Niche breadth reflects the extent to which taxa or communities can tolerate environmental variations, indicating their potential to respond to environmental changes. However, it remains unclear whether micro- and macro-organisms share similar patterns of niche breadth along the same environmental gradients, and which environmental filters regulates niche breadth across different trophic levels. In this study, 180 soil samples were collected from the northeastern and central Qinghai-Tibet Plateau. By integrating microbiome sequencing with plant community surveys, we quantified niche breadth for bacteria, fungi, and plants within a multidimensional environmental space defined by principal component analysis of environmental variables. We then compared niche breadth among the three groups and identified their primary environmental drivers. The results showed that fungal communities exhibited the broadest niche breadth overall, whereas plant communities displayed the greatest variability in mean niche breadth amongst sites. Elevation was a shared determinant of niche breadth in all groups, although with contrasting response patterns. Bacterial and fungal communities exhibited broader niche breadths at higher elevations, whereas plant communities reached their maximum niche breadths at mid-elevations, suggesting contrasting adaptive strategies. A combination of abiotic (geography and environment) and biotic (community diversity and composition) factors better explained the variation in niche breadth. In particular, compared with the niche breadth of fungal communities, that of bacterial and plant communities was more strongly regulated by biotic factors such as community composition. We further confirmed that abiotic factors influenced the niche breadth of the three biological groups, both directly and indirectly, by shaping their biotic attributes. From the perspective of niche breadth, this study revealed distinct environmental adaptation patterns and the underlying mechanisms of different biological groups in alpine grassland ecosystems. Better understanding of niche breadth patterns amongst different kingdoms of life may provide improved prediction of turnover and resilience of soil ecosystems under environmental change.

Little is known about the structure of plant communities across the vast Tibetan Plateau, which supports at least 12,000 species of alpine vascular plants including over 2000 endemics. We recorded species abundance in 485 sites stretching across 6000 km of the plateau. At each site, species abundance was measured in three quadrats that were 40 m apart, allowing us to quantify local β-diversity within the site. We found that local β-diversity in alpine meadows and steppes was significantly higher than expected by chance, indicating intraspecific aggregation within the sites. After controlling for random sampling effects, the magnitude of local β-diversity varied across the plateau: there was a positive relationship from west to east corresponding to increased rainfall; there were hump-shaped relationships with elevation and latitude. These patterns were driven mainly by regional variation in climate, but also by local soil properties and grazing regimes (our structural equation models (SEMs) explained 27 % and 26 % of variation in alpine meadows and steppes, respectively). Unexpectedly, precipitation-related variables were the strongest predictors in cold-wet alpine meadows while temperature-related variables were the strongest predictors in dry-warm alpine steppes. Our findings support the hypothesis that environmental filtering is largely responsible for local β-diversity of alpine grasslands across the Tibetan Plateau. We discuss how these findings inform efforts to conserve fragile alpine ecosystems threatened by rapid climate warming and overgrazing.

Hydrological changes under climate warming drive the biogeomorphic succession of wetlands and may trigger substantial carbon loss from the carbon-rich ecosystems. Although many studies have explored the responses of wetland carbon emissions to short-term hydrological change, it remains poorly understood how the carbon cycle evolves with hydrology-driven wetland succession. Here, we used a space-for-time approach across hydrological gradients on the Tibetan Plateau to examine the dynamics of ecosystem carbon fluxes (carbon dioxide (CO2) and methane (CH4)) and soil organic carbon pools during alpine wetland succession. We found that the succession from mesic meadow to fen changed the seasonality of both CO2 and CH4 fluxes, which was related to the shift in plant community composition, enhanced regulation of soil hydrology and increasing contribution of spring-thaw emission. The paludification caused a switch from net uptake of gaseous carbon to net release on an annual timescale but produced a large accumulation of soil organic carbon. We attempted to attribute the paradox between evidence from the carbon fluxes and pools to the lateral carbon input and the systematic changes of historical climate, given that the wetlands are spatially low-lying with strong temporal climate-carbon cycle interactions. These findings demonstrate a systematic change in the carbon cycle with succession and suggest that biogeomorphic succession and lateral carbon flows are both important for understanding the long-term dynamics of wetland carbon footprints.

