Community Assembly Correlates with Alfalfa Production by Mediating Rhizosphere Soil Microbial Community Composition in Different Planting Years and Regimes

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 (R 2 = 0.583, P < 0.001) increased with soil fertility. Significant differences were observed for bacteria (R ANOSIM = 0.955, P = 0.001) and fungal (R ANOSIM = 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.