Small-scale heterogeneity of elements in farmland affects fava bean growth through rhizosphere metabolites and microorganisms

Heterogeneity of soil properties at large scales have been acknowledged to affect crop growth. However, the effect of small-scale heterogeneity in farmland on crop growth is rarely reported. In this study, we observed that soil concentrations of As, B, Cd, Cr, Co, Cu, Mo, Ni, Zn and pH significantly differed in the rhizosphere of fava beans growing in adjacent rows in the field with the row-spacing is 30cm. Metagenomics and metabolomics analyses revealed that these differentiated soil properties substantially influenced growth of fava bean plants by altered the rhizosphere metabolites profiling and the relative abundance of specific soil microbial genera. Particularly, a total of 20 metabolites, including coniferyl alcohol, jasmonic acid, resveratrol, and L-aspartic acid, were found to be significantly correlated with fava bean growth. These metabolites were significantly enriched in 15 functional pathways such as nucleotide metabolism, pyrimidine metabolism, purine metabolism, biosynthesis of plant secondary metabolites, lysine biosynthesis, etc. which potentially promoted fava bean growth. Furthermore, 11 microbial genera including Thermostaphylospora, Sphingobium, etc. were measured as involving in these functional pathways and being significantly correlated with fava beans growth. Overall, the heterogeneity of soil element in small-scale farmland affected rhizosphere metabolite profiles and microorganisms, which functionally influencing fava bean growth. Soil heterogeneity in farmland needs to be notably addressed to optimize field managements for increasing crop production, which is crucial for the survival and sustainable development of humanity.