tailieunhanh - Báo cáo lâm nghiệp: "Whole tree hydraulic conductance and water loss regulation in Quercus during drought: evidence for stomatal control of embolism?"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế, đề tài: "Whole tree hydraulic conductance and water loss regulation in Quercus during drought: evidence for stomatal control of embolism?. | Ann Sci For 1995 53 197-206 Elsevier INRA 197 Original article Whole tree hydraulic conductance and water loss regulation in Quercus during drought evidence for stomatai control of embolism H Cochard N Bréda A Granier Unite d ecophysiologie forestiere Centre de Nancy Inra 54280 Champenoux France Received 2 January 1995 accepted 19 June 1995 Summary The water relations of 30-year-old Quercus petraea were studied for three consecutive growing seasons. Whole tree specific hydraulic conductances gL were computed from sap flow densities dF leaf water potential P eaf relationships. gL was clearly reduced with the development of the drought. The decrease of gL with Ppredawn was ofan exponential type ie high variations of gL were found whereas Ppredawn remained high and constant. These early variations of gL were most probably located in the soil-root compartment of the SPAC because no loss of hydraulic conductivity due to xylem embolism was detected in the crown of the trees. Although gL was reduced Tmjdday remained nearly constant and above -3 MPa throughout the drought period because dFmidday was also significantly reduced. As a consequence a good linear relation was found between dFmjdday and gL. Xylem embolism significantly developed in the petioles and twigs of Qpetraea when Pmidday became less than -3 MPa. We argue that because of changes in gL Q petraea progressively adjusted its water loss throughout the drought development with the effect of maintaining Pmidday above the cavitation threshold. It is shown that if no water loss regulation had occurred considerable tensions would have developed in the crown of these trees with predictable branch mortality due to runaway embolism. Quercus petraea drought water relation embolism hydraulic conductance Resume Conductance hydraulique totale et regulation des pertes en eau Chez Quercus en période de sécheresse preuve d un controls stomatique du développement de I embolie Les relations hydriques de chênes sessiles ages de