Effects of low light, interspecific competition, and their combination on flavonoid exudation patterns and rhizosphere fungal community in Juglans mandshurica and Fraxinus mandshurica roots

Plants emit exudates into the rhizosphere under environmental stresses, influencing fungal communities. The effects of reduced light, root competition, and combined stresses on root exudates and fungal regulation are unknown.

Our experiments assessed the effects of low light (L), interspecific competition (C), and combined stresses (LC) on flavonoid exudates and rhizosphere fungal communities in the roots of Juglans mandshurica and Fraxinus mandshurica. The correlation between differential exudates and fungal communities was examined.

In our study, fifty-nine exudates exhibited significant changes under single and combined stresses. Under low light, eleven exudates were upregulated and ten downregulated; under interspecific competition, ten were upregulated and four downregulated; and under combined stress, two were upregulated and thirteen downregulated. Meanwhile, nine shared exudates were upregulated and one downregulated under each stress. In addition, single and combined stress affected the composition and abundance of fungal communities in the rhizosphere. Ascomycota were synergistically affected by the combined stress, while Zygomycota and Mortierella were antagonistically affected by the combined stress in Juglans mandshurica. Exudated isorhamnetin, eriodictyol, kaempferol, vicenin, and rutin showed significant positive correlations with Ascomycota, Zygomycota, Nectriaceae, Chaetomiaceae, and Mortierella. On the other hand, apigenin, hesperidin, and kaempferol showed significant negative correlations with Sordariomycetes.

Low light, interspecific competition, and combined stress induce changes in flavonoid exudates that may correspond to the recruitment of potentially beneficial and the inhibition of potentially harmful fungal communities, underscoring rhizosphere adaptation.