אסיף מאגר המחקר החקלאי

Transpiration of Cupressus sempervirens L. as influenced by canopy structure

Year:

2004

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Volume :

52

Co-Authors:

Schiller, G., Dept. of Agronomy and Nat. Resources, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Moshe, Y., Dept. of Agronomy and Nat. Resources, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Ungar, E.D., Dept. of Agronomy and Nat. Resources, Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

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Abstract:

We hypothesized that for similar trunk circumferences and leaf masses, under similar climatic conditions, the canopy structure of Cupressus sempervirens L. influences transpiration rate such that the faster transpiring var. horizontalis exhausts the winter's allocation of rainfall earlier, to its own subsequent detriment. To verify this assumption, heat pulse velocity measurements, by means of the heat pulse method, were done at eight periods during the year in the stem xylem of eight matched pairs of trees, each pair composed of a var. horizontalis and a var. pyramidalis tree of similar dimensions. Results showed that during the daylight hours in winter and spring, midday sap flow velocity of var. horizontalis trees was greater than that of var. pyramidalis trees of similar trunk circumferences and foliage mass. Hence, the calculated average daily transpiration of var. horizontalis trees was nearly 50% greater than that of var. pyramidalis trees. During the wet period (November to May), mean daily transpiration of var. horizontalis exceeded, with 2.91 dm3 per tree, that of var. pyramidalis. This amount adds up to an additional water consumption of ∼500 dm3 per tree during 170 clear-sky days within that period. This higher water consumption by var. horizontalis reduces the spatial soil-water storage and availability in the late spring and early summer, thereby prolonging the water stress period that might become critical under droughty winter conditions. Thus, at afforestation sites under given soil and bedrock conditions, e.g., spatial and temporal water availability for each tree, the canopy structure will be the decisive factor influencing the development (time and amount) of the soil-water stress.

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