Climate projection requires an accurate understanding for soil organic carbon (SOC) decomposition and its response to warming. An emergent view considers that environmental constraints rather than chemical structure alone control SOC turnover and its temperature sensitivity (i.e., Q10 ), but direct long-term evidence is lacking. Here, using compound-specific radiocarbon analysis of soil profiles along a 3300-km grassland transect, we provide direct evidence for the rapid turnover of lignin-derived phenols compared with slower-cycling molecular components of SOC (i.e., long-chain lipids and black carbon). Furthermore, in contrast to the slow-cycling components whose turnover is strongly modulated by mineral association and exhibits low Q10 , lignin turnover is mainly regulated by temperature and has a high Q10 . Such contrasts resemble those between fast-cycling (i.e., light) and mineral-associated slow-cycling fractions from globally distributed soils. Collectively, our results suggest that warming may greatly accelerate the decomposition of lignin, especially in soils with relatively weak mineral associations.

近40年来,青藏高原经历了快速的增温,而且预计在将来的几十年里其温度会持续上升。由于气候变暖可能引起土壤水分、养分可利用性的变化,了解该变化是否会影响高寒草地对气候变暖的响应,是准确预测未来气候变暖背景下高寒草地生产力变化的重要前提。基于高（4 050 m）、中（3 700 m）、低（3 200 m） 3个海拔的开顶式增温箱（OTCs）增温与施肥（氮（N）肥、磷（P）肥）野外控制实验,该研究测定了高寒草地群落及其4种功能群（豆科、禾草、莎草、杂类草）的地上绝对和相对生物量,探讨了高寒草地地上生物量对气候变暖的响应以及土壤养分的调节作用。结果表明:1)增温处理的响应比与海拔之间存在显著的正相关关系。2)增温导致中、高海拔草地地上生物量的增加,而且在N、P添加下,增温均显著增加了3个海拔草地地上生物量。3)不同海拔的4种功能群相对生物量对增温的响应不一致,而且同一功能群因不同的养分条件对增温表现出了显著的差异。研究表明,高寒植物对增温的响应依赖于海拔,并且受到土壤养分可利用性的调节。

Field spectroscopy is a powerful tool for monitoring leaf functional traits in situ, but it remains unclear whether universal statistical models can be developed to predict traits from spectral information, or whether re-calibration is necessary as conditions vary. In particular, multiple leaf traits vary simultaneously across growing seasons, and it is an open question whether these temporal changes can be predicted successfully from hyperspectral data. To explore this question, monthly changes in 21 physiochemical leaf traits and plant spectra were measured for eight deciduous tree species from the UK. Partial least-squares regression (PLSR) was used to evaluate whether each trait could be predicted from a single PLSR model from reflectance spectra, or whether species- and month-level models were needed. Physiochemical traits and spectra varied greatly over the growing season, although there was less variation among mature leaves harvested between June and September. Importantly, leaf spectroscopy was able to predict seasonal variations of most leaf traits accurately, with accuracies of prediction generally higher for mature leaves. However, for several traits, the PLSR estimation models varied among species, and a single PLSR model could not be used to make accurate species-level predictions. Our findings demonstrate that leaf spectra can successfully predict multiple functional foliar traits through the growing season, establishing one of the fundamentals for monitoring and mapping plant functional diversity in temperate forests from air- and spaceborne imaging spectroscopy.

A growing body of work examines the direct and indirect effects of climate change on ecosystems, typically by using manipulative experiments at a single site or performing meta-analyses across many independent experiments. However, results from single-site studies tend to have limited generality. Although meta-analytic approaches can help overcome this by exploring trends across sites, the inherent limitations in combining disparate datasets from independent approaches remain a major challenge. In this paper, we present a globally distributed experimental network that can be used to disentangle the direct and indirect effects of climate change. We discuss how natural gradients, experimental approaches, and statistical techniques can be combined to best inform predictions about responses to climate change, and we present a globally distributed experiment that utilizes natural environmental gradients to better understand long-term community and ecosystem responses to environmental change. The warming and (species) removal in mountains (WaRM) network employs experimental warming and plant species removals at high- and low-elevation sites in a factorial design to examine the combined and relative effects of climatic warming and the loss of dominant species on community structure and ecosystem function, both above- and belowground. The experimental design of the network allows for increasingly common statistical approaches to further elucidate the direct and indirect effects of warming. We argue that combining ecological observations and experiments along gradients is a powerful approach to make stronger predictions of how ecosystems will function in a warming world as species are lost, or gained, in local communities.

