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Jain P, Huber AE, Rockwell FE, Sen S, Holbrook NM, Stroock AD. New approaches to dissect leaf hydraulics reveal large gradients in living tissues of tomato leaves. THE NEW PHYTOLOGIST 2024; 242:453-465. [PMID: 38413216 DOI: 10.1111/nph.19585] [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: 08/22/2023] [Accepted: 01/22/2024] [Indexed: 02/29/2024]
Abstract
The water status of the living tissue in leaves is critical in determining plant function and global exchange of water and CO2. Despite significant advances in the past two decades, persistent questions remain about the tissue-specific origins of leaf hydraulic properties and their dependence on water status. We use a fluorescent nanoparticle reporter that provides water potential in the mesophyll apoplast adjacent to the epidermis of intact leaves to complement existing methods based on the Scholander Pressure Chamber (SPC). Working in tomato leaves, this approach provides access to the hydraulic conductance of the whole leaf, xylem, and outside-xylem tissues. These measurements show that, as stem water potential decreases, the water potential in the mesophyll apoplast can drop below that assessed with the SPC and can fall significantly below the turgor loss point of the leaf. We find that this drop in potential, dominated by the large loss (10-fold) of hydraulic conductance of the outside-xylem tissue, is not however strong enough to significantly limit transpiration. These observations highlight the need to reassess models of water transfer through the outside-xylem tissues, the potential importance of this tissue in regulating transpiration, and the power of new approaches for probing leaf hydraulics.
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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
| | - N 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
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2
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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.
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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
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3
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Momayyezi M, Borsuk AM, Brodersen CR, Gilbert ME, Théroux‐Rancourt G, Kluepfel DA, McElrone AJ. Desiccation of the leaf mesophyll and its implications for CO 2 diffusion and light processing. PLANT, CELL & ENVIRONMENT 2022; 45:1362-1381. [PMID: 35141930 PMCID: PMC9314819 DOI: 10.1111/pce.14287] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 01/18/2022] [Accepted: 01/24/2022] [Indexed: 05/09/2023]
Abstract
Leaves balance CO2 and radiative absorption while maintaining water transport to maximise photosynthesis. Related species with contrasting leaf anatomy can provide insights into inherent and stress-induced links between structure and function for commonly measured leaf traits for important crops. We used two walnut species with contrasting mesophyll anatomy to evaluate these integrated exchange processes under non-stressed and drought conditions using a combination of light microscopy, X-ray microCT, gas exchange, hydraulic conductance, and chlorophyll distribution profiles through leaves. Juglans regia had thicker palisade mesophyll, higher fluorescence in the palisade, and greater low-mesophyll porosity that were associated with greater gas-phase diffusion (gIAS ), stomatal and mesophyll (gm ) conductances and carboxylation capacity. More and highly-packed mesophyll cells and bundle sheath extensions (BSEs) in Juglans microcarpa led to higher fluorescence in the spongy and in proximity to the BSEs. Both species exhibited drought-induced reductions in mesophyll cell volume, yet the associated increases in porosity and gIAS were obscured by declines in biochemical activity that decreased gm . Inherent differences in leaf anatomy between the species were linked to differences in gas exchange, light absorption and photosynthetic capacity, and drought-induced changes in leaf structure impacted performance via imposing species-specific limitations to light absorption, gas exchange and hydraulics.
