© 1998 Heron Publishing—Victoria, Canada
Canopy conductance of Pinus taeda, Liquidambar styraciflua and Quercus phellos under varying atmospheric and soil water conditions
D. E. Pataki (1), R. Oren (1), G. Katul (1) and J. Sigmon (1)
1. School of the Environment, Duke University, Durham, NC 22708, USA / Received October 9, 1996
Summary
Sap flow, and atmospheric and soil water data were collected in closed-top chambers under conditions of high soil water potential
for saplings of Liquidambar styraciflua L., Quercus phellos L. and Pinus taeda L., three co-occurring species in the southeastern USA. Responses of canopy stomatal conductance (gt) to water stress induced by high atmospheric water vapor demand or transpiration rate were evaluated at two temporal scales.
On a diurnal scale, the ratio of canopy stomatal conductance to maximum conductance (gt/gt,max) was related to vapor pressure deficit (D), and transpiration rate per unit leaf area (El). High D or El caused large reductions in gt/gt,max in L. styraciflua and P. taeda. The response of gt/gt,max to El was light dependent in L. styraciflua, with higher gt/gt,max on sunny days than on cloudy days. In both L. styraciflua and Q. phellos, gt/gt,max decreased linearly with increasing D (indicative of a feed-forward mechanism of stomatal control), whereas gt/gt,max of P. taeda declined linearly with increasing El (indicative of a feedback mechanism of stomatal control). Longer-term responses to depletion of soil water were observed
as reductions in mean midday gt/gt,max, but the reductions did not differ significantly between species. Thus, species that employ contrasting methods of stomatal
control may show similar responses to soil water depletion in the long term.
Keywords:
canopy stomatal conductance, feedback, feed forward, loblolly pine, sap flow, sweetgum, transpiration, willow oak.
