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.