The symbiosis with arbuscular mycorrhizal fungi contributes to plant tolerance to serpentine edaphic stress

Serpentine soils represent stressful environment with low calcium to magnesium ratio, deficiencies of essential macronutrients, increased concentrations of heavy metals and a low water-holding capacity. A considerable potential of arbuscular mycorrhizal fungi (AMF) to promote plant growth and nutrition can be expected under these adverse conditions. We tested a hypothesis that both host plants and AMF have evolved edaphic tolerance, which enable them to cope with the conditions of serpentine habitats. A reciprocal transplant experiment with a full factorial design was conducted, involving serpentine and non-serpentine substrates, host plants (Knautia arvensis, Dipsacaceae) and AMF isolates. After three-month cultivation under greenhouse conditions, plant growth and nutrition and AMF development were assessed. Our results evidenced the edaphic differentiation and higher tolerance of both plants and fungi of serpentine origin to serpentine soil. The better performance of serpentine plants was likely based on their tolerance to magnesium accumulation in shoot tissues. The serpentine AMF isolate not only developed higher root colonisation in serpentine conditions, but it was also more efficient in the growth promotion of and phosphorus uptake by the serpentine plants. As it had only a slight impact on magnesium uptake and no influence on calcium and nickel uptake by the serpentine plants, the improved P nutrition seemed to be the crucial mechanism of the mycorrhizal promotion effect. In conclusion, our study proved the tolerance of a plant-mycobiont complex to specific conditions of serpentine soils, which may indicate that not only the individual components of serpentine communities but also their functional interactions are subjected to selective evolutionary forces. (C) 2011 Elsevier Ltd. All rights reserved.