly higher SOCS and STNS in both ecosystems, with alpine steppe showing the greatest carbon and nitrogen gains. The shrub encroached plots had 34.24 % and 97.25 % higher carbon stocks and 70.87 % and 67.34 % higher nitrogen stocks than non-encroached plots at the alpine meadow and alpine steppe, respectively. Increases in carbon and nitrogen stocks occurred mostly at the 10–30 cm soil layer and were highly correlated with shrub-induced changes in the herbaceous community composition. Overall, our results indicated that (1) shrub encroachment promoted carbon and nitrogen accumulation in the soils of both alpine meadow and alpine steppe and (2) the degree of accumulation and the mechanisms behind these changes varied between the two alpine grasslands. Our findings advance the general understanding of the soil carbon and nitrogen dynamics in shrub‐encroached alpine grasslands and highlight the importance of investigating how this phenomenon affects different ecosystems within the same region.

Plant nitrogen retention in alpine grasslands of the Tibetan Plateau under multi-level nitrogen addition

Nitrogen (N) deposition might alleviate degradation of alpine grassland caused by N limitation on the Tibetan Plateau (TP). To determine such limitation and quantify the N-induced N retention in plant, a six-year fertilization experiment with six levels of N addition rates (0, 1, 2, 4, 8 and 16 g N m−2 yr−1) was conducted in the Namco alpine steppe and additional 89 experiments with multi-level N addition were also synthesized worldwide among which 27 sites were on the TP. In general, N addition promoted N retention in plants, and this increasing trend diminished at the critical N rate (Ncr). The maximum N retention capacity (MNRC) of plants at Ncr was strongly correlated with initial aboveground net primary productivity with a slope of 0.02, and the MNRC of grasslands globally ranged from 0.35 to 42.59 g N m−2 yr−1, approximately account for 39% of Ncr. Tibetan alpine grassland had a low average MNRC (2.24 g N m−2 yr−1) with distinct regional characteristic, which was much lower in the western TP (0.80 g N m−2 yr−1) than the eastern TP (4.10 g N m−2 yr−1). Our results inferred 0.33–1.21 Tg N yr−1 (0.22–0.79 g N m−2 yr−1) can be retained and 5.65–20.11 Tg C yr−1 (3.67–13.06 g C m−2 yr−1) can be gained by Tibetan alpine grasslands under current N deposition level. With the aggravation of N deposition, the alpine steppe ecosystem might continuously absorb N and C until N deposition reaches Ncr.

Interannual Variations of Water and Carbon Dioxide Fluxes over a Semiarid Alpine Steppe on the Tibetan Plateau

Water and carbon exchanges between grassland and the atmosphere are important processes for water balance and carbon balance. Based on eddy covariance observations over a semiarid alpine steppe ecosystem in Bange on the Tibetan Plateau during the growing season from 2014 to 2017, the variations in evapotranspiration (ET), net ecosystem exchange (NEE), and their components and the associated driving factors were analyzed. Linear and nonlinear models were applied to investigate the relationships between fluxes and their controlling factors over different timescales. The results show that the average ET for the growing season ranged from 1.1 to 2.4 mm/d with an average of 2.0 mm/d for the four consecutive years. Drought conditions reduced the surface conductance and hence the Priestley–Taylor coefficient. Mean T/ET was low (0.34) due to low vegetation cover. Plant growth increased the T/ET ratio during the growing season, whereas soil water content (SWC) explained most of the variation of ET and E on daily and monthly scales. The Enhanced Vegetation Index (EVI) was the most important controlling factor for temperature. Transpiration increased with SWC in dry conditions. For the growing season in 2014, 2016, and 2017, Bange was a carbon sink, while it was a carbon source in 2015. The largest CO2 flux was higher and the temperature sensitivity coefficient (Q10) was lower for 2015 than for the other three years. SWC affected these photosynthesis and respiration parameters. The ratio of respiration (Re) to gross primary production (GPP) was the highest during the 2015 growing season. Both on daily and monthly scales, Re was positively and linearly correlated with GPP. The most important controlling factor for the CO2 flux was EVI on daily and monthly scales.

