1
|
Ogée J. A step forward in the study of photosynthetic limitation by CO 2 diffusion into the mesophyll. THE NEW PHYTOLOGIST 2024. [PMID: 38887143 DOI: 10.1111/nph.19910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2024]
Affiliation(s)
- Jérôme Ogée
- INRAE, Bordeaux Science Agro, UMR 1391 ISPA, Villenave d'Ornon, 33140, France
| |
Collapse
|
2
|
Cernusak LA, Wong SC, Stuart-Williams H, Márquez DA, Pontarin N, Farquhar GD. Unsaturation in the air spaces of leaves and its implications. PLANT, CELL & ENVIRONMENT 2024. [PMID: 38867619 DOI: 10.1111/pce.15001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2024] [Revised: 05/26/2024] [Accepted: 05/31/2024] [Indexed: 06/14/2024]
Abstract
Modern plant physiological theory stipulates that the resistance to water movement from plants to the atmosphere is overwhelmingly dominated by stomata. This conception necessitates a corollary assumption-that the air spaces in leaves must be nearly saturated with water vapour; that is, with a relative humidity that does not decline materially below unity. As this idea became progressively engrained in scientific discourse and textbooks over the last century, observations inconsistent with this corollary assumption were occasionally reported. Yet, evidence of unsaturation gained little traction, with acceptance of the prevailing framework motivated by three considerations: (1) leaf water potentials measured by either thermocouple psychrometry or the Scholander pressure chamber are largely consistent with the framework; (2) being able to assume near saturation of intercellular air spaces was transformational to leaf gas exchange analysis; and (3) there has been no obvious mechanism to explain a variable, liquid-phase resistance in the leaf mesophyll. Here, we review the evidence that refutes the assumption of universal, near saturation of air spaces in leaves. Refining the prevailing paradigm with respect to this assumption provides opportunities for identifying and developing mechanisms for increased plant productivity in the face of increasing evaporative demand imposed by global climate change.
Collapse
Affiliation(s)
- Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Queensland, Australia
| | - Suan Chin Wong
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Hilary Stuart-Williams
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Diego A Márquez
- School of Biosciences, University of Birmingham, Birmingham, UK
| | - Nicole Pontarin
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| |
Collapse
|
3
|
Rao S, Liu T, Cernusak LA, Song X. Harnessing photosynthetic C 18O 16O discrimination dynamics under leaf water nonsteady state to estimate mesophyll conductance: a new, regression-based method. THE NEW PHYTOLOGIST 2024. [PMID: 38634162 DOI: 10.1111/nph.19767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2023] [Accepted: 03/27/2024] [Indexed: 04/19/2024]
Abstract
Mesophyll conductance (gm) is a crucial plant trait that can significantly limit photosynthesis. Measurement of photosynthetic C18O16O discrimination (Δ18O) has proved to be the only viable means of resolving gm in both C3 and C4 plants. However, the currently available methods to exploit Δ18O for gm estimation are error prone due to their inadequacy in constraining the degree of oxygen isotope exchange (θ) during mesophyll CO2 hydration. Here, we capitalized on experimental manipulation of leaf water isotopic dynamics to establish a novel, nonsteady state, regression-based approach for simultaneous determination of gm and θ from online Δ18O measurements. We demonstrated the methodological and theoretical robustness of this new Δ18O-gm estimation approach and showed through measurements on several C3 and C4 species that this approach can serve as a benchmark method against which to identify previously-unrecognized biases of the existing Δ18O-gm methods. Our results highlight the unique value of this nonsteady state-based approach for contributing to ongoing efforts toward quantitative understanding of mesophyll conductance for crop yield improvement and carbon cycle modeling.
