Improving soybean leaf physiological responses under drought stress by increasing seed zinc and iron concentration

To study the effects of both drought stress and seed zinc and iron concentrations on the photosynthesis, chlorophyll fluorescence, and proline and carbohydrate accumulations in soybean (Glycine max (L.) Merr. cv. M9) leaf, a split plot experiment was carried out in 2012 based on a randomized complete block design with three replications in greenhouse conditions at Yasouj University. Drought stress, based on 70% depletion of the available soil water, was designated as the main-plot that included drought stress at the flowering, pod filling, and seed filling stages. Zinc and iron concentrations were designated as sub-plot factors that included high zinc, iron and zinc+iron contents of the seed, and control as well as seed soaking in distilled water, 3% zinc sulfate, 3% iron sulfate, and 3% zinc+3% iron sulfate solutions. Results showed that photosynthesis characteristics, net photosynthesis rates, stomatal conductance, and transpiration rates decreased under the drought stress conditions. Drought stress also led to decreased water use efficiency (WUEi). Moreover, leaf proline and soluble carbohydrate contents increased in response to drought stress. While PSII quantum yield reduced under drought stress, it increased under high seed zinc and iron concentrations. It was concluded that enhanced seed zinc and iron concentration was capable of ameliorating the impacts of drought stress on leaf proline and carbohydrate concentrations.