Simulated acid rain offset a warming-induced increase in soil respiration but did not impact the temperature sensitivity of soil respiration in a cropland

Investigating the effects of warming and simulated acid rain on soil respiration and its temperature sensitivity is crucial in predicting the potential responses of soil C cycles to future climate warming. A three-year field experiment with six treatments (CK, WA, CK-4.0, WA-4.0, CK-2.0 and WA-2.0) of warming (coded as WA) and three simulated acid rain levels (coded as CK, pH 4.0 and pH 2.0) was performed in an annual winter wheat-soybean cropland to study the comprehensive effects of warming and simulated acid rain on soil respiration and its temperature sensitivity. The results indicated that warming significantly (P 0.001) increased soil respiration under no (CK) or low acid rain application (pH 4.0), while the warming effects on soil respiration were not significant under intensive acid rain conditions (pH 2.0). The annual mean soil respiration was 2.79 +/- 0.02, 3.02 +/- 0.01, 2.58 +/- 0.07, 2.79 +/- 0.03, 2.54 +/- 0.04 and 2.50 +/- 0.03 mu mol m- 2 s-1 in the CK, WA, CK-4.0, WA-4.0, CK2.0 and WA-2.0 plots, respectively. Warming induced an 8.0% increase in soil respiration compared with the CK. Intensive simulated acid rain (pH 2.0) offset the warming effects on soil respiration. A total of 36.9-55.5% of the seasonal variation in soil respiration was explained by soil temperature, while the moisture effects on soil respiration were not significant (P 0.001) decrease in the temperature sensitivity (Q10) of soil respiration. Simulated acid rain did not significantly (P 0.05) impact the Q10 of soil respiration.