Collapse
Affiliation(s)
- Sen Rao
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
- Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China
| | - Tao Liu
- College of Resources, Sichuan Agricultural University, Chengdu, 611130, China
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4878, Australia
| | - Xin Song
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
| |
Collapse
|
4
|
Jain P, Huber AE, Rockwell FE, Sen S, Holbrook NM, Stroock AD. Localized measurements of water potential reveal large loss of conductance in living tissues of maize leaves. PLANT PHYSIOLOGY 2024; 194:2288-2300. [PMID: 38128552 PMCID: PMC10980393 DOI: 10.1093/plphys/kiad679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 10/25/2023] [Accepted: 11/30/2023] [Indexed: 12/23/2023]
Abstract
The water status of the living tissue in leaves between the xylem and stomata (outside xylem zone (OXZ) plays a critical role in plant function and global mass and energy balance but has remained largely inaccessible. We resolve the local water relations of OXZ tissue using a nanogel reporter of water potential (ψ), AquaDust, that enables an in situ, nondestructive measurement of both ψ of xylem and highly localized ψ at the terminus of transpiration in the OXZ. Working in maize (Zea mays L.), these localized measurements reveal gradients in the OXZ that are several folds larger than those based on conventional methods and values of ψ in the mesophyll apoplast well below the macroscopic turgor loss potential. We find a strong loss of hydraulic conductance in both the bundle sheath and the mesophyll with decreasing xylem potential but not with evaporative demand. Our measurements suggest the OXZ plays an active role in regulating the transpiration path, and our methods provide the means to study this phenomenon.
Collapse
Affiliation(s)
- Piyush Jain
- Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Annika E Huber
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Fulton E Rockwell
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Sabyasachi Sen
- Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Noel Michele Holbrook
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Abraham D Stroock
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
- School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY 14853, USA
| |
Collapse
|
5
|
Diao H, Cernusak LA, Saurer M, Gessler A, Siegwolf RTW, Lehmann MM. Uncoupling of stomatal conductance and photosynthesis at high temperatures: mechanistic insights from online stable isotope techniques. THE NEW PHYTOLOGIST 2024; 241:2366-2378. [PMID: 38303410 DOI: 10.1111/nph.19558] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Accepted: 01/12/2024] [Indexed: 02/03/2024]
Abstract
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 H2 O 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.
Collapse
Affiliation(s)
- Haoyu Diao
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, 8903, Switzerland
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4879, Australia
| | - Matthias Saurer
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, 8903, Switzerland
| | - Arthur Gessler
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, 8903, Switzerland
- Institute of Terrestrial Ecosystems, ETH Zurich, Zurich, 8092, Switzerland
| | - Rolf T W Siegwolf
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, 8903, Switzerland
| | - Marco M Lehmann
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, 8903, Switzerland
| |
Collapse
|
6
|
Márquez DA, Stuart-Williams H, Cernusak LA, Farquhar GD. Assessing the CO 2 concentration at the surface of photosynthetic mesophyll cells. THE NEW PHYTOLOGIST 2023; 238:1446-1460. [PMID: 36751879 DOI: 10.1111/nph.18784] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 01/21/2023] [Indexed: 06/18/2023]
Abstract
We present a robust estimation of the CO2 concentration at the surface of photosynthetic mesophyll cells (cw ), applicable under reasonable assumptions of assimilation distribution within the leaf. We used Capsicum annuum, Helianthus annuus and Gossypium hirsutumas model plants for our experiments. We introduce calculations to estimate cw using independent adaxial and abaxial gas exchange measurements, and accounting for the mesophyll airspace resistances. The cw was lower than adaxial and abaxial estimated intercellular CO2 concentrations (ci ). Differences between cw and the ci of each surface were usually larger than 10 μmol mol-1 . Differences between adaxial and abaxial ci ranged from a few μmol mol-1 to almost 50 μmol mol-1 , where the largest differences were found at high air saturation deficits (ASD). Differences between adaxial and abaxial ci and the ci estimated by mixing both fluxes ranged from -30 to +20 μmol mol-1 , where the largest differences were found under high ASD or high ambient CO2 concentrations. Accounting for cw improves the information that can be extracted from gas exchange experiments, allowing a more detailed description of the CO2 and water vapor gradients within the leaf.
