Abstract
Growth and water use efficiency (WUE) of two, common Southwest landscape plants, red bird of paradise (Caesalpinia pulcherrima L.) and blue palo verde (Cercidium floridum Benth. Ex A. Gray), were studied in response to three irrigation regimens (frequent, moderate, and infrequent) that mimicked a range of residential landscape watering practices in Phoenix, AZ. During 50 to 58 and 138 to 147 days after the start of irrigation treatments (DAT), mid-day measurements of shoot water potential (Ψ), osmotic potential (Ψ0), and gas exchange were made. Concurrently, diurnal measurements of whole plant transpiration (T) and estimates of dry weight accrual were made to calculate WUE. More frequent irrigations increased shoot length of both species and dry weight of Cercidium. For both species, Ψ and Ψ0 showed patterns of osmotic regulation as the substrate dried between watering events for moderately and infrequently irrigated plants. Infrequently irrigated Caesalpinia and Cercidium had the lowest WUE, except for 138 to 147 DAT during which time infrequently irrigated Cercidium had the highest WUE. Instantaneous transpiration efficiency (ITE) was negatively correlated to the ratio of intracellular to ambient CO2 (Ci/Ca) in all treatments, suggesting that under more frequently irrigated conditions, WUE of Caesalpinia and Cercidium might be reduced by negative feedback effects of high Ci/Ca ratios on stomatal conductance.
Author notes
This research was funded, in part, by National Science Foundation grant no. DEB-9714833.
2Graduate Research Assistant and Associate Professor, respectively.