© 2003 Heron Publishing—Victoria, Canada
Diurnal and seasonal changes in stem increment and water use by yellow poplar trees in response to environmental stress
Samuel B. McLaughlin (1, 2, 3), Stan D. Wullschleger (1) and Miloslav Nosal (4)
1. Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6422, USA / 2. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37931, USA / 3. Author to whom correspondence should be addressed (mclaughlinsb@ornl.gov) / 4. Department of Mathematics and Statistics, University of Calgary, Alberta, Canada / Received October 17, 2002; accepted April 5, 2003; published online October 1, 2003
Summary
To evaluate indicators of whole-tree physiological responses to climate stress, we determined seasonal, daily and diurnal
patterns of growth and water use in 10 yellow poplar (Liriodendron tulipifera L.) trees in a stand recently released from competition. Precise measurements of stem increment and sap flow made with automated
electronic dendrometers and thermal dissipation probes, respectively, indicated close temporal linkages between water use
and patterns of stem shrinkage and swelling during daily cycles of water depletion and recharge of extensible outer-stem tissues.
These cycles also determined net daily basal area increment. Multivariate regression models based on a 123-day data series
showed that daily diameter increments were related negatively to vapor pressure deficit (VPD), but positively to precipitation
and temperature. The same model form with slight changes in coefficients yielded coefficients of determination of about 0.62
(0.57–0.66) across data subsets that included widely variable growth rates and VPDs. Model R2 was improved to 0.75 by using 3-day running mean daily growth data. Rapid recovery of stem diameter growth following short-term,
diurnal reductions in VPD indicated that water stored in extensible stem tissues was part of a fast recharge system that limited
hydration changes in the cambial zone during periods of water stress. There were substantial differences in the seasonal dynamics
of growth among individual trees, and analyses indicated that faster-growing trees were more positively affected by precipitation,
solar irradiance and temperature and more negatively affected by high VPD than slower-growing trees. There were no negative
effects of ozone on daily growth rates in a year of low ozone concentrations.
Keywords:
climate, dendrometers, growth, regression, sap flow.
