Nitrogen deposition slows down the litter decomposition induced by soil macrofauna in the soil of subtropical forests in China

As atmospheric nitrogen (N) deposition elevates, extensive researches into the consequences of N deposition on litter decomposition process have been triggered; yet, responses of aboveground macro-detritivores to atmospheric N deposition and their interactive effects on saprotrophic microorganisms and litter decomposition process are not thoroughly understood. By soil incubation, we assessed the influence of N deposition on the decomposition process of broad leaf (Quercus acutissima) and needle (Pinus massoniana) litter mediated by macro-detritivore isopods (Armadillidium vulgare) and soil microorganisms. Changes in litter chemical composition (total carbohydrate and N), litter mass loss, soil pH values, soil microbial biomass and the activities of degradative enzymes were determined during a 6-month laboratory incubation. Results showed that N addition enhanced Q. acutissima litter decomposition in the absence of A. vulgare, but decreased that when A. vulgare presence. N addition had no significant effect on P. massoniana litter decomposition regardless of A. vulgare presence or absence. However, N addition decreased isopod feeding contributions, with litter mass loss of 1.83-2.92 times lower than those of only isopod addition treatments in the two litter types. N addition inhibited soil microbial biomass and enzymatic activities related to N and phenolic metabolism of needle litter when isopods presence. Our findings suggest that N addition likely weakens the feeding activity of soil fauna and slows down the litter decomposition in broad-leaved forests. This implies that a long-term consequence of N deposition may induce the soil C accumulation and affect the balance of ecosystem nutrient flux in subtropical broad-leaved forests.