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Published online by Cambridge University Press: 04 August 2010
SUMMARY
This paper outlines the effects of environmental factors on the liquid and gaseous water flux through mature Maritime pine in a stand from southwest France. The sap flow density, expressed per unit area of the cross-section of sapwood, was measured throughout two growing seasons in the bole of a sample of trees. Stomatal conductance (gs), needle water potential, water table depth and soil water content were measured periodically. From daily courses of needle water potential and sap flow density, the bulk soil-leaf specific conductance (Ls) was computed. The soil water deficit revealed the most important environmental factor controlling the sap flow. It reduced the sap flow density by decreasing both the gradient of water potential between the soil and the leaves, and the bulk hydraulic conductance along this circuit. The reduction of bulk specific conductance might be attributed to variations in soil water potential for the day. In a similar way, a multifactorial model demonstrated the close dependence of gs on the predawn water potential and air vapour saturation deficit. This behaviour supports the hypothesis of stomatal control of cavitation.
INTRODUCTION
Maritime pine stands extend over more than four million hectares in southern Europe. In the natural area of this species, which includes the western Mediterranean coasts, and Atlantic coasts of Portugal, Spain and France up to the Loire estuary, summer drought lasts from one to three months. Even so, environmental and physiological control of water consumption and transpiration of Maritime pine {Pinus pinaster Ait.) are still poorly documented (Gash et al, 1989; Granier et al, 1990; Diawara, Loustau & Berbigier, 1991).
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