Synergy of diazotrophs with native soil microbes improves poplar traits

Nitrogen (N) nutrients are crucial for poplar ( Populus L.) survival and growth. However, whether N-fixing rhizosphere microorganisms (diazotrophs) regulate plant productivity and to what extent remain poorly understood. In this study, we analyzed differences in the morphological and chemical traits of poplar grown in the presence of different assemblies of rhizosphere microbiota. We found that the inoculation of diazotrophs into sterilized soils significantly promoted poplar growth with an average increase of 23.40 % for plant height and 51.16 % for root length as compared to the control (sterilization). More importantly, the inoculation of diazotrophs into soils with native microbiota aggravated the promotion of multiple poplars traits including plant height, stem weight, root volume, and root weight, particularly increasing root length by 114.27 %. This promotion of plant traits was facilitated by the greater diversity, niche breadth and ecological functions of the rhizosphere microbiota. Diazotroph inoculation enhanced the positive associations between plant traits and important microbial taxa while alleviating soil environmental stress. Our findings provide new insights into how inoculation with functional microorganisms contributes to poplar traits, with implications for plant cultivation and engineering programs. • Above- and underground poplar traits are largely affected by rhizosphere microbiota. • Inoculating diazotrophs into poplar rhizosphere facilitates poplar growth. • Inoculation of diazotrophs changes poplar rhizosphere microbiota. • Soil-native microbes enhance the positive effects of diazotrophic inocula. • N application is detrimental to the soil-microbe-plant partnership.