Controls on soil dissolved organic carbon along the 4000 km North-South forest transect in Eastern China

Abstract

Dissolved organic carbon (DOC) is both a potential source and stability indicator of soil organic carbon (SOC), and plays a pivotal role in global C cycling and sequestration. However, at a large scale, still not enough information is known about relations between DOC in soils and various controlling factors in natural forest ecosystems. We sampled 252 soil samples (6 replicates and 3 depths for each site) from four long-term forest ecosystem stations in Changbaishan, Beijng Donglingshan, Shennongjia and Dinghushan along a 4000 km North-South transect in Eastern China. We found that higher soil DOC concentrations were observed in subtropical forests over the North-South transect. The highest and lowest DOC concentrations in the upper 60 cm soil layer were found in monsoon evergreen broadleaved forest (DIII, 113.8 ± 1.4 mg C/L) and Yue spruce-fir forest (CIII, 57.6 ± 3.0 mg C/L), respectively. The Haplic ferralsol (DII-DIV, 89.7 mg C/L) and Haplic Andosol (CIII, 57.6 mg C/L) showed the highest and the lowest DOC concentrations in the upper 60 cm soil layer, respectively. The soil DOC concentrations generally decreased from surface soil to subsoil in the forests with mean annual precipitation (MAP) ≥ 1500 mm. The lower proportion of DOC accounting for SOC in the upper 20 cm soil layer in temperate forests, among which Yue spruce-fir forest (CIII, 3.2 %) presented the lowest ratio, indicated a larger long-term soil C sequestration potential. The DOC concentrations in the upper 60 cm soil layer significantly correlated with mean annual temperature (MAT) (R2 = 0.50) and MAP (R2 = 0.46). However, in the upper 20 cm soil layer, forest type (R2 = 0.48) was the most significant correlation factor to DOC concentration. We concluded that in the North-South transect of Eastern China, MAT, MAP and forest type are the most significant large-scale factors controlling soil DOC, with temperate forests (especially Yue spruce-fir forest) possessing the highest long-term soil C sequestration potential.