PARENT SESSION
Organized Oral Session 11: Hydraulic limitations in vascular plants
Organizer(s): F Berninger, L Lauzon, and E Nikinmaa
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 511 C, Level 5, Palais des congrès de Montréal
Trade-off between photosynthetic production, transpiration and leaf-area sapwood area relationship in Scots pine.
Nikinmaa, Eero*,1, Peramaki, Martti1, Karimaki, Janne1, Duursma, Remko1, Berninger, Frank2, Makela, Annikki1, 1 Department of Forest Ecology, Helsinki, Finland2 Departmnt of Biological Sciences, Montreal, Quebec, Canada
ABSTRACT- The limit to tree-height has been proposed to result from a pressure gradient increase with transport distance that is required to lift up water. Water tension cannot increase indefinitely due to risk of embolism. Small foliage area relative to uptake and transport tissue lowers the risk but also decreases the photosynthetic production of the tree. Alternatively, the scheduling of the opening of stomata can avoid excessive tensions in trees. Here we examine the trade-offs between Scots pine photosynthetic production, transpiration and structural relationships. We simulate photosynthetic production and transpiration with a canopy photosynthesis model with optimal control of stomata and convert the transpiration rate into water tension gradient with a xylem sap-flow model. The models are parameterized with measurements on 15m and 28m tall Scots pine trees. Measured climate and soil water data are the driving variables in the simulations. We repeat the simulations with varying severity of the control of stomata, and the leaf-area, sap-wood and root area relationships. The simulated results are compared against observations of diurnal xylem diameter variation. In the base case the minimum water potential of shoots was from -1.5 to -2 MPa. Relaxing the stomatal control to yield 10% higher daily transpiration increased the daily photosynthetic production about 3%. The higher maximum transpiration required either a 10% increase in the annual minimum shoot water potential or an equivalent 10% increase in the sapwood conducting area (compared with 2% increase in annual productivity). The observed leaf vs. sapwood area ratio is higher in the large trees than in the smaller trees. The results suggest that structural savings from wood growth with lower transpiration release more carbon for leaf growth than is lost due to hydraulic limitation of photosynthesis in large Scots pine.
Key words: stomatal control, sap-flow, water potential, Scots pine