Collapse
Affiliation(s)
- Diego A Márquez
- Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia
| | - Hilary Stuart-Williams
- Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4878, Australia
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia
| |
Collapse
|
7
|
Rockwell FE, Holbrook NM, Jain P, Huber AE, Sen S, Stroock AD. Extreme undersaturation in the intercellular airspace of leaves: a failure of Gaastra or Ohm? ANNALS OF BOTANY 2022; 130:301-316. [PMID: 35896037 PMCID: PMC9486918 DOI: 10.1093/aob/mcac094] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 07/21/2022] [Indexed: 06/09/2023]
Abstract
BACKGROUND Recent reports of extreme levels of undersaturation in internal leaf air spaces have called into question one of the foundational assumptions of leaf gas exchange analysis, that leaf air spaces are effectively saturated with water vapour at leaf surface temperature. Historically, inferring the biophysical states controlling assimilation and transpiration from the fluxes directly measured by gas exchange systems has presented a number of challenges, including: (1) a mismatch in scales between the area of flux measurement, the biochemical cellular scale and the meso-scale introduced by the localization of the fluxes to stomatal pores; (2) the inaccessibility of the internal states of CO2 and water vapour required to define conductances; and (3) uncertainties about the pathways these internal fluxes travel. In response, plant physiologists have adopted a set of simplifying assumptions that define phenomenological concepts such as stomatal and mesophyll conductances. SCOPE Investigators have long been concerned that a failure of basic assumptions could be distorting our understanding of these phenomenological conductances, and the biophysical states inside leaves. Here we review these assumptions and historical efforts to test them. We then explore whether artefacts in analysis arising from the averaging of fluxes over macroscopic leaf areas could provide alternative explanations for some part, if not all, of reported extreme states of undersaturation. CONCLUSIONS Spatial heterogeneities can, in some cases, create the appearance of undersaturation in the internal air spaces of leaves. Further refinement of experimental approaches will be required to separate undersaturation from the effects of spatial variations in fluxes or conductances. Novel combinations of current and emerging technologies hold promise for meeting this challenge.
Collapse
Affiliation(s)
| | - N Michele Holbrook
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA
| | - Piyush Jain
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Annika E Huber
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Sabyasachi Sen
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Abraham D Stroock
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| |
Collapse
|
8
|
Wong SC, Canny MJ, Holloway-Phillips M, Stuart-Williams H, Cernusak LA, Márquez DA, Farquhar GD. Humidity gradients in the air spaces of leaves. NATURE PLANTS 2022; 8:971-978. [PMID: 35941216 DOI: 10.1038/s41477-022-01202-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 06/22/2022] [Indexed: 06/15/2023]
Abstract
Stomata are orifices that connect the drier atmosphere with the interconnected network of more humid air spaces that surround the cells within a leaf. Accurate values of the humidities inside the substomatal cavity, wi, and in the air, wa, are needed to estimate stomatal conductance and the CO2 concentration in the internal air spaces of leaves. Both are vital factors in the understanding of plant physiology and climate, ecological and crop systems. However, there is no easy way to measure wi directly. Out of necessity, wi has been taken as the saturation water vapour concentration at leaf temperature, wsat, and applied to the whole leaf intercellular air spaces. We explored the occurrence of unsaturation by examining gas exchange of leaves exposed to various magnitudes of wsat - wa, or Δw, using a double-sided, clamp-on chamber, and estimated degrees of unsaturation from the gradient of CO2 across the leaf that was required to sustain the rate of CO2 assimilation through the upper surface. The relative humidity in the substomatal cavities dropped to about 97% under mild Δw and as dry as around 80% when Δw was large. Measurements of the diffusion of noble gases across the leaf indicated that there were still regions of near 100% humidity distal from the stomatal pores. We suggest that as Δw increases, the saturation edge retreats into the intercellular air spaces, accompanied by the progressive closure of mesophyll aquaporins to maintain the cytosolic water potential.
