Responses of soil fungal and bacterial communities to long-term organic and inorganic nitrogenous fertilizers in an alpine agriculture

Although nitrogen fertilizer is an important measure to increase grain yield, response of soil microbial community to nitrogen fertilizer is still unclear in alpine regions. Based on a long-term ( >10 years) nitrogen fertilizer experiment (control, CF: chemical fertilizer, SM: sheep manure; CS: chemical fertilizer + sheep manure) in an alpine agroecosystem of the Lhasa, Xizang, responses of soil bacteria and fungi communities to nitrogen fertilizer was investigated. The CF treatment reduced fungi operational taxonomic unit (OTU) by 13.08 %, phylogenetic diversity by 11.13 % at 10-20 cm, but increased fungi guild number at 0-10 cm by 17.71 %. The SM treatment reduced fungi OTU at 10-20 cm by 11.82 %. Compared to CF and SM treatments, CS treatment had stronger positive effects on bacterial alpha-diversity, considering that CS treatment but not CF and SM treatments increased bacterial mean nearest taxon distance, species Shannon and Simpson at 10-20 cm. The CF, SM and CS treatments altered fungal community composition at 0-10 and 10-20 cm, bacterial community composition at 10-20 cm, and bacterial species composition at 0-10 cm. The CF and CS treatments altered bacterial phylogenetic composition at 0-10 cm, and the SM and CS treatments altered bacterial functional composition at 0-10 cm. The decreased magnitude of the relative abundance of symbiotroph fungi caused by CS treatment (90.44 %) was stronger than that (65.14 % and 53.62 %) caused by CF and SM treatments at 10-20 cm. Therefore, the SM and CS treatments had stronger effects on soil bacterial functional composition, but the CF treatment had stronger effects on fungal alpha-diversity. Compared with single application of organic or inorganic nitrogen fertilizer, mixed application of organic and inorganic nitrogen fertilizer was more beneficial to the maintenance and improvement of soil bacterial diversity, but caused more reduction of soil symbiotic fungi and in turn greater potential risk. These scientific findings observed by this study can provide guidance for fertilizer management and soil fertility improvement.