Effects of nitrogen addition and root fungal inoculation on the seedling growth and rhizosphere soil microbial community of .

Nitrogen (N) availability is significant in different ecosystems, but the response of forest plant-microbial symbionts to global N deposition remains largely unexplored. In this study, the effects of different N concentration levels on four types of fungi, (Sg), (Pt), (Po), and sp. (Ps), isolated from the roots of were investigated . Then, the effects of the fungi on the growth performance, nutrient uptake, and rhizosphere soil microbial community structure of . under different N addition conditions (0, 40, and 80 kg hm year) were examined. The biomass and phytohormone contents of the Sg, Pt and Po strains increased with increasing N concentration, while those of the Ps strain first increased and then decreased. All four fungal strains could effectively colonize the plant roots and form a strain-dependent symbiosis with . . Although the effects depended on the fungal species, the growth and root development of inoculated seedlings were higher than those of uninoculated seedlings under N deficiency and normal N supply conditions. However, these positive effects disappeared and even became negative under high N supply conditions. The inoculation of the four fungal strains also showed significant positive effects on the shoot and root nutrient contents of . . Fungal inoculation significantly increased different microbial groups and the total soil microorganisms but decreased the microbial diversity under N deficiency stress. In summary, exogenous symbiotic fungal inoculations could increase the growth performance of . under N deficiency and normal N supply conditions, but the effects were negative under excessive N addition.