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Affiliation(s)
- Mina Momayyezi
- Department of Viticulture and EnologyUniversity of CaliforniaDavisCaliforniaUSA
| | - Aleca M. Borsuk
- School of the EnvironmentYale UniversityNew HavenConnecticutUSA
| | | | | | | | | | - Andrew J. McElrone
- Department of Viticulture and EnologyUniversity of CaliforniaDavisCaliforniaUSA
- USDA‐ARSCrops Pathology and Genetics Research UnitDavisCaliforniaUSA
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4
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A minimally disruptive method for measuring water potential in planta using hydrogel nanoreporters. Proc Natl Acad Sci U S A 2021; 118:2008276118. [PMID: 34074748 PMCID: PMC8201978 DOI: 10.1073/pnas.2008276118] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Gaps in our ability to document local water relations in leaves compromise our ability to build complete models of leaf and plant function and our understanding of ecophysiological phenomena, such as response and adaptation to drought. Macroscopically, leaf water potential has been shown to impact vegetative growth and yield, susceptibility to disease, and, in extreme drought, plant viability, making it a promising candidate trait to improve water-use efficiency in plants. In this paper, we present a nanoscale sensor (AquaDust) that provides minimally disruptive measurements of water potential in leaves of intact plants at high spatial and temporal resolution. This creates opportunities for improving our understanding of the mechanisms coupling variations in water potential to biological and physical processes. Leaf water potential is a critical indicator of plant water status, integrating soil moisture status, plant physiology, and environmental conditions. There are few tools for measuring plant water status (water potential) in situ, presenting a critical barrier for developing appropriate phenotyping (measurement) methods for crop development and modeling efforts aimed at understanding water transport in plants. Here, we present the development of an in situ, minimally disruptive hydrogel nanoreporter (AquaDust) for measuring leaf water potential. The gel matrix responds to changes in water potential in its local environment by swelling; the distance between covalently linked dyes changes with the reconfiguration of the polymer, leading to changes in the emission spectrum via Förster Resonance Energy Transfer (FRET). Upon infiltration into leaves, the nanoparticles localize within the apoplastic space in the mesophyll; they do not enter the cytoplasm or the xylem. We characterize the physical basis for AquaDust’s response and demonstrate its function in intact maize (Zea mays L.) leaves as a reporter of leaf water potential. We use AquaDust to measure gradients of water potential along intact, actively transpiring leaves as a function of water status; the localized nature of the reporters allows us to define a hydraulic model that distinguishes resistances inside and outside the xylem. We also present field measurements with AquaDust through a full diurnal cycle to confirm the robustness of the technique and of our model. We conclude that AquaDust offers potential opportunities for high-throughput field measurements and spatially resolved studies of water relations within plant tissues.
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5
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Liu X, Liu H, Gleason SM, Goldstein G, Zhu S, He P, Hou H, Li R, Ye Q. Water transport from stem to stomata: the coordination of hydraulic and gas exchange traits across 33 subtropical woody species. TREE PHYSIOLOGY 2019; 39:1665-1674. [PMID: 31314105 DOI: 10.1093/treephys/tpz076] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Revised: 04/28/2019] [Accepted: 06/23/2019] [Indexed: 06/10/2023]
Abstract
Coordination between sapwood-specific hydraulic conductivity (Ks) and stomatal conductance (gs) has been identified in previous studies; however, coordination between leaf hydraulic conductance (Kleaf) and gs, as well as between Kleaf and Ks is not always consistent. This suggests that there is a need to improve our understanding of the coordination among hydraulic and gas exchange traits. In this study, hydraulic traits (e.g., Ks and Kleaf) and gas exchange traits, including gs, transpiration (E) and net CO2 assimilation (Aarea), were measured across 33 co-occurring subtropical woody species. Kleaf was divided into two components: leaf hydraulic conductance inside the xylem (Kleaf-x) and outside the xylem (Kleaf-ox). We found that both Kleaf-x and Kleaf-ox were coordinated with gs and E, but the correlations between Kleaf-ox and gs (or E) were substantially weaker, and that Ks was coordinated with Kleaf-x, but not with Kleaf-ox. In addition, we found that Ks, Kleaf-x and Kleaf-ox together explained 63% of the variation in gs and 42% of the variation in Aarea across species, with Ks contributing the largest proportion of explanatory power, whereas Kleaf-ox contributed the least explanatory power. Our results demonstrate that the coordination between leaf water transport and gas exchange, as well as the hydraulic linkage between leaf and stem, were weakened by Kleaf-ox. This highlights the possibility that water transport efficiencies of stem and leaf xylem, rather than that of leaf tissues outside the xylem, are important determinants of stomatal conductance and photosynthetic capacity across species.
