Organic carbon content and distribution in soils under different land uses in 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 this 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 the Second National Soil Survey and the Vegetation Map of the People's Republic 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 relationship 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 than 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 meadow 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), respectively). The C density of paddy, bush and coppice forest soils showed a density of 12.6 and 14.6 kg C/m(2), respectively. Upland and grass-savanah soils ranked the lowest (9.4 and 10.5 kg C/m(2), respectively). In the east, meadow 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-leaf 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 various land uses in the region, the C density estimation is accompanied by relatively large variations.