Abstract: As an important source of soil nitrogen (N), litter inputs play a key role in soil N cycling. The present study was conducted to explore the effects of litter inputs (viz. no litter, double litter, normal litter input) on soil nitrogen mineralization in a natural Castanopsis carlesii forest in mid-subtropical China. The differences in potential soil net N mineralization under different treatments and the main influencing factors were investigated through laboratory incubation experiments. The results showed that: (1) Soil net ammoniation rates under different litter inputs were negative, and litter input did not affect soil net ammoniation and nitrification rates. Soil net N mineralization rate increased with increasing litter input quantity, with that under double litter input being significantly higher than that of no litter input. (2) Litter removal significantly decreased the concentrations of total N and soluble organic N in soil, while soil microbial biomass N (MBN) under double litter treatment was significantly higher than that under normal litter input treatment. There was no significant difference in the concentrations of NO₃^--N and NH₄⁺-N among different treatments. (3) Increasing litter inputs significantly increased soil β-N-acetylglucosaminidase (NAG) activity, which was 2.6 times higher under double litter input treatment than under normal litter input treatment, but there was no significant difference in soil leucine aminopeptidase activity among different treatments. (4) Soil N mineralization under different treatments was mainly affected by soil NAG activity, MBN, and NO₃^--N contents. Thus, under global environmental change, increased forest litter inputs in subtropical forests can provide sufficient nutrients for soil microorganisms. The turnover rate of soil N was enhanced by the promotion of NAG activity, which then increased soil N supply capacity.

Key words: litter quantity, soil nitrogen, enzyme activity, natural forest.