1
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Potkay A, Feng X. Do stomata optimize turgor-driven growth? A new framework for integrating stomata response with whole-plant hydraulics and carbon balance. THE NEW PHYTOLOGIST 2023; 238:506-528. [PMID: 36377138 DOI: 10.1111/nph.18620] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 11/11/2022] [Indexed: 06/16/2023]
Abstract
Every existing optimal stomatal model uses photosynthetic carbon assimilation as a proxy for plant evolutionary fitness. However, assimilation and growth are often decoupled, making assimilation less ideal for representing fitness when optimizing stomatal conductance to water vapor and carbon dioxide. Instead, growth should be considered a closer proxy for fitness. We hypothesize stomata have evolved to maximize turgor-driven growth, instead of assimilation, over entire plants' lifetimes, improving their abilities to compete and reproduce. We develop a stomata model that dynamically maximizes whole-stem growth following principles from turgor-driven growth models. Stomata open to assimilate carbohydrates that supply growth and osmotically generate turgor, while stomata close to prevent losses of turgor and growth due to negative water potentials. In steady state, the growth optimization model captures realistic stomatal, growth, and carbohydrate responses to environmental cues, reconciles conflicting interpretations within existing stomatal optimization theories, and explains patterns of carbohydrate storage and xylem conductance observed during and after drought. Our growth optimization hypothesis introduces a new paradigm for stomatal optimization models, elevates the role of whole-plant carbon use and carbon storage in stomatal functioning, and has the potential to simultaneously predict gross productivity, net productivity, and plant mortality through a single, consistent modeling framework.
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Affiliation(s)
- Aaron Potkay
- Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Twin Cities, Minneapolis, MN, 55455, USA
- Saint Anthony Falls Laboratory, University of Minnesota, Twin Cities, Minneapolis, MN, 55455, USA
| | - Xue Feng
- Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Twin Cities, Minneapolis, MN, 55455, USA
- Saint Anthony Falls Laboratory, University of Minnesota, Twin Cities, Minneapolis, MN, 55455, USA
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2
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Oberleitner F, Hartmann H, Hasibeder R, Huang J, Losso A, Mayr S, Oberhuber W, Wieser G, Bahn M. Amplifying effects of recurrent drought on the dynamics of tree growth and water use in a subalpine forest. PLANT, CELL & ENVIRONMENT 2022; 45:2617-2635. [PMID: 35610775 DOI: 10.1111/pce.14369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2021] [Revised: 04/16/2022] [Accepted: 05/11/2022] [Indexed: 06/15/2023]
Abstract
Despite recent advances in our understanding of drought impacts on tree functioning, we lack knowledge about the dynamic responses of mature trees to recurrent drought stress. At a subalpine forest site, we assessed the effects of three years of recurrent experimental summer drought on tree growth and water relations of Larix decidua Mill. and Picea abies (L. Karst.), two common European conifers representative for contrasting water-use strategies. We combined dendrometer and xylem sap flow measurements with analyses of xylem anatomy and non-structural carbohydrates and their carbon-isotope composition. Recurrent drought increased the effects of soil moisture limitation on growth and xylogenesis, and to a lesser extent on xylem sap flow. P. abies showed stronger growth responses to recurrent drought, reduced starch concentrations in branches and increased water-use efficiency when compared to L. decidua. Despite comparatively larger maximum tree water deficits than in P. abies, xylem formation of L. decidua was less affected by drought, suggesting a stronger capacity of rehydration or lower cambial turgor thresholds for growth. Our study shows that recurrent drought progressively increases impacts on mature trees of both species, which suggests that in a future climate increasing drought frequency could impose strong legacies on carbon and water dynamics of treeline species.
