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Biot-Granier Sensor: A Novel Strategy to Measuring Sap Flow in Trees. SENSORS 2020; 20:s20123538. [PMID: 32580426 PMCID: PMC7349400 DOI: 10.3390/s20123538] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 06/16/2020] [Accepted: 06/17/2020] [Indexed: 11/17/2022]
Abstract
The Biot-Granier (Gbt) is a new thermal dissipation-based sap flow measurement methodology, comprising sensors, data management and automatic data processing. It relies on the conventional Granier (Gcv) methodology upgraded with a modified Granier sensor set, as well as on an algorithm to measure the absolute temperatures in the two observation points and perform the Biot number approach. The work described herein addresses the construction details of the Gbt sensors and the characterization of the overall performance of the Gbt method after comparison with a commercial sap flow sensor and independent data (i.e., volumetric water content, vapor pressure deficit and eddy covariance technique). Its performance was evaluated in three trials: potted olive trees in a greenhouse and two vineyards. The trial with olive trees in a greenhouse showed that the transpiration measures provided by the Gbt sensors showed better agreement with the gravimetric approach, compared to those provided by the Gcv sensors. These tended to overestimate sap flow rates as much as 4 times, while Gbt sensors overestimated gravimetric values 1.5 times. The adjustments based on the Biot equations obtained with Gbt sensors contribute to reduce the overestimates yielded by the conventional approach. On the other hand, the heating capacity of the Gbt sensor provided a minimum of around 7 °C and maximum about 9 °C, contrasting with a minimum around 6 °C and a maximum of 12 °C given by the Gcv sensors. The positioning of the temperature sensor on the tip of the sap flow needle proposed in the Gbt sensors, closer to the sap measurement spot, allow to capture sap induced temperature variations more accurately. This explains the higher resolution and sensitivity of the Gbt sensor. Overall, the alternative Biot approach showed a significant improvement in sap flow estimations, contributing to adjust the Granier sap flow index, a vulnerability of that methodology.
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Nhean S, Isarangkool Na Ayutthaya S, Rocheteau A, Do FC. Multi-species test and calibration of an improved transient thermal dissipation system of sap flow measurement with a single probe. TREE PHYSIOLOGY 2019; 39:1061-1070. [PMID: 30865277 DOI: 10.1093/treephys/tpz017] [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: 10/15/2018] [Revised: 01/30/2019] [Indexed: 06/09/2023]
Abstract
Transient thermal dissipation (TTD) systems provide a simple way to measure xylem sap flow with dual or single Granier-type probe, which gives lower energy consumption and higher accuracy due to its lessor sensitivity to thermal interferences. A new system, TTD heat within 5 min (TTD5), proposed on the reduction of the heating duration. This evolution captured interest through decreased energy consumption and increased temporal resolution. Within our study, the first objective was to test and calibrate this new system with a single probe for young rubber tree - Hevea brasiliensis. The second objective was to explore the sources of variability in calibration such as species, individual cut-stems and probe-wood contact. The complementary species consisted of two diffuse-porous species (mango tree - Mangifera indica, eucalyptus tree - Eucalyptus camaldulensis) and one ring-porous species (teak tree - Tectonia grandis). Twenty-eight response curves were assessed over a large range of flux densities from 0.5 to 10 l dm-2 h-1. The incremental rise of temperature from 30 to 300 s (T300-30) after commencement of heating was sensitive to flux density over the complete range. Compared with the full signal at 300 s, the incremental signal markedly reduced the variability between response curves within species and between species. Moreover, a new index K2, defined as (T0 - Tu)/T0, normalized the responses between 0 and 1. However, the responses had a non-linear trend above 5 l dm-2 h-1. Within diffuse-porous wood type, the species did not differ in calibration, whereas the ring-porous species was markedly different. A sigmoid function provided the best fit for the diffuse-porous species. Individual stems were identified as the main source of within-species variability in calibration. The normalizing K2 index removed the influence of probe-wood contacts, controlled through drilling difference; however, there was still an effect of individual stems interacting with flux density (P = 0.019). Replications of cut-stems and response curves are necessary to assess a reliable averaged calibration. In conclusion, the applicability of the TTD5 system with a single probe has been confirmed and several sources of variability in calibration have been evaluated.