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Affiliation(s)
- Xiaorong Liu
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
- College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China
| | - Hui Liu
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
| | - Sean M Gleason
- Water Management and Systems Research Unit, USDA-ARS, Fort Collins, CO, USA
| | - Guillermo Goldstein
- Laboratorio de Ecología Funcional, Instituto de Ecologia Genetica y Evolucion, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Shidan Zhu
- Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning, China
| | - Pengcheng He
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
- College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China
| | - Hao Hou
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
- College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China
| | - Ronghua Li
- Institute of Tropical and Subtropical Ecology, South China Agricultural University, Guangzhou, China
| | - Qing Ye
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
- College of Life Sciences, Gannan Normal University, Ganzhou, China
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6
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Earles JM, Buckley TN, Brodersen CR, Busch FA, Cano FJ, Choat B, Evans JR, Farquhar GD, Harwood R, Huynh M, John GP, Miller ML, Rockwell FE, Sack L, Scoffoni C, Struik PC, Wu A, Yin X, Barbour MM. Embracing 3D Complexity in Leaf Carbon-Water Exchange. TRENDS IN PLANT SCIENCE 2019; 24:15-24. [PMID: 30309727 DOI: 10.1016/j.tplants.2018.09.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Revised: 09/06/2018] [Accepted: 09/11/2018] [Indexed: 06/08/2023]
Abstract
Leaves are a nexus for the exchange of water, carbon, and energy between terrestrial plants and the atmosphere. Research in recent decades has highlighted the critical importance of the underlying biophysical and anatomical determinants of CO2 and H2O transport, but a quantitative understanding of how detailed 3D leaf anatomy mediates within-leaf transport has been hindered by the lack of a consensus framework for analyzing or simulating transport and its spatial and temporal dynamics realistically, and by the difficulty of measuring within-leaf transport at the appropriate scales. We discuss how recent technological advancements now make a spatially explicit 3D leaf analysis possible, through new imaging and modeling tools that will allow us to address long-standing questions related to plant carbon-water exchange.
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Affiliation(s)
- J Mason Earles
- School of Forestry & Environmental Studies, Yale University, New Haven, CT 06511, USA; Equal contribution
| | - Thomas N Buckley
- Department of Plant Sciences, University of California Davis, CA 95916, USA; Equal contribution
| | - Craig R Brodersen
- School of Forestry & Environmental Studies, Yale University, New Haven, CT 06511, USA
| | - Florian A Busch
- Research School of Biology, Australian National University, Action, ACT 0200, Australia
| | - F Javier Cano
- Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW 2753, Australia
| | - Brendan Choat
- Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW 2753, Australia
| | - John R Evans
- Research School of Biology, Australian National University, Action, ACT 0200, Australia
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Action, ACT 0200, Australia
| | | | - Minh Huynh
- University of Sydney, Sydney, NSW 2006, Australia
| | - Grace P John
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, CA 90095, USA
| | - Megan L Miller
- College of Natural Resources, University of Idaho, Moscow, ID 83844, USA
| | - Fulton E Rockwell
- Department of Organism and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Lawren Sack
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, CA 90095, USA
| | - Christine Scoffoni
- Department of Biological Sciences, California State University Los Angeles, CA 90032, USA
| | - Paul C Struik
- Department of Plant Sciences, Wageningen University, Centre for Crop Systems Analysis, 6700 AK Wageningen, The Netherlands
| | - Alex Wu
- Centre for Plant Science, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Xinyou Yin
- Department of Plant Sciences, Wageningen University, Centre for Crop Systems Analysis, 6700 AK Wageningen, The Netherlands
| | - Margaret M Barbour
- University of Sydney, Sydney, NSW 2006, Australia; www.sydney.edu.au/science/people/margaret.barbour.
