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Leaf and canopy conductance in aspen and aspen-birch forests under free-air enrichment of carbon dioxide and ozone.
Tree Physiol 2009; 29(11):1367-80TP

Abstract

Increasing concentrations of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) have the potential to affect tree physiology and structure, and hence forest feedbacks on climate. Here, we investigated how elevated concentrations of CO2 (+45%) and O3 (+35%), alone and in combination, affected conductance for mass transfer at the leaf and canopy levels in pure aspen (Populus tremuloides Michx.) and in mixed aspen and birch (Betula papyrifera Marsh.) forests in the free-air CO2-O3 enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). The study was conducted during two growing seasons, when steady-state leaf area index (L) had been reached after > 6 years of exposure to CO2- and O3-enrichment treatments. Canopy conductance (g(c)) was estimated from stand sap flux, while leaf-level conductance of sun leaves in the upper canopy was derived by three different and independent methods: sap flux and L in combination with vertical canopy modelling, leaf 13C discrimination methodology in combination with photosynthesis modelling and leaf-level gas exchange. Regardless of the method used, the mean values of leaf-level conductance were higher in trees growing under elevated CO2 and/or O3 than in trees growing in control plots, causing a CO2 x O3 interaction that was statistically significant (P < or = 0.10) for sap flux- and (for birch) 13C-derived leaf conductance. Canopy conductance was significantly increased by elevated CO2 but not significantly affected by elevated O3. Investigation of a short-term gap in CO2 enrichment demonstrated a +10% effect of transient exposure of elevated CO2-grown trees to ambient CO2 on g(c). All treatment effects were similar in pure aspen and mixed aspen-birch communities. These results demonstrate that short-term primary stomatal closure responses to elevated CO2 and O3 were completely offset by long-term cumulative effects of these trace gases on tree and stand structure in determining canopy- and leaf-level conductance in pure aspen and mixed aspen-birch forests. Our results, together with the findings from other long-term FACE experiments with trees, suggest that model assumptions of large reductions in stomatal conductance under rising atmospheric CO2 are very uncertain for forests.

Authors+Show Affiliations

School of Natural Resources and Environment, University of Michigan, 440 Church Street, Ann Arbor, MI 48109, USA. johan.uddling@dpes.gu.seNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

19773339

Citation

Uddling, Johan, et al. "Leaf and Canopy Conductance in Aspen and Aspen-birch Forests Under Free-air Enrichment of Carbon Dioxide and Ozone." Tree Physiology, vol. 29, no. 11, 2009, pp. 1367-80.
Uddling J, Teclaw RM, Pregitzer KS, et al. Leaf and canopy conductance in aspen and aspen-birch forests under free-air enrichment of carbon dioxide and ozone. Tree Physiol. 2009;29(11):1367-80.
Uddling, J., Teclaw, R. M., Pregitzer, K. S., & Ellsworth, D. S. (2009). Leaf and canopy conductance in aspen and aspen-birch forests under free-air enrichment of carbon dioxide and ozone. Tree Physiology, 29(11), pp. 1367-80. doi:10.1093/treephys/tpp070.
Uddling J, et al. Leaf and Canopy Conductance in Aspen and Aspen-birch Forests Under Free-air Enrichment of Carbon Dioxide and Ozone. Tree Physiol. 2009;29(11):1367-80. PubMed PMID: 19773339.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Leaf and canopy conductance in aspen and aspen-birch forests under free-air enrichment of carbon dioxide and ozone. AU - Uddling,Johan, AU - Teclaw,Ronald M, AU - Pregitzer,Kurt S, AU - Ellsworth,David S, Y1 - 2009/09/22/ PY - 2009/9/24/entrez PY - 2009/9/24/pubmed PY - 2010/2/17/medline SP - 1367 EP - 80 JF - Tree physiology JO - Tree Physiol. VL - 29 IS - 11 N2 - Increasing concentrations of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) have the potential to affect tree physiology and structure, and hence forest feedbacks on climate. Here, we investigated how elevated concentrations of CO2 (+45%) and O3 (+35%), alone and in combination, affected conductance for mass transfer at the leaf and canopy levels in pure aspen (Populus tremuloides Michx.) and in mixed aspen and birch (Betula papyrifera Marsh.) forests in the free-air CO2-O3 enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). The study was conducted during two growing seasons, when steady-state leaf area index (L) had been reached after > 6 years of exposure to CO2- and O3-enrichment treatments. Canopy conductance (g(c)) was estimated from stand sap flux, while leaf-level conductance of sun leaves in the upper canopy was derived by three different and independent methods: sap flux and L in combination with vertical canopy modelling, leaf 13C discrimination methodology in combination with photosynthesis modelling and leaf-level gas exchange. Regardless of the method used, the mean values of leaf-level conductance were higher in trees growing under elevated CO2 and/or O3 than in trees growing in control plots, causing a CO2 x O3 interaction that was statistically significant (P < or = 0.10) for sap flux- and (for birch) 13C-derived leaf conductance. Canopy conductance was significantly increased by elevated CO2 but not significantly affected by elevated O3. Investigation of a short-term gap in CO2 enrichment demonstrated a +10% effect of transient exposure of elevated CO2-grown trees to ambient CO2 on g(c). All treatment effects were similar in pure aspen and mixed aspen-birch communities. These results demonstrate that short-term primary stomatal closure responses to elevated CO2 and O3 were completely offset by long-term cumulative effects of these trace gases on tree and stand structure in determining canopy- and leaf-level conductance in pure aspen and mixed aspen-birch forests. Our results, together with the findings from other long-term FACE experiments with trees, suggest that model assumptions of large reductions in stomatal conductance under rising atmospheric CO2 are very uncertain for forests. SN - 0829-318X UR - https://www.unboundmedicine.com/medline/citation/19773339/Leaf_and_canopy_conductance_in_aspen_and_aspen_birch_forests_under_free_air_enrichment_of_carbon_dioxide_and_ozone_ L2 - https://academic.oup.com/treephys/article-lookup/doi/10.1093/treephys/tpp070 DB - PRIME DP - Unbound Medicine ER -