Increasing flavonoid concentrations in root exudates enhance associations between arbuscular mycorrhizal fungi and an invasive plant

Baoliang Tian,Jianqing Ding,Yingchun Pei,Wei Huang,Evan Siemann

doi:10.1038/s41396-021-00894-1

Abstract

Many invasive plants have enhanced mutualistic arbuscular mycorrhizal (AM) fungal associations, however, mechanisms underlying differences in AM fungal associations between introduced and native populations of invasive plants have not been explored. Here we test the hypothesis that variation in root exudate chemicals in invasive populations affects AM fungal colonization and then impacts plant performance. We examined flavonoids (quercetin and quercitrin) in root exudates of native and introduced populations of the invasive plant Triadica sebifera and tested their effects on AM fungi and plant performance. We found that plants from introduced populations had higher concentrations of quercetin in root exudates, greater AM fungal colonization and higher biomass. Applying root exudates more strongly increased AM fungal colonization of target plants and AM fungal spore germination when exudate donors were from introduced populations. The role of root exudate chemicals was further confirmed by decreased AM fungal colonization when activated charcoal was added into soil. Moreover, addition of quercetin into soil increased AM fungal colonization, indicating quercetin might be a key chemical signal stimulating AM fungal associations. Together these results suggest genetic differences in root exudate flavonoids play an important role in enhancing AM fungal associations and invasive plants’ performance, thus considering root exudate chemicals is critical to unveiling mechanisms governing shifting plant-soil microbe interactions during plant invasions.

Highlights

Mutualisms are key plant biotic interactions with large impacts on plant fitness [1,2,3]
In this study we show clearly that Triadica plants from introduced populations had higher amounts of quercetin in their root exudates than those from native populations
Our work is the first to report the variation of root exudate chemicals in native and introduced populations of invasive plants and document the effects of such differences in root exudate chemicals in shaping arbuscular mycorrhizal (AM) fungal associations

Summary

Introduction

Mutualisms (e.g., mycorrhizae, rhizobia) are key plant biotic interactions with large impacts on plant fitness [1,2,3]. Secondary chemicals are key root exudate components that could significantly affect AM fungal growth and colonization [17,18,19,20,21] Flavonoids, such as quercetin and quercitrin, have been reported to stimulate AM fungal spore germination and/or hyphal growth [22, 23]. We tested the specific predictions: (1) root exudate secondary chemicals, such as flavonoids will differ between native and introduced populations, (2) chemicals that have higher concentrations in introduced populations will enhance AM fungal spore germination, (3) the effects of root exudates on AM fungal spore germination and colonization will be stronger for exudates of introduced than native populations, (4) activated carbon will eliminate differences in the effects of introduced vs native population root exudates These predictions, have never been tested with any invasive plant species

Materials and methods

Results

Discussion

Compliance with ethical standards