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University of California, Irvine (2013)

Evapotranspiration of urban plants in a semi-arid environment

Litvak Elizaveta

Titre : Evapotranspiration of urban plants in a semi-arid environment

Auteur : Litvak Elizaveta

University : University of California, Irvine

Grade : Doctor of Philosophy (PhD) 2013

Evapotransporation (ET) of irrigated urban plants is a large yet uncertain component of urban water budgets in semi-arid regions. A detailed understanding of plot scale ET and its sensitivity to plant species composition is necessary to improve estimates of urban water vapor fluxes and water balance. However, trees planted in urban landscapes in southern California are often exposed to an unusual combination of high atmospheric evaporative demand and moist soil conditions due to irrigation. The water relations of species transplanted into these conditions are uncertain. Here, I investigate the water relations of trees commonly planted in the urbanized, semi-arid Los Angeles Metropolitan area, establish quantitative links between plant hydraulic properties and the response of transpiration to atmospheric vapor pressure deficit, and quantify plot scale ET of urban lawns. I measured the sap flux and hydraulic properties of urban trees and used enclosed chambers to measure ET of turfgrass. (1) I found that coast redwood (Sequoia sempervirens) had relatively low water use and plot-level transpiration rates <1 mm d-¹. Studied coast redwood trees had relatively strong stomatal control that may lead to carbon limitation and other stresses in semi-arid, irrigated habitat. (2) I analyzed the sensitivity of tree level transpiration estimated from sap flux of 15 irrigated tree species. My results confirm systematic differences in water relations in ring-porous versus diffuse-porous species, but these differences appear to be more strongly related to the relationship between transpiration sensitivity and vulnerability to cavitation rather than to transpiration sensitivity per se. (3) Finally, ET of irrigated turfgrass reached a maximum of 10 mm d-¹ and was always higher than plot scale tree transpiration. In summer, reductions in turfgrass ET caused by shading effects of trees were more important in influencing total ET than the addition of tree transpiration. This suggests that adding trees to irrigated lawns may be a water saving measure. These findings improve our ability to understand plant water relations across a wide range of species in semi-arid irrigated environments, establish the importance of tree shading effects on plot scale ET, and have implications for developing water-efficient strategies for semi-arid cities.

Présentation (WorldCat)

Page publiée le 29 mai 2013, mise à jour le 7 octobre 2017