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Affiliation(s)
| | - Henrik Hartmann
- Department of Biogeochemical Processes, Max Planck Institute for Biogeochemistry, Jena, Germany
| | - Roland Hasibeder
- Department of Ecology, University of Innsbruck, Innsbruck, Austria
| | - Jianbei Huang
- Department of Biogeochemical Processes, Max Planck Institute for Biogeochemistry, Jena, Germany
| | - Adriano Losso
- Department of Botany, University of Innsbruck, Innsbruck, Austria
- Hawkesbury Institute for the Environment, Western Sydney University, Richmond, New South Wales, Australia
| | - Stefan Mayr
- Department of Botany, University of Innsbruck, Innsbruck, Austria
| | - Walter Oberhuber
- Department of Botany, University of Innsbruck, Innsbruck, Austria
| | - Gerhard Wieser
- Department of Botany, University of Innsbruck, Innsbruck, Austria
- Department of Alpine Timberline Ecophysiology, Federal Research and Training Centre for Forests, Natural Hazards and Landscape (BFW), Innsbruck, Austria
| | - Michael Bahn
- Department of Ecology, University of Innsbruck, Innsbruck, Austria
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3
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Giovannelli A, Mattana S, Emiliani G, Anichini M, Traversi ML, Pavone FS, Cicchi R. Localized stem heating from the rest to growth phase induces latewood-like cell formation and slower stem radial growth in Norway spruce saplings. TREE PHYSIOLOGY 2022; 42:1149-1163. [PMID: 34918169 DOI: 10.1093/treephys/tpab166] [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: 04/01/2021] [Accepted: 12/01/2021] [Indexed: 06/14/2023]
Abstract
Recent climate projections predict a more rapid increase of winter temperature than summer and global temperature averages in temperate and cold environments. As there is relatively little experimental knowledge on the effect of winter warming on cambium phenology and stem growth in species growing in cold environments, the setting of manipulative experiments is considered of primary importance, and they can help to decipher the effect of reduced winter chilling and increased forcing temperatures on cambium reactivation, growth and xylem traits. In this study, localized stem heating was applied to investigate the effect of warming from the rest to the growth phase on cambium phenology, intra-annual stem growth dynamics and ring wood features in Picea abies (L.) H.Karst. We hypothesized that reduced winter chilling induces a postponed cambium dormancy release and decrease of stem growth, while high temperature during cell wall lignification determines an enrichment of latewood-like cells. The heating device was designed to maintain a +5 °C temperature delta with respect to air temperature, thus allowing an authentic scenario of warming. Continuous stem heating from the rest (November) to the growing phase determined, at the beginning of radial growth, a reduction of the number of cell layers in the cambium, higher number of cell layers in the wall thickening phase and an asynchronous stem radial growth when comparing heated and ambient saplings. Nevertheless, heating did not induce changes in the number of produced cell layers at the end of the growing season. The analyses of two-photon fluorescence images showed that woody rings formed during heating were enriched with latewood-like cells. Our results showed that an increase of 5 °C of temperature applied to the stem from the rest to growth might not influence, as generally reported, onset of cambial activity, but it could affect xylem morphology of Norway spruce in mountain environments.
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Affiliation(s)
- Alessio Giovannelli
- Istituto di Ricerca sugli Ecosistemi Terrestri (IRET), Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, Sesto Fiorentino I-50019, Italy
| | - Sara Mattana
- Istituto Nazionale di Ottica (INO), Consiglio Nazionale delle Ricerche, Largo Fermi 6, Firenze 50125, Italy
| | - Giovanni Emiliani
- Istituto Protezione Sostenibile delle Piante (IPSP), Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, Sesto Fiorentino I-50019, Italy
| | - Monica Anichini
- Istituto per la Bioeconomia (IBE), Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, Sesto Fiorentino I-50019, Italy
| | - Maria Laura Traversi
- Istituto di Ricerca sugli Ecosistemi Terrestri (IRET), Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, Sesto Fiorentino I-50019, Italy
| | - Francesco Saverio Pavone
- Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, Sesto Fiorentino 50019, Italy
| | - Riccardo Cicchi
- Istituto Nazionale di Ottica (INO), Consiglio Nazionale delle Ricerche, Largo Fermi 6, Firenze 50125, Italy
- Laboratorio Europeo di Spettroscopie Non-lineari (LENS), Via N. Carrara 1, Sesto Fiorentino 50019, Italy
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4
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Zhao J, Yuan J, Chen Y, Wang Y, Chen J, Bi J, Lyu L, Yu C, Yuan S, Liu Z. MAPK CcSakA of the HOG Pathway Is Involved in Stipe Elongation during Fruiting Body Development in Coprinopsis cinerea. J Fungi (Basel) 2022; 8:jof8050534. [PMID: 35628789 PMCID: PMC9147448 DOI: 10.3390/jof8050534] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Revised: 05/17/2022] [Accepted: 05/18/2022] [Indexed: 12/22/2022] Open
Abstract
Mitogen-activated protein kinase (MAPK) pathways, such as the high-osmolarity glycerol mitogen-activated protein kinase (HOG) pathway, are evolutionarily conserved signaling modules responsible for transmitting environmental stress signals in eukaryotic organisms. Here, we identified the MAPK homologue in the HOG pathway of Coprinopsis cinerea, which was named CcSakA. Furthermore, during the development of the fruiting body, CcSakA was phosphorylated in the fast elongating apical part of the stipe, which meant that CcSakA was activated in the apical elongating stipe region of the fruiting body. The knockdown of CcSakA resulted in a shorter stipe of the fruiting body compared to the control strain, and the expression of phosphomimicking mutant CcSakA led to a longer stipe of the fruiting body compared to the control strain. The chitinase CcChiE1, which plays a key role during stipe elongation, was downregulated in the CcSakA knockdown strains and upregulated in the CcSakA phosphomimicking mutant strains. The results indicated that CcSakA participated in the elongation of stipes in the fruiting body development of C. cinerea by regulating the expression of CcChiE1. Analysis of the H2O2 concentration in different parts of the stipe showed that the oxidative stress in the elongating part of the stipe was higher than those in the non-elongating part. The results indicated that CcSakA of the HOG pathway may be activated by oxidative stress. Our results demonstrated that the HOG pathway transmits stress signals and regulates the expression of CcChiE1 during fruiting body development in C. cinerea.
