Abstract: As a key process of soil nitrogen (N) cycle, soil N mineralization drives N supply capacity of soil. However, the contribution of different biological factors such as roots, mycorrhizal mycelia, and asymbiotic microorganisms to soil N mineralization is poorly understood. In this study, we examined soil N mineralization of moso bamboo forest (Phyllostachys edulis) in Miaoshanwu Nature Reserve in Zhejiang Province, employing in situ incubation technique with anionic and cationic resin cores. Combined with different mesh sizes (1.45 mm: allowing all components to enter; 53 μm: excluding roots but allowing mycelium to enter; and 1 μm: excluding roots and mycelium to enter while only allowing free-living microorganisms to enter), the microcosm further distinguished the effects of roots, mycelium and free-living microorganisms. The results showed that: (1) In the treatments of different mesh size microcosms, the exclusion effect of 53 μm microcosm on roots reached 100% compared with 1.45 mm microcosm, and the exclusion effect of 1 μm microcosm on hyphae reached 70% compared with 53 μm microcosm. (2) The participation of different biological components in the soil N cycling mainly changed soil ammonification rate. Soil net ammonification rate after root system participated in the soil N cycle process (1.45 mm microcosm) was 36.58% lower than that when the roots were excluded (53 μm microcosm). However, there was no significant difference in soil net nitrification rate and net mineralization rate among microcosm devices with different mesh sizes. (3) The soil leucine aminopeptidase (LAP) and phenoloxidase (POX) activities were significantly higher in the 1.45 mm microcosm compared to the 53 μm microcosm by 27.59% and 61.54%, respectively, which in turn led to a decrease in soil net ammonification rate. This study quantified the contribution of rhizosphere (root, mycorrhizal mycelia) -mediated soil N mineralization process of bamboo forest. Free-living microorganisms are important biological factors affecting soil net nitrification and mineralization, while roots and mycorrhizal fungi played an important role in soil net ammonification.

Key words: bamboo forest, soil nitrogen cycling, rhizosphere, mycorrhizal fungi, net nitrification rate, net ammonification rate, net mineralization rate