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Morgner E, Holloway-Phillips M, Basler D, Nelson DB, Kahmen A. Effects of increasing atmospheric CO 2 on leaf water δ 18O values are small and are attenuated in grasses and amplified in dicotyledonous herbs and legumes when transferred to cellulose δ 18O values. New Phytol 2024. [PMID: 38575849 DOI: 10.1111/nph.19713] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Accepted: 03/08/2024] [Indexed: 04/06/2024]
Abstract
The oxygen isotope composition of cellulose (δ18O values) has been suggested to contain information on stomatal conductance (gs) responses to rising pCO2. The extent by which pCO2 affects leaf water and cellulose δ18O values (δ18OLW and δ18OC) and the isotope processes that determine pCO2 effects on δ18OLW and δ18OC are, however, unknown. We tested the effects of pCO2 on gs, δ18OLW and δ18OC in a glasshouse experiment, where six plant species were grown under pCO2 ranging from 200 to 500 ppm. Increasing pCO2 caused a decline in gs and an increase in δ18OLW, as expected. Importantly, the effects of pCO2 on gs and δ18OLW were small and pCO2 effects on δ18OLW were not directly transferred to δ18OC but were attenuated in grasses and amplified in dicotyledonous herbs and legumes. This is likely because of functional group-specific pCO2 effects on the model parameter pxpex. Our study highlights important uncertainties when using δ18OC as a proxy for gs. Specifically, pCO2-triggered gs effects on δ18OLW and δ18OC are possibly too small to be detected in natural settings and a pCO2 effect on pxpex may render the commonly assumed negative linkage between δ18OC and gs to be incorrect, potentially confounding δ18OC based gs reconstructions.
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Affiliation(s)
- Eva Morgner
- Department of Environmental Sciences - Botany, University of Basel, 4056, Basel, Switzerland
| | | | - David Basler
- Department of Environmental Sciences - Botany, University of Basel, 4056, Basel, Switzerland
| | - Daniel B Nelson
- Department of Environmental Sciences - Botany, University of Basel, 4056, Basel, Switzerland
| | - Ansgar Kahmen
- Department of Environmental Sciences - Botany, University of Basel, 4056, Basel, Switzerland
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2
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Vitali V, Schuler P, Holloway-Phillips M, D'Odorico P, Guidi C, Klesse S, Lehmann MM, Meusburger K, Schaub M, Zweifel R, Gessler A, Saurer M. Finding balance: Tree-ring isotopes differentiate between acclimation and stress-induced imbalance in a long-term irrigation experiment. Glob Chang Biol 2024; 30:e17237. [PMID: 38488024 DOI: 10.1111/gcb.17237] [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: 10/20/2023] [Revised: 02/05/2024] [Accepted: 02/09/2024] [Indexed: 03/19/2024]
Abstract
Scots pine (Pinus sylvestris L.) is a common European tree species, and understanding its acclimation to the rapidly changing climate through physiological, biochemical or structural adjustments is vital for predicting future growth. We investigated a long-term irrigation experiment at a naturally dry forest in Switzerland, comparing Scots pine trees that have been continuously irrigated for 17 years (irrigated) with those for which irrigation was interrupted after 10 years (stop) and non-irrigated trees (control), using tree growth, xylogenesis, wood anatomy, and carbon, oxygen and hydrogen stable isotope measurements in the water, sugars and cellulose of plant tissues. The dendrochronological analyses highlighted three distinct acclimation phases to the treatments: irrigated trees experienced (i) a significant growth increase in the first 4 years of treatment, (ii) high growth rates but with a declining trend in the following 8 years and finally (iii) a regression to pre-irrigation growth rates, suggesting the development of a new growth limitation (i.e. acclimation). The introduction of the stop treatment resulted in further growth reductions to below-control levels during the third phase. Irrigated trees showed longer growth periods and lower tree-ring δ13 C values, reflecting lower stomatal restrictions than control trees. Their strong tree-ring δ18 O and δ2 H (O-H) relationship reflected the hydrological signature similarly to the control. On the contrary, the stop trees had lower growth rates, conservative wood anatomical traits, and a weak O-H relationship, indicating a physiological imbalance. Tree vitality (identified by crown transparency) significantly modulated growth, wood anatomical traits and tree-ring δ13 C, with low-vitality trees of all treatments performing similarly regardless of water availability. We thus provide quantitative indicators for assessing physiological imbalance and tree acclimation after environmental stresses. We also show that tree vitality is crucial in shaping such responses. These findings are fundamental for the early assessment of ecosystem imbalances and decline under climate change.