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Affiliation(s)
- Jing Zhao
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Jing Yuan
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Yating Chen
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Yu Wang
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Jing Chen
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Jingjing Bi
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Linna Lyu
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Cigang Yu
- Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment, Nanjing 210042, China
- Correspondence: (C.Y.); (Z.L.)
| | - Sheng Yuan
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
| | - Zhonghua Liu
- Jiangsu Key Laboratory for Microbes and Microbial Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Science, Nanjing Normal University, Nanjing 210023, China; (J.Z.); (J.Y.); (Y.C.); (Y.W.); (J.C.); (J.B.); (L.L.); (S.Y.)
- Correspondence: (C.Y.); (Z.L.)
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5
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Potkay A, Hölttä T, Trugman AT, Fan Y. Turgor-limited predictions of tree growth, height and metabolic scaling over tree lifespans. TREE PHYSIOLOGY 2022; 42:229-252. [PMID: 34296275 DOI: 10.1093/treephys/tpab094] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 07/18/2021] [Indexed: 06/13/2023]
Abstract
Increasing evidence suggests that tree growth is sink-limited by environmental and internal controls rather than by carbon availability. However, the mechanisms underlying sink-limitations are not fully understood and thus not represented in large-scale vegetation models. We develop a simple, analytically solved, mechanistic, turgor-driven growth model (TDGM) and a phloem transport model (PTM) to explore the mechanics of phloem transport and evaluate three hypotheses. First, phloem transport must be explicitly considered to accurately predict turgor distributions and thus growth. Second, turgor-limitations can explain growth-scaling with size (metabolic scaling). Third, turgor can explain realistic growth rates and increments. We show that mechanistic, sink-limited growth schemes based on plant turgor limitations are feasible for large-scale model implementations with minimal computational demands. Our PTM predicted nearly uniform sugar concentrations along the phloem transport path regardless of phloem conductance, stem water potential gradients and the strength of sink-demands contrary to our first hypothesis, suggesting that phloem transport is not limited generally by phloem transport capacity per se but rather by carbon demand for growth and respiration. These results enabled TDGM implementation without explicit coupling to the PTM, further simplifying computation. We test the TDGM by comparing predictions of whole-tree growth rate to well-established observations (site indices) and allometric theory. Our simple TDGM predicts realistic tree heights, growth rates and metabolic scaling over decadal to centurial timescales, suggesting that tree growth is generally sink and turgor limited. Like observed trees, our TDGM captures tree-size- and resource-based deviations from the classical ¾ power-law metabolic scaling for which turgor is responsible.
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Affiliation(s)
- Aaron Potkay
- Department of Earth and Planetary Sciences, Rutgers University, New Brunswick, NJ 08854, USA
| | - Teemu Hölttä
- Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Helsinki FI-00014, Finland
| | - Anna T Trugman
- Department of Geography, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Ying Fan
- Department of Earth and Planetary Sciences, Rutgers University, New Brunswick, NJ 08854, USA
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6
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Dewar R, Hölttä T, Salmon Y. Exploring optimal stomatal control under alternative hypotheses for the regulation of plant sources and sinks. THE NEW PHYTOLOGIST 2022; 233:639-654. [PMID: 34637543 DOI: 10.1111/nph.17795] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 09/19/2021] [Indexed: 06/13/2023]
Abstract
Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade-off between leaf CO2 supply and NSLs, potentially involving source-sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain. We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading. All hypotheses led to realistic stomatal responses to light, CO2 and air humidity, including conservative behaviour for the intercellular-to-atmospheric CO2 concentration ratio. Sugar-regulated and water-regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor-regulated and sugar-regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris, Betula pendula, Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar-regulated NSLs and turgor-regulated unloading. Our analytical results provide a simple representation of stomatal responses to above-ground and below-ground environmental factors and sink activity.
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Affiliation(s)
- Roderick Dewar
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Plant Sciences Division, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Teemu Hölttä
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, PO Box 27, Latokartanonkaari 7, Helsinki, 00014, Finland
| | - Yann Salmon
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, PO Box 27, Latokartanonkaari 7, Helsinki, 00014, Finland
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7
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Epron D, Kamakura M, Azuma W, Dannoura M, Kosugi Y. Diurnal variations in the thickness of the inner bark of tree trunks in relation to xylem water potential and phloem turgor. PLANT-ENVIRONMENT INTERACTIONS (HOBOKEN, N.J.) 2021; 2:112-124. [PMID: 37283860 PMCID: PMC10168075 DOI: 10.1002/pei3.10045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 04/03/2021] [Accepted: 04/07/2021] [Indexed: 06/08/2023]
Abstract
The inner bark plays important roles in tree stems, including radial exchange of water with the xylem and translocation of carbohydrates. Both processes affect the water content and the thickness of the inner bark on a diurnal basis. For the first time, we simultaneously measured the diurnal variations in the inner bark thickness of hinoki cypress (Chamaecyparis obtusa) by using point dendrometers and those of local xylem potential by using stem psychrometers located next to the dendrometers to determine how these variations were related to each other, to phloem turgor and carbohydrate transport. We also estimated the axial hydrostatic pressure gradient by measuring the osmolality of the sap extracted from the inner bark. The inner bark shrunk during the day and swelled during the night with an amplitude related to day-to-day and seasonal variations in climate. The relationship between changes in xylem water potential and inner bark thickness exhibited a hysteresis loop during the day with a median lag of 2 h. A phloem turgor-related signal can be retrieved from the diurnal variations in the inner bark thickness, which was higher at the upper than at the lower position along the trunk. However, a downward hydrostatic pressure gradient was only observed at dawn, suggesting diurnal variations in the phloem sap flow velocity.
