Effects of Plant Litterfalls on Nitrogen Mineralization, Microbial Biomass and Enzyme Activities in Soils of a Poplar Ecosystem.

Litterfall is a primary source of soil organic matter in plantation ecosystems, is vital for conserving and sustaining soil productivity, and plays a critical role influencing nutrient cycling in forest ecosystems. The main objective was to evaluate the effects of different plant litterfalls on microbial and biochemical processes and parameters in soils of a poplar ecosystem. Litterfalls included poplar foliage (F), branch (B), root (R), and understory (U) or a mixture of F, B, and U (M). Soils, with or without different litterfalls, were incubated for up to 24 weeks at 25°C under 70% water holding capacity. The rates of nitrogen (N) mineralization, contents of microbial biomass carbon (C) and N, and activities of L-asparaginase and o-diphenol oxidase (o-DPO) were evaluated. In the initial four weeks of incubation, net N mineralization was detected in the soil without litterfall, but the mineral N content in soils amended with litterfalls decreased by 65 to 81%. Net N mineralized in the litterfall amended soils increased with increasing incubation time. At the termination of 24 weeks of incubation, net N mineralized was in the order of F > CK > U > M > R > B. During this incubation period, the activities of L-asparaginase and o-DPO in the litterfall amended soils increased by 15 to 64% and 17 to 29%, respectively. Furthermore, the content of microbial biomass C increased by 10 to 113% and those of microbial biomass N decreased by 8 to 13% in these soils during the 24 weeks of incubation. The obtained results suggested the predominant role of microbial community and enzyme activities governing N mineralization. These results also denoted that litterfall could significantly impact the release and retention of mineral N in the forest ecosystem, and therefore, should be an integral part when developing ecosystem management strategies.