Diurnal and seasonal changes in stem increment and water use by yellow poplar trees in response to environmental stress

Tree Physiology 23, 1125–1136 © 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,1–3 STAN D. WULLSCHLEGER1 and MILOSLAV NOSAL4 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 () 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 R 2 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. Introduction Physiological differences in response to environmental stress within and among tree species and across spatial and temporal scales significantly limit efforts to understand and predict forest responses to future global climate change. It is increasingly apparent that responses of seedling and sapling trees to environmental stresses may not provide a valid basis for estimating growth rates and stand dynamics of mature trees subjected to the same stresses. This generalization is supported by studies of the adverse effects of tropospheric ozone on forest trees (Chappelka and Samuelson 1998, Samuelson and Kelly 2001), the positive effects of atmospheric elevated CO2 concentrations (Norby et al. 2001, Oren et al. 2001), as well as tree responses to climatic stress, including drought (Orwig and Adams 1997, Hanson and Weltzin 2000). These differences can be related to the effects of tree size and geometry on photosynthesis and water transport pathways and resistances (Yoder et al. 1994), to the effects of tree size on carbohydrate allocation pathways (McLaughlin and Shriner 1980, Waring 1987) as well as to changes in the depth, extent and vigor of rooting systems (Joslin et al. 2000) as trees mature. Dendroecological studies suggest that there have been systematic shifts in the growth responses of mature trees to components of both physical and chemical climate in widespread regions over recent decades. These include reduced latewood density (Schweingruber et al. 1979) and growth (Briffa et al. 1998, Smith et al. 1999) of conifers associated with increasing temperatures in central Europe and increased sensitivity of red spruce to temperature (McLaughlin et al. 1987, Cook and Zedaker 1992) and rainfall (McLaughlin et al. 1997) at highelevation sites in the eastern USA, where acid deposition is high. In addition, there is evidence of increased sensitivity of mature loblolly pine (Zahner et al. 1989, McLaughlin and Downing 1995, 1996) and big cone Douglas-fir (Peterson et al. 1995) to drought in areas with high ozone concentrations. Ozone has also been identified as one of the most important climatic variables affecting growth of white pine in Maine (Bartholomay et al. 1997). Although the future distribution and amount of rainfall are uncertain, predictions of increased temperatures and greater climatic variability suggest that drought will increasingly af- † This paper was among those presented at the 17th North American Forest Biology Workshop “Rocky Mountain ecosystems: Diversity, complexity and interactions,” sponsored by the Tree Physiology and Forest Genetics working groups of the Society of American Foresters and held at Washington State University, Pullman, WA. 1126 MCLAUGHLIN, WULLSCHLEGER AND NOSAL fect forest health and productivity in the future (IPCC 1998). Thus studies of changes in water-use patterns in large forest trees in response to shorter-term variations in climatic stress are important for understanding and predicting future forest responses to chronic changes in physical and chemical climates, including regional ozone exposure. The use of sensitive dendrobands and multivariate statistical analyses to relate short-term changes in tree growth to climatic influences was introduced more than 40 years ago (Fritts 1962). Studies in the mid-1970s (Hinckley and Bruckerhoff 1975, Hinckley et al. 1976), as well as more recent investigations (Herzog et al. 1995, Downes et al. 1999, Zweiffel et al. 2001, McLaughlin et al. 2002), have documented that measures of stem increment at hourly or shorter intervals can provide useful insights into short-term, physiologically based responses of whole trees to environmental stimuli. Of particular interest have been insights into whole-tree patterns of water use and growth in response to changing external environmental and internal physiological and structural factors. Daily patterns of stem shrinkage of extensible tissues in developing sapwood, phloem and cambium during periods of high transpiration coupled with stem increments associated with recharge of stored water and growth as transpiration subsides later in the day can provide important insights into the magnitude and timing of factors influencing whole-tree water use and growth. Lassoie et al. (1979) observed that daily stem shrinkage and recovery in Douglas-fir were closely related to soil water potential and predawn twig xylem potential. Both the amoun (...truncated)