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Affiliation(s)
- Daniel Epron
- Graduate School of AgricultureKyoto UniversityKyotoJapan
- AgroParisTechINRAEUMR SILVAUniversité de LorraineNancyFrance
| | - Mai Kamakura
- Graduate School of AgricultureKyoto UniversityKyotoJapan
| | - Wakana Azuma
- Graduate School of Agricultural ScienceKobe UniversityKobeJapan
| | | | - Yoshiko Kosugi
- Graduate School of AgricultureKyoto UniversityKyotoJapan
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8
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Liesche J, Vincent C, Han X, Zwieniecki M, Schulz A, Gao C, Bravard R, Marker S, Bohr T. The mechanism of sugar export from long conifer needles. THE NEW PHYTOLOGIST 2021; 230:1911-1924. [PMID: 33638181 DOI: 10.1111/nph.17302] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 02/17/2021] [Indexed: 06/12/2023]
Abstract
The green leaves of plants are optimised for carbon fixation and the production of sugars, which are used as central units of carbon and energy throughout the plant. However, there are physical limits to this optimisation that remain insufficiently understood. Here, quantitative anatomical analysis combined with mathematical modelling and sugar transport rate measurements were used to determine how effectively sugars are exported from the needle-shaped leaves of conifers in relation to leaf length. Mathematical modelling indicated that phloem anatomy constrains sugar export in long needles. However, we identified two mechanisms by which this constraint is overcome, even in needles longer than 20 cm: (1) the grouping of transport conduits, and (2) a shift in the diurnal rhythm of sugar metabolism and export in needle tips. The efficiency of sugar transport in the phloem can have a significant influence on leaf function. The constraints on sugar export described here for conifer needles are likely to also be relevant in other groups of plants, such as grasses and angiosperm trees.
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Affiliation(s)
- Johannes Liesche
- College of Life Sciences & Biomass Energy Center for Arid and Semi-arid Lands, Northwest A&F University, Taicheng Road 3, Yangling, 712100, China
- Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, Düsseldorf, 40225, Germany
| | - Christopher Vincent
- Department of Horticultural Sciences, University of Florida, 700 Experiment Station Road, Lake Alfred, FL, 33850, USA
| | - Xiaoyu Han
- College of Life Sciences & Biomass Energy Center for Arid and Semi-arid Lands, Northwest A&F University, Taicheng Road 3, Yangling, 712100, China
| | - Maciej Zwieniecki
- Department of Plant Sciences, University of California, Davis One Shields Avenue, Davis, CA, 95616, USA
| | - Alexander Schulz
- Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, Frederiksberg, 1871, Denmark
| | - Chen Gao
- Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, Frederiksberg, 1871, Denmark
| | - Rodrigue Bravard
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, DK-2800, Denmark
| | - Sean Marker
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, DK-2800, Denmark
| | - Tomas Bohr
- Department of Physics, Technical University of Denmark, Kgs. Lyngby, DK-2800, Denmark
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9
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Peters RL, Steppe K, Cuny HE, De Pauw DJW, Frank DC, Schaub M, Rathgeber CBK, Cabon A, Fonti P. Turgor - a limiting factor for radial growth in mature conifers along an elevational gradient. THE NEW PHYTOLOGIST 2021; 229:213-229. [PMID: 32790914 DOI: 10.1111/nph.16872] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 07/29/2020] [Indexed: 05/17/2023]
Abstract
A valid representation of intra-annual wood formation processes in global vegetation models is vital for assessing climate change impacts on the forest carbon stock. Yet, wood formation is generally modelled with photosynthesis, despite mounting evidence that cambial activity is rather directly constrained by limiting environmental factors. Here, we apply a state-of-the-art turgor-driven growth model to simulate 4 yr of hourly stem radial increment from Picea abies (L.) Karst. and Larix decidua Mill. growing along an elevational gradient. For the first time, wood formation observations were used to validate weekly to annual stem radial increment simulations, while environmental measurements were used to assess the climatic constraints on turgor-driven growth. Model simulations matched the observed timing and dynamics of wood formation. Using the detailed model outputs, we identified a strict environmental regulation on stem growth (air temperature > 2°C and soil water potential > -0.6 MPa). Warmer and drier summers reduced the growth rate as a result of turgor limitation despite warmer temperatures being favourable for cambial activity. These findings suggest that turgor is a central driver of the forest carbon sink and should be considered in next-generation vegetation models, particularly in the context of global warming and increasing frequency of droughts.