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Affiliation(s)
- Valentina Vitali
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Philipp Schuler
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | | | - Petra D'Odorico
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Claudia Guidi
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Stefan Klesse
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Marco M Lehmann
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Katrin Meusburger
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Marcus Schaub
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Roman Zweifel
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
| | - Arthur Gessler
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
- Institute of Terrestrial Ecosystems, ETH Zurich, Zurich, Switzerland
| | - Matthias Saurer
- Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
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Holloway-Phillips M, Cernusak LA, Nelson DB, Lehmann MM, Tcherkez G, Kahmen A. Covariation between oxygen and hydrogen stable isotopes declines along the path from xylem water to wood cellulose across an aridity gradient. New Phytol 2023; 240:1758-1773. [PMID: 37680025 DOI: 10.1111/nph.19248] [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: 01/17/2023] [Accepted: 08/16/2023] [Indexed: 09/09/2023]
Abstract
Oxygen and hydrogen isotopes of cellulose in plant biology are commonly used to infer environmental conditions, often from time series measurements of tree rings. However, the covariation (or the lack thereof) between δ18 O and δ2 H in plant cellulose is still poorly understood. We compared plant water, and leaf and branch cellulose from dominant tree species across an aridity gradient in Northern Australia, to examine how δ18 O and δ2 H relate to each other and to mean annual precipitation (MAP). We identified a decline in covariation from xylem to leaf water, and onwards from leaf to branch wood cellulose. Covariation in leaf water isotopic enrichment (Δ) was partially preserved in leaf cellulose but not branch wood cellulose. Furthermore, whilst δ2 H was well-correlated between leaf and branch, there was an offset in δ18 O between organs that increased with decreasing MAP. Our findings strongly suggest that postphotosynthetic isotope exchange with water is more apparent for oxygen isotopes, whereas variable kinetic and nonequilibrium isotope effects add complexity to interpreting metabolic-induced δ2 H patterns. Varying oxygen isotope exchange in wood and leaf cellulose must be accounted for when δ18 O is used to reconstruct climatic scenarios. Conversely, comparing δ2 H and δ18 O patterns may reveal environmentally induced shifts in metabolism.
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Affiliation(s)
- Meisha Holloway-Phillips
- Department of Environmental Sciences-Botany, University of Basel, 4056, Basel, Switzerland
- Research Unit of Forest Dynamics, Research Group of Ecosystem Ecology, Stable Isotope Research Centre, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903, Birmendsorf, Switzerland
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4878, Australia
| | - Daniel B Nelson
- Department of Environmental Sciences-Botany, University of Basel, 4056, Basel, Switzerland
| | - Marco M Lehmann
- Research Unit of Forest Dynamics, Research Group of Ecosystem Ecology, Stable Isotope Research Centre, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903, Birmendsorf, Switzerland
| | - Guillaume Tcherkez
- Research School of Biology, College of Science, Australian National University, Canberra, ACT, 2601, Australia
- Institut de Recherche en Horticulture et Semences, Université d'Angers, INRAe, 42 rue Georges Morel, 49070, Beaucouzé, France
| | - Ansgar Kahmen
- Department of Environmental Sciences-Botany, University of Basel, 4056, Basel, Switzerland
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Tcherkez G, Holloway-Phillips M, Lothier J, Limami A, Ball MC. Revisiting yield in terms of phloem transport to grains suggests phloem sap movement might be homeostatic. Plant Cell Environ 2023. [PMID: 37303253 DOI: 10.1111/pce.14646] [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] [Grants] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 05/30/2023] [Accepted: 06/04/2023] [Indexed: 06/13/2023]
