Aeclimation of Photosynthesis to soil drying sycamore seedlings [Sudan]
1997
Khallil, A.A.M. (University of Juba Department of Forestry, Khartoum (Sudan)) | Grace, J. (University of Edinburgh (United Kingdom))
The effects of cyclic water stress on the responses of stomatal conductance and photosynthesis of sycamore seedlings to subsequent water stress were investigated, under controlled environmental conditions. Seedlings were either well-watered (non-acclimated) or subjected to four wet-dry cycles, in which seedlings received no water until apparent wilting (acclimated). After the preconditioning period, pressure-volume analysis was performed on leaves; henceforth all the seedlings were exposed to a final drying cycle, during which physiological parameters were measured. Repeated frying cycles induced a significant reduction of 0.3 MPa in osmotic potential at full and zero turgor, but had no effect on tissue bulk elastic modulus or relative water content at zero turgor. Photosynthesis and stomatal conductance became less sensitive to water stress, and continued at soil water content low enough to inhibit completely those of non-acclimated controls, resulting in higher water use efficiency in acclimated seedlings. Acclimation of the photosynthetic processes were the major factor responsible for the acclimation of photosynthesis to water stress, as attested by the concomitant decline in stomatal conductance and photosynthesis without correlated change in internal CO2 concentrations. Though the cyclic soil drying treatment had no effect on the total dry matter production, it induced a significant shift in biomass allocation, with a greater partitoning to root growth, resulting in a significant increase in root/shoot ratio. These modifications were concluded to be important for improvement of seedling drought tolerance prior to out planting
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