Linking microbial community compositions to cotton nitrogen utilization along soil salinity gradients

Accumulating evidence has shown that soil salinization is a global threat to microbial functional diversity and crop growth. However, the effects of microorganisms on crop growth, yield components, and nitrogen (N) utilization under salt stress are poorly understood. In this research, 16S rRNA, quantitative polymerase chain reaction (qPCR) sequencing, and ¹⁵N isotopic tracer method were used to identify associations between microbial community composition and cotton N utilization across four salinity gradients (control, 0–2 dS m⁻¹; low-salinity, 2–4 dS m⁻¹; mid-salinity, 4–8 dS m⁻¹; and high-salinity, 8–15 dS m⁻¹). These findings indicated that salinity is the primary driving force behind environmental degradation. Furthermore, the results showed that the effect of microbial community diversity on cotton ¹⁵N utilization was regulated by soil electrical conductivity. The promotional effect of Proteobacteria on cotton ¹⁵N utilization was gradually enhanced with increasing soil salinity, while the relative abundance of Actinomycetes first showed an increasing trend after which it decreased. The present study confirms that Actinobacteria dwelling in arid areas are capable of growing under selective soil salinity gradients. This study highlights the importance of focusing on microbial community diversity for cotton growth and yield, and for the first time to clarifying the differences in cotton N utilization under different soil salinity gradients in arid areas. In addition, the association between edaphic properties and cotton parts (rhizospheres, stems, leaves, and fruits) was evaluated more in-depth using the mediating and moderating effects model in the present study. Further investigations are required to ascertain whether salt-tolerant bacterial communities in the rhizosphere can be isolated to promote N utilization by cotton.