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Affiliation(s)
- Sophea Nhean
- Horticultural Section, Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
- Rubber Development Department, General Directorate of Rubber, Ministry of Agriculture, Forestry and Fisheries, Penh, Cambodia
| | | | - Alain Rocheteau
- IRD, University of Montpellier, Eco&Sols Unit, CIRAD, INRA, SupAgro, Montpellier, France
| | - Frederic C Do
- IRD, University of Montpellier, Eco&Sols Unit, CIRAD, INRA, SupAgro, Montpellier, France
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Peters RL, Fonti P, Frank DC, Poyatos R, Pappas C, Kahmen A, Carraro V, Prendin AL, Schneider L, Baltzer JL, Baron-Gafford GA, Dietrich L, Heinrich I, Minor RL, Sonnentag O, Matheny AM, Wightman MG, Steppe K. Quantification of uncertainties in conifer sap flow measured with the thermal dissipation method. THE NEW PHYTOLOGIST 2018; 219:1283-1299. [PMID: 29862531 DOI: 10.1111/nph.15241] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 04/24/2018] [Indexed: 06/08/2023]
Abstract
Trees play a key role in the global hydrological cycle and measurements performed with the thermal dissipation method (TDM) have been crucial in providing whole-tree water-use estimates. Yet, different data processing to calculate whole-tree water use encapsulates uncertainties that have not been systematically assessed. We quantified uncertainties in conifer sap flux density (Fd ) and stand water use caused by commonly applied methods for deriving zero-flow conditions, dampening and sensor calibration. Their contribution has been assessed using a stem segment calibration experiment and 4 yr of TDM measurements in Picea abies and Larix decidua growing in contrasting environments. Uncertainties were then projected on TDM data from different conifers across the northern hemisphere. Commonly applied methods mostly underestimated absolute Fd . Lacking a site- and species-specific calibrations reduced our stand water-use measurements by 37% and induced uncertainty in northern hemisphere Fd . Additionally, although the interdaily variability was maintained, disregarding dampening and/or applying zero-flow conditions that ignored night-time water use reduced the correlation between environment and Fd . The presented ensemble of calibration curves and proposed dampening correction, together with the systematic quantification of data-processing uncertainties, provide crucial steps in improving whole-tree water-use estimates across spatial and temporal scales.
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Affiliation(s)
- Richard L Peters
- Landscape Dynamics, Swiss Federal Research Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland
- Department of Environmental Sciences - Botany, Basel University, Schönbeinstrasse 6, CH-4056, Basel, Switzerland
| | - Patrick Fonti
- Landscape Dynamics, Swiss Federal Research Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland
| | - David C Frank
- Landscape Dynamics, Swiss Federal Research Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland
- Laboratory of Tree-Ring Research, 1215 E. Lowell Street, Tucson, AZ, 8572, USA
- Oeschger Centre for Climate Change Research, Falkenplatz 16, CH-3012, Bern, Switzerland
| | - Rafael Poyatos
- CREAF, E08193, Bellaterra (Cerdanyola del Vallès), Catalonia, Spain
- Faculty of Bioscience Engineering, Department of Plants and Crops, Laboratory of Plant Ecology, Ghent University, Coupure links 653, B-9000, Ghent, Belgium
| | - Christoforos Pappas
- Département de géographie and Centre d'études nordiques, Université de Montréal, Montréal, QC, H2V 2B8, Canada
| | - Ansgar Kahmen
- Department of Environmental Sciences - Botany, Basel University, Schönbeinstrasse 6, CH-4056, Basel, Switzerland
| | - Vinicio Carraro
- Department TeSAF Territorio e Sistemi Agro-Forestali, Università degli Studi di Padova, Viale dell'Università 16, I-35020, Legnaro, PD, Italy
| | - Angela Luisa Prendin
- Department TeSAF Territorio e Sistemi Agro-Forestali, Università degli Studi di Padova, Viale dell'Università 16, I-35020, Legnaro, PD, Italy
- Department of Bioscience, Ecoinformatic & Biodiversity, Aarhus University, Ny Munkegade 116, Building 1540, DK-8000, Aarhus C, Denmark
| | - Loïc Schneider
- Landscape Dynamics, Swiss Federal Research Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland
| | - Jennifer L Baltzer
- Biology Department, Wilfrid Laurier University, 75 University Ave. W, Waterloo, ON, N2L 3C5, Canada
| | - Greg A Baron-Gafford
- School of Geography and Development, University of Arizona, 1064 E Lowell St, Tucson, AZ, 85719, USA
| | - Lars Dietrich
- Department of Environmental Sciences - Botany, Basel University, Schönbeinstrasse 6, CH-4056, Basel, Switzerland
| | - Ingo Heinrich
- Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Climate Dynamics and Landscape Evolution, Telegrafenberg, 14473, Potsdam, Germany
| | - Rebecca L Minor
- School of Geography and Development, University of Arizona, 1064 E Lowell St, Tucson, AZ, 85719, USA
| | - Oliver Sonnentag
- Département de géographie and Centre d'études nordiques, Université de Montréal, Montréal, QC, H2V 2B8, Canada
