PARENT SESSION
Contributed Oral Session 16: Photosynthesis and Water Relations: Conductivity; Stress
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal
Low hydraulic conductance in boreal Scots pine trees and sensitivity to drought in fairly wet soils.
Duursma, Remko *,1, Nikinmaa, Eero1, Peramäki, Martti, Mäkelä, Annikki, 1 University of Helsinki, Helsinki, Finland
ABSTRACT- Plant productivity is ultimately limited by water availability. The overall conductance of the soil to leaf pathway determines the availability of water for transpiration, and thus carbon assimilation. In a boreal Scots pine forest in Finland, drought stress is mostly absent due to ample precipitation and low evaporative demand. However, both eddy flux and automated shoot cuvette data show some response to decreasing water availability in the summer of 2002, although bulk soil water potential always remained above -0.1 MPa, not considered dry in other systems. Based on measurements of diameter-fluctuation, leaf water potential, and sap-flux, we estimated leaf-specific hydraulic conductance (kL) for these Scots pines. Estimates of soil-to-root conductance come from a dynamic cylindrical flow model, and are much larger than plant conductance at these soil water potentials. Estimates of kL are in the low range of reported values for trees, and explain why low leaf water potentials are reached although the soil is still relatively wet. Measurements of diameter fluctuations allow separation of kL into above and belowground parts, and show in this case that the belowground conductance is much larger than aboveground. We argue that high belowground conductance results from ample roots surface, resulting from nitrogen limitation. The low aboveground conductance may come from a xylem structure that is resistant to cavitation as a result of freeze-thaw cycles, which are common during a large part of the year.
Key words: hydraulic conductance, gas exchange, Pinus sylvestris , Optimal stomatal control model