Journal Article

Elevated CO<sub>2</sub> enhances leaf senescence during extreme drought in a temperate forest

Jeffrey M. Warren, Richard J. Norby and Stan D. Wullschleger

Edited by Ram Oren

in Tree Physiology

Volume 31, issue 2, pages 117-130
Published in print February 2011 | ISSN: 0829-318X
Published online March 2011 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/tpr002
Elevated CO2 enhances leaf senescence during extreme drought in a temperate forest

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In 2007, an extreme drought and acute heat wave impacted ecosystems across the southeastern USA, including a 19-year-old Liquidambar styraciflua L. (sweetgum) tree plantation exposed to long-term elevated (ECO2) or ambient (ACO2) CO2 treatments. Stem sap velocities were analyzed to assess plant response to potential interactions between CO2 and these weather extremes. Canopy conductance and net carbon assimilation (Anet) were modeled based on patterns of sap velocity to estimate indirect impacts of observed reductions in transpiration under ECO2 on premature leaf senescence. Elevated CO2 reduced sap flow by 28% during early summer, and by up to 45% late in the drought during record-setting temperatures. Modeled canopy conductance declined more rapidly in ECO2 plots during this period, thereby directly reducing carbon gain at a greater rate than in ACO2 plots. Indeed, pre-drought canopy Anet was similar across treatment plots, but declined to ∼40% less than Anet in ACO2 as the drought progressed, likely leading to negative net carbon balance. Consequently, premature leaf senescence and abscission increased rapidly during this period, and was 30% greater for ECO2. While ECO2 can reduce leaf-level water use under droughty conditions, acute drought may induce excessive stomatal closure that could offset benefits of ECO2 to temperate forest species during extreme weather events.

Keywords: canopy conductance; FACE; leaf litter; root mortality; sap flow; sweetgum

Journal Article.  9877 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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