Regulation of branch-level gas exchange of boreal trees: roles of shoot water potential and vapor pressure difference.

Effects of shoot water potential (Psi) and leaf-to-atmosphere vapor pressure difference (VPD) on gas exchange of jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) B.S.P.), and aspen (Populus tremuloides Michx.) were investigated at the northern edge of the boreal forest in Manitoba, Canada. Laboratory measurements on cut branches showed that net photosynthesis (A(n)) and mesophyll conductance (g(m)) of jack pine and g(m) of black spruce did not respond to Psi until a threshold Psi was reached below which they decreased linearly. Photosynthesis of black spruce decreased slowly with decreasing Psi above the threshold and declined more rapidly thereafter. The threshold Psi was lower in black spruce than in jack pine. However, stomatal conductance (g(s)) of black spruce decreased continuously with decreasing Psi, whereas g(s) of jack pine showed a threshold response. Mesophyll limitations were primarily responsible for the decline in A(n) at low Psi for jack pine and black spruce in the middle of the growing season, but stomatal limitations became more important later in the season. Field measurements on in situ branches on warm sunny days showed that both conifer species maintained Psi above the corresponding threshold and there was no evidence of Psi limitation on A(n) of jack pine, black spruce or aspen. Vapor pressure difference was important in regulating gas exchange in all three species. An empirical model was used to quantify the g(s) response to VPD. When parameterized with laboratory data for the conifers, the model also fit the corresponding field data. When parameterized with field data, the model showed that stomata of aspen were the most sensitive of the three species to VPD, and stomata of black spruce were the least sensitive. For jack pine and aspen, stomata of foliage in the upper canopy were significantly more sensitive than stomata of foliage in the lower canopy. Vapor pressure difference had a greater impact on A(n) of aspen than on A(n) of the conifers as a result of aspen's greater stomatal sensitivity to VPD and greater slope of the relationship between A(n) and intercellular CO(2) concentration (C(i)). During the 1994 growing season, VPD averaged 1.0 kPa, corresponding to ratios of C(i) to ambient CO(2) of 0.77, 0.71 and 0.81 for jack pine, black spruce and aspen, respectively. We conclude that increases in VPD at the leaf surface in response to climate change should affect the absolute CO(2) and H(2)O fluxes per unit leaf area of the aspen component of a boreal forest landscape more than those of the conifer component.

[1]  D. Brand.  Estimating the surface area of spruce and pine foliage from displaced volume and length , 1987 .

[2]  J. Ehleringer,et al.  Photosynthesis and carbon isotope discrimination in boreal forest ecosystems: A comparison of functional characteristics in plants from three mature forest types , 1997 .

[3]  Richard H. Waring,et al.  Forest Ecosystems: Concepts and Management , 1985 .

[4]  I. Fung,et al.  Observational Contrains on the Global Atmospheric Co2 Budget , 1990, Science.

[5]  X. Zeng,et al.  Atmosphere-terrestrial ecosystem interactions: implications for coupled modeling , 1993 .

[6]  Ernst-Detlef Schulze,et al.  Carbon Dioxide and Water Vapor Exchange in Response to Drought in the Atmosphere and in the Soil , 1986 .

[7]  G. Edwards,et al.  Control of Photosynthesis and Stomatal Conductance in Ricinus communis L. (Castor Bean) by Leaf to Air Vapor Pressure Deficit. , 1992, Plant physiology.

[8]  P. Waggoner,et al.  Effects of changing stomatal width in a red pine forest on soil water content, leaf water potential, bole diameter, and growth. , 1968, Plant physiology.

[9]  P. Jarvis,et al.  Photosynthesis as related to xylem water potential and carbon dioxide concentration in Sitka spruce , 1981 .

[10]  Aberdeen Ab.  PHOTOSYNTHESIS IN SITKA SPRUCE (PICEA SITCHENSIS , 1978 .

[11]  I. R. Cowan,et al.  Stomatal function in relation to leaf metabolism and environment. , 1977, Symposia of the Society for Experimental Biology.

