Effects of different stoichiometric ratios on mineralisation of root exudates and its priming effect in paddy soil

Abstract

In paddy soil, the root exudates strongly influence the microbial activity and soil organic matter (SOM) mineralisation. However, the stoichiometric regulation of the mineralisation of root exudates and their priming effect on paddy soil remains unclear. Thus, we used manipulative laboratory incubations to measure the mineralisation of root exudates and the subsequent priming effect in paddy soil under different stoichiometric conditions. In this study, root exudates (simulated by 13C-labelled glucose, alanine, and oxalic acid) were added to the paddy soil along with four different amounts of N and P. The addition of simulated root exudates (SREs) enhanced the total CO2 and CH4 emissions. The mineralisation of SREs decreased by 20–45% after the addition of N and P when compared with exclusive SREs application. The addition of N and P inhibited the SREs-derived CH4 emissions when compared with SREs application alone. The mineralisation of soil organic matter (SOM) increased with SREs application, thereby generating a positive priming effect for CO2 and CH4 emissions. However, the priming effect for CO2 and CH4 emissions was reduced with increased amounts of N and P. Furthermore, the addition of SREs with increasing N and P significantly enhanced the microbial SREs-derived C-use efficiency. Structural equation models indicated that NH4+-N and Olsen P negatively influenced the priming effect, whereas the microbial biomass and enzyme stoichiometry positively influenced the priming effect. In conclusion, our data suggest that SREs combined with increasing amounts of N and P could meet microbial stoichiometric demands and regulate microbial activity, which finally inhibited the mineralisation of SREs-C and the priming effect on paddy soil and positively affected C sequestration.