Benefit, cost and water-use efficiency of arbuscular mycorrhizal durum wheat grown under drought stress

Arbuscular mycorrhizal fungi (AMF) living symbiotically with host plants enhance plant growth by improving the acquisition of mineral nutrients and water relations. This study determined the effects of AMF inoculation on growth, benefit/cost and water-use efficiency (grams dry matter produced per kilogram water evapotranspired) in two durum wheat genotypes (drought sensitive and drought tolerant) under water-stressed and well-watered conditions. Plants were grown in a low-P silty clay (Typic Xerochrept) soil mix in a greenhouse. Shoot and root dry matter (DM) and root AMF colonization were higher for well-watered than for water-stressed plants. The mycorrhizal plants were more water-use efficient than nonmycorrhizal plants. Shoot DM differences between mycorrhizal and nonmycorrhizal plants represent the benefit derived by plants from AMF-root associations. Shoot DM differences between mycorrhizal and nonmycorrhizal plants under similar conditions of water treatment represent the cost to the plant of AMF-root associations. Values of benefit/cost for AMF-root associations were highest when plants were water-stressed and decreased under well-watered conditions. Genotypic differences in calculated costs and benefits were pronounced. Benefit/cost analysis may be helpful in evaluating host plant genotypes in order to optimize efficiencies of AMF sym biosis under different environmental conditions.