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Affiliation(s)
- Richard L Peters
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, Birmensdorf, CH-8903, Switzerland
- Department of Environmental Sciences - Botany, Basel University, Schönbeinstrasse 6, Basel, CH-4056, Switzerland
- Laboratory of Plant Ecology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, Ghent, B-9000, Belgium
| | - Kathy Steppe
- Laboratory of Plant Ecology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, Ghent, B-9000, Belgium
| | - Henri E Cuny
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, Birmensdorf, CH-8903, Switzerland
- Institut National de l'Information Géographique et Forestière (IGN), 1 rue des blanches terres, Champigneulles, 54115, France
| | - Dirk J W De Pauw
- Laboratory of Plant Ecology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, Ghent, B-9000, Belgium
| | - David C Frank
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, Birmensdorf, CH-8903, Switzerland
- Laboratory of Tree-Ring Research, 1215 E. Lowell Street, Tucson, AZ, 8572, USA
| | - Marcus Schaub
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, Birmensdorf, CH-8903, Switzerland
| | | | - Antoine Cabon
- Joint Research Unit CTFC - AGROTECNIO, Solsona, E-25280, Spain
- CREAF, Cerdanyola del Vallès, Barcelona, E-08193, Spain
| | - Patrick Fonti
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, Birmensdorf, CH-8903, Switzerland
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10
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Salmon Y, Lintunen A, Dayet A, Chan T, Dewar R, Vesala T, Hölttä T. Leaf carbon and water status control stomatal and nonstomatal limitations of photosynthesis in trees. THE NEW PHYTOLOGIST 2020; 226:690-703. [PMID: 31955422 DOI: 10.1111/nph.16436] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 12/18/2019] [Indexed: 05/22/2023]
Abstract
Photosynthetic rate is concurrently limited by stomatal limitations and nonstomatal limitations (NSLs). However, the controls on NSLs to photosynthesis and their coordination with stomatal control on different timescales remain poorly understood. According to a recent optimization hypothesis, NSLs depend on leaf osmotic or water status and are coordinated with stomatal control so as to maximize leaf photosynthesis. Drought and notching experiments were conducted on Pinus sylvestris, Picea abies, Betula Pendula and Populus tremula seedlings in glasshouse conditions to study the dependence of NSLs on leaf osmotic and water status, and their coordination with stomatal control, on timescales of minutes and weeks, to test the assumptions and predictions of the optimization hypothesis. Both NSLs and stomatal conductance followed power-law functions of leaf osmotic concentration and leaf water potential. Moreover, stomatal conductance was proportional to the square root of soil-to-leaf hydraulic conductance, as predicted by the optimization hypothesis. Though the detailed mechanisms underlying the dependence of NSLs on leaf osmotic or water status lie outside the scope of this study, our results support the hypothesis that NSLs and stomatal control are coordinated to maximize leaf photosynthesis and allow the effect of NSLs to be included in models of tree gas-exchange.
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Affiliation(s)
- Yann Salmon
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland
| | - Anna Lintunen
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland
| | - Alexia Dayet
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland
| | - Tommy Chan
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland
| | - Roderick Dewar
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Plant Sciences Division, Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Timo Vesala
- Faculty of Science, Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, PO Box 68, Gustaf Hällströmin katu 2b, Helsinki, 00014, Finland
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland
| | - Teemu Hölttä
- Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Latokartanonkaari 7, PO Box 27, Helsinki, 00014, Finland
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11
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Measurement of Inner Bark and Leaf Osmolality. Methods Mol Biol 2020. [PMID: 31197792 DOI: 10.1007/978-1-4939-9562-2_11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Sugar transport in the phloem is driven by turgor pressure gradients which are created by osmotic gradients resulting from sugars loaded to the phloem at the source tissue and unloaded at the sink tissue. Therefore, osmolality is a key parameter that can be used to evaluate sugar status and get an indication of the driving force for phloem transport. Here we describe how osmotic concentration measurements from inner bark (practically, the phloem) and needles of trees can be measured. This protocol presents the procedure used by Lintunen et al. (Front Plant Sci 7:726, 2016) and Paljakka et al. (Plant Cell Environ 40:2160-2173, 2017), extended by practical advice and discussion of potential errors and caveats. We describe how to implement this procedure for gymnosperm as well as angiosperm trees. This method uses mechanical sap extraction with a centrifuge from inner bark and leaf samples, which have gone through a deep freeze treatment and thawing. The osmotic potential of these samples is then analyzed with a freezing point or vapor pressure osmometer. The aim of these measurements is to study the spatial and temporal dynamics of phloem function.