Collapse
Affiliation(s)
- Suan Chin Wong
- Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Martin J Canny
- Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Meisha Holloway-Phillips
- Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
- Physiological Plant Ecology Group, Department of Environmental Sciences-Botany, University of Basel, Basel, Switzerland
| | - Hilary Stuart-Williams
- Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Queensland, Australia
| | - Diego A Márquez
- Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Graham D Farquhar
- Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia.
| |
Collapse
|
9
|
Cernusak LA, Barbeta A, Bush RT, Eichstaedt (Bögelein) R, Ferrio JP, Flanagan LB, Gessler A, Martín‐Gómez P, Hirl RT, Kahmen A, Keitel C, Lai C, Munksgaard NC, Nelson DB, Ogée J, Roden JS, Schnyder H, Voelker SL, Wang L, Stuart‐Williams H, Wingate L, Yu W, Zhao L, Cuntz M. Do 2 H and 18 O in leaf water reflect environmental drivers differently? THE NEW PHYTOLOGIST 2022; 235:41-51. [PMID: 35322882 PMCID: PMC9322340 DOI: 10.1111/nph.18113] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 02/06/2022] [Indexed: 06/01/2023]
Abstract
We compiled hydrogen and oxygen stable isotope compositions (δ2 H and δ18 O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ2 H was more closely correlated with δ2 H of xylem water or atmospheric vapour, whereas leaf water δ18 O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ2 H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ18 O. We next expressed leaf water as isotopic enrichment above xylem water (Δ2 H and Δ18 O) to remove the impact of xylem water isotopic variation. For Δ2 H, leaf water still correlated with atmospheric vapour, whereas Δ18 O showed no such correlation. This was explained by covariance between air relative humidity and the Δ18 O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2 H and 18 O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.
Collapse
Affiliation(s)
- Lucas A. Cernusak
- College of Science and EngineeringJames Cook UniversityCairnsQld4878Australia
| | - Adrià Barbeta
- BEECADepartment of Evolutionary Biology, Ecology and Environmental SciencesUniversitat de BarcelonaBarcelonaCatalonia08028Spain
| | - Rosemary T. Bush
- Department of Earth and Planetary SciencesNorthwestern UniversityEvanstonIL60208USA
| | | | - Juan Pedro Ferrio
- ARAID‐Departamento de Sistemas AgrícolasForestales y Medio AmbienteCentro de Investigación y Tecnología Agroalimentaria de Aragón (CITA)Zaragoza50059Spain
| | - Lawrence B. Flanagan
- Department of Biological SciencesUniversity of LethbridgeLethbridgeABT1K 3M4Canada
| | - Arthur Gessler
- WSL Swiss Federal Institute for Forest, Snow and Landscape ResearchBirmensdorf8903Switzerland
| | - Paula Martín‐Gómez
- INRAEBordeaux Sciences AgroUMR ISPAVillenave d'Ornon 33140France
- Centre Tecnològic Forestal de Catalunya (CTFC)SolsonaCatalonia25280Spain
| | - Regina T. Hirl
- Technische Universität MünchenLehrstuhl für GrünlandlehreFreising‐Weihenstephan85354Germany
| | - Ansgar Kahmen
- Department of Environmental Sciences–BotanyUniversity of BaselBasel4056Switzerland
| | - Claudia Keitel
- School of Life and Environmental SciencesSydney Institute of AgricultureThe University of SydneyCamdenNSW2006Australia
| | - Chun‐Ta Lai
- Department of BiologySan Diego State UniversitySan DiegoCA92182USA
| | - Niels C. Munksgaard
- College of Science and EngineeringJames Cook UniversityCairnsQld4878Australia
| | - Daniel B. Nelson
- Department of Environmental Sciences–BotanyUniversity of BaselBasel4056Switzerland
| | - Jérôme Ogée
- INRAEBordeaux Sciences AgroUMR ISPAVillenave d'Ornon 33140France
| | - John S. Roden
- Department of BiologySouthern Oregon UniversityAshlandOR97520USA
| | - Hans Schnyder
- Technische Universität MünchenLehrstuhl für GrünlandlehreFreising‐Weihenstephan85354Germany
| | - Steven L. Voelker
- College of Forest Resources and Environmental ScienceMichigan Technological UniversityHoughtonMI49931USA
| | - Lixin Wang