Disentangling the assembly mechanisms of bacterial communities in a transition zone between the alpine steppe and alpine meadow ecosystems on the Tibetan Plateau

Alpine meadows and alpine steppes are two major grassland types distributed on the Tibetan Plateau. Due in large part to the differences in hydrothermal and nutrient conditions following the thawing of lakeshore permafrost, alpine meadows and alpine steppes which are characterized by disparate above- and below-ground biomass, could emerge together in the grassland transition zone between meadows and steppes of the Tibetan Plateau. Bacterial communities are essential components of alpine grassland ecosystems and respond rapidly to environmental changes. Despite their ecological significance, it remains poorly elucidated whether and how the assembly patterns of bacterial communities differed between alpine meadows and alpine steppes. Here, to disentangle the assembly mechanisms of bacterial communities from alpine meadows and alpine steppes, we collected samples from three diverse habitats (i.e., sediments, rhizosphere soils and bulk soils) in both alpine meadow and steppe ecosystems on the Tibetan Plateau. Our results indicated that in both meadows and steppes, rhizosphere bacterial communities exhibited higher alpha-diversity but lower beta-diversity compared to the bacterial communities in sediments and bulk soils. However, the close relationships of bacterial communities between different habitats weakened from meadows to steppes. Null model analysis indicated that the importance of environmental selection shaping bacterial community assemblages in all habitats decreased from meadows to steppes, whereas the role of dispersal limitation showed an opposite pattern. Moreover, pH was the primary driver of phylogenetic turnover of bacterial communities in the steppes across all habitats, whereas the dominant drivers of phylogenetic turnover of bacterial communities in meadows varied with habitat types. Overall, our findings provide novel insights into understanding the differences in microbial communities between meadows and steppes in the grassland transition zone on the Tibetan Plateau.

Divergences of soil carbon turnover and regulation in alpine steppes and meadows on the Tibetan Plateau

The grasslands of the Tibetan Plateau store approximately 2.5% of global soil organic carbon (SOC) and considerable soil inorganic carbon (SIC) and have the potential to become a vast carbon source or sink as climate change progresses. However, the soil carbon (C) sequestration mechanisms that occur across large-scale natural gradients remain unclear. Here, humic substances (HS) were utilized to trace soil C turnover at 0–20 cm, and we compared divergences among three main grassland types (alpine meadow, alpine steppe, and artificial plantation) using structural equation modeling (SEM). The results showed that the alpine meadows sequestered the most soil C (63.99 ± 4.41 g kg−1 SOC and 4.11 ± 0.63 g kg−1 SIC), sequestering 2–3 times more than the alpine steppe ecosystems (19.78 ± 1.98 g kg−1 SOC and 9.21 ± 0.66 g kg−1 SIC). The alpine steppe and artificial plantation regions have strong C sink potential due to their low C/N ratios (P < 0.05). Importantly, SIC played an important role in the alpine steppes, accounting for nearly 26–37% of soil C. The ratios of recalcitrant HS to SOC were estimated as 46.50%, 65.09%, and 78.17% in the alpine meadow, alpine steppe, and artificial plantation ecosystems, respectively, indicating that SOC in the alpine meadow was the most sensitive to climate change. Fulvic acid (FA) accounted for 50.86% of SOC in the 0–20-cm interval, contributing most to the formation of SOC in all vegetation types. In addition, in contrast to climatic controls on soil C turnover in the alpine meadow, climate conditions rarely controlled C turnover in the alpine steppe. Moreover, sand and silt were the main soil minerals involved in C turnover in alpine meadow and alpine steppe ecosystems, respectively. Our study improves understanding of the mechanism by which soil C sinks form on the Tibetan Plateau under warming and wetting conditions.

Warming and Increased Respiration Have Transformed an Alpine Steppe Ecosystem on the Tibetan Plateau From a Carbon Dioxide Sink Into a Source

AbstractCold region ecosystems store vast amounts of soil organic carbon (C), which upon warming and decomposition can affect the C balance and potentially change these ecosystems from C sinks to carbon dioxide (CO2) sources. We quantified the decadal year‐round CO2 flux from an alpine steppe‐ecosystem on the Tibetan Plateau using eddy covariance and automatic chamber approaches during a period of significant warming (0.13°C per 10 years; and 0.18°C in the non‐growing season alone: 1st October to next 30th April). The results showed that ongoing climate change, mainly warming within the topsoil layers, is the main reason for the site’s change from a sink for to a source of CO2 in the atmosphere. Non‐growing‐season ecosystem respiration accounted for 51% of the annual ecosystem respiration and has increased significantly. The growing seasons (1st May to 30th September) were consistent CO2 sink periods without significant changes over the study period. Observations revealed high‐emission events from the end of the non‐growing season to early in the growing season (1st March to fifteenth May), which significantly (p &lt; 0.01) increased at a rate of 22.6 g C m−2 decade−1, ranging from 14.6 ± 10.7 g C m−2 yr−1 in 2012 to 35.3 ± 12.1 g C m−2 yr−1 in 2017. Structural equation modeling suggested that active layer warming was the key factor in explaining changes in ecosystem respiration, leading to significant changes in net ecosystem exchange over the period 2011–2020 and indicated that these changes have already transformed the ecosystem from a CO2 sink into a source. These results can be used to improve our understanding of the sensitivity of ecosystem respiration to increased warming during the non‐growing period.

