Short-term response of soil respiration to simulated acid rain in Cunninghamia lanceolata and Michelia macclurei plantations

PURPOSE: Acid rain is a primary environmental problem in Southern China. However, the effect of acid rain on soil respiration rarely received attention, especially in ecosystems with different buffering capacities to acid rain. Thus, we explored how the response of soil respiration to simulated acid rain (SAR) in Cunninghamia lanceolata and Michelia macclurei plantations, which had great difference in the buffering capacities of their litter layers to acid rain. MATERIALS AND METHODS: The field experiment was subjected to a split-block experiment, with four main blocks in each plantation. Each block was split into A1 (SAR treatment, pH = 3) and A0 (deionized water, pH = 6.6) plots. Each plot was separated into subplots with (L0) and without (L1) litter treatments. SAR and deionized water were applied twice a month to A1 and A0 plots, respectively. From June 2016 to June 2017, soil respiration was measured twice per month using Li-8100 infrared gas analyzer. Soil temperature and moisture at a 5-cm depth were monitored using temperature and moisture sensors connected to Li-8100 during the measurement of soil respiration. RESULTS AND DISCUSSION: The result showed that SAR did not significantly influence soil respiration neither in C. lanceolate nor in M. macclurei plantations. However, the reasons for this result were probably different in the two plantations. The unchanged soil respiration in C. lanceolata plantation was mainly attributed to the negligible effect of SAR on fine root biomass and microbial biomass carbon (MBC) in C. lanceolata plantation because of the acclimation of fine root and microorganism to acid soil environment. In addition, the increase in fine root biomass and decrease in MBC may have resulted in the absence of the influence of SAR on soil respiration in M. macclurei plantation, because the variation of soil respiration derived from fine root under SAR may have offset that derived from microorganism. CONCLUSIONS: Although C. lanceolata and M. macclurei plantations had different buffering capacities to SAR, SAR did not significantly affect soil respiration in both plantations after 1 year of SAR treatment. Therefore, the long-term effect of SAR on soil respiration should be considered, particularly in forest types with different buffering capacities to acid rain.