Effects of simulated acid rain on microbial activities and litter decomposition

We assayed the effects of simulated acid rain on the mass loss, CO2 evolution, dehydrogenase activity, and microbialbiomass-C of decomposing Sorbus alnifolia leaf litter at the microcosm. The dilute sulfuric acid solution composed thesimulated acid rain, and the microcosm decomposition experiment was performed at 23°C and 40% humidity. Duringthe early decomposition stage, decomposition rate of S. alnifolia leaf litter, and microbial biomass, CO2 evolution anddehydrogenase activity were inhibited at a lower pH; however, during the late decomposition stage, these characteristicswere not affected by pH level. The fungal component of the microbial community was conspicuous at lower pH levels andat the late decomposition stage. Conversely, the bacterial community was most evident during the initial decompositionphase and was especially dominant at higher pH levels. These changes in microbial community structure resulting fromchanges in microcosm acidity suggest that pH is an important aspect in the maintenance of the decomposition process.Litter decomposition exhibited a positive, linear relationship with both microbial respiration and microbial biomass.Fungal biomass exhibited a significant, positive relationship with CO2 evolution from the decaying litter. Acid rain had asignificant effect on microbial biomass and microbial community structure according to acid tolerance of each microbialspecies. Fungal biomass and decomposition activities were not only more important at a low pH than at a high pH butalso fungal activity, such as CO2 evolution, was closely related with litter decomposition rate.