Winter Daytime Warming and Shift in Summer Monsoon Increase Plant Cover and Net CO2 Uptake in a Central Tibetan Alpine Steppe Ecosystem

AbstractOver the past decades, human‐induced climate change has led to a widespread wetting and warming of the Tibetan Plateau (TP), affecting both ecosystems and the carbon cycling therein. Whether the previously observed climate changes stimulate carbon uptake via enhanced photosynthesis or carbon loss via enhanced soil respiration remains unclear. Here we present 14 years of observations of carbon fluxes, meteorological variables and remotely sensed plant cover estimations from a central Tibetan alpine steppe ecosystem at Nam Co, the third largest lake on the TP. Using modified Mann‐Kendall trend tests, we found a significant increasing daily net carbon uptake of 0.5 g C m−2 decade−1, which can be explained by a widespread greening at the southern shore of lake Nam Co. The Plateau‐wide changes in temperature and precipitation are locally expressed as an increasing diurnal temperature range during winter, higher water availability during spring, higher cloud cover during early summer and less water availability during late summer. While these changes differ over the course of the year, they tend to stimulate plant growth more than microbial respiration, leading to an increased carbon uptake during all seasons. This study indicates that during the 14 years study period, a higher amplitude in winter temperatures and an earlier summer monsoon promote carbon uptake in a central Tibetan alpine steppe ecosystem.

Soil nutrient loss by gully erosion on sloping alpine steppe in the northern Qinghai-Tibetan Plateau

Global warming and grazing activities have exacerbated soil erosion in alpine steppe. Gully erosion is a great threat to land degradation in alpine steppe ecosystem. Yet, little is known about the in-situ effects of gully erosion on soil properties at cross section and lengthwise position in alpine steppe ecosystem on the Qinghai-Tibetan Plateau. Here, we used a paired sampling method to compare the soil properties of two erosion gullies (shallow gully and deep gully) at cross section and lengthwise position. The results showed that gully erosion generally induced serious soil nutrient loss and differed between shallow gully and deep gully. However, available phosphorus variation (ΔAP) showed an increase both in shallow gully (from −0.86% to 17.17%) and deep gully (from 8.00% to 45.60%), and pH variation (ΔpH) showed an increase (from −3.40% to 9.01%) in the deep gully. Soil sand content and soil nutrient properties were more sensitive to gully erosion in different cross sections than that in different lengthwise positions, which indicated that the depth of erosion gullies largely determining soil nutrients loss in erosion gullies. Therefore, it is necessary to pay more attention to the ecological restoration of deep erosion gullies to control soil loss and reduce the loss of soil nutrients. These results may conducive to offer a theoretical guidance to achieve the combined goal of gully erosion regulation of alpine steppe ecosystem on the Qinghai-Tibetan Plateau.

Large-Scale Patterns of Soil Nematodes across Grasslands on the Tibetan Plateau: Relationships with Climate, Soil and Plants

Soil nematodes are important contributors to soil biodiversity. Nonetheless, the distribution patterns and environmental drivers of soil nematode communities are poorly understood, especially at the large scale, where multiple environmental variables covary. We collected 520 soil samples from 104 sites representing alpine meadow and steppe ecosystems. First, we explored the soil nematode community characteristics and compared community patterns between the ecosystems. Then, we examined the contributions of aboveground and belowground factors on these patterns. The genus richness and abundance of nematodes on the Tibetan Plateau are lower than other alpine ecosystems, but are comparable to desert or polar ecosystems. Alpine meadows supported a higher nematode abundance and genus richness than alpine steppes; bacterial-based energy channels were pre-dominant in both the ecosystems. Soil factors explained the most variation in the soil nematode community composition in the alpine meadows, while plant factors were as essential as soil factors in the alpine steppes. Unexpectedly, the climate variables barely impacted the nematode communities. This is the first study to explore the spatial patterns of soil nematode compositions on the Tibetan Plateau, and we found that the contributions of climate, plants, and soil properties on soil nematodes community were essentially different from the previous knowledge for well-studied plant and animal communities.

