Variation in enzyme activities involved in carbon and nitrogen cycling in rhizosphere and bulk soil after organic mulching

Organic mulching provides C and N source to the soil, changing the soil environment and promoting plant growth. Soil enzymes play important roles in soil organic matter decomposition and nutrient cycling. However, changes in enzyme activity after organic mulching in urban forest ecosystems remain poorly understood, especially in rhizosphere soil. In this study, the effects of organic mulching on the activity levels of enzymes relevant to C and N in the rhizosphere and bulk soil were investigated in a 15-year-old Ligustrum lucidum urban forest. Invertase activity increased whereas urease activity decreased after organic mulching. Changes in peroxidase and dehydrogenase activity varied across seasons; these changes were greater and lasted longer than changes in invertase and urease activity because of the stronger organic matter decomposition via microbial action and soil substance cycling and transformation in a short period of time after organic mulching. Enzyme activity in the rhizosphere significantly correlated with that in bulk soil (P < 0.01), though the former was more affected by mulching due to the influence of accelerated root element cycling. Enzyme activity levels were significantly correlated with dissolved C, available N, and microbial biomass C and N, but not with soil organic C or total N. Enzyme activities were also affected by physical factors, such as soil temperature and water content. Frequent applications of small quantities of organic mulch may be conducive to soil improvement. Further long-term comprehensive studies, considering the effects of season and soil layer, are required to elucidate the effects and underlying mechanisms of organic mulching on the soil environment in forest ecosystems.