Effects of Ozone and Water Stress on Canopy Temperature, Water Use, and Water Use Efficiency of Alfalfa

Publisher Website
Google Scholar
Abstract
Ozone (O3) and soil water deficit are two environmental stresses that significantly affect the growth and yield of alfalfa (Medicago sativa L). However, little is known of the responses of field‐grown alfalfa to O3, and the effects of the interaction between O3 and water stress on canopy temperature and water relations of alfalfa have not been previously reported. The objective of this 2‐yr study was to determine the interactive effects of O3 and soil water deficits on canopy temperatures, water use, and water use efficiency (WUE) of alfalfa. Alfalfa (cv. WL‐514) was grown in 30‐3‐ by 5.5‐m plots on Wasco sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Torriorthents) in Shafter, CA, and was exposed in open‐top chambers to five levels of O3 for 12 h daily, from March to October of 1984 and 1985. Ozone treatments ranged from charcoal‐filtered air (CF) to twice ambient O3 concentrations. Each plot received either normal amounts of irrigation (NI) or 30% less than normal (WS). Canopy temperature‐air temperature differentials (Tc‐Ta) were significantly reduced by water stress an average of 27.9% in 1984 and 44.0% in 1985. Ozone also significantly reduced Tc ‐ Ta by 31% in NI and 37% in WS plots in 1984, but in 1985 O3 had no effect on Tc ‐ Ta. Water use, rate of soil water depletion, or depth of effective rooting zone were not affected by O3, hereas water stress significantly reduced all three. Water use efficiency was significantly reduced by O3, averaging 12% lower in nonfiltered compared with CF plots. The effects of O3 on WUE were attributed to premature senescence and abscission of older alfalfa leaves.