Aim An important research question in ecology is how climate and the biodiversity of aboveground plants and belowground microbiomes affect ecosystem functions such as nutrient pools. However, little is studied on the concurrent role of above- and belowground species composition in shaping the spatial distribution patterns of ecosystem functions across environmental gradients. Here, we investigated the relationships between the taxonomic composition of plants, soil bacteria and soil fungi and spatial turnover in nutrient pools, and assessed how species composition-nutrient pool relationships were mediated by contemporary climatic conditions. Location Qinghai-Tibetan Plateau. Time period Current. Major taxa studied Plants, soil bacteria and soil fungi. Methods We surveyed plant assemblages, sampled the taxonomic composition of soil bacteria and soil fungi, and measured plant- and soil-mediated nutrient pools at 60 alpine grasslands on the Qinghai-Tibetan Plateau. Using Mantel tests, structural equation models and general linear models, we investigated the relative importance of the taxonomic composition of plant, soil bacterial, and soil fungal communities on the spatial turnover of alpine grassland nutrient pools. Results We found that the taxonomic composition of plant, soil bacterial, and soil fungal communities was associated with local climate. However, the effects of local climate on the spatial turnover of plant- and soil-mediated nutrient pools were mainly indirect and mediated through plant and soil bacterial species composition, but not through soil fungal species composition. We further found that the replacement component of soil bacterial beta-diversity and the richness difference of plant beta-diversity were the direct predictors of nutrient pools in the alpine grasslands. Main conclusions These results highlight that belowground bacterial composition together with aboveground plant species composition are related to spatial turnover in nutrient pools, perhaps even driving it. Conserving above- and belowground biodiversity may therefore safeguard against the impacts of local climate on the functions of climate-sensitive alpine grasslands.

Microbial necromass carbon (MNC) is key to soil organic carbon (SOC) storage. However, mechanisms regulating MNC accumulation on large scales are poorly understood. Here we provide the first batch of regional-scale MNC data based on amino sugars for the Qinghai-Tibet Plateau alpine grasslands. We show that Qinghai-Tibet grasslands have similar microbial biomass carbon (MBC) but lower MNC concentrations in SOC than Mongolian and other grasslands. The low contribution of MNC to SOC is mainly attributed to high aridity and low net primary productivity of the Qinghai-Tibet grasslands. Our findings highlight climatic and plant influences on MNC accumulation at regional scales.

Aim Most existing studies that examined the biotic mechanisms of ecosystem stability have focused on aboveground biodiversity. Whether and how belowground biodiversity affects the stability of natural ecosystems is largely unknown. In the present study, we investigated the relationships between above- and belowground biodiversity and the temporal stability of grassland biomass production across a large gradient of soil and climatic conditions. Location Tibetan Plateau. Time period 2001-2016. Major taxa studied Alpine grass and soil bacteria, arbuscular mycorrhiza (AM) fungi and fauna. Methods We coupled a field biodiversity survey conducted in 54 alpine grassland ecosystems across the Tibetan Plateau with a satellite-sensed proxy (enhanced vegetation index, EVI) of ecosystem productivity during 2001-2016. The temporal stability of primary productivity was calculated as the ratio of the mean annual peak EVI to the standard deviation of the annual peak EVI over this period. Plant diversity was determined using a classic vegetation survey approach, soil bacterial and AM fungal diversity were measured using a high-throughput sequencing approach, and soil fauna was counted and identified at the order level after being extracted using a modified Berlese-Tullgren method. Results Our results demonstrated that both above- and belowground biodiversity were positively associated with ecosystem stability. Belowground biodiversity not only affected ecosystem stability directly, but also influenced it indirectly through plant diversity and soil fertility. Furthermore, soil pH, climate and its variability strongly influenced soil biodiversity, which in turn influenced ecosystem stability. Main conclusions Our study demonstrates the indispensable role of belowground biodiversity in regulating ecosystem stability, emphasizing the necessity of conserving this 'hidden' biodiversity in fragile alpine ecosystems facing ongoing environmental change.

