© 2007 Heron Publishing—Victoria, Canada
Temperature, light and leaf hydraulic conductance of little-leaf linden (Tilia cordata) in a mixed forest canopy
Arne Sellin (1,2) and Priit Kupper (1)
1. Institute of Botany and Ecology, University of Tartu, Lai 40, 51005 Tartu, Estonia / 2. Corresponding author (arne.sellin@ut.ee) / Received May 8, 2006; accepted June 19, 2006; published online February 1, 2007
Summary
Response of whole-leaf hydraulic conductance (GL) in little-leaf linden (Tilia cordata Mill.) to temperature and photosynthetic photon flux (QP) was estimated by the evaporative flux method under natural conditions in a mixed forest canopy. Mean midday GL in the lower- and upper-crown foliage was 1.14 and 3.06 mmol m–2 s–1 MPa–1, respectively. Over the study period, leaf temperature (TL) explained about 67% of the variation in GL, and QP explained about 10%. Leaf water potential and crown position also affected GL significantly. About a third of the temperature effect was attributable to changes in the viscosity of water, and two thirds
to changes in protoplast permeability (i.e., symplastic conductance). Leaf hydraulic conductance was highly sensitive to changes
in QP when QP was less than 200 µmol m–2 s–1, and GL sensitivity decreased with increasing irradiance. Sensitivity of GL to variation in TL increased consistently with increasing temperature in the range of 16 to 29 °C. There were positive interactions between
temperature and light in their effects on GL: the light response was more pronounced at higher leaf temperatures. Because of frequent rains during the study period, the
trees experienced no soil water deficit, and, within the range experienced, soil water potential had no effect on GL. Leaf hydraulic conductance exhibited a seasonal pattern that could be explained primarily by temporal variability in mean
air temperature and irradiance, in addition to which an age-related trend (P < 0.001) of increasing GL from the end of June to the beginning of August was observed.
Keywords:
evaporative flux method, leaf temperature, photosynthetic photon flux density, seasonal trend, within-crown variability.
