Journal
AGRICULTURAL AND FOREST METEOROLOGY
Volume 189, Issue -, Pages 2-10Publisher
ELSEVIER
DOI: 10.1016/j.agrformet.2013.12.007
Keywords
Stomatal control; Temperature response; Plant water use; Elevated CO2
Categories
Funding
- NSW government Climate Action Grant [NSW T07/CAG/016]
- Australian Government's Department of Climate Change for the Hawkesbury Forest Experiment
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Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure deficit (D). The mechanisms for the decrease in E at high D, known as the 'apparent feed-forward response', are strongly debated but explanations to date have exclusively focused on hydraulic processes. However, stomata also respond to signals related to photosynthesis. We investigated whether the apparent feed-forward response of E to D in the field can be explained by the response of photosynthesis to temperature (T), which normally co-varies with D in field conditions. As photosynthesis decreases with increasing T past its optimum, it may drive a decrease in stomatal conductance (g(s)) that is additional to the response of g, to increasing D alone. If this additional decrease is sufficiently steep and coupling between A and gs occurs, it could cause an overall decrease in E with increasing D. We tested this mechanism using a gas exchange model applied to leaf-scale and whole-tree CO2 and H2O fluxes measured on Eucalyptus saligna growing in whole-tree chambers. A peaked response of E to D was observed at both leaf and whole-tree scales. We found that this peaked response was matched by a gas exchange model only when T effects on photosynthesis were incorporated. We conclude that field-based studies of the relationship between E and D need to consider signals related to changing photosynthetic rates in addition to purely hydraulic mechanisms. (C) 2014 Elsevier B.V. All rights reserved.
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