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12
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Donnellan Barraclough A, Zweifel R, Cusens J, Leuzinger S. Disentangling the net: concomitant xylem and over-bark size measurements reveal the phloem-generated turgor signal behind daytime stem swelling in the mangrove Avicennia marina. FUNCTIONAL PLANT BIOLOGY : FPB 2019; 46:393-406. [PMID: 30940339 DOI: 10.1071/fp18155] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 12/25/2018] [Indexed: 06/09/2023]
Abstract
Daytime stem shrinking is a well recorded phenomenon: trees dip into their internal water stores to meet imbalances between water supply and demand. Uncertainty surrounds the mechanisms behind the unusual pattern of daytime stem swelling, presented by species like the mangrove Avicennia marina (Forssk.) Vierh., and which is thought to originate in the osmotic adjustment of storage tissues. We performed on-xylem radius change (XRC) and whole-stem radius change (SRC) measurements with point dendrometers to ascertain if the swelling of the stem is due to an increase in the thickness of the phloem and inner-bark (BRC). We measured leaf water potential (ψleaf), sap flow, leaf turgor and microclimate to understand the coupling between BRC and transpiration-driven changes in XRC. Our results present direct evidence of the type of mechanism responsible for daytime stem swelling. Inner-bark thickness increase concurrent with XRC decrease, sap-flow increase and leaf turgor loss, reveals a phloem-generated turgor signal behind daytime stem swelling of tree stems. On-xylem measurements were highly heterogeneous due to the variability in the three dimensional fish-net wood structure of the stem of A. marina. As daytime decreases in XRC were compensated by BRC and correlated with conditions of high water demand, we suggest a potential role of daytime stem swelling in the hydraulic safety of A. marina.
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Affiliation(s)
- Alicia Donnellan Barraclough
- Institute of Applied Ecology New Zealand, Auckland University of Technology, 34 St Paul Street, Auckland 1010, New Zealand; and Corresponding author.
| | - Roman Zweifel
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland
| | - Jarrod Cusens
- Institute of Applied Ecology New Zealand, Auckland University of Technology, 34 St Paul Street, Auckland 1010, New Zealand; and Wildland Consultants Ltd, 12 Nixon Street, Grey Lynn, Auckland 1021, New Zealand
| | - Sebastian Leuzinger
- Institute of Applied Ecology New Zealand, Auckland University of Technology, 34 St Paul Street, Auckland 1010, New Zealand
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13
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Dong T, Duan B, Korpelainen H, Niinemets Ü, Li C. Asymmetric pruning reveals how organ connectivity alters the functional balance between leaves and roots of Chinese fir. JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:1941-1953. [PMID: 30689933 DOI: 10.1093/jxb/erz013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2018] [Accepted: 01/04/2019] [Indexed: 06/09/2023]
Abstract
The functional balance between leaves and roots is believed to be mediated by the specific location of shoots and roots, i.e. differences in transport distances and degrees of organ connectivity. However, it remains unknown whether the adaptive responses of trees to biomass removal depend on the relative orientation of leaf and root pruning. Here, we applied five pruning treatments to saplings of Cunninghamia lanceolata (Chinese fir) under field and glasshouse conditions, namely no pruning (control), half of lateral branches pruned, half of lateral roots pruned, half of the branches and roots pruned on the same side of the plant, and half of the branches and roots pruned on opposite sides of the plant. The effects of pruning on the growth, carbon storage and allocation, and physiology of leaves and fine roots on the same and opposite sides of the plant were investigated. Compared with the effect of root-pruning on leaves, fine roots were more limited by carbon availability and their physiological activity was more strongly reduced by shoot pruning, especially when branches on the same side of the plant were removed. Pruning of branches and roots on the opposite side of the plant resulted in the lowest carbon assimilation rates and growth among all treatments. The results of a stable-isotope labeling indicated that less C was distributed to fine roots from the leaves on the opposite side of the plant compared to those on the same side, but N allocation from roots to leaves depended less on the relative root and leaf orientation. The results collectively indicate that the functional responses of C. lanceolata to pruning are not only determined by the source-sink balance model but are also related to interactions between leaves and fine roots. We argue that the connectivity among lateral branches and roots depends on their relative orientation, which is therefore critical for the functional balance between leaves and fine roots.