Different response of alpine meadow and alpine steppe to climatic and anthropogenic disturbance on the Qinghai-Tibetan Plateau

Climate change and anthropogenic disturbance are two main drivers for vegetation dynamics on the Qinghai-Tibetan Plateau (QTP). Alpine meadow and alpine steppe are the primary rangeland ecosystem types on the QTP. However, the vegetation trends of the two land cover types and the underlying mechanisms behind their variation remain under debate. In this study, we used Global Inventory Modeling and Mapping Studies (GIMMS) 3g Normalized Difference Vegetation Index (NDVI) (i.e., GIMMS NDVI3g) by coupling the Breaks for Additive Season and Trend (BFAST) model and the Boosted Regression Tree (BRT) model to analyze alpine meadow and alpine steppe vegetation trends on the QTP between 1982 and 2015. We also assessed vegetation variation response to climatic and anthropogenic indicators in conjunction with climatic and human footprint datasets. Results show that growing season NDVI (GSNDVI) values increased overall for both alpine meadow (0.0001 year−1, p = 0.33) and alpine steppe (0.0002 year−1, p < 0.05) throughout 1982–2015. Significant greening trends in both alpine meadow (0.0007 year−1; p < 0.05) and alpine steppe (0.0005 year−1; p < 0.05) ecosystems were obtained before 1998 and 2001, respectively. However, browning trends ascertained by GSNDVI (−0.0006 year−1; p = 0.12) in alpine meadows were observed throughout 1998–2015, while greening trends ascertained by GSNDVI (0.0002 year−1; p = 0.12) in alpine steppes were observed throughout during 2001–2015. Opposing trends in precipitation, solar radiation, and the Standardized Precipitation Evapotranspiration Index (SPEI) occurred before and after breakpoints in both ecosystems. For the alpine meadow ecosystem, adverse precipitation trends caused browning before 1998 followed by greening after 1998 in the Three-River-Source National Park (TNP). Conversely, opposing changes in precipitation, solar radiation, and SPEI resulted in greening before 1998 followed by browning after 1998 in southern Tibet and the southeastern QTP. Alpine meadow vegetation trends were generally dominated by solar radiation before 1998 and jointly by precipitation and solar radiation after 1998. Prior to 2001 variation in alpine steppe greenness was controlled by precipitation, while after 2001 solar radiation dominated. Along with an increase in human footprint pressure (HFP) gradients, greenness trends gradually increased before 1998 but reversed after 1998 in the alpine meadow ecosystem. Additionally, greenness trends gradually decreased before 2001 but remained unchanged after 2001 for the alpine steppe ecosystem. These results highlight the different effects that climate change and anthropogenic disturbances have had on alpine meadow and alpine steppe ecosystems on the QTP over different time frames.

Phylogenetic structure of alpine steppe plant communities along a precipitation and temperature gradient on the Tibetan Plateau

Exploring plant community phylogenetic structure along precipitation and temperature gradients can facilitate the study of mechanisms governing community assembly. Herein, we assessed the phylogenetic structure of alpine steppe plant communities along a precipitation and temperature gradient in Xigaze, Naqu and Ali on the Tibetan Plateau. We found that alpine steppe plant communities were generally phylogenetically clustered on both small (3 m2) and intermediate (1000 m2) scales. We found that mean annual precipitation (MAP), rather than mean annual temperature (MAT), influenced plant species richness and phylogenetic diversity on an intermediate scale. In contrast, MAT, rather than MAP, influenced the phylogenetic structure of plant communities on an intermediate scale such that higher MAT was associated with greater plant community clustering. Additionally, no changes in phylogenetic structure were observed across scales (3 m2 vs 1000 m2). In summary, precipitation is an important regulator of plant diversity, whereas temperature is a key factor that influences the phylogenetic structure of plant communities on the Tibetan Plateau. Our data offer new insights that may better guide current understanding regarding community assembly mechanisms in alpine steppe ecosystems on the Tibetan Plateau faced with global climate change.