| | - Ashley M Matheny
- Department of Geological Sciences, Jackson School of Geosciences, 2305 Speedway Stop, C1160, Austin, TX, USA
| | - Maxwell G Wightman
- College of Forestry, Oregon State University, 1500 SW Jefferson St, Corvallis, OR, 97331, USA
| | - Kathy Steppe
- Faculty of Bioscience Engineering, Department of Plants and Crops, Laboratory of Plant Ecology, Ghent University, Coupure links 653, B-9000, Ghent, Belgium
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Ghimire CP, Bruijnzeel LA, Lubczynski MW, Zwartendijk BW, Odongo VO, Ravelona M, van Meerveld HJI. Transpiration and stomatal conductance in a young secondary tropical montane forest: contrasts between native trees and invasive understorey shrubs. TREE PHYSIOLOGY 2018; 38:1053-1070. [PMID: 29688549 DOI: 10.1093/treephys/tpy004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Accepted: 01/09/2018] [Indexed: 06/08/2023]
Abstract
It has been suggested that vigorous secondary tropical forests can have very high transpiration rates, but sap flow and stomatal conductance dynamics of trees and shrubs in these forests are understudied. In an effort to address this knowledge gap, sap flow (thermal dissipation method, 12 trees) and stomatal conductance (porometry, six trees) were measured for young (5-7 years) Psiadia altissima (DC.) Drake trees, a widely occurring species dominating young regrowth following abandonment of swidden agriculture in upland eastern Madagascar. In addition, stomatal conductance (gs) was determined for three individuals of two locally common invasive shrubs (Lantana camara L. and Rubus moluccanus L.) during three periods with contrasting soil moisture conditions. Values of gs for the three investigated species were significantly higher and more sensitive to climatic conditions during the wet period compared with the dry period. Further, gs of the understorey shrubs was much more sensitive to soil moisture content than that of the trees. Tree transpiration rates (Ec) were relatively stable during the dry season and were only affected somewhat by soil water content at the end of the dry season, suggesting the trees had continued access to soil water despite drying out of the topsoil. The Ec exhibited a plateau-shaped relation with vapour pressure deficit (VPD), which was attributed to stomatal closure at high VPD. Vapour pressure deficit was the major driver of variation in Ec, during both the wet and the dry season. Overall water use of the trees was modest, possibly reflecting low site fertility after three swidden cultivation cycles. The observed contrast in gs response to soil water and climatic conditions for the trees and shrubs underscores the need to take root distributions into account when modelling transpiration from regenerating tropical forests.
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Affiliation(s)
- Chandra Prasad Ghimire
- Faculty of Geo-information and Earth Observation (ITC), University of Twente, Enschede, Hengelosestraat 99, AE Enschede, The Netherlands
| | - L Adrian Bruijnzeel
- Department of Geography, King's College London, London, UK
- Tropical Forests and People Research Centre, University of the Sunshine Coast, Maroochydore DC, QLD, Queensland, Australia
| | - Maciek W Lubczynski
- Faculty of Geo-information and Earth Observation (ITC), University of Twente, Enschede, Hengelosestraat 99, AE Enschede, The Netherlands
| | - Bob W Zwartendijk
- Department of Geography, Hydrology and Climate, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland
| | - Vincent Omondi Odongo
- Department of Agricultural Engineering, Egerton University, PO Box 536, Egerton, Njoro, Kenya
- Water Resources Management Group, Wageningen University & Research, AA Wageningen, The Netherlands
| | - Maafaka Ravelona
- Laboratoire des Radio-Isotopes, University of Antananarivo, BP 3383, Route d'Andraisoro, 101 Antananarivo, Madagascar
| | - H J Ilja van Meerveld
- Department of Geography, Hydrology and Climate, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland
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Marañón-Jiménez S, Van den Bulcke J, Piayda A, Van Acker J, Cuntz M, Rebmann C, Steppe K. X-ray computed microtomography characterizes the wound effect that causes sap flow underestimation by thermal dissipation sensors. TREE PHYSIOLOGY 2018; 38:287-301. [PMID: 28981912 DOI: 10.1093/treephys/tpx103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 08/04/2017] [Indexed: 05/26/2023]
Abstract
