There was no significant interaction effect between nitrogen and
water level for all the parameters measured in this study. Water stress
significantly decreased stomatal conductance. Closing of the stomata is
a physiological mechanism employed by plants to cope with water
stress. However, because stomata are the pathway for water and CO2
exchange with the atmosphere, this mechanism has a negative effect
on photosynthesis, and therefore on plant growth and yield.Microscopic
observations confirmed that P. sidoides, like most other plant species,
respond to water stress by closing their stomata. It was also observed
that water stress resulted in closing of the stomata on the adaxial side
of the leaves first, followed by closing of those on the abaxial side.
Morphologically, plants respond to water stress by leaf senescence,
smaller canopy, and smaller leaves, among others. Pelargonium sidoides
showed similar response with reductions in LAI, plant height and leaf
area per plant. These observed morphological responses and reduced
fresh root yield were probably the result of reduced photosynthetic
rate, since CO2 uptake was decreased by closing of the stomata.
Nitrogen had a significant effect on number of leaves per plant, but
not on leaf area,whichmeans that although more leaveswere stimulated,
they were not bigger in size and therefore did not result in higher
LAI. The study presented the first results on response of P. sidoides to
water stress and nitrogen levels, which could be important in the
establishment of nitrogen and water management guidelines for
cultivation of P. sidoides.