A long-term (2005–2019) eddy covariance data set of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes from the Tibetan alpine steppe

Abstract. The Tibetan alpine steppe ecosystem covers an area of roughly 800 000 km2 and contains up to 3.3 % soil organic carbon in the uppermost 30 cm, summing up to 1.93 Pg C for the Tibet Autonomous Region only (472 037 km2). With temperatures rising 2 to 3 times faster than the global average, these carbon stocks are at risk of loss due to enhanced soil respiration. The remote location and the harsh environmental conditions on the Tibetan Plateau (TP) make it challenging to derive accurate data on the ecosystem–atmosphere exchange of carbon dioxide (CO2) and water vapor (H2O). Here, we provide the first multiyear data set of CO2 and H2O fluxes from the central Tibetan alpine steppe ecosystem, measured in situ using the eddy covariance technique. The calculated fluxes were rigorously quality checked and carefully corrected for a drift in concentration measurements. The gas analyzer self-heating effect during cold conditions was evaluated using the standard correction procedure and newly revised formulations (Burba et al., 2008; Frank and Massman, 2020). A wind field analysis was conducted to identify influences of adjacent buildings on the turbulence regime and to exclude the disturbed fluxes from subsequent computations. The presented CO2 fluxes were additionally gap filled using a standardized approach. The very low net carbon uptake across the 15-year data set highlights the special vulnerability of the Tibetan alpine steppe ecosystem to become a source of CO2 due to global warming. The data are freely available at https://doi.org/10.5281/zenodo.3733202 (Nieberding et al., 2020a) and https://doi.org/10.11888/Meteoro.tpdc.270333 (Nieberding et al., 2020b) and may help us to better understand the role of the Tibetan alpine steppe in the global carbon–climate feedback.

Aboveground community composition and soil moisture play determining roles in restoring ecosystem multifunctionality of alpine steppe on Qinghai-Tibetan Plateau

Alpine steppe is one of the most important grassland ecosystems on Qinghai-Tibetan Plateau (QTP), which has been greatly degraded in past decades. However, few studies have paid attention to the ecosystem multifunctionality (EMF) of restored degraded alpine steppes. Four treatments of alpine steppes (degraded alpine steppes, cultivated alpine steppes, fenced alpine steppes and intact alpine steppes) were investigated to explore the effect of treatment, biotic (above- and belowground community composition) and abiotic factors (pH and soil moisture) on restoring nine ecosystem functions (above- and belowground plant biomass, plant nitrogen content, soil organic carbon, soil nitrogen, soil phosphorus, soil microbial biomass carbon, microbial biomass nitrogen and microbial biomass phosphorus) and EMF of alpine steppe ecosystem in Madoi County of Qinghai Province, China. Our results showed that both grassland cultivation and fencing significantly promoted EMF of the degraded alpine steppes. Aboveground plant community composition was more significantly correlated with EMF of the alpine steppes than belowground soil community composition in the process of ecological restoration. Combining abiotic factors with biotic factors could improve the ability to explain EMF than biotic factors alone. Overall, aboveground community composition and soil moisture played determining roles in restoring EMF of alpine steppes.

Influences of litter diversity and soil moisture on soil microbial communities in decomposing mixed litter of alpine steppe species

Many studies have examined the effects of plant diversity and soil water availability on litter decomposition, but little is known about how these two factors interactively influence soil microbial communities, especially in alpine ecosystems. Therefore, the objective of this work was to investigate how litter diversity influences soil microbial communities under different moisture conditions in an alpine steppe ecosystem in Northern Tibet. We collected litter of four abundant plant species (Stipa purpurea, Sp; Carex moorcroftii, Cm; Leontopodium pusillum, Lp; and Artemisia nanschanica, An), and used phospholipid fatty acid (PLFA) analysis to measure soil microbial biomass and community structure. A fully factorial litter mixing experiment under different soil moisture conditions (i.e., 20%, 30% and 40% water holding capacity) was employed. The results showed that litter composition, rather than species richness, significantly affected soil microbial biomass and community composition. The presence of Sp, Cm and An exerted positive or negative effects on soil microbial communities. Litter quality (i.e., C:N ratio) could explain the effects of litter composition on soil microbial communities. High soil moisture facilitated the growth of gram-negative bacteria, while gram-positive bacteria and fungi were more abundant in lower moisture soil. We did not detect any interactive effects of litter species richness and soil moisture on the microbial communities. However, the effects of litter composition on soil microbial communities were dependent on soil moisture condition. These findings indicate that litter composition, rather than species richness, shows interactive effects with soil moisture on soil microbes, and both factors are important in regulating ecosystem functions.