Effects of arbuscular mycorrhizal fungi on microbial activity and nutrient release are sensitive to acid deposition during litter decomposition in a subtropical Cinnamomum camphora forest

Arbuscular mycorrhizal fungi (AMF) play an important role on litter decomposition, which is increasing suffering the negative impact of acid deposition. In this study, we investigated the AMF effects on litter decomposition via suppressing AMF and simulating acid deposition in a subtropical Cinnamomum camphora forest. The results showed that acid deposition and AMF suppression decelerated C. camphora leaf litter decomposition, especially at late decomposition stage; soil water content was the main factor restricting early-stage decomposition. The inhibiting effect of acid deposition was enhanced with acid intensity increase and AMF suppression aggravated the negative effect of acid stress on decomposition. Nitrogen-cycling enzymatic activity was significantly higher in later than in early decomposition stage, and acid deposition and AMF suppression significantly decreased microbial activity. Despite the seasonal effect was overwhelming, we still detected the effects of acid deposition and AMF suppression on litter nutrient release. Without or under low acid deposition, AMF suppression significantly increased organic matter and decreased alkali-hydrolyzable nitrogen content of detritusphere soil. Acid deposition significantly reduced soil organic matter content, while high acid deposition intensity increased alkali-hydrolyzable nitrogen content after 2- and 12-month decomposition, and decreased it at other months. Both acid deposition and AMF suppression decreased available phosphorus content, but did not affect phosphatase activity. AMF effects on invertase and nitrogen-release enzyme activities, and alkali-hydrolyzable nitrogen and available phosphorus contents of detritusphere soil were highly sensitive to acid deposition. Our results revealed that AMF effects on microbial activity and nutrient release during litter decomposition are sensitive to acid deposition.