Simulated acid rain changed the proportion of heterotrophic respiration in soil respiration in a subtropical secondary forest

Acid rain is a matter of concern in southern China. We explored how soil respiration (R-s) and heterotrophic respiration (R-h) rates changed when subjected to simulated acid rain (SAR) environment for 3 years (from March 2010 to February 2013) in a secondary forest in subtropical China. The field experiment was arranged in a split-plot design, with 4 main blocks. Each block was split into un-trenched (R-s) and trenched (R-h) treatments. Four SAR treatments of CK (control, deionized water), A1 (pH 4.0), A2 (pH 3.0), and A3 (pH 2.0) were randomly assigned in each of the R-s and R-h treatments. Soil CO2 fluxes as well as soil temperature and moisture at a depth of 5 cm were measured weekly. Different SAR treatments exhibited similar seasonal patterns of R-s and R-h. Mean annual R-s rates in CK, A1, A2, and A3 plots were 878.2 +/- 100.8, 919.4 +/- 33.1, 865.6 +/- 62.5, and 925.2 +/- 20.5 g C m(-2) yr(-1), respectively, over 3 years; SAR had no significant effects on R-s. R-h, however, was significantly (P < 0.05) affected by the lowest SAR pH level (A3). On overage of 3 years, annual R-h rates in CK, A1, A2 and A3 plots were 606.7 +/- 52.4, 663.5 +/- 35.5, 728.2 +/- 60.7, and 760.1 +/- 42.2 g C m(-2) yr(-1), respectively. Statistical analysis showed that SAR significantly (P < 0.05) increased the proportion of R-h in R-s. The relationship between residual R-s (or R-h) based on soil temperature and observed R-s (or R-h) and soil moisture could be well fitted in a quadratic model. (C) 2014 Elsevier B.V. All rights reserved.