Diurnal and seasonal changes in xylem water potential, stomatal conductance and abscisic acid in five different habitat types of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

Graduation date: 1980Sapling Douglas-fir trees on five sites in the Coastal and\ud Cascade Mountain ranges of Oregon were measured five times during\ud the year from the summer of 1977 through the spring of 1978 for\ud diurnal patterns of xylem water potential, stomatal conductance and\ud abscisic acid. Vapor pressure deficit and solar radiation were\ud measured as well.\ud During the summer diurnal patterns of stomatal conductance and\ud xylem water potential were similar to those found by others. High\ud winter and fall stomatal conductances were found and suggest that\ud the potential for photosynthesis exists during these times of the\ud year especially at the coastal site. At some of the sites during the\ud winter an inverted diurnal xylem water potential pattern occurred\ud which may indicate an adaptation of Douglas-fir to a relatively mild\ud winter climate. During the summer stomatal conductance was most\ud highly correlated with vapor pressure deficit, while during the fall\ud and spring stomatal conductance was correlated with xylem water\ud potential.\ud Abscisic acid showed large diurnal fluctuations in the summer\ud and fall at some of the sites, and remained relatively constant in\ud the winter and spring. For the most part the diurnal abscisic acid\ud curves showed no clear relationship with the other variables