Abstract
Phloem sap transport, velocity and allocation have been proposed to play a role in physiological limitations of crop yield, along with photosynthetic activity or water use efficiency. Although there is clear evidence that carbon allocation to grains effectively drives yield in cereals like wheat (as reflected by the harvest index), the influence of phloem transport rate and velocity is less clear. Here, we took advantage of previously published data on yield, respiration, carbon isotope composition, nitrogen content and water consumption in winter wheat cultivars grown across several sites with or without irrigation, to express grain production in terms of phloem sucrose transport and compare with xylem water transport. Our results suggest that phloem sucrose transport rate follows the same relationship with phloem N transport regardless of irrigation conditions and cultivars, and seems to depend mostly on grain weight (i.e., mg per grain). Depending on the assumption made for phloem sap sucrose concentration, either phloem sap velocity or its proportionality coefficient to xylem velocity change little with environmental conditions. Taken as a whole, phloem transport from leaves to grains seems to be homeostatic within a narrow range of values and following relationships with other plant physiological parameters across cultivars and conditions. This suggests that phloem transport per se is not a limitation for yield in wheat but rather, is controlled to sustain grain filling.
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Affiliation(s)
- Guillaume Tcherkez
- Research School of Biology, Australian National University, Canberra, Australia
- Institut de Recherche en Horticulture et Semences, Université d'Angers, Beaucouzé, France
| | - Meisha Holloway-Phillips
- Department of Environmental Sciences, Bernoulli Straße 32, University of Basel, Basel, Switzerland
| | - Jérémy Lothier
- Institut de Recherche en Horticulture et Semences, Université d'Angers, Beaucouzé, France
| | - Anis Limami
- Institut de Recherche en Horticulture et Semences, Université d'Angers, Beaucouzé, France
| | - Marilyn C Ball
- Research School of Biology, Australian National University, Canberra, Australia
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Baan J, Holloway-Phillips M, Nelson DB, Kahmen A. The metabolic sensitivity of hydrogen isotope fractionation differs between plant compounds. Phytochemistry 2023; 207:113563. [PMID: 36528118 DOI: 10.1016/j.phytochem.2022.113563] [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: 04/12/2022] [Revised: 12/10/2022] [Accepted: 12/11/2022] [Indexed: 06/17/2023]
Abstract
Hydrogen stable isotope analyses (δ2H) of plant derived organic compounds are a useful tool for ecological, environmental, and palaeoclimatological research. However, during organic compound synthesis, variable biosynthetic 2H-fractionation has been suggested to occur as a result of changes in plant carbon fluxes. So far, inference has been based on examining the δ2H patterns of plant compounds along environmental gradients, among plant species, and between plant organs. In an alternative approach, we used four plant species with four different types of mutations that cause impaired starch synthesis to assess whether variability in carbon metabolism affects the biosynthetic 2H-fractionation during cellulose, phytol, and acetogenic lipid synthesis. We found that mutants with impaired starch synthesis always had higher cellulose and phytol δ2H values compared to the wild type. By contrast, 2H-fractionation during acetogenic lipid biosynthesis generally did not show strong metabolic sensitivity. We rationalise these differences by considering the biosynthetic pathway of each compound and the likely source of the variable isotope fractionation. In different organic compounds, the sensitivity of variable biosynthetic 2H-fractionation to changes in C-metabolism depends on incorporation of specific H atoms from precursor molecules. As such, we determined that the similar increase in cellulose and phytol δ2H values as an effect of impaired starch synthesis most likely originates in triose-phosphates.