[12]  V. Lieffers,et al.  Rooting of peatland black spruce and tamarack in relation to depth of water table , 1987 .

[13]  G. Goldstein,et al.  Stomatal and environmental control of transpiration in a lowland tropical forest tree , 1993 .

[14]  A. Lindroth,et al.  Numerical analysis of pine forest evaporation and surface resistance , 1986 .

[15]  E. Hogg,et al.  Sap flow in trembling aspen: implications for stomatal responses to vapor pressure deficit. , 1997, Tree physiology.

[16]  J. Pereira,et al.  The control of leaf conductance of white lupin by xylem ABA concentration decreases with the severity of water deficits , 1995 .

[17]  M. Abrams,et al.  Gas exchange, leaf structure and nitrogen in contrasting successional tree species growing in open and understory sites during a drought. , 1995, Tree physiology.

[18]  Holger Brix,et al.  The Effect of Water Stress on the Rates of Photosynthesis and Respiration in Tomato Plants and Loblolly Pine Seedlings , 1962 .

[19]  Graham D. Farquhar,et al.  Responses to Humidity by Stomata of Nicotiana glauca L. And Corylus avellana L. Are Consistent With the Optimization of Carbon Dioxide Uptake With Respect to Water Loss , 1980 .

[20]  J. Sperry.  Limitations on Stem Water Transport and Their Consequences , 1995 .

[21]  C. Field,et al.  Scaling physiological processes: leaf to globe. , 1995 .

[22]  C. Justice,et al.  A Revised Land Surface Parameterization (SiB2) for Atmospheric GCMS. Part II: The Generation of Global Fields of Terrestrial Biophysical Parameters from Satellite Data , 1996 .

[23]  K. G. McNaughton,et al.  Effects of spatial scale on stomatal control of transpiration , 1991 .

[24]  G. Collatz,et al.  Physiological and environmental regulation of stomatal conductance, photosynthesis and transpiration: a model that includes a laminar boundary layer , 1991 .

[25]  S. Pallardy,et al.  Stomatal and nonstomatal limitations to net photosynthesis in seedlings of woody angiosperms. , 1992, Plant physiology.

[26]  G. F. Dykstra.  Photosynthesis and Carbon Dioxide Transfer Resistance of Lodgepole Pine Seedlings in Relation to Irradiance, Temperature, and Water Potential , 1974 .

[27]  P. Jarvis,et al.  Stomatal responses to humidity in selected conifers. , 1986, Tree physiology.

[28]  P. Jarvis,et al.  Leaf Conductance as Related to Xylem Water Potential and Carbon Dioxide Concentration in Sitka Spruce , 1979 .

[29]  G. S. Puritch.  Effect of Water Stress on Photosynthesis, Respiration, and Transpiration of Four Abies Species , 1973 .

[30]  Neil C. Turner,et al.  Adaptive significance of stomatal responses to water stress. , 1980 .

[31]  Jon D. Johnson,et al.  Stomatal response to vapour pressure deficit and the effect of plant water stress , 1983 .

[32]  Daniel B. Botkin,et al.  Sensitivity of Cool-Temperate Forests and their Fossil Pollen Record to Rapid Temperature Change , 1985, Quaternary Research.

[33]  J. Riov,et al.  The effect of water stress on photosynthesis and related parameters in Pinus halepensis , 1985 .

[34]  Christopher B. Field,et al.  Stomatal responses to increased CO2: implications from the plant to the global scale , 1995 .

[35]  J. Ehleringer,et al.  Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies. , 1997, Tree physiology.

[36]  I. R. Cowan,et al.  Leaf Conductance in Relation to Rate of CO(2) Assimilation: III. Influences of Water Stress and Photoinhibition. , 1985, Plant physiology.

[37]  V. Lieffers,et al.  Effects of depth of water table and substrate temperature on root and top growth of Piceamariana and Larixlancina seedlings , 1986 .

[38]  U. Siegenthaler,et al.  Atmospheric carbon dioxide and the ocean , 1993, Nature.