Owing to different soil environments and organic carbon sources, soil organic carbon (SOC) composition and preservation mechanisms may vary substantially in deep versus surface soils. This study examines vertical variation of various SOC components (including lignin phenols, cutin, suberin and microbial lipids) across the Chinese-Mongolian grasslands. Lignin phenols and hydrolysable lipids were isolated by cupric oxide oxidation and alkaline hydrolysis, respectively. A comprehensive list of environmental variables was compiled to disentangle influencing factors for the variation of various components at four different depths. Lignin phenols, suberin and microbial lipids were most abundant in the surface soil (0–10 cm). Ratios of cutin to suberin and microbial lipids to lignin phenols (in the alpine grasslands) were higher in the bottom-most soil. Calcium (Ca) rather than iron (Fe) plays an important role in the preservation of cutin and microbial lipids in the bottom soil with a high Ca:Fe ratio and high pH. The incorporation efficiency of suberin was higher in deeper than surface soils and showed an increasing trend with depth in the alpine (but not temperate) grasslands. Compared to surface soils, the incorporation of root-derived carbon into SOC is more efficient in deeper soils due to stronger mineral protection and weaker microbial decomposition. Root-derived carbon is more important for SOC accrual in the alpine than temperate grasslands, especially at depth. These findings reveal differential distribution patterns and preservation mechanisms for SOC components in the surface versus deep soils, providing new information to understand SOC stability at different depths.

AimsAs a major plant-derived soil organic carbon (SOC) component, lignin-derived phenolic compounds show varying biogeochemical characteristics compared to plant-derived lipid moieties. Comparing their distribution patterns can provide information on mechanisms governing SOC preservation and dynamics. However, the large-scale distribution pattern and stability of lignin versus plant-derived lipids are still poorly constrained. Here we investigated the distribution of lignin phenols versus plant-derived lipids in the surface soils across the alpine versus temperate grasslands of China and Mongolia.MethodsLignin phenols were isolated by cupric oxide oxidation method and compared with the previously analyzed plant-derived lipids (cutin and suberin). A comprehensive list of environmental variables was compiled to disentangle the climatic, edaphic and vegetation influences on lignin phenols' distribution in the soil.ResultsLignin phenols showed similar SOC-normalized concentrations in the alpine and temperate grassland soils despite a higher plant input to the latter, suggesting better lignin preservation in the cold region. However, compared with plant-derived lipids (cutin and suberin), lignin seems to be less stabilized. The variation of lipid versus lignin components is mainly related to climate (particularly aridity) in the alpine grassland soils, while the relative abundance of plant lipids and lignin phenols is more related to reactive mineral contents in the temperate grassland soils.ConclusionsLignin contributes differentially to SOC accumulation in the alpine and temperate soils: while lignin seems to be better preserved in the cold region, lignin phenols decrease relative to other carbon components with SOC accrual in the temperate region. Overall, lignin distribution and fate may be more sensitive to carbon source variations than temperature shifts in the grasslands.

Wetlands are predicted to experience lowered water tables due to permafrost degradation in the Tibetan Plateau. These changes may affect carbon cycle processes such as soil respiration (R-s). However, the magnitude, patterns and controls of R-s remain poorly understood in alpine wetlands with their distinct hydrological regimes. Here, we conducted a field study on R-s from 2012 to 2014 in three alpine ecosystems on the Tibetan Plateau-fen, wet meadow and meadow-with soil water decreases along hydrological gradients. From 2012 to 2014, the annual R-s was 128.9-193.3 g C m(-2)yr(-1), 281.5-342.9 g C m(-2)yr(-1), and 663.4-709.1 g C m(-2)yr(-1) for the fen, wet meadow, and meadow, respectively. An abrupt increase in CO2 emissions was caused by the spring thawing of the frozen soil in the fen and wet meadow, contributing 20.4-37.6% and 13.2-17.4%, respectively, to the annual R-s. The diurnal variation in the R-s was site specific among the three ecosystems, with one peak at 1300 h in the fen and meadow and two peaks at 1300 h and 1900 h in the wet meadow. The temperature-independent components of the diurnal variation in R-s were generally explained by photosynthetically active radiation in the fen and wet meadow, but not in the meadow. The temperature sensitivity of the R-s (unconfounded Q(10)) varied significantly among the three ecosystems, with the highest values occurring in the wet meadow, implying that permafrost thaw-induced wetland drying from the fen to the wet meadow could enhance the response of CO2 emissions to climate warming but that further drying from the wet meadow to the meadow probably weakens the effect of warming on the R-s. Our study emphasized the important role of the hydrological regime in regulating the temporal variation in R-s and its response to climate warming.

