Effects of Simulated Acid Rain on Soil Enzyme Activity and Related Chemical Indexes in Woodlands

Abstract

In order to explore the effects of different concentrations of acid rain on soil nutrient content and nutrient utilization efficiency, and to provide a basis for an improvement in acidified soil in acid rain regions, a year-long acid rain experiment was conducted in a typical evergreen broad-leaved forest and coniferous and broad-leaved mixed forest in Jinyun Mountain of Chongqing. Four pH treatments (pH 4.5, 4.0, 3.25, and 2.5) were established to simulate acid rain. The results showed that: (1) Acid rain promoted the accumulation of soil nutrients, and the contents of organic carbon (SOC), total nitrogen (TN), and hydrolyzed nitrogen (HN) significantly increased during the experiment (p < 0.05). (2) Soil SOC content was significantly positively correlated with acid rain concentration (p < 0.01), HN content was negatively correlated with acid rain concentration, and TN and total phosphorus (TP) contents were not significantly correlated with acid rain concentration. (3) The activities of soil sucrase, urease, and acid phosphatase were negatively correlated with acid rain concentration (p < 0.01) and the activity of soil cellulase was positively correlated with acid rain concentration (p < 0.01). (4) The enzyme activity changed differently, depending on the concentration of acid rain during the study period. (5) According to RDA analysis, soil total nitrogen content and hydrolyzed nitrogen content had significant effects on enzyme activity (p < 0.05). Conclusions: Acid rain did not significantly alter the overall soil nutrient content but reduced the available nutrient content and seriously inhibited enzyme activity—most notably, the soil enzymes involved in nutrient utilization efficiency.