Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Tree water relations and climatic variations at the alpine timberline: seasonal changes of sap flux and xylem water potential in Larix decidua Miller, Picea abies (L.) Karst. and Pinus cembra L. | Ann. Sci. For. 1998 55 159-172 Inra Elsevier Paris 159 Original article Tree water relations and climatic variations at the alpine timberline seasonal changes of sap flux and xylem water potential in Larix decidua Miller Pỉcea abies L. Karst and Pinus cembra L. Tommaso Anfodillo Stefano Rento Vinicio Carraro Luca Furlanetto Carlo Urbinati Marco Carrer Dipartimento Territorio e Sistemi Agro Forestall University of Padova Agripolis Via Romea 16 35020 Legnaro PD Italy Received 15 January 1997 accepted 15 September 1997 Abstract - Trees growing at the alpine timberline very seldom undergo severe water stress because of high precipitation during the vegetative period. Since trees are adapted to moist conditions moderate water deficit may lead to a strong reduction in transpiration. Transpiration and xylem water potential were measured in two individuals each of Pinus cembra Larix decidua and Picea abies growing at the timberline 2 080 m . in the north-eastern Italian Alps. From June to October 1996 predawn water potential was between and MPa with moderate differences among species. Throughout the growing period L. decidua showed a progressive decrease in the minimum water potential from to MPa in p. abies and p. cembra variations were more correlated to weather conditions with minima and MPa respectively during a mild drought period. L. decidua showed the mean daily maximum sap flux density about dm3 dm 2 h while mean maximum values in p. abies and p. cembra were about and respectively. High daily fluctuations of sap flow were observed in relation to rapid variations in weather conditions particularly in L. decidua. Regardless of species a very high stomatai sensitivity to vapour pressure deficit was recorded. The three species seem to have evolved different drought avoidance strategies. L. decidua maintained a relatively high transpiration even during moderate water deficit periods because of its high water uptake .
