Organic mulching masks rhizosphere effects on carbon and nitrogen fractions and enzyme activities in urban greening space

Abstract

Organic mulching is an effective forest management technique that improves the soil environment and promotes plant growth. The rhizosphere is an important interface connecting root systems and soil. However, the rhizosphere effects (REs) after organic mulching are still unknown. We conducted a field experiment in a 15-year-old Ligustrum lucidum forest of urban greening space. Changes in REs on carbon and nitrogen fractions, enzyme activity after organic mulching were measured, and their relationships with fine-root traits and soil properties were analysed. Organic mulching reduced or inverted REs for most enzyme activities and carbon and nitrogen fractions but only significantly decreased the positive REs for urease activities and weakened the negative REs for peroxidase activities. Furthermore, more enzymes were affected over time, and more organic mulch application had greater effects. Seasons affected REs more than organic mulching; seasons contributed more to changes in fine-root traits and soil properties. REs on biotic factors (microbial biomass carbon, microbial biomass nitrogen, urease, and peroxidase activities), which are more sensitive than other soil carbon and nitrogen fractions we measured, were primarily related to fine-root traits (specific root length, specific surface area, and carbon and nitrogen content) and soil properties (temperature, water content, and bulk density). Organic mulching masks the REs on most soil carbon and nitrogen fractions, as well as on enzyme activities, and the REs on enzyme activities are more sensitive. Understanding the variation in REs will improve our knowledge of element cycling between soil and plants.