51
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Skelton R, Diaz J. Quantifying losses of plant hydraulic function: seeing the forest, the trees and the xylem. TREE PHYSIOLOGY 2020; 40:285-289. [PMID: 31972024 DOI: 10.1093/treephys/tpz141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Revised: 12/11/2019] [Accepted: 12/18/2019] [Indexed: 06/10/2023]
Affiliation(s)
- Robert Skelton
- South African Environmental Observation Network, Fynbos Node, CBC Building, Rhodes Drive, Newlands, 7735, Cape Town, South Africa
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Jessica Diaz
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA, 94720, USA
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52
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Brodribb TJ, Carriquí M, Delzon S, McAdam SAM, Holbrook NM. Advanced vascular function discovered in a widespread moss. NATURE PLANTS 2020; 6:273-279. [PMID: 32170283 DOI: 10.1038/s41477-020-0602-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 01/22/2020] [Indexed: 05/13/2023]
Abstract
The evolution of terrestrial plants capable of growing upwards into the dry atmosphere profoundly transformed the Earth. A transition from small, 'non-vascular' bryophytes to arborescent vascular plants during the Devonian period is partially attributed to the evolutionary innovation of an internal vascular system capable of functioning under the substantial water tension associated with vascular water transport. Here, we show that vascular function in one of the most widespread living bryophytes (Polytrichum commune) exhibits strong functional parallels with the vascular systems of higher plants. These parallels include vascular conduits in Polytrichum that resist buckling while transporting water under tension, and leaves capable of regulating transpiration, permitting photosynthetic gas exchange without cavitation inside the vascular system. The advanced vascular function discovered in this tallest bryophyte family contrasts with the highly inefficient water use found in their leaves, emphasizing the importance of stomatal evolution enabling photosynthesis far above the soil surface.
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Affiliation(s)
- T J Brodribb
- School of Natural Sciences, University of Tasmania, Hobart, Tasmania, Australia.
| | - M Carriquí
- School of Natural Sciences, University of Tasmania, Hobart, Tasmania, Australia
- Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears - Instituto de Investigaciones Agroambientales y de la Economía del Agua, Palma, Spain
| | - S Delzon
- Université Bordeaux, BIOGECO, INRAE, Pessac, France
| | - S A M McAdam
- Purdue Center for Plant Biology, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA
| | - N M Holbrook
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
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53
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Smith‐Martin CM, Skelton RP, Johnson KM, Lucani C, Brodribb TJ. Lack of vulnerability segmentation among woody species in a diverse dry sclerophyll woodland community. Funct Ecol 2020. [DOI: 10.1111/1365-2435.13519] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Chris M. Smith‐Martin
- Department of Ecology, Evolution and Evolutionary Biology Columbia University New York NY USA
| | - Robert Paul Skelton
- South African Environmental Observation NetworkKirstenbosch Botanical Gardens Cape Town South Africa
| | - Kate M. Johnson
- School of Biological Sciences University of Tasmania Hobart TAS Australia
| | - Christopher Lucani
- School of Biological Sciences University of Tasmania Hobart TAS Australia
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54
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Li X, Smith R, Choat B, Tissue DT. Drought resistance of cotton (Gossypium hirsutum) is promoted by early stomatal closure and leaf shedding. FUNCTIONAL PLANT BIOLOGY : FPB 2020; 47:91-98. [PMID: 31825787 DOI: 10.1071/fp19093] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 09/06/2019] [Indexed: 05/11/2023]
Abstract
Water relations have been well documented in tree species, but relatively little is known about the hydraulic characteristics of crops. Here, we report on the hydraulic strategy of cotton (Gossypium hirsutum L.). Leaf gas exchange and in vivo embolism formation were monitored simultaneously on plants that were dried down in situ under controlled environment conditions, and xylem vulnerability to embolism of leaves, stems and roots was measured using intact plants. Water potential inducing 50% embolised vessels (P50) in leaves was significantly higher (less negative) than P50 of stems and roots, suggesting that leaves were the most vulnerable organ to embolism. Furthermore, the water potential generating stomatal closure (Pgs) was higher than required to generate embolism formation, and complete stomatal closure always preceded the onset of embolism with declining soil water content. Although protracted drought resulted in massive leaf shedding, stem embolism remained minimal even after ~90% leaf area was lost. Overall, cotton maintained hydraulic integrity during long-term drought stress through early stomatal closure and leaf shedding, thus exhibiting a drought avoidance strategy. Given that water potentials triggering xylem embolism are uncommon under field conditions, cotton is unlikely to experience hydraulic dysfunction except under extreme climates. Results of this study provide physiological evidence for drought resistance in cotton with regard to hydraulics, and may provide guidance in developing irrigation schedules during periods of water shortage.
