Root Fungal Endophytes Enhance Heavy-Metal Stress Tolerance of Clethra barbinervis Growing Naturally at Mining Sites via Growth Enhancement, Promotion of Nutrient Uptake and Decrease of Heavy-Metal Concentration

Abstract

Clethra barbinervis Sieb. et Zucc. is a tree species that grows naturally at several mine sites and seems to be tolerant of high concentrations of heavy metals, such as Cu, Zn, and Pb. The purpose of this study is to clarify the mechanism(s) underlying this species’ ability to tolerate the sites’ severe heavy-metal pollution by considering C. barbinervis interaction with root fungal endophytes. We measured the heavy metal concentrations of root-zone soil, leaves, branches, and fine roots collected from mature C. barbinervis at Hitachi mine. We isolated fungal endophytes from surface-sterilized root segments, and we examined the growth, and heavy metal and nutrient absorption of C. barbinervis seedlings growing in sterilized mine soil with or without root fungal endophytes. Field analyses showed that C. barbinervis contained considerably high amounts of Cu, Zn, and Pb in fine roots and Zn in leaves. The fungi, Phialocephala fortinii, Rhizodermea veluwensis, and Rhizoscyphus sp. were frequently isolated as dominant fungal endophyte species. Inoculation of these root fungal endophytes to C. barbinervis seedlings growing in sterilized mine soil indicated that these fungi significantly enhanced the growth of C. barbinervis seedlings, increased K uptake in shoots and reduced the concentrations of Cu, Ni, Zn, Cd, and Pb in roots. Without root fungal endophytes, C. barbinervis could hardly grow under the heavy-metal contaminated condition, showing chlorosis, a symptom of heavy-metal toxicity. Our results indicate that the tree C. barbinervis can tolerate high heavy-metal concentrations due to the support of root fungal endophytes including P. fortinii, R. veluwensis, and Rhizoscyphus sp. via growth enhancement, K uptake promotion and decrease of heavy metal concentrations.

Assembly processes of trophic guilds in the root mycobiome of temperate forests

“…Similarly, the trophic composition of RAMs along a successional gradient of willows and birches was also relatively stable with a strong enrichment of mycorrhizas (>56% read abundance) compared with saprotrophs and endophytes (together 17%); however, ericoid fungal taxa were enriched in later successional stages (Kolaříková et al., ). Ericoid fungi occur frequently on nonericoid plants, such as conifers, as well as other tree species (Chambers, Curlevski, & Cairney, ; Dučić, Berthold, Langenfeld‐Heyser, Beese, & Polle, ; Jankowiak, Bilański, Paluch, & Kołodziej, ; Leopold, ; Maghnia et al., ; Reininger & Schlegel, ; Toju, Sato, et al., ; Toju, Yamamoto, et al., ), facilitate seedling growth on stressed soils (Yamaji et al., ) and enhance the host N supply from recalcitrant organic sources in nutrient‐poor environments (Wei, Chen, Zhang, & Pan, ; Wurzburger, Higgins, & Hendrick, ). We found a higher fraction of endophytes in Pinaceae than Fagaceae roots.…”

Root endophytic Chaetomium cupreum promotes plant growth and detoxifies aluminum in Miscanthus sinensisAndersson growing at the acidic mine site

“…; Yamaji et al . ). Ecological correspondence for soil and plants should be considered (Verheyen et al .…”

Host affinity of endophytic fungi and the potential for reciprocal interactions involving host secondary chemistry

“…The presence of certain endophytes or the composition of endophytic communities can have distinct outcomes for the health of their host. Some fungal endophytes have been shown to benefit host plants by facilitating nutrient acquisition (Hiruma et al., ; Christian et al., ) and promoting abiotic stress tolerance (Bae et al., ; Yamaji et al., ). Further, endophytic fungal communities have been shown to reduce pathogen and herbivore damage in a wide range of host plants (Arnold et al., ; Estrada et al., ; Mejía et al., ; Cosme et al., ; Christian et al., ).…”

“…host plants by facilitating nutrient acquisition (Hiruma et al, 2016;Christian et al, 2019) and promoting abiotic stress tolerance (Bae et al, 2009;Yamaji et al, 2016). Further, endophytic fungal communities have been shown to reduce pathogen and herbivore damage in a wide range of host plants (Arnold et al, 2003;Estrada et al, 2013;Mejía et al, 2014;Cosme et al, 2016;Christian et al, 2017).…”