© 2001 Heron Publishing—Victoria, Canada
Mean canopy stomatal conductance responses to water and nutrient availabilities in Picea abies and Pinus taeda
Brent E. Ewers (1, 2), Ram Oren (1), Nathan Phillips (1, 3), Monika Strömgren (4) and Sune Linder (4)
1. Nicholas School of the Environment, Duke University, Durham, NC 27708, USA / 2. Department of Forest Ecology and Management, University of Wisconsin, 1630 Linden Dr., Madison, WI 53706, USA / 3. Department of Geography, Boston University, Boston, MA 02215, USA / 4. Department for Production Ecology, Swedish University of Agricultural Sciences, P.O. Box 7042, SE-750 07 Uppsala, Sweden / Received August 18, 2000
Summary
We compared sap-flux-scaled, mean, canopy stomatal conductance (GS) between Picea abies (L.) Karst. in Sweden and Pinus taeda (L.) in North Carolina, both growing on nutritionally poor soils. Stomatal conductance of Picea abies was approximately half that of Pinus taeda and the sensitivity of GS in Picea abies to vapor pressure deficit (D) was lower than in Pinus taeda. Optimal fertilization increased leaf area index (L) two- and threefold in Pinus taeda and Picea abies, respectively, regardless of whether irrigation was increased. Although it increased L, fertilization did not increase GS in Picea abies unless irrigation was also provided. In Pinus taeda growing on coarse, sandy soils, the doubling of L in response to fertilization reduced GS sharply unless irrigation was also provided. The reduction in GS with fertilization in the absence of irrigation resulted from the production of fine roots with low saturated hydraulic conductivity.
When Pinus taeda received both fertilization and irrigation, the increase in L was accompanied by a large increase in GS. In Pinus taeda, a reference GS (defined as GS at D = 1 kPa; GSR) decreased in all treatments with decreasing volumetric soil water content (θ). In Picea abies, θ varied little within a treatment, but overall, GSR declined with θ, reaching lowest values when drought was imposed by the interception of precipitation. Despite the large
difference in GS both between Picea abies and Pinus taeda and among treatments, stem growth was related to absorbed radiation, and stem growth response to treatment reflected mostly
the changes in L.
Keywords:
fertilization, irrigation, loblolly pine, Norway spruce, sap flux, shade tolerance.
