A deeper look at crop residue and soil warming impact on the soil C pools

Abstract

The response of the carbon (C) cycle to global warming in terrestrial ecosystems is a major issue that must be considered when predicting future climate change. Due to warming simultaneously affects both vegetation and soil, therefore the response of soil organic carbon (SOC) has shown contradictory results in different warming experiments. A 7-year soil warming experiment using plastic film mulching (PM) was conducted with and without plants in a dryland agriculture system to determine the responses of SOC and its fractions to warming. Under different treatments, the δ13C signature and a C model were applied to analyze changes in SOC and its sub-pools: soil heavy-fraction organic C (HFOC) and light-fraction organic C (LFOC). The results showed that PM-induced soil warming controlled the LFOC change and the crop-produced C inputs controlled the HFOC change. The LFOC significantly decreased (p < 0.05) and HFOC did not significantly change under treatments with and without warming and planting; however, total SOC was significantly decreased in warming treatments at the end of the experiment. The crop C input and warming significantly increased (p < 0.05) the turnover rates of C3-sourced C (C3-C) in LFOC and had no significant (p > 0.05) impact in HFOC. The C4-sourced C (C4-C) had longer mean residence time (MRT) than C3-C in both LFOC and HFOC, and soil warming reduced MRT of C4-C in LFOC. Soil warming significantly reduced the new C accumulation in LFOC (17.77% lower) and had no effect on new C accumulation in HFOC (1.71% lower); therefore, the crop residue C return ratio is crucial to recover decomposed LFOC and for SOC sustainability in a PM system. Different residue return ratios can alter the SOC change trend, and SOC changes under PM for different residue management should be compared with caution.