The relative contribution of roots versus shoots to soil organic carbon (SOC) is a long‐debated topic related to soil carbon formation and dynamics. However, the variation of root‐ and shoot‐derived carbon in natural soils remains poorly constrained due to limited tools to separate them. Here we overcome the difficulty by analyzing biomarkers for root (suberin) and shoot (cutin) in grassland soils spanning >7,000 km on the Qinghai‐Tibetan and Mongolian Plateaus. Coupled with a comprehensive list of climatic, edaphic, and vegetation variables, we assess their inputs, distribution, and preservation patterns. We find that while suberin was a root‐specific tracer, cutin biomarkers that occurred only in trace amount in roots also had a minor but nonnegligible contribution from belowground sources due to the massive root mass in the alpine grasslands. Both components had higher SOC‐normalized concentrations in the alpine than temperate grasslands, along with a higher preservation percentage against net primary productivity and a lower degradation parameter, suggesting a better preservation of these plant‐derived lipid components in the alpine region. Moreover, while cutin and suberin abundances were affected by plant inputs and other SOC constituents, the root mass normalized incorporation efficiency of suberin was only positively correlated to SOC in both regions with a steeper slope in the alpine grasslands and also negatively correlated to root mass in the alpine soils. These results imply that root carbon incorporation is sensitive to environmental variations in the cold region, suggesting potentially more dynamic alterations to root carbon sequestration with environmental changes.

ABSTRACT Soil bacteria are key to ecosystem function and maintenance of soil fertility. Leveraging associations of current geographic distributions of bacteria with historic climate, we predict that soil bacterial diversity will increase across the majority (∼75%) of the Tibetan Plateau and northern North America if bacterial communities equilibrate with existing climatic conditions. This prediction is possible because the current distributions of soil bacteria have stronger correlations with climate from ∼50 years ago than with current climate. This lag is likely associated with the time it takes for soil properties to adjust to changes in climate. The predicted changes are location specific and differ across bacterial taxa, including some bacteria that are predicted to have reductions in their distributions. These findings illuminate the widespread potential of climate change to influence belowground diversity and the importance of considering bacterial communities when assessing climate impacts on terrestrial ecosystems. IMPORTANCE There have been many studies highlighting how plant and animal communities lag behind climate change, causing extinction and diversity debts that will slowly be paid as communities equilibrate. By virtue of their short generation times and dispersal abilities, soil bacteria might be expected to respond to climate change quickly and to be effectively in equilibrium with current climatic conditions. We found strong evidence to the contrary in Tibet and North America. These findings could significantly improve understanding of climate impacts on soil microbial communities.

The distributions of many species show climate-driven shifts towards higher elevations, but evidence for elevational shifts is scarce for the alpine grasslands on the Qinghai-Tibetan Plateau. The upward shift of alpine grassland distribution from 2000 to 2014 was assessed with field measurements and satellite remote sensing data obtained across six elevational transects on the Qinghai-Tibetan Plateau. The aboveground biomass (AGB) of alpine grasslands varied with altitude and its data produced a bell-shaped curve. This was mainly due to the elevational dependency of climate change at the surface (i.e., producing drier climate at low elevations and wetter climate at middle elevations). The normalized difference vegetation index (NDVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) exhibited a positive exponential relationship with the AGB of alpine grasslands. Overall, MODIS NDVI initially increased, then peaked at median altitude sites, then decreased with altitude on each elevational transect. MODIS NDVI at the upper limit of alpine grassland distribution did not show a significant increasing trend from 2000 to 2014, even though land surface temperature increased and precipitation remained approximately constant. High spatial resolution Landsat data supported this result. Further analyses of MODIS NDVI at all other sites found no general increase in AGB towards higher elevations. The results suggest that the distribution of alpine grasslands on the Qinghai-Tibetan Plateau did not show an upward shift despite rapid climate warming having occurred from 2000 to 2014.

Chinese grasslands hold a third of the national soil organic carbon (OC) stocks but remain poorly investigated in terms of soil molecular components and their distribution patterns. Such information is important for understanding mechanisms governing grassland soil OC dynamics and its response to global changes. Here employing solvent-extractable compounds as a group of widely used biomarkers, we present a large-scale study on the distribution of different soil OC components (including plant- and microbial-derived carbohydrates and aliphatic and cyclic lipids) in the surface soils of Chinese grasslands, spanning from temperate grasslands in the arid/semiarid regions to alpine grasslands on the Qinghai-Tibetan Plateau. We show that alpine grassland soils are more enriched with carbohydrates and plant-derived compounds relative to the temperate counterparts due to temperature-inhibited decomposition. While plant belowground biomass plays a key role in explaining the spatial variation of compounds in the alpine grasslands, climatic variables do in the temperate region. In particular, aliphatic lipids accumulate with increasing mean annual temperature in the temperate grasslands due to a preferential decay of labile soil OC, whereas they decrease in the alpine grasslands owing to dilution by an enhanced plant input of nonlipid components. Collectively, these results demonstrate different mechanisms governing the distribution of solvent-extractable compounds in grassland soils, with climate-mediated decomposition processes dominating in the temperate grasslands and plant inputs being more important in the alpine region. In the context of climate change, alterations to soil OC input and decomposition processes may have varied impacts on soil carbon cycling in these two regions.

