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Sun W, Maseyk K, Lett C, Seibt U. Restricted internal diffusion weakens transpiration-photosynthesis coupling during heatwaves: Evidence from leaf carbonyl sulphide exchange. Plant Cell Environ 2024; 47:1813-1833. [PMID: 38321806 DOI: 10.1111/pce.14840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 11/13/2023] [Accepted: 01/22/2024] [Indexed: 02/08/2024]
Abstract
Increasingly frequent and intense heatwaves threaten ecosystem health in a warming climate. However, plant responses to heatwaves are poorly understood. A key uncertainty concerns the intensification of transpiration when heatwaves suppress photosynthesis, known as transpiration-photosynthesis decoupling. Field observations of such decoupling are scarce, and the underlying physiological mechanisms remain elusive. Here, we use carbonyl sulphide (COS) as a leaf gas exchange tracer to examine potential mechanisms leading to transpiration-photosynthesis decoupling on a coast live oak in a southern California woodland in spring 2013. We found that heatwaves suppressed both photosynthesis and leaf COS uptake but increased transpiration or sustained it at non-heatwave levels throughout the day. Despite statistically significant decoupling between transpiration and photosynthesis, stomatal sensitivity to environmental factors did not change during heatwaves. Instead, midday photosynthesis during heatwaves was restricted by internal diffusion, as indicated by the lower internal conductance to COS. Thus, increased evaporative demand and nonstomatal limitation to photosynthesis act jointly to decouple transpiration from photosynthesis without altering stomatal sensitivity. Decoupling offered limited potential cooling benefits, questioning its effectiveness for leaf thermoregulation in xeric ecosystems. We suggest that adding COS to leaf and ecosystem flux measurements helps elucidate diverse physiological mechanisms underlying transpiration-photosynthesis decoupling.
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Affiliation(s)
- Wu Sun
- Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA
| | - Kadmiel Maseyk
- School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, UK
| | - Céline Lett
- Department of Environmental Research and Innovation, Luxembourg Institute of Science and Technology, Belvaux, Luxembourg
| | - Ulli Seibt
- Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
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Bellasio C, Stuart-Williams H, Farquhar GD, Flexas J. C 4 maize and sorghum are more sensitive to rapid dehydration than C 3 wheat and sunflower. New Phytol 2023; 240:2239-2252. [PMID: 37814525 DOI: 10.1111/nph.19299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 09/03/2023] [Indexed: 10/11/2023]
Abstract
The high productive potential, heat resilience, and greater water use efficiency of C4 over C3 plants attract considerable interest in the face of global warming and increasing population, but C4 plants are often sensitive to dehydration, questioning the feasibility of their wider adoption. To resolve the primary effect of dehydration from slower from secondary leaf responses originating within leaves to combat stress, we conducted an innovative dehydration experiment. Four crops grown in hydroponics were forced to a rapid yet controlled decrease in leaf water potential by progressively raising roots of out of the solution while measuring leaf gas exchange. We show that, under rapid dehydration, assimilation decreased more steeply in C4 maize and sorghum than in C3 wheat and sunflower. This reduction was due to a rise of nonstomatal limitation at triple the rate in maize and sorghum than in wheat and sunflower. Rapid reductions in assimilation were previously measured in numerous C4 species across both laboratory and natural conditions. Hence, we deduce that high sensitivity to rapid dehydration might stem from the disturbance of an intrinsic aspect of C4 bicellular photosynthesis. We posit that an obstruction to metabolite transport between mesophyll and bundle sheath cells could be the cause.
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Affiliation(s)
- Chandra Bellasio
- Laboratory of Theoretical and Applied Crop Ecophysiology, School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland
- Biology of Plants Under Mediterranean Conditions, Department of Biology, University of the Balearic Islands, Illes Balears, Palma, 07122, Spain
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia
| | | | - Graham D Farquhar
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia
| | - Jaume Flexas
- Biology of Plants Under Mediterranean Conditions, Department of Biology, University of the Balearic Islands, Illes Balears, Palma, 07122, Spain
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3
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Salvi AM, Gosetti SG, Smith DD, Adams MA, Givnish TJ, McCulloh KA. Hydroscapes, hydroscape plasticity and relationships to functional traits and mesophyll photosynthetic sensitivity to leaf water potential in Eucalyptus species. Plant Cell Environ 2022; 45:2573-2588. [PMID: 35706133 DOI: 10.1111/pce.14380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2022] [Revised: 06/06/2022] [Accepted: 06/13/2022] [Indexed: 06/15/2023]
Abstract
The isohydric-anisohydric continuum describes the relative stringency of stomatal control of leaf water potential (ψleaf ) during drought. Hydroscape area (HA)-the water potential landscape over which stomata regulate ψleaf -has emerged as a useful metric of the iso/anisohydric continuum because it is strongly linked to several hydraulic, photosynthetic and structural traits. Previous research on HA focused on broad ecological patterns involving several plant clades. Here we investigate the relationships between HA and climatic conditions and functional traits across ecologically diverse but closely related species while accounting for phylogeny. Across a macroclimatic moisture gradient, defined by the ratio of mean annual precipitation to mean annual pan evaporation (P/Ep ), HA decreased with increased P/Ep across 10 Eucalyptus species. Greater anisohydry reflects lower turgor loss points and greater hydraulic safety, mirroring global patterns. Larger HA coincides with mesophyll photosynthetic capacity that is more sensitive to ψleaf . Hydroscapes exhibit little plasticity in response to variation in water supply, and the extent of plasticity does not vary with P/Ep of native habitats. These findings strengthen the case that HA is a useful metric for characterizing drought tolerance and water-status regulation.
