Distinct kin strategies of the legume soybean and the non-legume balsam by accomplishing different nitrogen acquisition and rhizosphere microbiome composition

Kin selection has been proposed vvto be an important mechanism for plant relatives growing together. To reveal kin recognition, we used N-15 labeling to assess the short-term nitrogen (N) acquisition (uptake of nitrate and ammonium), long-term N utilization (recovery of added urea), N-use efficiency (NUE) and rhizosphere microbiome in leguminous Glycine max and non-leguminous Impatiens balsamina. Individuals of each species were planted pairwise with either a sibling or a stranger. Enzyme activity and soil microbial composition were compared between kinship groups. Compared with strangers, G. max siblings increased aboveground biomass, NUE, and nitrogenase activity, whereas I. balsamina siblings decreased root biomass and increased uptake rate of nitrate and potential nitrification rate. Plant kinship affected soil bacterial communities by enriching specific groups possessing explicit eco-functions (Rhizobiales for G. max and Nitrospira for I. balsamina). Kinship-sensitive operational taxonomic units formed independent modules in the bacterial co-occurrence network and were positively correlated with plant growth performance, N acquisition and enzymatic activity. Plant kin recognition may depend on the growth strategies of the plant species. Kin selection was dominant in G. max by enhancing biological N fixation through the enrichment of symbiotic rhizobia (demonstrated by aboveground growth and NUE superiority among siblings). Kin selection and niche partitioning occurred simultaneously in I. balsamina, expressed through reduced root allocation but increased nitrate uptake, and enhanced soil N nitrification, by enriching functional microbial groups. Kin recognition responses are the consequence of complex interactions among the host plant, the microbiome, and soil nutrient cycling and utilization processes.