Picea crassifolia and P. wilsonii , commonly used for afforestation in northern China, are increasingly likely to be subjected to high temperatures and soil drought stress as a result of global warming. However, little is known about the effects of these stresses on foliar photosynthesis in the two species. To investigate how photosynthetic characteristics and sensitivity respond to prolonged high temperatures and soil drought, foliar gas exchange and other closely related parameters were recorded from four-year-old seedlings of both species. Seedlings were grown under two temperature treatments (25/15 and 35/25 °C) and four soil water regimes [80, 60, 40 and 20% of maximum field capacity (FC)] for 4 months. Although all treatments significantly reduced photosynthetic rates ( P n ) of both species, P. crassifolia exhibited greater photosynthetic acclimation than P. wilsonii . Differences in photosynthetic acclimation were mainly related to variations in stomatal conductance ( Cond ) and the maximum quantum yield of PSII ( F v / F m ) between treatments. Indeed, higher Cond and F v / F m in all treatments were shown for P. crassifolia than for P. wilsonii . Moreover, photosynthesis in P. crassifolia exhibited inherently lower temperature sensitivities (broader span for the temperature response curves; lower b ) and higher thermostability (invariable b between treatments). Further, severe drought stress (20% FC) limited the survival of P. wilsonii . Our results indicate that P. wilsonii is more susceptible to high temperatures and soil drought stress. Planting P. crassifolia would be more expected to survive these conditions and hence be of greater benefit to forest stability if predicted increases in drought and temperature in northern China occur.

Based on field observations, remote sensing, and modeling, recent studies have reported inconsistent changes in soil organic carbon (SOC) stocks in grasslands of the Tibetan Plateau over the past few decades. However, direct evidence about the changes in SOC stocks in the plateau's grasslands coming from in situ, site-by-site, repeated surveys is rare. In this study, we carried out a repeated soil sampling to assess the changes in SOC stocks in the alpine grasslands across the Tibetan Plateau. Across all 41 sites in the alpine grasslands, SOC stocks exhibited a significant increase from 2002 to 2011 at an overall rate of 4.66 g C m− 2 yr− 1. Mesic and low-temperature-limited alpine meadows showed an average carbon gain of 25.8 g C m− 2 yr− 1, whereas the relatively dry alpine steppes exhibited a slight carbon loss of 11.9 g C m− 2 yr− 1. Spatially, the changes in SOC stocks were significantly related to the original SOC stocks across alpine steppes, and soils with low carbon tended to gain carbon. Moreover, the changes in SOC stocks were also associated with March–April precipitation in alpine meadows, and with mean annual precipitation (MAP) in alpine steppes, with drier sites generally gaining carbon. Overall, the alpine grasslands of the Tibetan Plateau significantly accumulated SOC over this 10-year period, but many more site surveys are needed to comprehensively access the changes in SOC stocks across alpine grasslands on the plateau; and management strategies enhancing the ability of C sequestration should differ between alpine meadows and steppes due to their contrasting climate conditions.

Unraveling the fate of organic carbon (OC) in soils is essential to understanding the impact of global changes on the global carbon cycle. Previous studies have shown that while various soil OC components have different decomposability, chemically labile OC can have old 14C ages. However, few studies have compared the 14C age of various soil OC components on a large scale, which may provide important information on the link between the age or turnover of soil OC components to their sources, molecular structures as well as environmental variables. In this project, a suite of soil profiles were sampled along a large-scale transect of temperate and alpine grasslands across the Tibetan and Mongolian Plateaus in China with contrasting climatic, vegetation and soil properties. Bulk OC and source-specific compounds (including fatty acids (FAs), diacids (DAs) and lignin phenols) were radiocarbon-dated to …