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Affiliation(s)
- Ximeng Li
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
| | - Renee Smith
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
| | - Brendan Choat
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
| | - David T Tissue
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia; and Corresponding author.
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55
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Pratt RB, Castro V, Fickle JC, Jacobsen AL. Embolism resistance of different aged stems of a California oak species (Quercus douglasii): optical and microCT methods differ from the benchtop-dehydration standard. TREE PHYSIOLOGY 2020; 40:5-18. [PMID: 31553460 DOI: 10.1093/treephys/tpz092] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2019] [Revised: 07/30/2019] [Accepted: 08/15/2019] [Indexed: 06/10/2023]
Abstract
Vulnerability of xylem to embolism is an important trait related to drought resistance of plants. Methods continue to be developed and debated for measuring embolism. We tested three methods (benchtop dehydration/hydraulic, micro-computed tomography (microCT) and optical) for assessing the vulnerability to embolism of a native California oak species (Quercus douglasii Hook. & Arn.), including an analysis of three different stem ages. All three methods were found to significantly differ in their estimates, with a greater resistance to embolism as follows: microCT > optical > hydraulic. Careful testing was conducted for the hydraulic method to evaluate multiple known potential artifacts, and none was found. One-year-old stems were more resistant than older stems using microCT and optical methods, but not hydraulic methods. Divergence between the microCT and optical methods from the standard hydraulic method was consistent with predictions based on known errors when estimating theoretical losses in hydraulic function in both microCT and optical methods. When the goal of a study is to describe or predict losses in hydraulic conductivity, neither the microCT nor optical methods are reliable for accurately constructing vulnerability curves of stems; nevertheless, these methods may be useful if the goal of a study is to identify embolism events irrespective of hydraulic conductivity or hydraulic function.
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Affiliation(s)
- R Brandon Pratt
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA
| | - Viridiana Castro
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA
| | - Jaycie C Fickle
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA
| | - Anna L Jacobsen
- Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA
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56
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Fontes CG, Cavender-Bares J. Toward an integrated view of the 'elephant': unlocking the mysteries of water transport and xylem vulnerability in oaks. TREE PHYSIOLOGY 2020; 40:1-4. [PMID: 31748794 DOI: 10.1093/treephys/tpz116] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/21/2019] [Accepted: 10/24/2019] [Indexed: 06/10/2023]
Affiliation(s)
- Clarissa G Fontes
- Department of Ecology, Evolution and Behavior, University of Minnesota, 1479 Gortner Avenue, Saint Paul, MN 55108, USA
| | - Jeannine Cavender-Bares
- Department of Ecology, Evolution and Behavior, University of Minnesota, 1479 Gortner Avenue, Saint Paul, MN 55108, USA
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57
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Brodribb TJ, Cochard H, Dominguez CR. Measuring the pulse of trees; using the vascular system to predict tree mortality in the 21st century. CONSERVATION PHYSIOLOGY 2019; 7:coz046. [PMID: 31423313 PMCID: PMC6691484 DOI: 10.1093/conphys/coz046] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 06/10/2019] [Accepted: 06/18/2019] [Indexed: 06/01/2023]
Abstract
Tree mortality during hot and dry conditions presents a stark reminder of the vulnerability of plant species to climatic extremes. The current global warming trend makes predicting the impacts of hot/dry events on species survival an urgent task; yet, the standard tools for this purpose lack a physiological basis. This review examines a diversity of recent evidence demonstrating how physiological attributes of plant vascular systems can explain not only why trees die during drought, but also their distributional limits according to rainfall. These important advances in the science of plant water transport physiology provide the basis for new hydraulic models that can provide credible predictions of not only how but when, where and which species will be impacted by changes in rainfall and temperature in the future. Applying a recently developed hydraulic model using realistic parameters, we show that even apparently safe mesic forest in central France is predicted to experience major forest mortality before the end of the century.
