© 2001 Heron Publishing—Victoria, Canada
Response of stomatal conductance to drought in ponderosa pine: implications for carbon and ozone uptake
Jeanne A. Panek (1) and Allen H. Goldstein (1)
1. Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA / Received August 30, 1999
Summary
To gain insight into the limitations imposed by a typical Mediterranean-climate summer drought on the uptake of carbon and
ozone in the ponderosa pine (Pinus ponderosa Dougl. ex Laws.) ecosystem, we compared diurnal trends in leaf physiology of young trees in a watered and a control plot located in
the Sierra Nevada Mountains, CA, USA (Blodgett Forest, 38°53′ N, 120°37′ W, 1315 m elevation). Predawn water potential of
trees in the watered plot remained above –0.3 MPa throughout the growing season, whereas it dropped in the control plot from
–0.24 to –0.52 MPa between late May and mid-August. Photosynthesis and stomatal conductance of trees in the watered plot were
relatively insensitive to atmospheric vapor pressure deficit (VPD), whereas gas exchange of trees in the control plot varied
with changes in soil water, VPD and temperature. Although the 1998 growing season was abnormally wet, we saw a pronounced
drought effect at the control site. Over the 2 months following the onset of watering, carbon and ozone uptake were measured
on three days at widely spaced intervals. Carbon uptake per unit leaf area by 1-year-old foliage of trees in the control plot
was 39, 35 and 30% less, respectively, than in the watered plot, and estimated ozone deposition per unit leaf area (ozone
concentration times stomatal conductance) was 36, 46 and 41% less.
Keywords:
carbon flux, drought stress, ozone flux, photosynthesis, soil water.
