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As CO2 concentrations continue to rise and drive global climate change, much effort has been put into estimating soil carbon (C) stocks and dynamics over time. However, the inconsistent methods employed by researchers hamper the comparability of such works, creating a pressing need to standardize the methods for soil organic C (SOC) quantification by the various methods. Here, we collected 712 soil samples from 36 sites of alpine grasslands on the Tibetan Plateau covering different soil depths and vegetation and soil types. We used an elemental analyzer for soil total C (STC) and an inorganic carbon analyzer for soil inorganic C (SIC), and then defined the difference between STC and SIC as SOCCNS. In addition, we employed the modified Walkley-Black (MWB) method, hereafter SOCMWB. Our results showed that there was a strong correlation between SOCCNS and SOCMWB across the data set, given the application of a correction factor of 1.103. Soil depth and soil type significantly influenced on the recovery, defined as the ratio of SOCMWB to SOCCNS, and the recovery was closely associated with soil carbonate content and pH value as well. The differences of recovery between alpine meadow and steppe were largely driven by soil pH. In addition, statistically, a relatively strong correlation between SOCCNS and STC was also found, suggesting that it is feasible to estimate SOCCNS stocks through the STC data across the Tibetan grasslands. Therefore, our results suggest that in order to accurately estimate the absolute SOC stocks and its change in the Tibetan alpine grasslands, adequate correction of the modified WB measurements is essential with correct consideration of the effects of soil types, vegetation, soil pH and soil depth. [ABSTRACT FROM AUTHOR]

In this study, we assessed the abundance and diversity of bacterial communities by 16S rRNA gene-based qPCR and T-RFLP across different soil depths of three sites located on the Tibetan Plateau which are affected by discontinuous permafrost or characterized as seasonally frozen ground. Our data indicates that bacterial community structure was significantly influenced by soil depth mainly at the site affected by seasonal freezing and thawing. In contrast at sites affected by permafrost, diversity pattern of bacterial communities in the top soil and deeper soil layers changed to a far lower extend. This might be related to the fact that the investigated sites were not waterlogged at the permafrost layer, thus no processes that shifts towards bacterial communities, which require anoxic environments, could be expected. Overall, at all sites, labile and stable C as well as N pools act as main drivers for bacterial communities. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau reacts particularly sensitively to possible effects of climate change. Approximately two thirds of the total area is affected by permafrost. To get a better understanding of the role of permafrost on soil organic carbon pools and stocks, investigations were carried out including both discontinuous (site Huashixia, HUA) and continuous permafrost (site Wudaoliang, WUD). Three organic carbon fractions were isolated using density separation combined with ultrasonic dispersion: the light fractions (<1.6 g cm−3) of free particulate organic matter (FPOM) and occluded particulate organic matter (OPOM), plus a heavy fraction (>1.6 g cm−3) of mineral associated organic matter (MOM). The fractions were analyzed for C, N, and their portion of organic C. FPOM contained an average SOC content of 252 g kg−1. Higher SOC contents (320 g kg−1) were found in OPOM while MOM had the lowest SOC contents (29 g kg−1). Due to their lower density the easily decomposable fractions FPOM and OPOM contribute 27% (HUA) and 22% (WUD) to the total SOC stocks. In HUA mean SOC stocks (0–30 cm depth) account for 10.4 kg m−2, compared to 3.4 kg m−2 in WUD. 53% of the SOC is stored in the upper 10 cm in WUD, in HUA only 39%. Highest POM values of 36% occurred in profiles with high soil moisture content. SOC stocks, soil moisture and active layer thickness correlated strongly in discontinuous permafrost while no correlation between SOC stocks and active layer thickness and only a weak relation between soil moisture and SOC stocks could be found in continuous permafrost. Consequently, permafrost-affected soils in discontinuous permafrost environments are susceptible to soil moisture changes due to alterations in quantity and seasonal distribution of precipitation, increasing temperature and therefore evaporation. [ABSTRACT FROM AUTHOR]

