Gas exchanges and chlorophyll fluorescence of soybean genotypes subjected to flooding stress

- The objective of this work was to evaluate the ecophysiological responses of soybean subjected to soil flooding. The experiment was conducted in a completely randomized design with five replications. A 3 x 3 factorial scheme was used, consisting of three soybean genotypes (tolerant, sensitive and a commercial cultivar), and three water conditions (control treatment - soil was maintained at 70% of field capacity throughout the plant cycle; soil flooding for 10 days in the vegetative period + 10 days in the reproductive period; and soil flooding for 10 days only in the reproductive period). Three evaluations were carried out regarding chlorophyll fluorescence and gas exchange: after flooding in the vegetative period (V2); after flooding in the reproductive period (R2), and ten days after draining the water. Tolerant genotypes and sensitive genotypes experienced reductions in photosynthetic rate and stomatal conductance when subjected to water stress in the reproductive stage. However, under stress in the vegetative stage, only the tolerant and sensitive genotypes reduced the actual quantum efficiency and electron transport rate, and at the moment of flooding in the reproductive stage, all had changes and did not show recovery for these variables. As for non -photochemical quenching, only the sensitive genotype increased the rate, under stress in stages V2/R2 and R2. The local commercial cultivar is more adapted to soil flooding conditions, as it shows better physiological responses to adapt to soil flooding conditions.