Insertion of thermal dissipation (TD) sap flow sensors in living tree stems causes damage of the wood tissue, as is the case with other invasive methods. The subsequent wound formation is one of the main causes of underestimation of tree water-use measured by TD sensors. However, the specific alterations in wood anatomy in response to inserted sensors have not yet been characterized, and the linked dysfunctions in xylem conductance and sensor accuracy are still unknown. In this study, we investigate the anatomical mechanisms prompting sap flow underestimation and the dynamic process of wound formation. Successive sets of TD sensors were installed in the early, mid and end stage of the growing season in diffuse- and ring-porous trees, Fagus sylvatica (Linnaeus) and Quercus petraea ((Mattuschka) Lieblein), respectively. The trees were cut in autumn and additional sensors were installed in the cut stem segments as controls without wound formation. The wounded area and volume surrounding each sensor was then visually determined by X-ray computed microtomography (X-ray microCT). This technique allowed the characterization of vessel anatomical transformations such as tyloses formation, their spatial distribution and quantification of reduction in conductive area. MicroCT scans showed considerable formation of tyloses that reduced the conductive area of vessels surrounding the inserted TD probes, thus causing an underestimation in sap flux density (SFD) in both beech and oak. Discolored wood tissue was ellipsoidal, larger in the radial plane, more extensive in beech than in oak, and also for sensors installed for longer times. However, the severity of anatomical transformations did not always follow this pattern. Increased wound size with time, for example, did not result in larger SFD underestimation. This information helps us to better understand the mechanisms involved in wound effects with TD sensors and allows the provision of practical recommendations to reduce biases associated with wounding in field sap flow measurements.
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Affiliation(s)
- S Marañón-Jiménez
- University of Granada, Department of Applied Physics, Av. Fuentenueva s/n, 18071 Granada, Spain
| | - J Van den Bulcke
- UGCT - Woodlab-UGent, Laboratory of Wood Technology, Department of Forest and Water Management, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium
| | - A Piayda
- UFZ, Helmholtz Centre for Environmental Research, Department Computational Hydrosystems, Permoserstraße 15, 04318 Leipzig, Germany
- Thünen Institute of Climate-Smart Agriculture, Bundesallee 50, 38116 Braunschweig, Germany
| | - J Van Acker
- UGCT - Woodlab-UGent, Laboratory of Wood Technology, Department of Forest and Water Management, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium
| | - M Cuntz
- UFZ, Helmholtz Centre for Environmental Research, Department Computational Hydrosystems, Permoserstraße 15, 04318 Leipzig, Germany
- INRA, Université de Lorraine, UMR1137 Ecologie et Ecophysiologie Forestières, 54280 Champenoux, France
| | - C Rebmann
- UFZ, Helmholtz Centre for Environmental Research, Department Computational Hydrosystems, Permoserstraße 15, 04318 Leipzig, Germany
| | - K Steppe
- Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium
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Tree Shelterbelts as an Element to Improve Water Resource Management in Central Asia. WATER 2017. [DOI: 10.3390/w9110842] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Wiedemann A, Marañón-Jiménez S, Rebmann C, Herbst M, Cuntz M. An empirical study of the wound effect on sap flux density measured with thermal dissipation probes. TREE PHYSIOLOGY 2016; 36:1471-1484. [PMID: 27587487 DOI: 10.1093/treephys/tpw071] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Revised: 06/22/2016] [Accepted: 07/02/2016] [Indexed: 06/06/2023]
Abstract
The insertion of thermal dissipation (TD) sensors on tree stems for sap flux density (SFD) measurements can lead to SFD underestimations due to a wound formation close to the drill hole. However, the wound effect has not been assessed experimentally for this method yet. Here, we propose an empirical approach to investigate the effect of the wound healing on measured sap flux with TD probes. The approach was performed for both, diffuse-porous (Fagus sylvatica (Linnaeus)) and ring-porous (Quercus petraea (Lieblein)) species. Thermal dissipation probes were installed on different dates along the growing season to document the effects of the dynamic wound formation. The trees were cut in autumn and additional sensors were installed in the cut stems, therefore, without potential effects of wound development. A range of water pressures was applied to the stem segments and SFDs were simultaneously measured by TD sensors as well as gravimetrically in the laboratory. The formation of wounds around sensors installed in living tree stems led to underestimation of SFD by 21.4 ± 3 and 47.5 ± 3.8% in beech and oak, respectively. The differences between SFD underestimations of diffuse-porous beech and ring-porous oak were, however, not statistically significant. Sensors with 5-, 11- and 22-week-old wounds also showed no significant differences, which implies that the influence of wound formation on SFD estimates was completed within the first few weeks after perforation. These results were confirmed by time courses of SFD measurements in the field. Field SFD values decreased immediately after sensor installation and reached stable values after ~2 weeks with similar underestimations to the ones observed in the laboratory. We therefore propose a feasible approach to correct directly field observations of SFD for potential underestimations due to the wound effect.
