Uncoupling of stomatal conductance and photosynthesis at high temperatures: mechanistic insights from online stable isotope techniques

Diao, Haoyu, Cernusak, Lucas A., Saurer, Matthias, Gessler, Arthur, Siegwolf, Rolf T.W., and Lehmann, Marco M. (2024) Uncoupling of stomatal conductance and photosynthesis at high temperatures: mechanistic insights from online stable isotope techniques. New Phytologist, 241 (6). pp. 2366-2378.

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The strong covariation of temperature and vapour pressure deficit (VPD) in nature limits our understanding of the direct effects of temperature on leaf gas exchange. Stable isotopes in CO2 and H2O vapour provide mechanistic insight into physiological and biochemical processes during leaf gas exchange.

We conducted combined leaf gas exchange and online isotope discrimination measurements on four common European tree species across a leaf temperature range of 5–40°C, while maintaining a constant leaf-to-air VPD (0.8 kPa) without soil water limitation.

Above the optimum temperature for photosynthesis (30°C) under the controlled environmental conditions, stomatal conductance (gs) and net photosynthesis rate (An) decoupled across all tested species, with gs increasing but An decreasing. During this decoupling, mesophyll conductance (cell wall, plasma membrane and chloroplast membrane conductance) consistently and significantly decreased among species; however, this reduction did not lead to reductions in CO2 concentration at the chloroplast surface and stroma.

We question the conventional understanding that diffusional limitations of CO2 contribute to the reduction in photosynthesis at high temperatures. We suggest that stomata and mesophyll membranes could work strategically to facilitate transpiration cooling and CO2 supply, thus alleviating heat stress on leaf photosynthetic function, albeit at the cost of reduced water-use efficiency.

Item ID: 82046
Item Type: Article (Research - C1)
ISSN: 1469-8137
Keywords: carbon isotopes, leaf gas exchange, mesophyll conductance, oxygen isotopes, vapour pressure deficit
Copyright Information: © 2024 New Phytologist Foundation. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Date Deposited: 21 Mar 2024 03:55
FoR Codes: 31 BIOLOGICAL SCIENCES > 3108 Plant biology > 310806 Plant physiology @ 100%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280102 Expanding knowledge in the biological sciences @ 100%
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