Effect of simulated acid rain on soil CO2, CH4 and N2O emissions and microbial communities in an agricultural soil

Since the advent of industrialization and urbanization, acid rain has emerged as one of the quintessential global environmental issues. However, the effects of acid rain on carbon (C) and nitrogen (N) cycles of terrestrial ecosystems are still far from fully understood, though some studies have reported the sensitivity of living organisms and soil physicochemical properties to acidic conditions. Herein, we conducted intact soil core experiments to understand the effects of artificial acid rains of pH 5.0, 4.0 and 3.0 on soil CO2, CH4, and N2O fluxes and microbial communities in an agricultural soil of southern China. We did not detect any effect of acid rain on CO2 and N2O fluxes as compared to the control; however, acid rain of pH 3.0 significantly reduced the cumulative CH4 flux from the soil. Most noticeably, both acid rains of pH 4.0 and pH 3.0 significantly increased the total amount of soil microbial phospholipid fatty acids (PLFAs) by increasing the PLFA contents of gram-positive bacteria, actinomycetes, fungi, and arbuscular mycorrhizal fungi, though all the acid rain treatments did not change the relative abundance of microbial groups. In addition, both CO2 and CH4 fluxes negatively correlated with the total amount of soil microbial PLFAs; however, the N2O flux positively correlated to soil NO3(-)-N contents (p < 0.05). These results confirm the recent theoretical predictions that N-addition (e.g., by acid rain) may alter microbial C utilization pattern by allocating more C to the microbial biomass than to respiration. Overall, our results demonstrated that acid rain substantially altered the soil microbial biomass, and reduced the cumulative CH4 flux from the agricultural soil during the experimental period. Given these findings, we suggest further research to investigate the responses of soil greenhouse gas emissions and microbial communities to longterm acid rain exposures in the context of climate change.