Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: " Environmental and endogenous controls on leaf- and stand-level water conductance in a Scots pine plantation Neils Sturm Barbara Köstner Wolfram a John D. | Ann. Sci. For. 1998 55 237-253 Inra Elsevier Paris 237 Original article Environmental and endogenous controls on leaf- and stand-level water conductance in a Scots pine plantation Neils Sturma Barbara Kostnera Wolfram Hartungb John D. Tenhunena Department of Plant Ecology II Bayreuth Institute for Terrestrial Ecosystem Research University of Bayreuth 95440 Bayreuth Germany bJulius-von-Sachs-Institut fur Biowissenschaften der Universităt Wurzburg Lehrstuhl fur Botanik I Mittlerer Dallenbergweg 64 97082 Wurzburg Germany Received 12 March 1997 accepted 31 July 1997 Abstract - Measurements of leaf level gas exchange and conductance tree transpiration via sapflow monitoring soil moisture and water extraction predawn water potential and xylem abscisic acid ABA concentration were carried out over the course of the 1993 and 1994 summer seasons at the Hartheim Pinus sylvestris plantation on the Upper Rhein Plain Germany. Periodic leaf level conductance determinations with porometry established a maximum value of ca 280 mmol m2 s 1 mm s 1 . Half maximal conductance was attained at 40 pmol m2 s_ and 90 of light saturation occurred at ca 500 pmol m 2 s 1 PPFD. Conductance decreased strongly with increases in vapor pressure deficit above 10 hPa while the temperature optimum was 22 C at light saturation. Strong restrictions on maximum conductance at both leaf and stand levels were apparent below a soil moisture content of 16 volume percent. Although less strongly conductance also decreased with initial drying of the upper soil layers and decreases in predawn water potential from -0 4 to MPa. In this range of water potential change xylem ABA increased to between 200 and 500 nmol L 1. Thus an immediate leaf-level reaction to the onset of summer weather conditions is observed . leaf conductance and water use decrease. We hypothesize that ABA functions as a key control on water balance transmitting information about soil water status and endogenously modifying canopy .