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Affiliation(s)
- Jochem Baan
- University of Basel, Department of Environmental Sciences - Botany, Schönbeinstrasse 6, 4056, Basel, Switzerland.
| | - Meisha Holloway-Phillips
- University of Basel, Department of Environmental Sciences - Botany, Schönbeinstrasse 6, 4056, Basel, Switzerland
| | - Daniel B Nelson
- University of Basel, Department of Environmental Sciences - Botany, Schönbeinstrasse 6, 4056, Basel, Switzerland
| | - Ansgar Kahmen
- University of Basel, Department of Environmental Sciences - Botany, Schönbeinstrasse 6, 4056, Basel, Switzerland
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Holloway-Phillips M, Baan J, Nelson DB, Lehmann MM, Tcherkez G, Kahmen A. Species variation in the hydrogen isotope composition of leaf cellulose is mostly driven by isotopic variation in leaf sucrose. Plant Cell Environ 2022; 45:2636-2651. [PMID: 35609972 DOI: 10.1111/pce.14362] [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] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 05/11/2022] [Indexed: 06/15/2023]
Abstract
Experimental approaches to isolate drivers of variation in the carbon-bound hydrogen isotope composition (δ2 H) of plant cellulose are rare and current models are limited in their application. This is in part due to a lack in understanding of how 2 H-fractionations in carbohydrates differ between species. We analysed, for the first time, the δ2 H of leaf sucrose along with the δ2 H and δ18 O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. The δ2 H of sucrose explained 66% of the δ2 H variation in cellulose (R2 = 0.66), which was associated with species differences in the 2 H enrichment of sucrose above leaf water ( ε sucrose <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0001" wiley:location="equation/pce14362-math-0001.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mtext>\unicode{x003B5}</mtext><mtext>sucrose</mtext></msub></mrow></math> : -126% to -192‰) rather than by variation in leaf water δ2 H itself. ε sucrose <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0002" wiley:location="equation/pce14362-math-0002.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mtext>\unicode{x003B5}</mtext><mtext>sucrose</mtext></msub></mrow></math> was positively related to dark respiration (R2 = 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover time of carbohydrates (R2 = 0.38), but only when ε sucrose <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0003" wiley:location="equation/pce14362-math-0003.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><msub><mi mathvariant="normal">\unicode{x003B5}</mi><mtext>sucrose</mtext></msub></mrow></mrow></math> was fixed to the literature accepted value of - 171 <math altimg="urn:x-wiley:01407791:media:pce14362:pce14362-math-0004" wiley:location="equation/pce14362-math-0004.png" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>\unicode{x02212}</mo><mn>171</mn></mrow></mrow></math> ‰. No relation was found between isotopic exchange of hydrogen and oxygen, suggesting large differences in the processes shaping post-photosynthetic fractionation between elements. Our results strongly advocate that for robust applications of the leaf cellulose hydrogen isotope model, parameterization utilizing δ2 H of sugars is needed.
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Affiliation(s)
| | - Jochem Baan
- Department of Environmental Science-Botany, University of Basel, Basel, Switzerland
| | - Daniel B Nelson
- Department of Environmental Science-Botany, University of Basel, Basel, Switzerland
| | - Marco M Lehmann
- Research Unit of Forest Dynamics, Research Group of Ecosystem Ecology, Stable Isotope Research Centre, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmendsorf, Switzerland
| | - Guillaume Tcherkez
- Research School of Biology, College of Science, Australian National University, Canberra, Australian Capital Territory, Australia
- Institut de Recherche en Horticulture et Semences, Université d'Angers, INRAe, Beaucouzé, France
| | - Ansgar Kahmen
- Department of Environmental Science-Botany, University of Basel, Basel, Switzerland
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Wong SC, Canny MJ, Holloway-Phillips M, Stuart-Williams H, Cernusak LA, Márquez DA, Farquhar GD. Humidity gradients in the air spaces of leaves. Nat Plants 2022; 8:971-978. [PMID: 35941216 DOI: 10.1038/s41477-022-01202-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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.
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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.