- Department of Earth SciencesIndiana University–Purdue University IndianapolisIndianapolisIND46202USA
| | | | - Lisa Wingate
- INRAEBordeaux Sciences AgroUMR ISPAVillenave d'Ornon 33140France
| | - Wusheng Yu
- Key Laboratory of Tibetan Environmental Changes and Land Surface ProcessesInstitute of Tibetan Plateau ResearchChinese Academy of SciencesBeijing100101China
| | - Liangju Zhao
- Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying CapacityCollege of Urban and Environmental SciencesNorthwest UniversityXi'an 710127China
| | - Matthias Cuntz
- Université de LorraineAgroParisTechINRAEUMR SilvaNancy54000France
| |
Collapse
|
10
|
Farquhar GD, Griffani DS, Barbour MM. The effects on isotopic composition of leaf water and transpiration of adding a gas-exchange cuvette. PLANT, CELL & ENVIRONMENT 2021; 44:2844-2857. [PMID: 33938016 DOI: 10.1111/pce.14076] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 04/24/2021] [Accepted: 04/26/2021] [Indexed: 06/12/2023]
Abstract
An expression was earlier derived for the non-steady state isotopic composition of a leaf when the composition of the water entering the leaf was not necessarily the same as that of the water being transpired (Farquhar and Cernusak 2005). This was relevant to natural conditions because the associated time constant is typically sufficiently long to ensure that the leaf water composition and fluxes of the isotopologues are rarely steady. With the advent of laser-based measurements of isotopologues, leaves have been enclosed in cuvettes and time courses of fluxes recorded. The enclosure modifies the time constant by effectively increasing the resistance to the one-way gross flux out of the stomata because transpiration increases the vapour concentration within the chamber. The resistance is increased from stomatal and boundary layer in series, to stomata, boundary layer and chamber resistance, where the latter is given by the ratio of leaf area to the flow rate out of the chamber. An apparent change in concept from one-way to net flux, introduced by Song, Simonin, Loucos and Barbour (2015) is resolved, and shown to be unnecessary, but the value of their data is reinforced.
Collapse
Affiliation(s)
- Graham D Farquhar
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Danielle S Griffani
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Margaret M Barbour
- School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia
- Te Aka Mātuatua-School of Science, The University of Waikato, Hamilton, New Zealand
| |
Collapse
|
11
|
Adnew GA, Hofmann MEG, Pons TL, Koren G, Ziegler M, Lourens LJ, Röckmann T. Leaf scale quantification of the effect of photosynthetic gas exchange on Δ 47 of CO 2. Sci Rep 2021; 11:14023. [PMID: 34234170 PMCID: PMC8263724 DOI: 10.1038/s41598-021-93092-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 06/15/2021] [Indexed: 11/30/2022] Open
Abstract
The clumped isotope composition (Δ47, the anomaly of the mass 47 isotopologue relative to the abundance expected from a random isotope distribution) of CO2 has been suggested as an additional tracer for gross CO2 fluxes. However, the effect of photosynthetic gas exchange on Δ47 has not been directly determined and two indirect/conceptual studies reported contradicting results. In this study, we quantify the effect of photosynthetic gas exchange on Δ47 of CO2 using leaf cuvette experiments with one C4 and two C3 plants. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate the important roles of the Δ47 value of CO2 entering the leaf, kinetic fractionation as CO2 diffuses into, and out of the leaf and CO2–H2O isotope exchange with leaf water. We experimentally confirm the previously suggested dependence of Δ47 of CO2 in the air surrounding a leaf on the stomatal conductance and back-diffusion flux. Gas exchange can enrich or deplete the Δ47 of CO2 depending on the Δ47 of CO2 entering the leaf and the fraction of CO2 exchanged with leaf water and diffused back to the atmosphere, but under typical ambient conditions, it will lead to a decrease in Δ47.
