Photosynthesis and Water Relations in Brazilian Sugarcane

摘要

The expansion of sugarcane (Saccharum spp.) in Brazil has been boosted by the growing demand for bio-fuelsall over the world and requires the occupation of new agricultural areas, including regions with unfavorable agro-climaticconditions. This observational study makes an analysis of the relationship between stomatal conductance, gas exchangeand photosynthesis in sugarcane fields subject to different ambient conditions and growth phases. It was noted that thestomatal conductance had a much higher control on photosynthesis than on transpiration. Even under high stomatal conductance,photosynthesis maintained a high correlation to it. Sugarcane had an instantaneous water use efficiency of approximately4.4 μmol of fixed CO2 for each mmol of H20 expended in transpiration. Lower leaf water potential, besidesleading to an internal reduction of CO2, also reduced the instantaneous carboxylation efficiency, indicating that the photosynthesisapparatus was also affected. The variety RB92579, seems to have good water absorption system, because evenunder low leaf water potential, it maintained a good stomatal conductance, with a higher transpiration and photosynthesisthan the others varieties. These results suggest that this variety has a tolerance mechanism to endure rather than avoiddrought.