Arbuscular mycorrhizal fungi enhance tolerance of two Cucurbitaceae species to bicarbonate in irrigation water

With the aim of determining whether the arbuscular mycorrhizal (AM) inoculation would give an advantage to overcome soil alkalinity problems, two greenhouse experiments were carried out to determine yield, fruit quality, and mineral composition of two Cucurbitaceae species: cucumber (Cucumis sativus L.) and zucchini squash (Cucurbita pepo L.) with AM (+AM) and non-AM (-AM). Plants were supplied with nutrient solutions having two levels of pH (6.0 or 8.1). The high pH nutrient solution had the same basic composition plus an additional of 10 mM NaHCO3 and 0.5 g L-1 CaCO3. For both cucumber and zucchini, increasing the concentration of NaHCO3 from 0 to 10 mM in the nutrient solution significantly decreased yield, final leaf area, net assimilation of CO2 (ACO2), N, P, K, and Fe concentration in leaf tissue. The +AM cucumber and zucchini plants under alkaline conditions had higher marketable yield, and fruit mean weight than -AM plants. Mycorrhizal cucumber and zucchini plants grown under alkaline conditions had a higher macro- (P and K) and micro (Fe) concentration in leaf tissue compared to -AM plants. The highest yield production in +AM plants seems to be related to the capacity of maintaining higher net ACO2 and to a better nutritional status in response to bicarbonate stress with respect to -AM plants.