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Affiliation(s)
- Tingfa Dong
- Key Laboratory of Southwest China Wildlife Resources Conservation, Ministry of Education, and College of Life Sciences, China West Normal University, Nanchong, Sichuan, China
| | - Baoli Duan
- Key Laboratory of Mountain Surface Processes and Ecological Regulation, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, China
| | - Helena Korpelainen
- Department of Agricultural Sciences, Viikki Plant Science Centre, University of Helsinki, Finland
| | - Ülo Niinemets
- Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi, Tartu, Estonia
- Estonian Academy of Sciences, Kohtu, Tallinn, Estonia
| | - Chunyang Li
- College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou, China
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14
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Epron D, Dannoura M, Ishida A, Kosugi Y. Estimation of phloem carbon translocation belowground at stand level in a hinoki cypress stand. TREE PHYSIOLOGY 2019; 39:320-331. [PMID: 29474703 DOI: 10.1093/treephys/tpy016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 01/15/2018] [Accepted: 01/27/2018] [Indexed: 06/08/2023]
Abstract
At stand level, carbon translocation in tree stems has to match canopy photosynthesis and carbohydrate requirements to sustain growth and the physiological activities of belowground sinks. This study applied the Hagen-Poiseuille equation to the pressure-flow hypothesis to estimate phloem carbon translocation and evaluate what percentage of canopy photosynthate can be transported belowground in a hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc.) stand. An anatomical study revealed that, in contrast to sieve cell density, conductive phloem thickness and sieve cell hydraulic diameter at 1.3 m in height increased with increasing tree diameter, as did the concentration of soluble sugars in the phloem sap. At tree level, hydraulic conductivity increased by two orders of magnitude from the smallest to the largest trees in the stand, resulting in a stand-level hydraulic conductance of 1.7 × 10-15 m Pa-1 s-1. The osmotic potential of the sap extracted from the inner bark was -0.75 MPa. Assuming that phloem water potential equalled foliage water potential at predawn, the turgor pressure in the phloem at 1.3 m in height was estimated at 0.22 MPa, 0.59 MPa lower than values estimated in the foliage. With this maximal turgor pressure gradient, which would be lower during day-time when foliage water potential drops, the estimated stand-level rate of carbon translocation was 2.0 gC m-2 day-1 (30% of daily gross canopy photosynthesis), at a time of the year when aboveground growth and related respiration is thought to consume a large fraction of photosynthate, at the expense of belowground activity. Despite relying on some assumptions and approximations, this approach, when coupled with measurements of canopy photosynthesis, may further be used to provide qualitative insight into the seasonal dynamics of belowground carbon allocation.
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Affiliation(s)
- Daniel Epron
- Université de Lorraine, INRA, UMR SILVA, Faculté des Sciences et Technologies, Vandœuvre-lès-Nancy, France
- Kyoto University, Laboratory of Ecosystem Production and Dynamics, Graduate School of Global Environmental Studies, Kyoto, Japan
| | - Masako Dannoura
- Kyoto University, Laboratory of Ecosystem Production and Dynamics, Graduate School of Global Environmental Studies, Kyoto, Japan
- Kyoto University, Laboratory of Forest Utilization, Graduate School of Agriculture, Kyoto, Japan
| | - Atsushi Ishida
- Kyoto University, Center for Ecological Research, Otsu, Shiga, Japan
| | - Yoshiko Kosugi
- Kyoto University, Laboratory of Forest Hydrology, Graduate School of Agriculture, Kyoto, Japan
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15
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Dannoura M, Epron D, Desalme D, Massonnet C, Tsuji S, Plain C, Priault P, Gérant D. The impact of prolonged drought on phloem anatomy and phloem transport in young beech trees. TREE PHYSIOLOGY 2019; 39:201-210. [PMID: 29931112 DOI: 10.1093/treephys/tpy070] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 05/04/2018] [Accepted: 05/18/2018] [Indexed: 06/08/2023]
Abstract
Phloem failure has recently been recognized as one of the mechanisms causing tree mortality under drought, though direct evidence is still lacking. We combined 13C pulse-labelling of 8-year-old beech trees (Fagus sylvatica L.) growing outdoors in a nursery with an anatomical study of the phloem tissue in their stems to examine how drought alters carbon transport and phloem transport capacity. For the six trees under drought, predawn leaf water potential ranged from -0.7 to -2.4 MPa, compared with an average of -0.2 MPa in five control trees with no water stress. We also observed a longer residence time of excess 13C in the foliage and the phloem sap in trees under drought compared with controls. Compared with controls, excess 13C in trunk respiration peaked later in trees under moderate drought conditions and showed no decline even after 4 days under more severe drought conditions. We estimated higher phloem sap viscosity in trees under drought. We also observed much smaller sieve-tube radii in all drought-stressed trees, which led to lower sieve-tube conductivity and lower phloem conductance in the tree stem. We concluded that prolonged drought affected phloem transport capacity through a change in anatomy and that the slowdown of phloem transport under drought likely resulted from a reduced driving force due to lower hydrostatic pressure between the source and sink organs.
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Affiliation(s)
- Masako Dannoura
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
- Laboratory of Ecosystem Production and Dynamics, Graduate School of Global Environmental Studies, Kyoto University, Kyoto, Japan
- Laboratory of Forest Utilization, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Daniel Epron
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| | - Dorine Desalme
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| | - Catherine Massonnet
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| | - Shoko Tsuji
- Laboratory of Ecosystem Production and Dynamics, Graduate School of Global Environmental Studies, Kyoto University, Kyoto, Japan
| | - Caroline Plain
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| | - Pierrick Priault
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| | - Dominique Gérant
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
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16
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Lazzarin M, Zweifel R, Anten N, Sterck FJ. Does phloem osmolality affect diurnal diameter changes of twigs but not of stems in Scots pine? TREE PHYSIOLOGY 2019; 39:275-283. [PMID: 30371898 DOI: 10.1093/treephys/tpy121] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Revised: 09/12/2018] [Accepted: 10/08/2018] [Indexed: 06/08/2023]
Abstract
Diel stem diameter changes measured at the stem base of temperate tree species can be mostly explained by a hydraulic system of flow and storage compartments passively driven by transpiration. Active, osmotic processes are considered to play a minor role only. Here we explore whether such osmotic processes have a stronger impact on diel changes in twig diameter than in stem diameter because twigs are closer to the leaves, the main source of newly acquired carbon. We investigated stem and twig diameter changes of wood and bark of pine trees in parallel to fluctuations of the osmolality in needles and in the bark at the stem base. We found consistent twig bark size increments concurrent with twig wood size decreases during daylight hours whereas needle osmolality was not consistently increasing even on sunny days. The size changes of bark and wood either reversed or ran in parallel from late afternoon onwards until the next morning. No such patterns were measurable at the stem base. Stem wood was hardly changing in size, whereas stem bark followed the regular pattern of a decrease during the daylight hours and an increase during the night. Osmolality at the stem base showed no particular course over 24 h. We conclude that assimilates from the needles were rapidly transported to the twigs where they increased the osmolality of the bark tissue by sugar loading, explaining the bark size increase (over-) compensating the xylem size decrease. The stem base largely followed the expectation of a passive, hydraulic system without a measurable role of osmoregulation. Diameter changes thus follow different diurnal dynamics in twigs and at the stem base.
