Yamaji Keiko, Watanabe Yumiko, Masuya Hayato, Shigeto Arisa, Yui Hiroshi, Haruma Toshikatsu
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Tohoku Research Center, Forestry and Forest Products Research Institute, Morioka, Iwate, Japan.
PLoS One. 2016 Dec 28;11(12):e0169089. doi: 10.1371/journal.pone.0169089. eCollection 2016.
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.
毛叶桤木是一种自然生长在多个矿区的树种，似乎能够耐受高浓度的重金属，如铜、锌和铅。本研究的目的是通过考虑毛叶桤木与根际真菌内生菌的相互作用，阐明该树种耐受矿区严重重金属污染的机制。我们测量了从日立矿采集的成熟毛叶桤木的根际土壤、叶片、树枝和细根中的重金属浓度。我们从表面消毒的根段中分离出真菌内生菌，并研究了在有无根际真菌内生菌的灭菌矿土中生长的毛叶桤木幼苗的生长情况以及重金属和养分吸收情况。野外分析表明，毛叶桤木的细根中含有相当高含量的铜、锌和铅，叶片中含有锌。真菌福尔蒂尼瓶霉、韦吕韦根根皮菌和根盘菌属经常作为优势真菌内生菌种被分离出来。将这些根际真菌内生菌接种到在灭菌矿土中生长的毛叶桤木幼苗上，结果表明这些真菌显著促进了毛叶桤木幼苗的生长，增加了地上部对钾的吸收，并降低了根中铜、镍、锌、镉和铅的浓度。没有根际真菌内生菌，毛叶桤木在重金属污染条件下几乎无法生长，表现出黄化，这是重金属毒性的症状。我们的结果表明，由于包括福尔蒂尼瓶霉、韦吕韦根根皮菌和根盘菌属在内的根际真菌内生菌通过促进生长、促进钾吸收和降低重金属浓度的作用，毛叶桤木能够耐受高浓度的重金属。
