Organic carbon content and distribution in soils under different land usesin tropical and subtropical China

Tropical and subtropical China comprises a land area of about 215 Mha, but reports on its soil C storage and contents are limited. The objective of th is study was to investigate the C density, stocks and distribution in soils of this region under different land uses by using soil species data from t he Second National Soil Survey and the Vegetation Map of the People's Repub lic of China (1:4 M). It was estimated that there is a total of about 28.7 +/-8.2 Pg organic C stored in the upper 1 m of soils of the entire region. Changes of C content (C) with depth (D) were observed following a relations hip of C = (c + D)/ (a + bD), or C = 1/(a + bD). Of the various patterns of land uses in the region, soil C density was generally higher in the west t han in the east, and while small differences were found in croplands, there were large variations in natural soils. In the west, the C density of mead ow and herbaceous swamp soil was the highest (about 40 kg C/m(2)), followed by coniferous and broad-leaf forest soils (19.6 and 19.2 kg C/m(2), respec tively). The C density of paddy, bush and coppice forest soils showed a den sity of 12.6 and 14.6 kg C/m(2), respectively. Upland and grass-savanah soi ls ranked the lowest (9.4 and 10.5 kg C/m(2), respectively). In the east, m eadow and herbaceous swamp soil had the highest C density (25.2 kg C/m(2)), but differences in C density among soils under coniferous forest, broad-le af forest, bush and coppice forest, and rice were small, varying from 10.2 to 11.4 kg C/m(2). The C density of upland soil (7.2 kg C/m(2)), appeared a little higher than that of grass-savanah soil (6.3 kg C/m(2)). For the var ious land uses in the region, the C density estimation is accompanied by re latively large variations.