Effect of superabsorbent polymer on photosynthetic traits, chlorophyll content and chlorophyll fluorescence indices of bean (Phaseolus vulgaris L.) under drought stress

In order to investigate the effect of using superabsorbent polymer on photosynthetic traits, chlorophyll content, and chlorophyll fluorescence indices of beans (Phaseolus vulgaris L.) under drought stress, an experiment was conducted using a split-plot arrangement in randomized complete block design with 4 replications in the Research Field of Islamic Azad University, Kaleibar Branch, Iran in crop year 2018. Experimental treatments included irrigation intervals in the main plots (after 70, 140, and 210 mm water evaporation from class A evaporation pan) and application of different amounts of superabsorbent polymer (0, 75, and 150 Kg.ha-1) in sub plots. Results showed that the main effect of drought stress and superabsorbent were significantly different in most measured traits (p≤0.01). Interaction between drought stress and superabsorbent was significant only in the stomatal conductance, cell membrane stability, and chlorophyll index. Mean comparison results showed that severe drought stress significantly reduced maximum photochemical efficiency of PSII, maximal fluorescence (Fm), chlorophyll content, transpiration rate, CO2 concentration under stomatal chamber, and photosynthesis rate, indicating the role of stomatal factors in reducing photosynthesis under stress conditions. The use of superabsorbent significantly increased photosynthetic rate, stomatal conductance, transpiration rate, cell membrane stability, maximum photochemical efficiency of PSII, maximal fluorescence (Fm), minimum fluorescence (F0) and chlorophyll index while CO2 concentration under stomatal chamber reduced. The highest records of most measured traits were observed in 75 Kg.ha-1 superabsorbent polymer treatment. In general, it was concluded that superabsorbent improves photosynthetic properties, the maximum photochemical efficiency of PSII, and chlorophyll content of beans under drought stress.