[Effects of Simulated Acid Rain on Soil Respiration and Heterotrophic Respiration in a Secondary Forest]

In order to investigate the effects of simulated acid rain on soil respiration and heterotrophic respiration in a secondary forest, a field experiment was carried out. A split-plot experiment was arranged in field. There were 4 blocks; each block had two main plots which were trenched and un-trenched plots. In each main plot, 4 simulated acid rain treatments of control (CK), pH 4.0 (A1), pH 3.0 (A2), and pH 2.0 (A3) were randomly assigned. Soil respiration in the un-trenched plots and heterotrophic respiration in the trenched plots were measured weekly. Soil temperature and moisture at a depth of 5 cm were measured during the respiration measurements. The results indicated that different simulated acid rain treatments exhibited similar seasonal patterns of soil respiration and heterotrophic respiration. Heterotrophic respiration in the trenched plots was significantly lower than soil respiration in the un-trenched plots. The annual mean soil respiration rates for the CK, A1, A2, and A3 treatments in the un-trenched plots were (2.47±0.31), (2.52±0.22), (2.38±0.17), and (2.43±0.22) μmol·(m²·s)^-1, respectively, while the annual mean heterotrophic respiration rates for the 4 treatments in the trenched plots were (1.55±0.10), (1.65±0.22), (1.77±0.08), and (1.78±0.27) μmol·(m²·s)^-1, respectively. ANOVA showed that simulated acid rain had no significant effects on soil respiration in the un-trenched plots and heterotrophic respiration in the trenched plots. Regression analysis suggested that there was a significant linear regression relationship between soil respiration and heterotrophic respiration. Simulated acid rain significantly (P<0.001) decreased the ratio of soil respiration to heterotrophic respiration. Soil temperature was the main controlling factor regulating the seasonal patterns of soil respiration and heterotrophic respiration for each of the SAR treatment, while soil moisture had no significant effects on the seasonal variability in soil respiration and heterotrophic respiration.