4.2 Photosynthetic gas exchange parameters
Plants that were treated by amaranth leachate showed significant differences in photosynthetic gas exchange parameters compared to control. In wheat plant, a sharp decrease in net assimilation rate, transpiration rate, and stomatal conductance was observed. It seems that both stomatal and non-stomatal factors have been involved in decreasing photosynthesis rate in wheat plant. On the other hand, although decreasing stomatal conductance and increasing stomatal resistance as stomatal factors have been involved in photosynthesis decline in this plant, these are not all the reasons however. Chlorophyll fluorescence studies as well as the results of photosynthetic pigments contents indicate the involvement of non-stomatal factors in reducing photosynthesis. In the treated cucumber plants, the parameters of net assimilation rate, transpiration rate, and stomatal conductance increased. The interpretations provided for the wheat plant also justify the behavior of the cucumber plant in relation to the photosynthetic gas exchange parameters. Photosynthetic gas exchange parameters in wheat plant were more affected than cucumber, but by studying the water use efficiency and stomatal resistance, contrary evidence was witnessed. Significant decrease in water use efficiency and stomatal resistance was observed in cucumber plants treated by redroot pigweed leachate, whereas photosynthesis and transpiration rate of this plant was not increased significantly. In wheat plant, despite decrease in photosynthesis and transpiration rate due to decrease in stomatal opening, increase in water use efficiency and stomatal resistance were observed. When increasing photosynthesis, cucumber plant was exposed to very extreme water loss situation, while wheat increased water use efficiency by increasing stomatal resistance and decreasing water loss.