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Affiliation(s)
- Timothy J Brodribb
- School of Natural Sciences, University of Tasmania, Bag 55 ,Hobart, Tasmania, Australia
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58
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Venturas MD, Pratt RB, Jacobsen AL, Castro V, Fickle JC, Hacke UG. Direct comparison of four methods to construct xylem vulnerability curves: Differences among techniques are linked to vessel network characteristics. PLANT, CELL & ENVIRONMENT 2019; 42:2422-2436. [PMID: 30997689 DOI: 10.1111/pce.13565] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 04/12/2019] [Accepted: 04/15/2019] [Indexed: 06/09/2023]
Abstract
During periods of dehydration, water transport through xylem conduits can become blocked by embolism formation. Xylem embolism compromises water supply to leaves and may lead to losses in productivity or plant death. Vulnerability curves (VCs) characterize plant losses in conductivity as xylem pressures decrease. VCs are widely used to characterize and predict plant water use at different levels of water availability. Several methodologies for constructing VCs exist and sometimes produce different results for the same plant material. We directly compared four VC construction methods on stems of black cottonwood (Populus trichocarpa), a model tree species: dehydration, centrifuge, X-ray-computed microtomography (microCT), and optical. MicroCT VC was the most resistant, dehydration and centrifuge VCs were intermediate, and optical VC was the most vulnerable. Differences among VCs were not associated with how cavitation was induced but were related to how losses in conductivity were evaluated: measured hydraulically (dehydration and centrifuge) versus evaluated from visual information (microCT and optical). Understanding how and why methods differ in estimating vulnerability to xylem embolism is important for advancing knowledge in plant ecophysiology, interpreting literature data, and using accurate VCs in water flux models for predicting plant responses to drought.
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Affiliation(s)
- Martin D Venturas
- School of Biological Sciences, University of Utah, Salt Lake City, 84112, Utah, USA
| | - R Brandon Pratt
- Department of Biology, California State University Bakersfield, Bakersfield, 93311, California, USA
| | - Anna L Jacobsen
- Department of Biology, California State University Bakersfield, Bakersfield, 93311, California, USA
| | - Viridiana Castro
- Department of Biology, California State University Bakersfield, Bakersfield, 93311, California, USA
| | - Jaycie C Fickle
- Department of Biology, California State University Bakersfield, Bakersfield, 93311, California, USA
| | - Uwe G Hacke
- Department of Renewable Resources, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada
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59
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Skelton RP, Anderegg LDL, Papper P, Reich E, Dawson TE, Kling M, Thompson SE, Diaz J, Ackerly DD. No local adaptation in leaf or stem xylem vulnerability to embolism, but consistent vulnerability segmentation in a North American oak. THE NEW PHYTOLOGIST 2019; 223:1296-1306. [PMID: 31059125 DOI: 10.1111/nph.15886] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 04/21/2019] [Indexed: 05/23/2023]
Abstract
Vulnerability to embolism varies between con-generic species distributed along aridity gradients, yet little is known about intraspecific variation and its drivers. Even less is known about intraspecific variation in tissues other than stems, despite results suggesting that roots, stems and leaves can differ in vulnerability. We hypothesized that intraspecific variation in vulnerability in leaves and stems is adaptive and driven by aridity. We quantified leaf and stem vulnerability of Quercus douglasii using the optical technique. To assess contributions of genetic variation and phenotypic plasticity to within-species variation, we quantified the vulnerability of individuals growing in a common garden, but originating from populations along an aridity gradient, as well as individuals from the same wild populations. Intraspecific variation in water potential at which 50% of total embolism in a tissue is observed (P50 ) was explained mostly by differences between individuals (>66% of total variance) and tissues (16%). There was little between-population variation in leaf/stem P50 in the garden, which was not related to site of origin aridity. Unexpectedly, we observed a positive relationship between wild individual stem P50 and aridity. Although there is no local adaptation and only minor phenotypic plasticity in leaf/stem vulnerability in Q. douglasii, high levels of potentially heritable variation within populations or strong environmental selection could contribute to adaptive responses under future climate change.
