Arbuscular mycorrhizal fungi enhance nutrient acquisition and reduce aluminum toxicity in Lespedeza formosa under acid rain.

Abstract

Lespedeza formosa is an economically important shrub in the agroecosystems of southern China, where acid rain (AR) is an increasingly serious environmental issue. However, the roles of arbuscular mycorrhizal fungi (AMF) in adapting the plants to AR stress are poorly understood. In this study, L. formosa seedlings were cultivated in a greenhouse, where the inoculated (colonization with Rhizophagus irregularis and Diversispora versiformis, alone and in combination) and non-inoculated plants were treated with three AR regimes (pH 5.6, 4.0, and 2.5) to evaluate the roles of AMF under acidic conditions. The results showed that AR individually suppressed plant growth by inhibiting photosynthetic parameters and induced Al phytotoxicity in non-mycorrhizal plants. However, mycorrhizal inoculation, especially in combination, significantly increased the total dry weight, photosynthetic capabilities, shoot nitrogen (N) concentration (average 15.8 and 16.7mgg-1 for non-mycorrhizal and mycorrhizal plants, respectively) and plant phosphorus (P) concentration (average 1.6 and 2.3mgg-1 for non-mycorrhizal and mycorrhizal plants, respectively) at pH 4.0, reduced N/P ratio (average 9.5 and 6.9for non-mycorrhizal and mycorrhizal plants, respectively) at pH 4.0, and protected roots against Al phytotoxicity (average 2.0 and 1.4mgg-1 for non-mycorrhizal and mycorrhizal roots, respectively), indicating that AMF could mitigate some of the detrimental effects of AR. Moreover, our findings suggest that AMF mainly benefited the plant through the combined effects of N concentrations and N/P ratios in shoots and Al3+ concentrations in roots under acidic conditions.