Effects of arbuscular mycorrhizal symbiosis on growth and N2 fixation of Trifolium alexandrinum under late drought stress conditions.

Several experiments, mostly carried out under controlled conditions, have shown that arbuscular mycorrhizal (AM) symbiosis enhances nutrient uptake and improves drought tolerance of host plants. The present research, carried out in a typical Mediterranean environment, evaluated the effect of AM symbiosis on berseem clover (Trifolium alexandrinum L.) grown in the field under both late drought stress and well-watered conditions. The crop was subjected to repeated defoliation. N2 fixation was estimated using the 15N dilution method and using ryegrass (Lolium multiflorum var. Westervoldicum) as the reference crop. In late drought conditions, AM symbiosis resulted in a significant increase in biomass yield, total N uptake, total amount of N fixed, and proportion of N derived from the atmosphere. The results suggest that AM symbiosis could play a key role in alleviating the stress effects of late drought on berseem forage production in the field.