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7
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Rockwell FE, Gersony JT, Holbrook NM. Where does Münch flow begin? Sucrose transport in the pre-phloem path. CURRENT OPINION IN PLANT BIOLOGY 2018; 43:101-107. [PMID: 29704829 DOI: 10.1016/j.pbi.2018.04.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 03/30/2018] [Accepted: 04/09/2018] [Indexed: 06/08/2023]
Abstract
Current conceptions of sucrose export largely neglect the effect of transpiration-induced water potential gradients within leaf mesophyll, even as the mix of convection and diffusion in the pre-phloem path remains uncertain. It is also generally held that the relative importance of convection and diffusion in the pre-phloem path is controlled by the ratio of their respective mass transfer coefficients. Here, we consider pre-phloem sucrose transport in the presence of adverse water potential gradients, finding that whether convection impedes or aids sucrose delivery to the phloem is independent of the permeability of the plasmodesmata to bulk flow, and depends only on assimilation rate, path-length, and the diffusivity. For most tissues subject to transpiration, convection through plasmodesmata pushes sugar away from the phloem.
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Affiliation(s)
- Fulton E Rockwell
- Harvard University, Department of Organismic and Evolutionary Biology, 26 Oxford Street, Cambridge, MA 02138, USA
| | - Jessica T Gersony
- Harvard University, Department of Organismic and Evolutionary Biology, 26 Oxford Street, Cambridge, MA 02138, USA
| | - N Michele Holbrook
- Harvard University, Department of Organismic and Evolutionary Biology, 26 Oxford Street, Cambridge, MA 02138, USA.
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8
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Binks O, Meir P, Rowland L, da Costa ACL, Vasconcelos SS, de Oliveira AAR, Ferreira L, Mencuccini M. Limited acclimation in leaf anatomy to experimental drought in tropical rainforest trees. TREE PHYSIOLOGY 2016; 36:1550-1561. [PMID: 27614360 PMCID: PMC5165703 DOI: 10.1093/treephys/tpw078] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 07/12/2016] [Accepted: 07/16/2016] [Indexed: 05/10/2023]
Abstract
Dry periods are predicted to become more frequent and severe in the future in some parts of the tropics, including Amazonia, potentially causing reduced productivity, higher tree mortality and increased emissions of stored carbon. Using a long-term (12 year) through-fall exclusion (TFE) experiment in the tropics, we test the hypothesis that trees produce leaves adapted to cope with higher levels of water stress, by examining the following leaf characteristics: area, thickness, leaf mass per area, vein density, stomatal density, the thickness of palisade mesophyll, spongy mesophyll and both of the epidermal layers, internal cavity volume and the average cell sizes of the palisade and spongy mesophyll. We also test whether differences in leaf anatomy are consistent with observed differential drought-induced mortality responses among taxa, and look for relationships between leaf anatomy, and leaf water relations and gas exchange parameters. Our data show that trees do not produce leaves that are more xeromorphic in response to 12 years of soil moisture deficit. However, the drought treatment did result in increases in the thickness of the adaxial epidermis (TFE: 20.5 ± 1.5 µm, control: 16.7 ± 1.0 µm) and the internal cavity volume (TFE: 2.43 ± 0.50 mm3 cm-2, control: 1.77 ± 0.30 mm3 cm-2). No consistent differences were detected between drought-resistant and drought-sensitive taxa, although interactions occurred between drought-sensitivity status and drought treatment for the palisade mesophyll thickness (P = 0.034) and the cavity volume of the leaves (P = 0.025). The limited response to water deficit probably reflects a tight co-ordination between leaf morphology, water relations and photosynthetic properties. This suggests that there is little plasticity in these aspects of plant anatomy in these taxa, and that phenotypic plasticity in leaf traits may not facilitate the acclimation of Amazonian trees to the predicted future reductions in dry season water availability.
