Responses of soil nutrients, enzyme activities, and soil microbial carbon metabolic activity of Cunninghamia lanceolata to acid rain stress and post-stress recovery dynamics

Acid rain pollution has historically been a serious issue in Southern China, where the dominant acid rain anion is SO42−. In recent decades, China has undertaken multiple measures to reduce acid deposition, leading to significant decreases in SO2 emissions year on year. However, understanding ecological effects during and after acid rain remains important, especially for other rapidly industrializing regions worldwide. Therefore, it is important to study changes in the ecological effects between acid rain deposition periods and the absence of acid rain. For this study, we designed a one-year simulated acid rain experiment. Subsequently, after the simulated acid rain was stopped, we conducted a nine-month continuous monitoring of the relevant experimental plots. We investigated soil nutrients, soil enzyme activities, and soil microbial carbon metabolic activity. The results revealed that acid rain had no significant effects on TN, AP, AK; however, it was difficult to return soil nutrients to their original status once the simulated acid rain was stopped. In addition, the acid rain treatments decreased the activities of soil enzymes, particularly under the high intensity acid rain treatment. Soil enzyme activities (except for sucrase activity under the high intensity acid rain treatment) reverted to their original status once the acid rain was stopped. Further, the moderate and high intensity acid rain treatments negatively affected the activities of soil microbial carbon metabolic. When the simulated acid rain was stopped for the CK treatment, soil microbial carbon metabolic activity recovered over time. During the simulated acid rain treatment and its cessation, four main categories (carbohydrates, carboxylic acids, amino acids, and polymers) were dominantly utilized. The utilization of L-Asparagine and Tween40 resulted in changes in the peak values of the C substrate groups during the non-acid rain period. Finally, the soil enzyme activities were intimately associated with the utilization of carbohydrates, carboxylic acid, amino acids, and phenols. Our results suggested that short-term acid rain contamination showed potential for recovery, but the process occurred over an extended time period.