Collapse
Affiliation(s)
- Getachew Agmuas Adnew
- Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands.
| | - Magdalena E G Hofmann
- Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands.,Picarro B.V., 's-Hertogenbosch, The Netherlands
| | - Thijs L Pons
- Institute of Environmental Biology, Utrecht University, Utrecht, The Netherlands
| | - Gerbrand Koren
- Meteorology and Air Quality Group, Wageningen University, Wageningen, The Netherlands
| | - Martin Ziegler
- Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
| | - Lucas J Lourens
- Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
| | - Thomas Röckmann
- Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands
| |
Collapse
|
12
|
Evans JR. Mesophyll conductance: walls, membranes and spatial complexity. THE NEW PHYTOLOGIST 2021; 229:1864-1876. [PMID: 33135193 DOI: 10.1111/nph.16968] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 08/28/2020] [Indexed: 06/11/2023]
Abstract
A significant resistance to CO2 diffusion is imposed by mesophyll tissue inside leaves. Mesophyll resistance, rm (or its reciprocal, mesophyll conductance, gm ), reduces the rate at which Rubisco can fix CO2 , increasing the water and nitrogen costs of carbon acquisition. gm varies in proportion to the surface area of chloroplasts exposed to intercellular airspace per unit leaf area. It also depends on the thickness and effective porosity of the cell wall and the CO2 permeabilities of membranes. As no measurements exist for the effective porosity of mesophyll cell walls, and CO2 permeability values are too low to account for observed rates of CO2 assimilation, conclusions from modelling must be treated with caution. There is great variation in the mesophyll resistance per unit chloroplast area for a given cell wall thickness, which may reflect differences in effective porosity. While apparent gm can vary with CO2 and irradiance, the underlying conductance at the cellular level may remain unchanged. Dynamic changes in apparent gm arise for spatial reasons and because chloroplasts differ in their photosynthetic composition and operate in different light environments. Measurements of the temperature sensitivity of membrane CO2 permeability are urgently needed to explain variation in temperature responses of gm .
Collapse
Affiliation(s)
- John R Evans
- ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| |
Collapse
|
13
|
Sonawane BV, Cousins AB. Mesophyll CO 2 conductance and leakiness are not responsive to short- and long-term soil water limitations in the C 4 plant Sorghum bicolor. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2020; 103:1590-1602. [PMID: 32438487 DOI: 10.1111/tpj.14849] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 04/30/2020] [Accepted: 05/05/2020] [Indexed: 05/13/2023]
Abstract
Breeding economically important C4 crops for enhanced whole-plant water-use efficiency (WUEplant ) is needed for sustainable agriculture. WUEplant is a complex trait and an efficient phenotyping method that reports on components of WUEplant , such as intrinsic water-use efficiency (WUEi , the rate of leaf CO2 assimilation relative to water loss via stomatal conductance), is needed. In C4 plants, theoretical models suggest that leaf carbon isotope composition (δ13 C), when the efficiency of the CO2 -concentrating mechanism (leakiness, ϕ) remains constant, can be used to screen for WUEi . The limited information about how ϕ responds to water limitations confines the application of δ13 C for WUEi screening of C4 crops. The current research aimed to test the response of ϕ to short- or long-term moderate water limitations, and the relationship of δ13 C with WUEi and WUEplant , by addressing potential mesophyll CO2 conductance (gm ) and biochemical limitations in the C4 plant Sorghum bicolor. We demonstrate that gm and ϕ are not responsive to short- or long-term water limitations. Additionally, δ13 C was not correlated with gas-exchange estimates of WUEi under short- and long-term water limitations, but showed a significant negative relationship with WUEplant . The observed association between the δ13 C and WUEplant suggests an intrinsic link of δ13 C with WUEi in this C4 plant, and can potentially be used as a screening tool for WUEplant in sorghum.