[39]  D. Randall,et al.  A Revised Land Surface Parameterization (SiB2) for Atmospheric GCMS. Part I: Model Formulation , 1996 .

[40]  A. Gosselin,et al.  Photosynthesis and transpiration of in vitro cultured asparagus plantlets , 1992 .

[41]  D. Whitehead,et al.  Response of transpiration and photosynthesis to a transient change in illuminated foliage area for a Pinus radiata D. Don tree , 1996 .

[42]  J. A. Fites,et al.  CO2 and water vapor exchange of Pinustaeda in relation to stomatal behavior: test of an optimization hypothesis , 1988 .

[43]  D. Randall,et al.  Latitudinal gradient of atmospheric CO2 due to seasonal exchange with land biota , 1995, Nature.

[44]  Piers J. Sellers,et al.  Effects of implementing the simple biosphere model in a general circulation model , 1989 .

[45]  J. Mitchell.  The seasonal response of a general circulation model to changes in CO2 and sea temperatures , 1983 .

[46]  M. R. Raupach.  Vegetation-atmosphere interaction in homogeneous and heterogeneous terrain: some implications of mixed-layer dynamics , 1991 .

[47]  Y. Kawamitsu,et al.  Humidity pretreatment affects the responses of stomata and CO2 assimilation to vapor pressure difference in C3 and C4 plants , 1993 .

[48]  H. Margolis,et al.  Relation between the permeability and the anatomy of jack pine sapwood with stand development , 1989 .

[49]  T. Webb,,et al.  Computer-Aided Reconstruction of Late-Quaternary Landscape Dynamics , 1985 .

[50]  M. G. Ryan,et al.  A physiological basis for biosphere-atmosphere interactions in the boreal forest: an overview. , 1997, Tree physiology.

[51]  D. Baldocchi,et al.  Seasonal variation of carbon dioxide exchange rates above and below a boreal jack pine forest , 1997 .

[52]  John Grace,et al.  Abscisic acid concentrations and fluxes in droughted conifer saplings , 1995 .

[53]  W. K. Ferrell,et al.  The relationship of abscisic acid metabolism to stomatal conductance in Douglas-fir during water stress , 1982 .

[54]  T. Davenport,et al.  Movement and Endogenous Levels of Abscisic Acid during Water-Stress-induced Abscission in Cotton Seedlings. , 1977, Plant physiology.

[55]  M. R. Thorpe,et al.  Responses of apple leaf stomata to environmental factors , 1980 .

[56]  J. D. Stewart,et al.  Stomatal and mesophyll limitations of photosynthesis in black spruce seedlings during multiple cycles of drought. , 1995, Tree physiology.

[57]  S. Running.  Environmental control of leaf water conductance in conifers , 1976 .

[58]  D. Baldocchi,et al.  Energy and CO(2) flux densities above and below a temperate broad-leaved forest and a boreal pine forest. , 1996, Tree physiology.

[59]  K. Jon Ranson,et al.  The Boreal Ecosystem-Atmosphere Study (BOREAS) : an overview and early results from the 1994 field year , 1995 .

[60]  Debbie Whitall,et al.  WETLANDS , 1995, Restoration & Management Notes.

[61]  W. R. Watts,et al.  Photosynthesis in Sitka Spruce (Picea sitchensis (Bong.) Carr.). VIII. Measurements of Stomatal Conductance and 14 CO 2 Uptake in Controlled Environments , 1978 .

[62]  D. Grantz,et al.  Coordination of stomatal, hydraulic, and canopy boundary layer properties: Do stomata balance conductances by measuring transpiration? , 1991 .

[63]  William T. Pockman,et al.  Limitation of transpiration by hydraulic conductance and xylem cavitation in Betula occidentalis , 1993 .

[64]  H. Margolis,et al.  Patterns of change of saturated sapwood permeability and sapwood conductance with stand development , 1989 .

[65]  William J. Davies,et al.  Root Signals and the Regulation of Growth and Development of Plants in Drying Soil , 1991 .