Impact of Simulated Acid Rain on Soil Base Cations Dissolution between Eucalyptus Pure Plantations and Eucalyptus-Castanopsis fissa Mixed Plantations

The soils of Eucalyptus pure plantations and Eucalyptus-Castanopsis fissa mixed plantations were studied using soil column leaching experiments with acid solutions to mimic the effects of acid rain on the soils. This helped researchers learn more about how soil base ions react to acid deposition and their ability to protect the soil from excessive acidity under pure and mixed-species plantations. The results showed that acid rain leaching increased the leaching loss, desorption, and desorption rate of soil base ions while decreasing the soil pH value, adsorption, and adsorption rate of soil base ions. The soil pH value and the leaching loss ranges of K+, Na+, and Mg2+ were all greater in the pure plantations than in the mixed plantations, while the leaching range of Ca2+ was greater in the mixed plantation than in the pure plantations. In the two types of plantations, the adsorption rates of Ca2+ and Na+ in the mixed plantations were higher than in the pure plantations, while K+ and Mg2+ showed higher adsorption rates in the pure plantations than in the mixed plantations. Therefore, soil pH and base ions were greatly affected by the pH value of acid rain. Compared with the pure plantations, the establishment of Eucalyptus-Castanopsis fissa mixed plantations can slow soil acidification and leaching of K+, Na+, and Mg2+ and contribute to the adsorption of Ca2+ and Na+, which is beneficial for the soil nutrient fixation of Eucalyptus plantations. The mixed plantations were found to increase the exchange reaction between H+ and base ions, thereby improving the acid buffer performance of the soil. This, in turn, helped to mitigate the decline in soil fertility. Therefore, establishment of Eucalyptus-Castanopsis fissa mixed-species plantations can slow down the impact of acid rain on soil acidification in artificial plantation land to a certain extent and play an important role in optimizing the plantation structure of Eucalyptus stands and maintaining their productivity.