Both a Growth‐Defence Trade‐Off and a Leaf N: P Stoichiometric Imbalance Can Account For Ectomycorrhizal Hyphae Inhibited Non‐Host Plant Growth

Previous studies indicated that ectomycorrhizal (EM) hyphae can access non-host plant roots and inhibit their growth, with the underlying mechanisms remaining largely unexplored. This study established a tripartite co-culture system consisting of EM fungi supported Quercus Mongolica and non-host plants Arabidopsis thaliana or Setaria italica. Plant growth, nutrient concentrations, transcriptome, microbial communities and fatty acids were determined to comprehensively understand the effects of EM on non-host plants. The results showed that roots of non-host plants were colonised by EM hyphae of Scleroderma, which significantly inhibited non-host growth and decreased their leaf [N], but increased leaf [P] and leaf free fatty acid concentrations. A small amount of ¹⁵N was transferred from non-host to Q. mongolica leaves. Foliar N application alleviated EM hyphae inhibited non-host plant growth. Genes associated with plant-pathogen interaction and defence hormone responses were activated, but those involved in photosynthesis and growth hormone responses were suppressed in A. thaliana leaves. Our findings suggest that a growth-defence trade-off, in conjunction with a leaf N: P stoichiometric imbalance, may explain the observed inhibition of non-host plant growth by EM hyphae. This study provides insights into ectomycorrhiza mediated host and non-host plants interaction, which is important for plant community establishment.