Stable and radioactive carbon in forest soils of Chhattisgarh, Central India: Implications for tropical soil carbon dynamics and stable carbon isotope evolution

摘要

Soils from two sites viz. Kotumsar and Tirathgarh, located similar to 5 km apart in a tropical reserve forest (18 degrees 52'N, 81 degrees 56'E) in central India, have been explored for soil organic carbon (SOC) content, its mean residence time (MRT) and the evolution of stable carbon isotopic composition (delta C-13). SOC stocks in the upper 30 cm of soil layers are similar to 5.3 kg/m(2) and similar to 3.0 kg/m(2); in the upper 110 m are similar to 10.7 kg/m(2) and similar to 7.8 kg/m(2) at Kotumsar and Tirathgarh, respectively. SOC decreases with increasing depth. Bomb carbon signature is observed in the upper similar to 10 cm. Organic matters in the top soil layers (0-10 cm) have MRTs of the order of a century which increases gradually with depths, reaching 3500-5000 yrs at similar to 100 cm. delta C-13 values of SOC increase with depth, the carbon isotopic fractionation is obtained to be -1.2 parts per thousand and -3 parts per thousand for soils at Kotumsar and Tirathgarh, respectively, confirmed using Rayleigh isotopic fractionation model. The evolution of delta C-13 in soils was also studied using a modified Rayleigh fractionation model incorporating a continuous input into the reservoir: the depth profiles of delta C-13 for SOC show that the input organic matter from surface into the deeper soil layers is either insignificant or highly labile and decomposes quite fast in the top layers, thus making little contribution to the residual biomasses of the deeper layers. This is an attempt to understand the distillation processes that take place in SOC, assess the extent of decomposition by microbes and effect of percolation of fresh organic matter into dipper soil layers which are important for stable isotope based paleoclimate and paleovegetation reconstruction and understanding the dynamics of organic carbon in soils. (C) 2016 Elsevier Ltd. All rights reserved.