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Cathleen Feser, Rolston St. Hilaire, and Dawn VanLeeuwen

Mexican elder (Sambucus mexicana Presl.) is used in arid landscapes of the Southwest, but the plant is known for its unpredictable performance in those landscapes. We studied drought responses of mexican elder plants grown in an arid environment using an in-ground nursery production system. Plants were maintained as well-irrigated controls or exposed to cyclic drought and irrigated based on evapotranspiration. Drought treatment lasted 165 days. Plants exposed to drought had more negative predawn and midday water potentials than well-watered plants. The ratio of variable to maximal fluorescence (Fv/Fm) for the drought group (0.76), was near the optimum value of 0.8, suggesting that chloroplasts of drought-stressed plants maintained high levels of activity. Drought cycle, but not drought treatment affected stomatal conductance. Drought-stressed plants had lower transpiration rates than controls except at drought cycle five when transpiration rates were similar between irrigation treatments. Relative water content was higher in controls (76%) than plants exposed to drought (66%). Leaf area of well-irrigated plants was over four times higher than that of plants exposed to drought. Leaf area to root dry weight ratio of drought-stressed plants was 79% lower than control plants. Severely reduced leaf area of drought-stressed plants might be one reason why landscape personnel conclude that mexican elder plants perform poorly in arid landscapes.

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Rolston St. Hilaire, Cathleen F. Feser, Theodore W. Sammis, and Anderson S. St. Hilaire

Accurate measurement of evapotranspiration (ET) is difficult and expensive for large, in-ground container (pot-in-pot) plants. We engineered and used a simple and inexpensive system to determine evapotranspiration of in-ground container trees. The system was shop-assembled and used a block and tackle system attached to a collapsible tripod. A unique container harness system attached to the block and tackle system was used to lift containers that were sunken in the ground. Containers were weighed with a battery-operated balance that was accurate to 1 g (0.04 oz) at its maximum load capacity of 60 kg (132.3 lb). One person operated the system, and the weight of the system exclusive of the balance was 17.5 kg (38.50 lb). Gravimetric water use data obtained with the system werecombined with meteorological data to compute crop coefficients (Kc) of mexican elder (Sambucus mexicana). The system detected small changes in daily water use of mexican elder trees grown in 76-L (20-gal) in-ground containers. Crop coefficients ranged from 0.17 to 0.71. The acquisition of evapotranspiration data from relatively large, containerized landscape plants may be facilitated because the system is simple, inexpensive, and accurate.