Moisture regime influence on soil carbon stock and carbon sequestration rates in semi-arid forests of the National Capital Region, India

Abstract

Understanding the dynamics of soil carbon is crucial for assessing the soil carbon storage and predicting the potential of mitigating carbon dioxide from the atmosphere to the biomass and soil. The present study evaluated variations of soil carbon stock in semi-arid forests in India under different moisture regimes. Soil organic carbon (SOC) and soil inorganic carbon (SIC) stocks were determined in different moisture regimes i.e. monsoon, post-monsoon, winter and pre-monsoon seasons at 0–10 and > 10–20 cm depths. SOC stock showed significant variations under different moisture regimes. The highest SOC stock was during winter (22.81 Mg C ha−1) and lowest during the monsoon season (2.34 Mg C ha−1) among all the ridge forests under study. SOC and SIC stock under different moisture regimes showed significant negative correlation with soil moisture (p < 0.05), as a sudden increase in soil moisture after rainfall results in an increase in carbon loss due to microbial decomposition of accumulated carbon during the dry period. There was an increase in annual SOC stock and a decrease (or no change in some cases), in SIC stock at both the depths during the study period. The SOC and SIC sequestration rates were estimated as any increase/decrease in the respective stock during each successive year. SOC sequestered ranged between 0.046 and 0.741 Mg C ha−1 y−1. Similarly, SIC sequestration ranged between 0.013 and 0.023 Mg C ha−1 y−1 over all ridge forests up to 20 cm depth. The Delhi ridge forests, which accounts to 0.007% of the semi-arid regions of India, contribute 0.25–0.32% of the national potential (semi-arid region) for SOC sequestration up to 20 cm depth. The estimates of the rate of C sequestration in this study provide a realistic image of carbon dynamics under present climatic conditions of semi-arid forests, and could be used in developing a database and formulating new strategies for carbon dioxide mitigation by enhancing soil C sequestration rates.