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Affiliation(s)
- Amanda M Salvi
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Sophia G Gosetti
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Duncan D Smith
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin, USA
- School of Ecosystem and Forest Sciences, University of Melbourne, Creswick, Victoria, Australia
- Swinburne University of Technology, Hawthorn, Victoria, Australia
| | - Mark A Adams
- Swinburne University of Technology, Hawthorn, Victoria, Australia
| | - Thomas J Givnish
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin, USA
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Dewar R, Hölttä T, Salmon Y. Exploring optimal stomatal control under alternative hypotheses for the regulation of plant sources and sinks. New Phytol 2022; 233:639-654. [PMID: 34637543 DOI: 10.1111/nph.17795] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 09/19/2021] [Indexed: 06/13/2023]
Abstract
Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade-off between leaf CO2 supply and NSLs, potentially involving source-sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain. We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading. All hypotheses led to realistic stomatal responses to light, CO2 and air humidity, including conservative behaviour for the intercellular-to-atmospheric CO2 concentration ratio. Sugar-regulated and water-regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor-regulated and sugar-regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris, Betula pendula, Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar-regulated NSLs and turgor-regulated unloading. Our analytical results provide a simple representation of stomatal responses to above-ground and below-ground environmental factors and sink activity.
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Affiliation(s)
- Roderick Dewar
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Plant Sciences Division, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Teemu Hölttä
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, PO Box 27, Latokartanonkaari 7, Helsinki, 00014, Finland
| | - Yann Salmon
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, PO Box 27, Latokartanonkaari 7, Helsinki, 00014, Finland
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Dewar R, Mauranen A, Mäkelä A, Hölttä T, Medlyn B, Vesala T. New insights into the covariation of stomatal, mesophyll and hydraulic conductances from optimization models incorporating nonstomatal limitations to photosynthesis. New Phytol 2018; 217:571-585. [PMID: 29086921 DOI: 10.1111/nph.14848] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 09/10/2017] [Indexed: 05/08/2023]
Abstract
Optimization models of stomatal conductance (gs ) attempt to explain observed stomatal behaviour in terms of cost--benefit tradeoffs. While the benefit of stomatal opening through increased CO2 uptake is clear, currently the nature of the associated cost(s) remains unclear. We explored the hypothesis that gs maximizes leaf photosynthesis, where the cost of stomatal opening arises from nonstomatal reductions in photosynthesis induced by leaf water stress. We analytically solved two cases, CAP and MES, in which reduced leaf water potential leads to reductions in carboxylation capacity (CAP) and mesophyll conductance (gm ) (MES). Both CAP and MES predict the same one-parameter relationship between the intercellular : atmospheric CO2 concentration ratio (ci /ca ) and vapour pressure deficit (VPD, D), viz. ci /ca ≈ ξ/(ξ + √D), as that obtained from previous optimization models, with the novel feature that the parameter ξ is determined unambiguously as a function of a small number of photosynthetic and hydraulic variables. These include soil-to-leaf hydraulic conductance, implying a stomatal closure response to drought. MES also predicts that gs /gm is closely related to ci /ca and is similarly conservative. These results are consistent with observations, give rise to new testable predictions, and offer new insights into the covariation of stomatal, mesophyll and hydraulic conductances.
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Affiliation(s)
- Roderick Dewar
- Plant Sciences Division, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Aleksanteri Mauranen
- Department of Physics, University of Helsinki, PO Box 68, Helsinki, FI-00014, Finland
| | - Annikki Mäkelä
- Department of Forest Sciences, University of Helsinki, PO Box 27, Helsinki, FI-00014, Finland
| | - Teemu Hölttä
- Department of Forest Sciences, University of Helsinki, PO Box 27, Helsinki, FI-00014, Finland
| | - Belinda Medlyn
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia
| | - Timo Vesala
- Department of Physics, University of Helsinki, PO Box 68, Helsinki, FI-00014, Finland
- Department of Forest Sciences, University of Helsinki, PO Box 27, Helsinki, FI-00014, Finland
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