Abstract: Root exudates play an important role in regulating forest soil function and soil biogeochemical cycling. However, current understanding on input characteristics of forest root exudates and C and N processes mediated by rhizosphere soil under N deposition is still limited. This study took cypress (Cupressus funebris) plantation in the hilly area of central Sichuan as the research object. Different levels of N addition were used to simulate atmospheric N deposition. In 2020, root exudates were collected and analyzed in different seasons, and microbial biomass and C and N mineralization rate of rhizosphere/non-rhizosphere soils were analyzed, to reveal the seasonal variations of C input rate of root exudates, and the differences in soil C and N microbial process mediated by root exudates under different N addition treatments. The results showed that: (1) N addition significantly reduced C input rate and annual flux of root exudates in cypress plantation, with higher N addition having stronger inhibitory effect on C input of root exudates. (2) N addition significantly inhibited the rhizosphere effects of soil C and N mineralization and soil microbial C and N, with stronger inhibition effect of higher N treatment on soil C and N microbial processes. (3) The rhizosphere effect of root C and N process showed seasonal variation that gradually increased in spring and summer, and decreased in autumn and winter, peaking in summer. Our results demonstrated that N addition significantly reduced the rate and flux of root exudates of cypress forest, and significantly inhibited the microbial C and N transformation in rhizosphere soil. The intensity of inhibitory effect was related to N addition level, which confirmed the close relationship between forest root mexudatesmicrobial characteristics transformation processes of soil nutrients. Our results improved the understanding of forest rhizosphere processes under global change and provided scientific basis for adaptive management and ecological restoration of large-scale plantation forests in hilly area of central Sichuan.

Key words: Cupressus funebris, hilly region of central Sichuan, root exudation, rhizosphere effect, C and N transformation process.