Cienciala E, Lindroth A, Cermak J, Hallgren JE, Kucera J
The Effects of Water Availability on Transpiration, Water Potential and Growth of Picea-Abies During a Growing-Season
Journal of Hydrology: 1994 155:57-71
Transpiration, pre-dawn shoot water potential and growth of Norway spruce trees were measured for one growing season, under three water regimes, giving a seasonal water input of 696 mm (irrigated), 579 mm (control) and 270 mm (drought). Potential transpiration was calculated from the Penman-Monteith equation, using maximal canopy conductance as a function of vapour pressure deficit. Sap flow was measured by a tree-trunk heat balance method and the data were expressed per unit ground surface. This allowed calculation of canopy conductance (g(c)) for the three treatments. The median of the daytime g(c) was about 1.1 cm s-1 for non-limiting water conditions, and about 0.5 cm s-1 for the conditions of a moderate water deficit. Pre-dawn water potential did not decrease until daily transpiration rates were substantially reduced, with corresponding g(c) of 0.2 cm s-1. The type of control which limits transpiration is discussed. The basal-area growth was related closely to the amount of water infiltrated into the soil. The estimated long-term tree water-use efficiency (the total dry matter produced per unit of water transpired) was on average 4.8 g kg-1, with insignificant differences between the treatments. Seasonal transpiration reached 380 mm, 325 mm and 209 mm for the irrigated, control and drought treatment, respectively.
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