Spatial distribution of vegetation carbon stock among different organs over the Tibetan Plateau: on an intensive field survey

Tibetan Plateau, as one of the most carbon intensive regions in China, is crucial in the carbon cycle, and accurately estimating its vegetation carbon density (CVEG) is essential for assessing regional and national carbon balance. However, the spatial distribution of regional CVEG is not available remains highly uncertain due to lack of systematic research, especially for different organs. Here, we investigated the spatial distribution patterns and driving factors of CVEG among different plant organs (leaf, branch, trunk and root) by systematically field grid-sampling 2040 field-plots of plant communities over the Tibetan Plateau from 2019 to 2020. The results showed that the carbon content of plant organs ranged from 255.53 to 515.58 g kg-1, with the highest in branches and the lowest in roots. Among the different plant functional groups, the highest CVEG was found in evergreen coniferous forests, and the lowest in desert grasslands, with an average CVEG of 1603.98 g m-2. CVEG increased spatially from northwest to southeast over the Tibetan Plateau, with MAP being the dominant factor. Furthermore, the total vegetation carbon stock on the Tibetan Plateau was estimated to be 1965.62 Tg for all vegetation types. Based on the comprehensive field survey dataset, the Random Forest model effectively predicted and mapped the spatial distribution of CVEG (including aboveground, belowground, and the total biomass carbon density) over the Tibetan Plateau with notable accuracy (validation R2 values were 71%, 56%, and 64% for CAGB, CBGB, and CVEG, respectively) at a spatial resolution of 1 km x 1 km. Our findings can help improve the accuracy of regional carbon stock estimations and provide parameters for carbon cycle model optimization and remote sensing calibration in the future.