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Affiliation(s)
- Robert P Skelton
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
| | - Leander D L Anderegg
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
- Carnegie Science, Stanford University, Stanford, CA, 94305, USA
| | - Prahlad Papper
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
| | - Emma Reich
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
| | - Todd E Dawson
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
- Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, 94720, USA
| | - Matthew Kling
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
| | - Sally E Thompson
- Department of Civil and Environmental Engineering, University of California, Berkeley, CA, 94720, USA
- School of Civil, Environmental and Mining Engineering, University of Western Australia, Perth, 6907, Australia
| | - Jessica Diaz
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
| | - David D Ackerly
- Department of Integrative Biology, University of California, Berkeley, CA, 94720, USA
- Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, 94720, USA
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60
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Hochberg U, Ponomarenko A, Zhang YJ, Rockwell FE, Holbrook NM. Visualizing Embolism Propagation in Gas-Injected Leaves. PLANT PHYSIOLOGY 2019; 180:874-881. [PMID: 30842264 PMCID: PMC6548249 DOI: 10.1104/pp.18.01284] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 02/20/2019] [Indexed: 05/15/2023]
Abstract
Because the xylem in leaves is thought to be at the greatest risk of cavitation, reliable and efficient methods to characterize leaf xylem vulnerability are of interest. We report a method to generate leaf xylem vulnerability curves (VCs) by gas injection. Using optical light transmission, we visualized embolism propagation in grapevine (Vitis vinifera) and red oak (Quercus rubra) leaves injected with positive gas pressure. This resulted in a rapid, stepwise reduction of transmitted light, identical to that observed during leaf dehydration, confirming that the optical method detects gas bubbles and provides insights into the air-seeding hypothesis. In red oak, xylem VCs generated using gas injection were similar to those generated using bench dehydration, but indicated 50% loss of conductivity at lower tension (∼0.4 MPa) in grapevine. In determining VC, this method eliminates the need to ascertain xylem tension, thus avoiding potential errors in water potential estimations. It is also much faster (1 h per VC). However, severing the petiole and applying high-pressure gas could affect air-seeding and the generated VC. We discuss potential artifacts arising from gas injection and recommend comparison of this method with a more standard procedure before it is assumed to be suitable for a given species.
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Affiliation(s)
- Uri Hochberg
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
- ARO Volcani Center, Institute of Soil, Water and Environmental Sciences, Bet Dagan, 7505101 Israel
| | - Alexandre Ponomarenko
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
| | - Yong-Jiang Zhang
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
- School of Biology and Ecology, University of Maine, Orono, Maine 04469
| | - Fulton E Rockwell
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
| | - N Michele Holbrook
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138
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61
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Skelton RP. Injecting New Life into a Classic Technique. PLANT PHYSIOLOGY 2019; 180:706-707. [PMID: 31160528 PMCID: PMC6548244 DOI: 10.1104/pp.19.00500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Affiliation(s)
- Robert P Skelton
- Department of Integrative Biology, University of California Berkeley, Berkeley, California 94720
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62
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Brodersen CR, Roddy AB, Wason JW, McElrone AJ. Functional Status of Xylem Through Time. ANNUAL REVIEW OF PLANT BIOLOGY 2019; 70:407-433. [PMID: 30822114 DOI: 10.1146/annurev-arplant-050718-100455] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Water transport in vascular plants represents a critical component of terrestrial water cycles and supplies the water needed for the exchange of CO2 in the atmosphere for photosynthesis. Yet, many fundamental principles of water transport are difficult to assess given the scale and location of plant xylem. Here we review the mechanistic principles that underpin long-distance water transport in vascular plants, with a focus on woody species. We also discuss the recent development of noninvasive tools to study the functional status of xylem networks in planta. Limitations of current methods to detect drought-induced xylem blockages (e.g., embolisms) and quantify corresponding declines in sap flow, and the coordination of hydraulic dysfunction with other physiological processes are assessed. Future avenues of research focused on cross-validation of plant hydraulics methods are discussed, as well as a proposed fundamental shift in the theory and methodology used to characterize and measure plant water use.
