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In the field of agro-grassland, the synergism of phosphate (P) fertilization and Trichoderma inoculation in alfalfa production and the underlying mechanism of rare and abundant microbes that regulate rhizosphere soil processes in various environments are key but rarely studied topics. Here, we conducted field research through the inoculation/noninoculation of Trichoderma and five levels of phosphorus fertilizer to explore the biological relationships of rhizosphere soil properties, rare and abundant taxa, and alfalfa yields. Our results demonstrate that using Trichoderma inoculation and 15 g/m2 of phosphorus fertilizer exhibited optimal alfalfa yield compared with other treatments. alfalfa yields significantly (R2 = 0.33; p < 0.001) increased along with soil fertility. Both rare (RANOSIM = 0.900; p = 0.001) and abundant (RANOSIM = 0.769; p = 0.001) bacterial communities were significantly different under Trichoderma inoculation and P fertilization in a nonmetric multidimensional scaling (NMDS) analysis. Furthermore, different ecological processes dominated the rare and abundant bacterial community assembly. PLS-PM analysis showed that Trichoderma inoculation positively regulated the abundant bacteria community and P fertilization regimes manipulated the rare bacteria community, synergistically contributing to alfalfa yields. Overall, this article believes that inoculation with Trichoderma and appropriate application of phosphorus fertilizer can significantly increase alfalfa yield and affect soil enzyme activity, and the rhizosphere soil abundant and rare bacterial community characteristics have different responses to the synergistic effect of Trichoderma and phosphorus fertilizer. Our research emphasizes the fundamental role of abundant and rare microbes in maintaining crop production using Trichoderma inoculation and P fertilization. Therefore, distinguishing rare and abundant species is beneficial to comprehensively understanding microbial-driven processes and providing theoretical support for maintaining ecosystem productivity. [ABSTRACT FROM AUTHOR]

Unravelling the community assembly processes of arbuscular mycorrhizal fungi (AMF) and diazotrophs as well as their co‐existence under different soil fertility environments are vital to develop a better understanding of agroecosystem functions, which is a crucial yet poorly understood topic. We examined the soils from 99 typical alfalfa cultivation systems to formulate a comprehensive picture of AMF and diazotrophic community and presented the first simultaneous investigation of the assembly processes and their co‐existence. The distributions of both AMF and diazotrophic communities were significantly (p < 0.05) corresponded to soil integrated fertility index (IFI). We quantified the relative contributions of five ecological processes in AMF and diazotrophic community assembly under different soil fertility environments, with stochastic assembly primarily determined across all soil fertility groups. The coexistence networks of AMF and diazotrophs were also notably different among typical soil fertility systems, where the most complex interactions were observed in high fertility system while medium fertility system was found to be the simplest. The active hubs detected in different fertility system were sensitively responded to different soil variables. We offered new opportunities to improve agroecosystem functions, especially for legumes, by regulating the potential key species or indirectly manipulating their drivers. [ABSTRACT FROM AUTHOR]

Background and aims: Maintaining sustainable high yield and soil fertility is the key to cultivate perennial alfalfa grassland. However, little is known about the effects of rhizosphere microbes on soil fertility and alfalfa yield in different planting years and regimes. Methods: We sampled 10 alfalfa fields to investigate the rhizosphere soil microbial community and yields in monoculture and rotation systems in different planting years. Results: The alfalfa yield in monoculture was significantly declined (P < 0.05) starting in 6 yr. Wheat-corn-alfalfa rotation generated higher (P < 0.05) soil fertility index and alfalfa yield than wheat-alfalfa rotation and 2 yr alfalfa monoculture. The alfalfa yield significantly (R2 = 0.583, P < 0.001) increased with soil fertility. Significant differences were observed for bacteria (RANOSIM = 0.955, P = 0.001) and fungal (RANOSIM = 0.889, P = 0.001) communities in different planting years and regimes. Different ecological processes dominated bacterial and fungal communities assembly. Blastococcus and Massilia were important biomarkers, which had a significant (P < 0.05) positive correlation with alfalfa yield. PLS-PM analysis identified that planting regimes had positive impacts on alfalfa yield through edaphic variables, microbial genera and fungal community composition. Conversely, planting years had negative effects on alfalfa yield by indirectly regulating fungal genera and community composition through fungal community assembly. Conclusions: This study could help improve our understanding of the role and importance of rhizosphere soil microbial changes in regulating farmland soil processes and crop productivity. [ABSTRACT FROM AUTHOR]