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Affiliation(s)
- Oliver Binks
- School of Geosciences, The Crew Building, The King's Buildings, University of Edinburgh, Edinburgh, EH9 3JN, UK
| | - Patrick Meir
- School of Geosciences, The Crew Building, The King's Buildings, University of Edinburgh, Edinburgh, EH9 3JN, UK
- Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Lucy Rowland
- College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4QD, UK
| | | | | | | | | | - Maurizio Mencuccini
- School of Geosciences, The Crew Building, The King's Buildings, University of Edinburgh, Edinburgh, EH9 3JN, UK
- ICREA at CREAF , 08193 Cerdanyola del Vallés, Spain
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9
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Kwang-Hua CR. Effects of activation energy and activation volume on the temperature-dependent viscosity of water. Phys Rev E 2016; 94:022424. [PMID: 27627349 DOI: 10.1103/physreve.94.022424] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Indexed: 06/06/2023]
Abstract
Water transport in a leaf is vulnerable to viscosity-induced changes. Recent research has suggested that these changes may be partially due to variation at the molecular scale, e.g., regulations via aquaporins, that induce reductions in leaf hydraulic conductance. What are the quantitative as well as qualitative changes in temperature-dependent viscosity due to the role of aquaporins in tuning activation energy and activation volume? Using the transition-state approach as well as the boundary perturbation method, we investigate temperature-dependent viscosity tuned by activation energy and activation volume. To validate our approach, we compare our numerical results with previous temperature-dependent viscosity measurements. The rather good fit between our calculations and measurements confirms our present approach. We have obtained critical parameters for the temperature-dependent (shear) viscosity of water that might be relevant to the increasing and reducing of leaf hydraulic conductance. These parameters are sensitive to temperature, activation energy, and activation volume. Once the activation energy increases, the (shear) viscosity of water increases. Our results also show that as the activation volume increases (say, 10^{-23}m^{3}), the (shear) viscosity of water decreases significantly and the latter induces the enhancing of leaf hydraulic conductance. Within the room-temperature regime, a small increase in the activation energy will increase the water viscosity or reduce the leaf hydraulic conductance. Our approach and results can be applied to diverse plant or leaf attributes.
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Affiliation(s)
- Chu Rainer Kwang-Hua
- Transfer Centre, 4/F, No. 16, Lane 21, Kwang-Hui Road, Taipei, Taiwan 116, Republic of China and Distribution Centre, Golmud Mansion, 33, Road Yingbin, Golmud 816000, China
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10
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Way DA, Oren R, Kroner Y. The space-time continuum: the effects of elevated CO2 and temperature on trees and the importance of scaling. PLANT, CELL & ENVIRONMENT 2015; 38:991-1007. [PMID: 25737035 DOI: 10.1111/pce.12527] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Revised: 01/15/2015] [Accepted: 02/17/2015] [Indexed: 05/27/2023]
Abstract
To predict how forests will respond to rising temperatures and atmospheric CO₂ concentrations, we need to understand how trees respond to both of these environmental factors. In this review, we discuss the importance of scaling, moving from leaf-level responses to those of the canopy, and from short-term to long-term responses of vegetation to climate change. While our knowledge of leaf-level, instantaneous responses of photosynthesis, respiration, stomatal conductance, transpiration and water-use efficiency to elevated CO₂ and temperature is quite good, our ability to scale these responses up to larger spatial and temporal scales is less developed. We highlight which physiological processes are least understood at various levels of study, and discuss how ignoring differences in the spatial or temporal scale of a physiological process impedes our ability to predict how forest carbon and water fluxes forests will be altered in the future. We also synthesize data from the literature to show that light respiration follows a generalized temperature response across studies, and that the light compensation point of photosynthesis is reduced by elevated growth CO₂. Lastly, we emphasize the need to move beyond single factorial experiments whenever possible, and to combine both CO₂ and temperature treatments in studies of tree performance.
