Morpho-physiological traits of soybean plants in symbiosis with Gigaspora sp. and submitted to water restriction.

In agricultural production, periods in which there is a lack of water can affect the productivity of soybean crops. One alternative is the use of arbuscular mycorrhizal fungi (AMF), which maximize water absorption, biochemical regulation, leaf elasticity and transpiration, and water use regulation. The present study aimed to analyze the morphological and physiological traits of soybean plants associated with Gigaspora margarita and Gigaspora gigantea submitted to water restriction in nonsterilized soil. The soybean plants received 31 g of the AMF Gigaspora margarita or 46 g of Gigaspora gigantea separately at sowing and were cultivated in a greenhouse under natural light conditions with controlled relative humidity and temperature. Water restriction was imposed when the plants reached the V3 stage and were divided into three levels: irrigated (80%), moderate (60%), and severe (40%) field capacity (FC). The experimental design was completely randomized in a 3 × 3 factorial design (three inoculation treatments × three water restriction levels). Physiological and morphological parameters, photosynthetic pigments, electrolyte leakage, root colonization of soybean plants, and percentage of fungal spores were evaluated. The inoculation of Gigaspora gigantea promoted the adaptation of physiological (photosynthesis rate, transpiration, stomatal conductance, Ci/Ca ratio, and carboxylation) and morphological traits (plant height and stem diameter), with greater colonization of soybean roots under conditions of water restriction, and maximized the tolerance of plants to drought, mitigating the negative effects of these conditions regardless of the level of water restriction. Mycorrhizal inoculation promoted better functioning of the photosynthetic apparatus and growth of soybean plants.