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Holloway-Phillips M. Agriculture futurist: Don Ort. Plant Physiol 2021; 185:16-20. [PMID: 33631803 PMCID: PMC8133541 DOI: 10.1093/plphys/kiaa024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
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Schuldt B, Buras A, Arend M, Vitasse Y, Beierkuhnlein C, Damm A, Gharun M, Grams TE, Hauck M, Hajek P, Hartmann H, Hiltbrunner E, Hoch G, Holloway-Phillips M, Körner C, Larysch E, Lübbe T, Nelson DB, Rammig A, Rigling A, Rose L, Ruehr NK, Schumann K, Weiser F, Werner C, Wohlgemuth T, Zang CS, Kahmen A. A first assessment of the impact of the extreme 2018 summer drought on Central European forests. Basic Appl Ecol 2020. [DOI: 10.1016/j.baae.2020.04.003] [Citation(s) in RCA: 172] [Impact Index Per Article: 43.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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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. Nat Plants 2020; 6:245-258. [PMID: 32170287 DOI: 10.1038/s41477-020-0606-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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.
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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
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Holloway-Phillips M. Variation in Xylem Resistance to Cavitation Explains Why Some Leaves Within a Canopy Are More Likely to Die under Water Stress. Plant Physiol 2020; 182:450-452. [PMID: 31908323 PMCID: PMC6945845 DOI: 10.1104/pp.19.01394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
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Holloway-Phillips M, Cernusak LA, Stuart-Williams H, Ubierna N, Farquhar GD. Two-Source δ 18O Method to Validate the CO 18O-Photosynthetic Discrimination Model: Implications for Mesophyll Conductance. Plant Physiol 2019; 181:1175-1190. [PMID: 31519787 PMCID: PMC6836848 DOI: 10.1104/pp.19.00633] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 09/05/2019] [Indexed: 05/10/2023]
Abstract
Theoretical models of photosynthetic isotopic discrimination of CO2 (13C and 18O) are commonly used to estimate mesophyll conductance (g m). This requires making simplifying assumptions and assigning parameter values so that g m can be solved for as the residual term. Uncertainties in g m estimation occur due to measurement noise and assumptions not holding, including parameter uncertainty and model parametrization. Uncertainties in the 13C model have been explored previously, but there has been little testing undertaken to determine the reliability of g m estimates from the 18O model (g m18). In this study, we exploited the action of carbonic anhydrase in equilibrating CO2 with leaf water and manipulated the observed photosynthetic discrimination (Δ18O) by changing the oxygen isotopic composition of the source gas CO2 and water vapor. We developed a two-source δ18O method, whereby two measurements of Δ18O were obtained for a leaf with its gas-exchange characteristics otherwise unchanged. Measurements were performed in broad bean (Vicia faba) and Algerian oak (Quercus canariensis) in response to light and vapor pressure deficit. Despite manipulating the Δ18O by over 100‰, in most cases we observed consistency in the calculated g m18, providing confidence in the measurements and model theory. Where there were differences in g m18 estimates between source-gas measurements, we explored uncertainty associated with two model assumptions (the isotopic composition of water at the sites of CO2-water exchange, and the humidity of the leaf internal airspace) and found evidence for both. Finally, we provide experimental guidelines to minimize the sensitivity of g m18 estimates to measurement errors. The two-source δ18O method offers a flexible tool for model parameterization and provides an opportunity to refine our understanding of leaf water and CO2 fluxes.
