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Harvard Forest Symposium Abstract 2005
- Title: Interspecific Variation in Nighttime Transpiration and Stomatal Conductance
- Primary Author: Michael Daley (Boston University)
- Additional Authors: Nathan Phillips (Boston University)
- Abstract:
Transpiration is generally assumed to be insignificant at night when stomata close in response to the lack of photosynthetically active radiation. However, there is increasing evidence that the stomata of some species remain open at night which would allow for nighttime transpiration if there were a sufficient environmental driving force. The purpose of this research was to examine nighttime water use in co-occurring species in a mixed deciduous stand at Harvard Forest, MA using whole-tree water use measurements. Diurnal whole-tree water use was monitored continuously using Granier-style sap flux sensors in paper birch (Betula papyrifera), red oak (Quercus rubra), and red maple (Acer Rubrum). A nearby meteorological station provided hourly data on environmental conditions. An analysis was conducted in which nighttime water flux could be partitioned between refilling of internal water stores and transpiration. Substantial nighttime sap flux was observed in all species and much of this flux can be attributed to the refilling of depleted water stores. However, nighttime sap flux in paper birch frequently exceeded recharge estimates. On nights with elevated vapor pressure deficit, sap flux continued in paper birch through the night while sap flux stopped in red oak and red maple. Over the course of the growing season, nighttime transpiration in paper birch represented 3.5% of the total sap flux. The maximum nighttime sap flux observed was over 30% of the daily flux. The study highlights differences in ecophysiological controls on sap flux exerted by co-occurring species. Measurements of leaf-level gas exchange on a night with elevated vapor pressure deficit show conductance and transpiration rates 50% of daytime maximums.
- Research Category:
