title: Alpine grassland soil organic carbon stock and its uncertainty in the three rivers source region of the Tibetan Plateau.
abstract: Alpine grassland of the Tibetan Plateau is an important component of global soil organic carbon (SOC) stocks, but insufficient field observations and large spatial heterogeneity leads to great uncertainty in their estimation. In the Three Rivers Source Region (TRSR), alpine grasslands account for more than 75% of the total area. However, the regional carbon (C) stock estimate and their uncertainty have seldom been tested. Here we quantified the regional SOC stock and its uncertainty using 298 soil profiles surveyed from 35 sites across the TRSR during 2006-2008. We showed that the upper soil (0-30 cm depth) in alpine grasslands of the TRSR stores 2.03 Pg C, with a 95% confidence interval ranging from 1.25 to 2.81 Pg C. Alpine meadow soils comprised 73% (i.e. 1.48 Pg C) of the regional SOC estimate, but had the greatest uncertainty at 51%. The statistical power to detect a deviation of 10% uncertainty in grassland C stock was less than 0.50. The required sample size to detect this deviation at a power of 90% was about 6-7 times more than the number of sample sites surveyed. Comparison of our observed SOC density with the corresponding values from the dataset of Yang et al. indicates that these two datasets are comparable. The combined dataset did not reduce the uncertainty in the estimate of the regional grassland soil C stock. This result could be mainly explained by the underrepresentation of sampling sites in large areas with poor accessibility. Further research to improve the regional SOC stock estimate should optimize sampling strategy by considering the number of samples and their spatial distribution.
authors.affiliation: State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, China; Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, China.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Chang
authors.affiliation: Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China.
authors.forename: Shiping
authors.initials: S
authors.lastname: Wang
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, China; University of Chinese Academy of Science, Beijing, China.
authors.forename: Shujuan
authors.initials: S
authors.lastname: Cui
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, China; University of Chinese Academy of Science, Beijing, China.
authors.forename: Xiaoxue
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, China.
authors.forename: Caiyun
authors.initials: C
authors.lastname: Luo
authors.affiliation: Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Science, Xining, China.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: World Agroforestry Centre East Asia Programme, Beijing, China.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wilkes
mesh_terms: D002244:Carbon / Q000032:analysis*; D065948:Grassland; D045483:Rivers; D012987:Soil / Q000737:chemistry*; D018609:Tibet; D035501:Uncertainty
chemical_list: D012987:Soil; D002244:Carbon