Rhizospheric compensation of nutrient cycling functions dominates crop productivity and nutrient use efficiency

The influence of fertilization on crop nutrient use efficiency (NUE) and productivity remain unclear. Here, to assess how fertilization management influences the soil microbial communities and their functional profiles and consequently affects NUE and crop productivity, we established a field experiment with mineral and combined organic-mineral fertilization as well as mineral fertilizer reduction practices. The composition of the microbial community was measured by high-throughput amplicon sequencing, and its functional profile was predicted using PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) software. Our results demonstrated that fertilization management significantly shifted the rhizosphere bacterial community and regulated the compensation intensity of nutrient cycling-related functions, which means the rhizosphere bacterial community assembles to harbour greater nutrient cycling-related functions in lower available nutrient conditions to meet the nutrient requirements of the host plant. Moderate compensation intensity of nutrient cycling functions contributed to the highest NUE and crop productivity being achieved in the combined organic-mineral fertilization treatment. However, insufficient fertilizer input induced intense functional compensation, while standard mineral fertilizer input resulted in weakened functional compensation of nutrient cycling functions, both of which decreased NUE and crop productivity. Overall, this study provides new insights into the key roles of the rhizosphere microbiome in improving NUE, and suggests that the functional compensation characteristics of the rhizosphere microbial community may be a sensitive indicator of nutrient supply and demand relationships as well as a predictor of NUE.