Collapse
Affiliation(s)
- Balasaheb V Sonawane
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| |
Collapse
|
14
|
Grossiord C, Buckley TN, Cernusak LA, Novick KA, Poulter B, Siegwolf RTW, Sperry JS, McDowell NG. Plant responses to rising vapor pressure deficit. THE NEW PHYTOLOGIST 2020; 226:1550-1566. [PMID: 32064613 DOI: 10.1111/nph.16485] [Citation(s) in RCA: 327] [Impact Index Per Article: 81.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 02/04/2020] [Indexed: 05/24/2023]
Abstract
Recent decades have been characterized by increasing temperatures worldwide, resulting in an exponential climb in vapor pressure deficit (VPD). VPD has been identified as an increasingly important driver of plant functioning in terrestrial biomes and has been established as a major contributor in recent drought-induced plant mortality independent of other drivers associated with climate change. Despite this, few studies have isolated the physiological response of plant functioning to high VPD, thus limiting our understanding and ability to predict future impacts on terrestrial ecosystems. An abundance of evidence suggests that stomatal conductance declines under high VPD and transpiration increases in most species up until a given VPD threshold, leading to a cascade of subsequent impacts including reduced photosynthesis and growth, and higher risks of carbon starvation and hydraulic failure. Incorporation of photosynthetic and hydraulic traits in 'next-generation' land-surface models has the greatest potential for improved prediction of VPD responses at the plant- and global-scale, and will yield more mechanistic simulations of plant responses to a changing climate. By providing a fully integrated framework and evaluation of the impacts of high VPD on plant function, improvements in forecasting and long-term projections of climate impacts can be made.
Collapse
Affiliation(s)
- Charlotte Grossiord
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
- École Polytechnique Fédérale de Lausanne EPFL, School of Architecture, Civil and Environmental Engineering ENAC, 1015, Lausanne, Switzerland
| | - Thomas N Buckley
- Department of Plant Sciences, University of California, Davis, Davis, CA, 95616, USA
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4814, Australia
| | - Kimberly A Novick
- School of Public and Environmental Affairs, Indiana University Bloomington, Bloomington, IN, 47405, USA
| | - Benjamin Poulter
- Biospheric Sciences Lab, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
| | - Rolf T W Siegwolf
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
| | - John S Sperry
- Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA
| | - Nate G McDowell
- Earth Systems Science Division, Pacific Northwest National Laboratory, Richland, WA, 99354, USA
| |
Collapse
|
15
|
Busch FA, Holloway-Phillips M, Stuart-Williams H, Farquhar GD. Revisiting carbon isotope discrimination in C 3 plants shows respiration rules when photosynthesis is low. NATURE PLANTS 2020; 6:245-258. [PMID: 32170287 DOI: 10.1038/s41477-020-0606-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 01/23/2020] [Indexed: 05/12/2023]
Abstract
Stable isotopes are commonly used to study the diffusion of CO2 within photosynthetic plant tissues. The standard method used to interpret the observed preference for the lighter carbon isotope in C3 photosynthesis involves the model of Farquhar et al., which relates carbon isotope discrimination to physical and biochemical processes within the leaf. However, under many conditions the model returns unreasonable results for mesophyll conductance to CO2 diffusion (gm), especially when rates of photosynthesis are low. Here, we re-derive the carbon isotope discrimination model using modified assumptions related to the isotope effect of mitochondrial respiration. In particular, we treat the carbon pool associated with respiration as separate from the pool of primary assimilates. We experimentally test the model by comparing gm values measured with different CO2 source gases varying in their isotopic composition, and show that our new model returns matching gm values that are much more reasonable than those obtained with the previous model. We use our results to discuss CO2 diffusion properties within the mesophyll.
Collapse
Affiliation(s)
- Florian A Busch
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia.
