Effects of sulfuric, nitric, and mixed acid rain on litter decomposition, soil microbial biomass, and enzyme activities in subtropical forests of China

Acid rain pollution is changing gradually from sulfuric acid rain (SAR) to mixed acid rain (MAR) andthen to nitric acid rain (NAR) with the rapidly growing number of motor vehicles. The influences ofchanged acid rain types on ecosystem functions, particularly on litter decomposition, remain unclear. Twodominant litter types from a coniferous forest and a broad-leaved forest were incubated in microcosmswith original forest soils and treated by five types of acid rain with different SO42-to NO3-ratios (1: 0,5: 1, 1: 1, 1: 5, and 0: 1). During a six-month incubation period, litter mass losses, soil microbial biomass, and enzyme activities were investigated. Results showed that various acid treatments inhibited litterdecomposition, soil microbial biomass, and most enzyme activities, and the inhibitory effects of NAR weremore significant than those of SAR and MAR. The resistance to external acid of microbial communitiesin broad-leaved forest was higher than that in coniferous forest. NAR and MAR treatments slowed downsoil carbon (C), nitrogen (N), and phosphorus (P) mineralization by attenuating the correlations betweenlitter mass losses and the enzymes involved in C, N, and P cycling. Results reveal that the ratio of SO(4)(2)to NO3-in acid rain is an important factor which profoundly influences litter decomposition process. Inthe future, a decreasing ratio of SO42-to NO3-in acid rain will be observed in subtropical forests. Thus, soil C would accumulate as a consequence of future acid precipitation, and this may seriously affect thebalance of ecosystem C, N flux. (C) 2014 Published by Elsevier B.