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Affiliation(s)
- Meisha Holloway-Phillips
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601 Australia
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Queensland, 4870 Australia
| | - Hilary Stuart-Williams
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601 Australia
| | - Nerea Ubierna
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601 Australia
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601 Australia
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Ubierna N, Cernusak LA, Holloway-Phillips M, Busch FA, Cousins AB, Farquhar GD. Critical review: incorporating the arrangement of mitochondria and chloroplasts into models of photosynthesis and carbon isotope discrimination. Photosynth Res 2019; 141:5-31. [PMID: 30955143 DOI: 10.1007/s11120-019-00635-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [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: 11/17/2018] [Accepted: 03/07/2019] [Indexed: 06/09/2023]
Abstract
The arrangement of mitochondria and chloroplasts, together with the relative resistances of cell wall and chloroplast, determine the path of diffusion out of the leaf for (photo)respired CO2. Traditional photosynthesis models have assumed a tight arrangement of chloroplasts packed together against the cell wall with mitochondria located behind the chloroplasts, deep inside the cytosol. Accordingly, all (photo)respired CO2 must cross the chloroplast before diffusing out of the leaf. Different arrangements have recently been considered, where all or part of the (photo)respired CO2 diffuses through the cytosol without ever entering the chloroplast. Assumptions about the path for the (photo)respiratory flux are particularly relevant for the calculation of mesophyll conductance (gm). If (photo)respired CO2 can diffuse elsewhere besides the chloroplast, apparent gm is no longer a mere physical resistance but a flux-weighted variable sensitive to the ratio of (photo)respiration to net CO2 assimilation. We discuss existing photosynthesis models in conjunction with their treatment of the (photo)respiratory flux and present new equations applicable to the generalized case where (photo)respired CO2 can diffuse both into the chloroplast and through the cytosol. Additionally, we present a new generalized Δ13C model that incorporates this dual diffusion pathway. We assess how assumptions about the fate of (photo)respired CO2 affect the interpretation of photosynthetic data and the challenges it poses for the application of different models.
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Affiliation(s)
- Nerea Ubierna
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia.
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, QLD, Australia
| | | | - Florian A Busch
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia
| | - Asaph B Cousins
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-4236, USA
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Acton, ACT, 2601, Australia
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Holloway-Phillips M, Cernusak LA, Barbour M, Song X, Cheesman A, Munksgaard N, Stuart-Williams H, Farquhar GD. Leaf vein fraction influences the Péclet effect and 18 O enrichment in leaf water. Plant Cell Environ 2016; 39:2414-2427. [PMID: 27391079 DOI: 10.1111/pce.12792] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [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: 03/13/2016] [Revised: 06/22/2016] [Accepted: 06/23/2016] [Indexed: 06/06/2023]
Abstract
The process of evaporation results in the fractionation of water isotopes such that the lighter 16 O isotope preferentially escapes the gas phase leaving the heavier 18 O isotope to accumulate at the sites of evaporation. This applies to transpiration from a leaf with the degree of fractionation dependent on a number of environmental and physiological factors that are well understood. Nevertheless, the 18 O enrichment of bulk leaf water is often less than that predicted for the sites of evaporation. The advection of less enriched water in the transpiration stream has been suggested to limit the back diffusion of enriched evaporative site water (Péclet effect); however, evidence for this effect has been varied. In sampling across a range of species with different vein densities and saturated water contents, we demonstrate the importance of accounting for the relative 'pool' sizes of the vascular and mesophyll water for the interpretation of a Péclet effect. Further, we provide strong evidence for a Péclet signal within the xylem that if unaccounted for can lead to confounding of the estimated enrichment within the mesophyll water. This has important implications for understanding variation in the effective path length of the mesophyll and hence potentially the δ18 O of organic matter.
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Affiliation(s)
- Meisha Holloway-Phillips
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia.
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Queensland, Australia
| | - Margaret Barbour
- Centre for Carbon, Water and Food, Faculty of Agriculture and Environment, The University of Sydney, Camden, New South Wales, Australia
| | - Xin Song
- Centre for Carbon, Water and Food, Faculty of Agriculture and Environment, The University of Sydney, Camden, New South Wales, Australia
| | - Alexander Cheesman
- College of Science and Engineering, James Cook University, Cairns, Queensland, Australia
| | - Niels Munksgaard
- College of Science and Engineering, James Cook University, Cairns, Queensland, Australia
- Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory, Australia
| | - Hilary Stuart-Williams
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Graham D Farquhar
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
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Givnish TJ, Wong SC, Stuart-Williams H, Holloway-Phillips M, Farquhar GD. Determinants of maximum tree height inEucalyptusspecies along a rainfall gradient in Victoria, Australia. Ecology 2014. [DOI: 10.1890/14-0240.1] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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