Five years’ exposure of elevated atmospheric CO2 and temperature enriched recalcitrant carbon in soil of subtropical humid climate

Abstract

Atmospheric CO2 and temperature levels are predicted to increase to 550 μmol mol−1 and by 2.0–4.5 °C higher than the present, respectively, by the middle of the 21st century. Our experiment was focused to study the impact of elevated atmospheric carbon dioxide (CO2) (500 ± 20 ppm) and temperature (> 2 °C than ambient) and their association on soil respiration and total organic carbon (TOC) along with its different pools such as: active pool (AP), passive pool (PP), particulate organic carbon (POC) and mineral-associated organic carbon (MOC) in 0−30 cm soil depth under field based open-top chambers for 5years (2011–2016). Elevated CO2 (eCO2), elevated temperature (eTemp) and their association (eCO2+eTemp) resulted in significant 3.09, 11.1 and 2.76 % reduction in TOC, respectively, in 0−30 cm soil depth over ambient condition. In all predicted climatic conditions, depletion of AP and POC were observed. Conversely, carbon enriched in PP and MOC. The outcome of the soil respiration study revealed that even though cumulative carbon mineralization values were lower in soil exposed to eCO2 and eTemp, under carbon depleted condition, the carbon mineralization efficiencies were higher. So, it can be concluded that in future climate scenario soil will act as a net source to atmospheric CO2 in subtropical humid climatic regions.