Effects of simulated acid rain on soil respiration in a monsoon evergreen broad-leaved forest at Dinghushan Nature Reserve
Determining the effects of elevated acid rain on forest soil respiration can provide useful information for under-standing of the process of carbon cycle of forest ecosystem and its response to global change. Therefore, a simulated acid rain ( SAR ) experiment was conducted in a monsoon evergreen broad-leaved forest at the Dinghushan Nature Reserve. SAR treatments included CK ( the local lake water, pH4.5) , T1( pH4.0) , T2( pH3.5) , T3( pH3.0) with three replicates. SAR experiments were initiated in June 2009 and were sprayed twice a month during the study period. Re-sponses of soil respiration to SAR were studied from April 2010 to March 2012 with a LI-8100 soil CO2 efflux system. The results showed that mean annual soil respiration rates for the CK, T1, T2, and T3 treatments were (3.07±0.08), (3.06±0.17), (2.78±0.29), (2.56±0.08) μmol·m-2·s-1, respectively, and the T3 treatment was significant lower than the CK and T1 treatments (P<0.05), indicating that soil respiration was depressed under SAR. These negative effects were evident in the warm-wet seasons ( P<0.05) , but not in the cool-dry ones. In addition, by analyzing the an-nual soil respiration of each year, we found that these negative effects had been strengthened over time with significant difference among treatments occurred only in the second year. The depression of soil respiration may be related to the re-duction of heterotrophic respiration and CO2 production from litter caused by soil acidification under SAR, as we found that soil pH value and soil microbial biomass carbon and nitrogen significantly decreased after exposure to SAR for two years;and litter decomposition rate was also depressed during the study period. Coincide with the situation of soil respi-ration, the negative effects SAR on these index had been strengthened over time with significant differences among treat-ments mostly occurring in the later stage of the study period. Furthermore, we found the effects of SAR on the tempera-ture response of soil respiration, with a decline in Q10 during the study period, suggesting that SAR would decrease the temperature sensitivity of soil respiration. According to the results of this study, soil carbon in forests of subtropical Chi-na would accumulate as the reduction of soil respiration under the continued acid rain in the future.
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