We investigated the main parameters [e.g. mean annual air temperature , mean annual soil temperature, mean annual precipitation, soil moisture (SM), soil chemistry, and physics] influencing soil organic carbon (Corg), soil total nitrogen (Nt) as well as plant available nitrogen (Nmin) at 47 sites along a 1200 km transect across the high-altitude and low-latitude permafrost region of the central-eastern Tibetan Plateau. This large-scale survey allows testing the hypothesis that beside commonly used ecological variables, diversity of pedogenesis is another major component for assessing carbon (C) and nitrogen (N) cycling. The aim of the presented research was to evaluate consequences of permafrost degradation for C and N stocks and hence nutrient supply for plants, as the transect covers all types of permafrost including heavily degraded areas and regions without permafrost. Our results show that SM is the dominant parameter explaining 64% of Corg and 60% of N variation. The extent of the effect of SM is determined by permafrost, current aeolian sedimentation occurring mostly on degraded sites, and pedogenesis. Thus, the explanatory power for C and N concentrations is significantly improved by adding CaCO3 content ( P=0.012 for Corg; P=0.006 for Nt) and soil texture ( P=0.077 for Corg; P=0.015 for Nt) to the model. For soil temperature, no correlations were detected indicating that in high-altitude grassland ecosystems influenced by permafrost, SM overrides soil temperature as the main driving parameter at landscape scale. It was concluded from the current study that degradation of permafrost and corresponding changes in soil hydrology combined with a shift from mature stages of pedogenesis to initial stages, have severe impact on soil C and plant available N. This may alter biodiversity patterns as well as the development and functioning of the ecosystems on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Permafrost soils store enormous quantities of organic carbon. Especially on the alpine Qinghai-Tibet Plateau, global warming induces strong permafrost thawing, which strengthens the microbial decomposition of organic carbon and the emission of the greenhouse gas carbon dioxide (CO 2 ). Enhanced respiration rates may intensify climate warming in turn, but the magnitude of future CO 2 emissions from this data-scarce region in a changing climate remains highly uncertain. Here, we aim at an area-wide estimation of future potential CO 2 emissions for the permafrost region on the Qinghai-Tibet Plateau as key region for climate change studies due to its size and sensitiveness. We calculated four potential soil respiration scenarios for 2050 and 2070 each. Using a regression model, results from laboratory experiments and C stock estimations from other studies, we provide an approximation of total potential soil CO 2 emissions on a regional scale ranging from 737.90 g CO 2 m −2 y −1 –4224.77 g CO 2 m −2 y −1 . Our calculations as first estimate of thawing-induced CO 2 emissions (51.23 g CO 2 m −2 y −1 –3002.82 g CO 2 m −2 y −1 ) from permafrost soils of the Qinghai-Tibet Plateau under global warming appear to be consistent to measurements of C loss from thawing permafrost soils measured within other studies. Thawing-induced soil CO 2 emissions from permafrost soils with a organic C content ranging from 2.42 g C kg −1 to 425.23 g C kg −1 increase general soil respiration by at least about one third on average at a temperature of 5 °C. Differences between scenarios remain < 1% and thawing-induced CO 2 emissions generally decrease over time comparing 2015, 2050 and 2070. With this spatial approximation at a regional scale, a first area-wide estimate of potential CO 2 emissions for 2050 and 2070 from permafrost soils of the Qinghai-Tibet Plateau is provided. This offers support of assessing potential area-specific greenhouse gas emissions and more differentiated climate change models. [ABSTRACT FROM AUTHOR]

Alpine ecosystems like the Qinghai-Tibet Plateau strongly respond to global warming. Their soils, containing large carbon stocks, release more carbon dioxide as a possible consequence. Reciprocally, this may intensify climate warming. The Qinghai-Tibet plateaús large and almost inaccessible terrain results in a general data scarcity for this area making the quantification of soil carbon dynamics challenging. The current study provides an area-wide estimation of soil respiration for the Qinghai-Tibet Plateau, which is a key region for climate change studies due to its size and sensitivity. We compared the ability of six regression models to predict soil respiration that were developed within different studies and are based on mean annual air temperature, mean annual precipitation and belowground biomass. We used the WorldClim data sets to approximate annual soil respiration on a regional scale. Compared to field measurements of soil respiration at single spots in different vegetation zones on the Qinghai-Tibet Plateau (max. 1876.63 g C m −2 year −1 ), our predicted results (max. 1765.13 g C m −2 year −1 ) appear to be consistent. The basic difference between grasslands and forests in soil respiration is indicated by all regression models, however, a more precise differentiation between vegetation types is only exhibited by the regression model based on mean annual precipitation. Overall, this model performs best for most and the largest vegetation zones. Nevertheless, the approximations of the model based on mean annual temperature by Raich and Schlesinger (1992) with a lower constant better represent the vegetation zone of the alpine steppe. With this spatial estimation of soil respiration at a regional scale, a basis for assessing an area-specific potential of greenhouse gas emissions on the Qinghai-Tibet Plateau is provided. Moreover, we quantify a complex soil ecological process for this data-scarce area. [ABSTRACT FROM AUTHOR]