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Affiliation(s)
- Andreas Wiedemann
- Department Computational Hydrosystems, UFZ-Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany
- Institute for Geological Sciences, Friedrich-Schiller-University Jena, Burgweg 11, 07749 Jena, Germany
| | - Sara Marañón-Jiménez
- Department Computational Hydrosystems, UFZ-Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany
- Institute for Geological Sciences, Friedrich-Schiller-University Jena, Burgweg 11, 07749 Jena, Germany
- Department of Applied Physics, University of Granada, Av. Fuentenueva s/n, E-18071 Granada, Spain
| | - Corinna Rebmann
- Department Computational Hydrosystems, UFZ-Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany
| | - Mathias Herbst
- Thünen Institute of Climate Smart Agriculture, Bundesallee 50, 38116 Braunschweig, Germany
| | - Matthias Cuntz
- Department Computational Hydrosystems, UFZ-Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany
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Vandegehuchte MW, Burgess SSO, Downey A, Steppe K. Influence of stem temperature changes on heat pulse sap flux density measurements. TREE PHYSIOLOGY 2015; 35:346-353. [PMID: 25145698 DOI: 10.1093/treephys/tpu068] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 07/13/2014] [Indexed: 06/03/2023]
Abstract
While natural spatial temperature gradients between measurement needles have been thoroughly investigated for continuous heat-based sap flow methods, little attention has been given to how natural changes in stem temperature impact heat pulse-based methods through temporal rather than spatial effects. By modelling the theoretical equation for both an ideal instantaneous pulse and a step pulse and applying a finite element model which included actual needle dimensions and wound effects, the influence of a varying stem temperature on heat pulse-based methods was investigated. It was shown that the heat ratio (HR) method was influenced, while for the compensation heat pulse and Tmax methods changes in stem temperatures of up to 0.002 °C s(-1) did not lead to significantly different results. For the HR method, rising stem temperatures during measurements led to lower heat pulse velocity values, while decreasing stem temperatures led to both higher and lower heat pulse velocities, and to imaginary results for high flows. These errors of up to 40% can easily be prevented by including a temperature correction in the data analysis procedure, calculating the slope of the natural temperature change based on the measured temperatures before application of the heat pulse. Results of a greenhouse and outdoor experiment on Pinus pinea L. show the influence of this correction on low and average sap flux densities.
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Affiliation(s)
- Maurits W Vandegehuchte
- Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium
| | - Stephen S O Burgess
- School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
| | - Alec Downey
- School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia ICT International, 211 Mann St, Armidale, NSW 2350, Australia
| | - Kathy Steppe
- Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium
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Kim HK, Park J, Hwang I. Investigating water transport through the xylem network in vascular plants. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:1895-904. [PMID: 24609652 DOI: 10.1093/jxb/eru075] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Our understanding of physical and physiological mechanisms depends on the development of advanced technologies and tools to prove or re-evaluate established theories, and test new hypotheses. Water flow in land plants is a fascinating phenomenon, a vital component of the water cycle, and essential for life on Earth. The cohesion-tension theory (CTT), formulated more than a century ago and based on the physical properties of water, laid the foundation for our understanding of water transport in vascular plants. Numerous experimental tools have since been developed to evaluate various aspects of the CTT, such as the existence of negative hydrostatic pressure. This review focuses on the evolution of the experimental methods used to study water transport in plants, and summarizes the different ways to investigate the diversity of the xylem network structure and sap flow dynamics in various species. As water transport is documented at different scales, from the level of single conduits to entire plants, it is critical that new results be subjected to systematic cross-validation and that findings based on different organs be integrated at the whole-plant level. We also discuss the functional trade-offs between optimizing hydraulic efficiency and maintaining the safety of the entire transport system. Furthermore, we evaluate future directions in sap flow research and highlight the importance of integrating the combined effects of various levels of hydraulic regulation.
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Affiliation(s)
- Hae Koo Kim
- International Maize and Wheat Improvement Center, CIMMYT-Ethiopia, P.O. Box 5689, Addis Ababa, Ethiopia
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