Roles of leaf functional traits in fungal endophyte colonization: Potential implications for host–pathogen interactions

Abstract

Abstract Fungal endophytes (FE) are an important component of leaf microbial communities. They usually live asymptomatically within leaf tissues; however, FE can provide additional defensive features against microbial pathogens to the host. Leaf functional traits (LFTs) regulate FE entry, colonization and community composition in plants. There is evidence that thin leaves with less structural and chemical traits but high nutrient content are more prone to FE colonization than well‐defended thick leaves. This illustrates the relevance of trade‐offs (= an increase in a trait, with a decrease in another trait) in LFTs, suggesting that the leaf economics spectrum (LES, which describes relationships in a suite of leaf traits aligned from a resource‐acquisitive to a resource‐conservative ecological strategy) may be a predictor of FE colonization and community composition in plants. We hypothesize that LES‐modulated changes in the leaf internal environment (i.e. thin, low‐defended vs. thick, well‐defended leaves) will (a) have consequences for host resistance to pathogens due to changes in the FE colonization and diversity and, subsequently, in the foliar chemical profile and (b) may cause a switch in FE behaviour to a pathogenic lifestyle. Synthesis. Still, our knowledge of how the coexistence between host plants and FE is regulated remains limited. LFTs may act as relevant ecological hub of FE colonization, community composition and life behaviour in natural ecosystems, with potential bottom‐up effects on other organisms, including pathogens. We highlight and discuss critical aspects in this topic and end by proposing new avenues of research in this emerging field.