Effects of arbuscular mycorrhiza and phosphorus application on arsenic toxicity in sunflower (Helianthus annuus L.) and on the transformation of arsenic in the rhizosphere |
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Authors: | V U Ultra Jr S Tanaka K Sakurai K Iwasaki |
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Institution: | (1) United Graduate School of Agricultural Sciences, Ehime University, Matsuyama 790-8566, Japan;(2) Graduate School of Kuroshio Science, Kochi University, Nankoku, Kochi 783-8502, Japan;(3) Faculty of Agriculture, Kochi University, Nankoku, Kochi 783-8502, Japan |
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Abstract: | Effects of arbuscular mycorrhiza (AM) and phosphorus (P) application on arsenic (As) toxicity were studied in a rhizobox system
with As-contaminated soil collected from Shimane Prefecture, Japan. The treatments consisted of a combination of two levels
of AM (Glomus aggregatum) inoculation (−AM and +AM) and two levels of P application (−P and +P at 30 mg P kg−1). Sunflower (Helianthus annuus L.) seedlings were cultured in rhizoboxes for 6 weeks. Rates of root AM infection in +AM treatments were about 40% regardless
of P application. AM inoculation as well as P application reduced As toxicity symptoms, most clearly so in the +AM−P treatment.
Plant growth was highest in the +AM + P treatment. Shoot As concentrations were slightly reduced by AM inoculation but enhanced
by P application. Shoot P concentration in the +AM−P treatment was similar to that of +P treatments and was higher than in
−AM−P. Analyses of rhizosphere soils at the end of the cultivation period indicated that P application increased water-soluble
As (WS−As) in all compartments while AM inoculation increased WS−As in the central compartment only. Both the WS−arsenite
WS−As(III)] and the dominant form, arsenate WS−As(V)], showed gradients toward the root surface. Dimethylarsine (DMAA) was detected in the +AM treatments only. To our knowledge,
this is the first report of the occurrence of DMAA in the mycorrhizosphere. AM inoculation increased WS−P similarly as +P
treatments did and promoted acid phosphatase activity in the soil. In conclusion, AM inoculation alleviated the effects of
As toxicity by improving P nutrition without increasing As concentrations in the shoots. Moreover, AM appeared to be involved
in the transformation of soil inorganic As into less toxic organic forms. |
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Keywords: | Arbuscular mycorrhiza Arsenic Phosphorus Rhizosphere Sunflower |
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