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Affiliation(s)
- Craig R Brodersen
- School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA;
| | - Adam B Roddy
- School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA;
| | - Jay W Wason
- School of Forest Resources, University of Maine, Orono, Maine 04469, USA
| | - Andrew J McElrone
- US Department of Agriculture, Agricultural Research Service, Davis, California 95616, USA
- Department of Viticulture and Enology, University of California, Davis, California 95616, USA
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63
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Konrad W, Katul G, Roth-Nebelsick A, Jensen KH. Xylem functioning, dysfunction and repair: a physical perspective and implications for phloem transport. TREE PHYSIOLOGY 2019; 39:243-261. [PMID: 30299503 DOI: 10.1093/treephys/tpy097] [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: 05/31/2018] [Revised: 07/31/2018] [Accepted: 08/08/2018] [Indexed: 05/02/2023]
Abstract
Xylem and phloem are the two main conveyance systems in plants allowing exchanges of water and carbohydrates between roots and leaves. While each system has been studied in isolation for well over a century, the coupling and coordination between them remains the subject of inquiry and active research and frames the scope of the review here. Using a set of balance equations, hazards of bubble formation and their role in shaping xylem pressure and its corollary impact on phloem pressure and sugar transport are featured. The behavior of an isolated and freely floating air bubble within the xylem is first analyzed so as to introduce key principles such as the Helmholtz free energy and its links to embryonic bubble sizes. These principles are extended by considering bubbles filled with water vapor and air arising from air seeding. Using this framework, key results about stability and hazards of bubbles in contact with xylem walls are discussed. A chemical equilibrium between phloem and xylem systems is then introduced to link xylem and osmotic pressures. The consequences of such a link for sugar concentration needed to sustain efficient phloem transport by osmosis in the loading zone is presented. Catastrophic cases where phloem dysfunction occurs are analyzed in terms of xylem function and its vulnerability to cavitation. A link between operating pressures in the soil system bounded by field capacity and wilting points and maintenance of phloem functioning are discussed as conjectures to be tested in the future.
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Affiliation(s)
- Wilfried Konrad
- Department of Geosciences, University of Tübingen, Hoelderlinstrasse 12, Tübingen, Germany
- Institute of Botany, Technische Universität Dresden, Zellescher Weg 20b, Dresden, Germany
| | - Gabriel Katul
- Nicholas School of the Environment and Earth Sciences, Levine Science Research Center, Duke University, Durham, NC, USA
| | - Anita Roth-Nebelsick
- Deptartment of Palaeontology, State Museum of Natural History Stuttgart, Rosenstein 1, Stuttgart, Germany
| | - Kaare H Jensen
- Department of Physics, Technical University of Denmark, Fysikvej Building 309, Kgs. Lyngby, Denmark
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64
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John GP, Henry C, Sack L. Leaf rehydration capacity: Associations with other indices of drought tolerance and environment. PLANT, CELL & ENVIRONMENT 2018; 41:2638-2653. [PMID: 29978483 DOI: 10.1111/pce.13390] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2017] [Accepted: 06/19/2018] [Indexed: 06/08/2023]
Abstract
Clarifying the mechanisms of leaf and whole plant drought responses is critical to predict the impacts of ongoing climate change. The loss of rehydration capacity has been used for decades as a metric of leaf dehydration tolerance but has not been compared with other aspects of drought tolerance. We refined methods for quantifying the percent loss of rehydration capacity (PLRC), and for 18 Southern California woody species, we determined the relative water content and leaf water potential at PLRC of 10%, 25%, and 50%, and, additionally, the PLRC at important stages of dehydration including stomatal closure and turgor loss. On average, PLRC of 10% occurred below turgor loss point and at similar water status to 80% decline of stomatal conductance. As hypothesized, the sensitivity to loss of leaf rehydration capacity varied across species, leaf habits, and ecosystems and correlated with other drought tolerance traits, including the turgor loss point and structural traits including leaf mass per area. A new database of PLRC for 89 species from the global literature indicated greater leaf rehydration capacity in ecosystems with lower growing season moisture availability, indicating an adaptive role of leaf cell dehydration tolerance within the complex of drought tolerance traits.
