Root exudates induce rhizosphere effect benefits for plant N use efficiency and fitness of relatives for Glycine max

Aims: Kin recognition has been used to explain plant interactions among siblings. However, the phenotypic-based measurements have drawn various results, and the mechanism of plant kin recognition remains unclear. Here, we tested plant kin recognition based on plant nitrogen (N) use efficiency induced by the rhizosphere effect, plant growth performance and fitness. Methods: Glycine max (L.) Merr. was planted pairwise either with siblings or with non-siblings (strangers). Several characteristics, including plant height, specific leaf area (SLA), plant biomass, fitness, chlorophyll content, and plant N use efficiency (NUE) were measured. The root exudation rates of carbon (C) and N, soil microbial biomass C (MBC) and N, and the abundance of functional genes, as well as soil archaeal, bacterial, and fungal abundance, were quantified. Results: Significant increases in plant height, seed and shoot biomass, chlorophyll content, and NUE were observed in G. max plants living with siblings compared to strangers, suggesting that plant kin recognition results in superior growth and fitness. The root exudation rate of C was significantly higher in individuals living with siblings than with strangers. The input of C from root exudates further induced the rhizosphere effect, enhancing the soil MBC and increasing the abundance of soil archaea and soil ammonia-oxidizing archaea (AOAs). Plants living with siblings increased NUE for enriched available N in soil, and increased aboveground growth and fitness compared to those living with strangers for G. max. Conclusions: The rhizosphere effect on soil microbes and N turnover triggered by the root exudates depend on the neighbor's identity and could be a potential underground feedback mechanism for plant kin recognition.