TWO MICROMETEOROLOGICAL APPROACHES TO UNDERSTANDING PLANT/ENVIRONMENT INTERACTIONS (NORWAY, SUGAR MAPLE, RED OAK, DEFOLIATED)

Part I. A model for the estimation of transpiration from individual tree crowns has been tested and run using data from Norway maple (Acer platanoides L.) and sugar maple (Acer saccharum Marsh.) and sugar maple (Acer saccharum Marsh.) saplings, and the results compared to lysimetrically determined water loss for the tree crowns. Inputs to the model include both micrometeorological and plant physiological parameters, and the output from the model includes hourly estimates of leaf water potential, leaf-air temperature differential, leaf resistance to water vapor diffusion and the radiation regime for each of a number of crown sampling points, and an estimate of hourly water loss for the entire crown.Part II. Red oak (Quercus rubra L.) leaves were artificially defoliated by cutting off portions of the leaves to simulate defoliation by the gypsy moth (Lymantria dispar L.) in the third, fourth and fifth instars. The effects of this defoliation on the water status of trees grown under "wet", "moist", and "dry" soil moisture conditions are described and related to undefoliated control trees grown under similar conditions. Within each soil mixture regime, the levels of three tree water status indicators--leaf water potential, leaf-air temperature gradient and leaf diffusive conductance (l/resistance)--were recorded and their relationships to their driving forces were checked to determine the effect of defoliation on tree water status.Leaf diffusive conductance was the only tree water status indicator to exhibit significant differences in response between defoliated and undefoliated treatments. Under "wet" and "dry" soil moisture conditions no significant differences in response were observed with defoliation treatment. Under "moist" soil water conditions, however, the difference in respone was significant, with the response of the defoliated tree similar to that of the "wet" trees and the response of the undefoliated tree similar to that of the "dry" trees. Artificial defoliation appeared to reduce stress induced stomatal closure on the defoliated tree under moderately limiting soil moisture conditions.The model has been shown to be marginally adequate for use on a number of trees if the results are averaged over those trees. The model estimates of parameters for individual trees show much deviation from the measured values of those same parameters for the trees, and it is recognized that the various physiological submodels require further refinement to correct this deficiency in the crown model. These refinements would be aided by the existence of a more complete body of information on the physiological responses to water stress of individual taxa.