Litter, soil carbon and nitrogen fractions and enzyme activity in a typical broadleaved forest invaded by Moso bamboo

We investigated the effects of bamboo invasion on the quantity and quality of litter input, soil carbon (C) and nitrogen (N) fractions and enzyme activities across an invasion sequence composed of evergreen broadleaved forest, mixed broadleaved and bamboo forest, and pure Moso bamboo forest. The results showed that stan-ding litter biomass, annual litter production, and the litter C content in mixed broadleaved and Moso bamboo forest was lower than the broadleaved forest by 49.0%, 7.3% and 8.2%, respectively, while that in pure Moso bamboo forest was lower than the broadleaved forest by 59.5%, 48.6%, and 18.7%. Bamboo invasion resulted in a significant decrease in soil organic C in broadleaved forest. Compared with broadleaved forest, soil organic C and total N in pure Moso bamboo forest were decreased by 52.1% and 15.0%. There was no significant difference between the mixed forest and broadleaved forest. Bamboo invasion significantly increased soil microbial biomass C and N, but decreased soil labile and recalcitrant C pools, as well as the proportion of recalcitrant C pool to soil organic C. The activities of soil phenol oxidase, peroxidase and β-glucosidase in mixed forest and pure bamboo forest were generally lower than those in broadleaved forest. The specific enzyme activities (per unit of soil organic C) in bamboo forest was significantly higher than that in the broadleaved forest and mixed forest. Soil organic C content and the recalcitrant C fraction were significantly positively correlated with annual litter production, standing litter biomass, and litter C content, but negatively correlated with the specific enzyme activities of phenol oxidase and peroxidase. Results of structural equation modeling showed that Moso bamboo invasion decreased recalcitrant C pool mainly by reducing litter input and enhancing the specific activities of enzymes involved in organic C degradation. In conclusion, Moso bamboo invasion reduced litter C input, increased the specific activities of soil enzymes involved in soil organic matter decomposition, which was not conducive to the accumulation of soil organic matter in broadleaved forest.