Photosynthesis and Water Use by Saltcedar

Near Buckeye, Arizona, saltcedar (Tamarix pentandra) was grown on a battery of evapotranspirometers under various conditions of plant density, soil salinity, and access to water. Growth and development of these plants declined sharply at the beginning of each July, although before that time rates of growth and development had been very high. It was initially postulated that carbon dioxide might have become the limiting factor. Measurements of CO2 content of the air made at different heights inside and outside the evapotranspirometers, however, showed that this was not the case. Analysis of the data shows a close correlation between CO2 and water vapor fluxes (computed by means of mass transfer equations) above the saltcedar thickets. A reduction in fluxes during hot afternoons appears to be due to ambient temperatures over 40°C. Water use is similarly affected.