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Affiliation(s)
- Grace P John
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, California, USA
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA
| | - Christian Henry
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, California, USA
| | - Lawren Sack
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, California, USA
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65
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Skelton RP, Dawson TE, Thompson SE, Shen Y, Weitz AP, Ackerly D. Low Vulnerability to Xylem Embolism in Leaves and Stems of North American Oaks. PLANT PHYSIOLOGY 2018; 177:1066-1077. [PMID: 29789436 PMCID: PMC6052988 DOI: 10.1104/pp.18.00103] [Citation(s) in RCA: 80] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/11/2018] [Indexed: 05/05/2023]
Abstract
Although recent findings suggest that xylem embolism represents a significant, drought-induced damaging process in land plants, substantial debate surrounds the capacity of long-vesseled, ring-porous species to resist embolism. We investigated whether recent methodological developments could help resolve this controversy within Quercus, a long-vesseled, ring-porous temperate angiosperm genus, and shed further light on the importance of xylem vulnerability to embolism as an indicator of drought tolerance. We used the optical technique to quantify leaf and stem xylem vulnerability to embolism of eight Quercus species from the Mediterranean-type climate region of California to examine absolute measures of resistance to embolism as well as any potential hydraulic segmentation between tissue types. We demonstrated that our optical assessment reflected flow impairment for a subset of our sample species by quantifying changes in leaf hydraulic conductance in dehydrating branches. Air-entry water potential varied 2-fold in leaves, ranging from -1.7 ± 0.25 MPa to -3.74 ± 0.23 MPa, and 4-fold in stems, ranging from -1.17 ± 0.04 MPa to -4.91 ± 0.3 MPa. Embolism occurred earlier in leaves than in stems in only one out of eight sample species, and plants always lost turgor before experiencing stem embolism. Our results show that long-vesseled North American Quercus species are more resistant to embolism than previously thought and support the hypothesis that avoiding stem embolism is a critical component of drought tolerance in woody trees. Accurately quantifying xylem vulnerability to embolism is essential for understanding species distributions along aridity gradients and predicting plant mortality during drought.
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Affiliation(s)
- Robert Paul Skelton
- Department of Integrative Biology, University of California, Berkeley, California 94720
| | - Todd E Dawson
- Department of Integrative Biology, University of California, Berkeley, California 94720
| | - Sally E Thompson
- Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720
| | - Yuzheng Shen
- Department of Integrative Biology, University of California, Berkeley, California 94720
| | - Andrew P Weitz
- Department of Integrative Biology, University of California, Berkeley, California 94720
| | - David Ackerly
- Department of Integrative Biology, University of California, Berkeley, California 94720
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66
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Zhang Y, Lamarque LJ, Torres-Ruiz JM, Schuldt B, Karimi Z, Li S, Qin DW, Bittencourt P, Burlett R, Cao KF, Delzon S, Oliveira R, Pereira L, Jansen S. Testing the plant pneumatic method to estimate xylem embolism resistance in stems of temperate trees. TREE PHYSIOLOGY 2018; 38:1016-1025. [PMID: 29474679 PMCID: PMC6025199 DOI: 10.1093/treephys/tpy015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 01/19/2018] [Accepted: 01/31/2018] [Indexed: 05/23/2023]
Abstract
Methods to estimate xylem embolism resistance generally rely on hydraulic measurements, which can be far from straightforward. Recently, a pneumatic method based on air flow measurements of terminal branch ends was proposed to construct vulnerability curves by linking the amount of air extracted from a branch with the degree of embolism. We applied this novel technique for 10 temperate tree species, including six diffuse, two ring-porous and two gymnosperm species, and compared the pneumatic curves with hydraulic ones obtained from either the flow-centrifuge or the hydraulic-bench dehydration method. We found that the pneumatic method provides a good estimate of the degree of xylem embolism for all angiosperm species. The xylem pressure at 50% and 88% loss of hydraulic conductivity (i.e., Ψ50 and Ψ88) based on the methods applied showed a strongly significant correlation for all eight angiosperms. However, the pneumatic method showed significantly reduced Ψ50 values for the two conifers. Our findings suggest that the pneumatic method could provide a fast and accurate approach for angiosperms due to its convenience and feasibility, at least within the range of embolism resistances covered by our samples.
