Response of arbuscular mycorrhiza fungi to long-term organic and inorganic fertilization in agricultural soils in dry farming regions

The dynamics of arbuscular mycorrhiza (AM) fungal communities are important for effective, long-term soil ecosystem management. To reveal the response mechanisms of soil AM fungi to long-term combined applicatoin of organic and inorganic fertilizers in dryland farming regions, the effects of no fertilizer application (T0), long-term chemical fertilizer application (T1), long-term combined applicatoin of chemical fertilizer and cow manure organic fertilizer (T2), and long-term combined applicatoin of chemical fertilizer and sheep manure organic fertilizer (T3) on soil were investigated using a one-way randomized group design based on 11 consecutive years of locality testing and high-throughput sequencing methods. Differences in the composition and diversity of soil AM fungal communities were compared, and the factors affecting the soil environment and interaction effects that drive changes in soil AM fungal community composition and diversity were investigated. The results indicated that the soil total nitrogen and organic matter contents significantly increased, whereas the pH significantly decreased (P<0.05) under the T2 and T3 treatments compared to those under T0. Furthermore, compared with eight years of fertilization, 11 years of fertilization significantly decreased the total phosphorus and available potassium contents of the soil in the T0, T1, and T3 treatments. The dominant genera of soil AM fungi under organic and inorganic fertilization were Glomus and Paraglomus, respectively. However, the relative abundance of Claroideoglomus decreased significantly and changed from dominant to non-dominant. In contrast, the relative abundance of Claroideoglomus was more susceptible to long-term fertilization than that of Glomus and Paraglomus. After a period of eight years of combined applicaiton of organic and inorganic fertilizers, the relative abundance of AM fungi, specifically Claroideoglomus and Ambispora, in soils under T2 and T3 treatments was significantly different from that of T0 (P<0.05). Over the 11-years fertilization period, the relative abundances of Claroideoglomus and Ambispora under T2 and T3 treatments were not significantly different from those under T0. With the extension of fertilization time, differences in the α diversity of soil AM fungal communities disappeared among treatments. NMDS analysis showed that long-term fertilization changed the β diversity of the soil AM fungal community, but the soil AM fungal community was more similar between the T2 and T3 treatments. During the continuous application of fertilizer, significant changes were observed in the structural composition and diversity of the soil AM fungal community. Moreover, the soil environmental factors influencing changes in the AM fungal community shifted from soil total nitrogen and pH to soil total phosphorus. Long-term combined applicatoin of organic and inorganic fertilizers did not simultaneously improve the main physicochemical properties of soil, such as total phosphorus and available potassium. As the number of years of fertilization increased, the soil factors that drove changes in the structure and diversity of the soil AM fungal communities were significantly altered. The AM fungal community is more easily influenced by sensitive driving factors with changes in all soil environments.