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Affiliation(s)
- Danielle A Way
- Department of Biology, University of Western Ontario, London, ON, N6A 5B7, Canada; Nicholas School of the Environment, Duke University, Durham, NC, 27708, USA
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11
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Rockwell FE, Wheeler JK, Holbrook NM. Cavitation and its discontents: opportunities for resolving current controversies. PLANT PHYSIOLOGY 2014; 164:1649-60. [PMID: 24501002 PMCID: PMC3982731 DOI: 10.1104/pp.113.233817] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 02/02/2014] [Indexed: 05/18/2023]
Abstract
Cavitation has long been recognized as a key constraint on the structure and functional integrity of the xylem. Yet, recent results call into question how well we understand cavitation in plants. Here, we consider embolism formation in angiosperms at two scales. The first focuses on how air-seeding occurs at the level of pit membranes, raising the question of whether capillary failure is an appropriate physical model. The second addresses methodological uncertainties that affect our ability to infer the formation of embolism and its reversal in plant stems. Overall, our goal is to open up fresh perspectives on the structure-function relationships of xylem.
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Affiliation(s)
- Fulton E. Rockwell
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853 (F.E.R.); and
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 (J.K.W., N.M.H.)
| | - James K. Wheeler
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853 (F.E.R.); and
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 (J.K.W., N.M.H.)
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12
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Rockwell FE, Holbrook NM, Stroock AD. The competition between liquid and vapor transport in transpiring leaves. PLANT PHYSIOLOGY 2014; 164:1741-58. [PMID: 24572172 PMCID: PMC3982738 DOI: 10.1104/pp.114.236323] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
In leaves, the transpirational flux of water exits the veins as liquid and travels toward the stomata in both the vapor and liquid phases before exiting the leaf as vapor. Yet, whether most of the evaporation occurs from the vascular bundles (perivascular), from the photosynthetic mesophyll cells, or within the vicinity of the stomatal pore (peristomatal) remains in dispute. Here, a one-dimensional model of the competition between liquid and vapor transport is developed from the perspective of nonisothermal coupled heat and water molecule transport in a composite medium of airspace and cells. An analytical solution to the model is found in terms of the energy and transpirational fluxes from the leaf surfaces and the absorbed solar energy load, leading to mathematical expressions for the proportions of evaporation accounted for by the vascular, mesophyll, and epidermal regions. The distribution of evaporation in a given leaf is predicted to be variable, changing with the local environment, and to range from dominantly perivascular to dominantly peristomatal depending on internal leaf architecture, with mesophyll evaporation a subordinate component. Using mature red oak (Quercus rubra) trees, we show that the model can be solved for a specific instance of a transpiring leaf by combining gas-exchange data, anatomical measurements, and hydraulic experiments. We also investigate the effect of radiation load on the control of transpiration, the potential for condensation on the inside of an epidermis, and the impact of vapor transport on the hydraulic efficiency of leaf tissue outside the xylem.
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13
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Rockwell FE, Holbrook NM, Stroock AD. Leaf hydraulics II: vascularized tissues. J Theor Biol 2014; 340:267-84. [PMID: 24012489 DOI: 10.1016/j.jtbi.2013.08.027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Revised: 08/21/2013] [Accepted: 08/24/2013] [Indexed: 11/29/2022]
Abstract
Current models of leaf hydration employ an Ohm's law analogy of the leaf as an ideal capacitor, neglecting the resistance to flow between cells, or treat the leaf as a plane sheet with a source of water at fixed potential filling the mid-plane, neglecting the discrete placement of veins as well as their resistance. We develop a model of leaf hydration that considers the average conductance of the vascular network to a representative areole (region bounded by the vascular network), and represent the volume of tissue within the areole as a poroelastic composite of cells and air spaces. Solutions to the 3D flow problem are found by numerical simulation, and these results are then compared to 1D models with exact solutions for a range of leaf geometries, based on a survey of temperate woody plants. We then show that the hydration times given by these solutions are well approximated by a sum of the ideal capacitor and plane sheet times, representing the time for transport through the vasculature and tissue respectively. We then develop scaling factors relating this approximate solution to the 3D model, and examine the dependence of these scaling factors on leaf geometry. Finally, we apply a similar strategy to reduce the dimensions of the steady state problem, in the context of peristomatal transpiration, and consider the relation of transpirational gradients to equilibrium leaf water potential measurements.
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Affiliation(s)
- Fulton E Rockwell
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA.
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