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Affiliation(s)
- Ya Zhang
- Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, Ulm, Germany
| | - Laurent J Lamarque
- BIOGECO, INRA, University of Bordeaux, Pessac, France
- EGFV, INRA, University of Bordeaux, Villenave d’Ornon, France
| | | | - Bernhard Schuldt
- Albrecht-von-Haller-Institute for Plant Sciences, Göttingen University, Göttingen, Germany
| | - Zohreh Karimi
- Department of Biology, Faculty of Science, Golestan University, Gorgan, Iran
| | - Shan Li
- Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, Ulm, Germany
- Department of Wood Anatomy and Utilization, Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing, PR China
| | - De-Wen Qin
- Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning, PR China
| | - Paulo Bittencourt
- Department of Plant Biology, Institute of Biology, PO Box 6109, University of Campinas – UNICAMP, Campinas, SP, Brazil
| | - Régis Burlett
- BIOGECO, INRA, University of Bordeaux, Pessac, France
| | - Kun-Fang Cao
- Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning, PR China
| | | | - Rafael Oliveira
- Department of Plant Biology, Institute of Biology, PO Box 6109, University of Campinas – UNICAMP, Campinas, SP, Brazil
| | - Luciano Pereira
- Department of Plant Biology, Institute of Biology, PO Box 6109, University of Campinas – UNICAMP, Campinas, SP, Brazil
| | - Steven Jansen
- Institute of Systematic Botany and Ecology, Ulm University, Albert-Einstein-Allee 11, Ulm, Germany
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67
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Rodriguez-Dominguez CM, Carins Murphy MR, Lucani C, Brodribb TJ. Mapping xylem failure in disparate organs of whole plants reveals extreme resistance in olive roots. THE NEW PHYTOLOGIST 2018; 218:1025-1035. [PMID: 29528498 DOI: 10.1111/nph.15079] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 02/04/2018] [Indexed: 05/25/2023]
Abstract
The capacity of plant species to resist xylem cavitation is an important determinant of resistance to drought, mortality thresholds, geographic distribution and productivity. Unravelling the role of xylem cavitation vulnerability in plant evolution and adaptation requires a clear understanding of how this key trait varies between the tissues of individuals and between individuals of species. Here, we examine questions of variation within individuals by measuring how cavitation moves between organs of individual plants. Using multiple cameras placed simultaneously on roots, stems and leaves, we were able to record systemic xylem cavitation during drying of individual olive plants. Unlike previous studies, we found a consistent pattern of root > stem > leaf in terms of xylem resistance to cavitation. The substantial variation in vulnerability to cavitation, evident among individuals, within individuals and within tissues of olive seedlings, was coordinated such that plants with more resistant roots also had more resistant leaves. Preservation of root integrity means that roots can continue to supply water for the regeneration of drought-damaged aerial tissues after post-drought rain. Furthermore, coordinated variation in vulnerability between leaf, stem and root in olive plants suggests a strong selective pressure to maintain a fixed order of cavitation during drought.
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Affiliation(s)
| | - Madeline R Carins Murphy
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tas., 7001, Australia
| | - Christopher Lucani
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tas., 7001, Australia
| | - Timothy J Brodribb
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tas., 7001, Australia
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68
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Losso A, Beikircher B, Dämon B, Kikuta S, Schmid P, Mayr S. Xylem Sap Surface Tension May Be Crucial for Hydraulic Safety. PLANT PHYSIOLOGY 2017; 175:1135-1143. [PMID: 28982780 PMCID: PMC5664478 DOI: 10.1104/pp.17.01053] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 10/02/2017] [Indexed: 05/05/2023]
Abstract
The surface tension (γ) of xylem sap plays a key role in stabilizing air-water interfaces at the pits between water- and gas-filled conduits to avoid air seeding at low water potentials. We studied seasonal changes in xylem sap γ in Picea abies and Pinus mugo growing at the alpine timberline. We analyzed their vulnerability to drought-induced embolism using solutions of different γ and estimated the potential effect of seasonal changes in γ on hydraulic vulnerability. In both species, xylem sap γ showed distinct seasonal courses between about 50 and 68 mn m-1 Solutions with low γ caused higher vulnerability to drought-induced xylem embolism. The water potential at 50% loss of hydraulic conductivity in P. abies and P. mugo was -3.35 and -3.86 MPa at γ of 74 mn m-1 but -2.11 and -2.09 MPa at 45 mn m-1 This indicates up to about 1 MPa seasonal variation in 50% loss of hydraulic conductivity. The results revealed pronounced effects of changes in xylem sap γ on the hydraulic safety of trees in situ. These effects also are relevant in vulnerability analyses, where the use of standard solutions with high γ overestimates hydraulic safety. Thus, γ should be considered carefully in hydraulic studies.
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Affiliation(s)
- Adriano Losso
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria
| | | | - Birgit Dämon
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria
| | - Silvia Kikuta
- Institute of Botany, University of Natural Resources and Life Sciences, BOKU Vienna, 1180 Vienna, Austria
| | - Peter Schmid
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria
| | - Stefan Mayr
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria
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