© 2000 Heron Publishing—Victoria, Canada
Quantifying stomatal and non-stomatal limitations to carbon assimilation resulting from leaf aging and drought in mature deciduous
tree species
Kell B. Wilson (1), Dennis D. Baldocchi (1, 3) and Paul J. Hanson (2)
1. Atmospheric Turbulence and Diffusion Division, NOAA, P.O. Box 2456, Oak Ridge, TN 37831, USA / 2. Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA / 3. Department of Environmental Science, Policy and Management, University of California, Berkeley, 151 Hilgard Hall, Berkeley,
CA 94720, USA / Received September 10, 1999
Summary
Gas exchange techniques were used to investigate light-saturated carbon assimilation and its stomatal and non-stomatal limitations
over two seasons in mature trees of five species in a closed deciduous forest. Stomatal and non-stomatal contributions to
decreases in assimilation resulting from leaf age and drought were quantified relative to the maximum rates obtained early
in the season at optimal soil water contents. Although carbon assimilation, stomatal conductance and photosynthetic capacity
(Vcmax) decreased with leaf age, decreases in Vcmax accounted for about 75% of the leaf-age related reduction in light-saturated assimilation rates, with a secondary role for
stomatal conductance (around 25%). However, when considered independently from leaf age, the drought response was dominated
by stomatal limitations, accounting for about 75% of the total limitation. Some of the analytical difficulties associated
with computing limitation partitioning are discussed, including path dependence, patchy stomatal closure and diffusion in
the mesophyll. Although these considerations may introduce errors in our estimates, our analysis establishes some reasonable
boundaries on relative limitations and shows differences between drought and non-drought years. Estimating seasonal limitations
under natural conditions, as shown in this study, provides a useful basis for comparing limitation processes between years
and species.
Keywords:
A/Ci curve, leaf age, maple, oak, photosynthetic limitations, stomata.