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Affiliation(s)
- Martina Lazzarin
- Forest Ecology and Forest Management Group, Wageningen, The Netherlands
| | - Roman Zweifel
- Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) Zürcherstrasse 111, Birmensdorf, Switzerland
| | - Niels Anten
- Centre for Crop Systems Analysis, 6708PB Wageningen, The Netherlands
| | - Frank J Sterck
- Forest Ecology and Forest Management Group, Wageningen, The Netherlands
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17
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Liesche J, Schulz A. Phloem transport in gymnosperms: a question of pressure and resistance. CURRENT OPINION IN PLANT BIOLOGY 2018; 43:36-42. [PMID: 29304388 DOI: 10.1016/j.pbi.2017.12.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2017] [Revised: 12/14/2017] [Accepted: 12/15/2017] [Indexed: 06/07/2023]
Abstract
Even in the highest trees, carbon is efficiently distributed from leaves to heterotrophic tissues like fruit, flowers and roots. This long-distance transport happens in the highly specialized sieve elements of the phloem. In gymnosperms, sieve element anatomy appears to be less suited for mass flow of phloem sap than that of angiosperms. This review covers available data on gymnosperm phloem to evaluate if it functions differently from that of angiosperms. Although current evidence suggests that, despite a higher pathway resistance, a single source-to-sink turgor pressure gradient can drive mass flow, several questions remain unanswered. These include how endoplasmic reticulum-complexes in sieve elements influence flow, as well as what the effect of symplasmic coupling along the whole phloem pathway could be.
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Affiliation(s)
- Johannes Liesche
- College of Life Science, Department of Biology, Northwest A&F University, 3 Taicheng Road, 712100 Yangling, Shaanxi, China
| | - Alexander Schulz
- Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
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18
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Carvalho MR, Losada JM, Niklas KJ. Phloem networks in leaves. CURRENT OPINION IN PLANT BIOLOGY 2018; 43:29-35. [PMID: 29306742 DOI: 10.1016/j.pbi.2017.12.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 12/04/2017] [Accepted: 12/16/2017] [Indexed: 06/07/2023]
Abstract
The survival of all vascular plants depends on phloem and xylem, which comprise a hydraulically coupled tissue system that transports photosynthates, water, and a variety of other molecules and ions. Although xylem hydraulics has been extensively studied, until recently, comparatively little is known quantitatively about the phloem hydraulic network and how it is functionally coupled to the xylem network, particularly in photosynthetic leaves. Here, we summarize recent advances in quantifying phloem hydraulics in fully expanded mature leaves with different vascular architectures and show that (1) the size of phloem conducting cells across phylogenetically different taxa scales isometrically with respect to xylem conducting cell size, (2) cell transport areas and lengths increase along phloem transport pathways in a manner that can be used to model Münch's pressure-flow hypothesis, and (3) report observations that invalidate da Vinci's and Murray's hydraulic models as plausible constructs for understanding photosynthate transport in the leaf lamina.
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Affiliation(s)
- Mónica R Carvalho
- Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA; Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancón, Panama
| | - Juan M Losada
- Arnold Arboretum, Harvard University, 1300 Centre St., Boston, MA 02131, USA
| | - Karl J Niklas
- Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA.
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19
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Abstract
The phloem plays a central role in transporting resources and signalling molecules from fully expanded leaves to provide precursors for, and to direct development of, heterotrophic organs located throughout the plant body. We review recent advances in understanding mechanisms regulating loading and unloading of resources into, and from, the phloem network; highlight unresolved questions regarding the physiological significance of the vast array of proteins and RNAs found in phloem saps; and evaluate proposed structure/function relationships considered to account for bulk flow of sap, sustained at high rates and over long distances, through the transport phloem.
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Affiliation(s)
- Johannes Liesche
- Biomass Energy Center for Arid and Semi-arid lands, Northwest A&F University, Yangling, China
- College of Life Science, Northwest A&F University, Yangling , China
| | - John Patrick
- Department of Biological Sciences, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, Australia
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