TOR-NGERN, Pantana; OREN, Ram; WARD, Eric J.; PALMROTH, Sari; MCCARTHY, Heather R.; DOMEC, Jean-Christophe

doi:10.1111/nph.13148

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TOR-NGERN, Pantana
Nicholas School of the Environment and Earth Sciences
Department of Forest Ecology and Management

OREN, Ram
Nicholas School of the Environment and Earth Sciences
Department of Forest Ecology and Management

WARD, Eric J.
Department of Forestry and Environmental Resources

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New Phytologist. 2015, vol. 205, n° 2, p. 518-525

Wiley

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Models of forest energy, water and carbon cycles assume decreased stomatal conductance with elevated atmospheric CO2 concentration ([CO2]) based on leaf-scale measurements, a response not directly translatable to canopies. Where canopy-atmosphere are well-coupled, [CO2]-induced structural changes, such as increasing leaf-area index (L-D), may cause, or compensate for, reduced mean canopy stomatal conductance (G(S)), keeping transpiration (E-C) and, hence, runoff unaltered. We investigated G(S) responses to increasing [CO2] of conifer and broadleaved trees in a temperate forest subjected to 17-yr free-air CO2 enrichment (FACE; +200molmol(-1)). During the final phase of the experiment, we employed step changes of [CO2] in four elevated-[CO2] plots, separating direct response to changing [CO2] in the leaf-internal air-space from indirect effects of slow changes via leaf hydraulic adjustments and canopy development. Short-term manipulations caused no direct response up to 1.8xambient [CO2], suggesting that the observed long-term 21% reduction of G(S) was an indirect effect of decreased leaf hydraulic conductance and increased leaf shading. Thus, E-C was unaffected by [CO2] because 19% higher canopy L-D nullified the effect of leaf hydraulic acclimation on G(S). We advocate long-term experiments of duration sufficient for slow responses to manifest, and modifying models predicting forest water, energy and carbon cycles accordingly.< Réduire

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(FACE)

Liquidambar styraciflua

Pinus taeda

transpiration

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canopy stomatal conductance

elevated CO2

free-air CO2 enrichment

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Increases in atmospheric CO(2) have little influence on transpiration of a temperate forest canopy

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