| | - Meisha Holloway-Phillips
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia
- Department of Environmental Sciences, University of Basel, Basel, Switzerland
| | - Hilary Stuart-Williams
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia
| | - Graham D Farquhar
- Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, Australian Capital Territory, Australia
| |
Collapse
|
16
|
Cousins AB, Mullendore DL, Sonawane BV. Recent developments in mesophyll conductance in C3, C4, and crassulacean acid metabolism plants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2020; 101:816-830. [PMID: 31960507 DOI: 10.1111/tpj.14664] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2019] [Accepted: 12/19/2019] [Indexed: 05/24/2023]
Abstract
The conductance of carbon dioxide (CO2 ) from the substomatal cavities to the initial sites of CO2 fixation (gm ) can significantly reduce the availability of CO2 for photosynthesis. There have been many recent reviews on: (i) the importance of gm for accurately modelling net rates of CO2 assimilation, (ii) on how leaf biochemical and anatomical factors influence gm , (iii) the technical limitation of estimating gm , which cannot be directly measured, and (iv) how gm responds to long- and short-term changes in growth and measurement environmental conditions. Therefore, this review will highlight these previous publications but will attempt not to repeat what has already been published. We will instead initially focus on the recent developments on the two-resistance model of gm that describe the potential of photorespiratory and respiratory CO2 released within the mitochondria to diffuse directly into both the chloroplast and the cytosol. Subsequently, we summarize recent developments in the three-dimensional (3-D) reaction-diffusion models and 3-D image analysis that are providing new insights into how the complex structure and organization of the leaf influences gm . Finally, because most of the reviews and literature on gm have traditionally focused on C3 plants we review in the final sections some of the recent developments, current understanding and measurement techniques of gm in C4 and crassulacean acid metabolism (CAM) plants. These plants have both specialized leaf anatomy and either a spatially or temporally separated CO2 concentrating mechanisms (C4 and CAM, respectively) that influence how we interpret and estimate gm compared with a C3 plants.
Collapse
Affiliation(s)
- Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Daniel L Mullendore
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Balasaheb V Sonawane
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| |
Collapse
|
17
|
Julkowska MM. Keep it Steamy: Improved Quantification of the Humidity within the Leaf. PLANT PHYSIOLOGY 2019; 181:1396. [PMID: 31767789 PMCID: PMC6878022 DOI: 10.1104/pp.19.01275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
|
18
|
Cernusak LA, Goldsmith GR, Arend M, Siegwolf RTW. Effect of Vapor Pressure Deficit on Gas Exchange in Wild-Type and Abscisic Acid-Insensitive Plants. PLANT PHYSIOLOGY 2019; 181:1573-1586. [PMID: 31562233 PMCID: PMC6878010 DOI: 10.1104/pp.19.00436] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 09/08/2019] [Indexed: 05/25/2023]
Abstract
Stomata control the gas exchange of terrestrial plant leaves, and are therefore essential to plant growth and survival. We investigated gas exchange responses to vapor pressure deficit (VPD) in two gray poplar (Populus × canescens) lines: wild type and abscisic acid-insensitive (abi1) with functionally impaired stomata. Transpiration rate in abi1 increased linearly with VPD, up to about 2 kPa. Above this, sharply declining transpiration was followed by leaf death. In contrast, wild type showed a steady or slightly declining transpiration rate up to VPD of nearly 7 kPa, and fully recovered photosynthetic function afterward. There were marked differences in discrimination against 13CO2 (Δ13C) and C18OO (Δ18O) between abi1 and wild-type plants. The Δ13C indicated that intercellular CO2 concentrations decreased with VPD in wild-type plants, but not in abi1 plants. The Δ18O reflected progressive stomatal closure in wild type in response to increasing VPD; however, in abi1, stomata remained open and oxygen atoms of CO2 continued to exchange with 18O enriched leaf water. Coupled measurements of Δ18O and gas exchange were used to estimate intercellular vapor pressure, e i In wild-type leaves, there was no evidence of unsaturation of e i, even at VPD above 6 kPa. In abi1 leaves, e i approached 0.6 times saturation vapor pressure before the precipitous decline in transpiration rate. For wild type, a sensitive stomatal response to increasing VPD was pivotal in preventing unsaturation of e i In abi1, after taking unsaturation into account, stomatal conductance increased with increasing VPD, consistent with a disabled active response of guard cell osmotic pressure.
Collapse
Affiliation(s)
- Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Queensland 4879, Australia
| | - Gregory R Goldsmith
- Ecosystem Fluxes and Stable Isotope Research Group, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Matthias Arend
- Physiological Plant Ecology Group, University of Basel, 4001 Basel, Switzerland
| | - Rolf T W Siegwolf
- Ecosystem Fluxes and Stable Isotope Research Group, Paul Scherrer Institute, 5232 Villigen, Switzerland
| |
Collapse
|