Article

A physiological model of softwood cambial growth.

Department of Forest Sciences, University of Helsinki, Helsinki, Finland.
Tree Physiology (Impact Factor: 3.41). 10/2010; 30(10):1235-52. DOI: 10.1093/treephys/tpq068
Source: PubMed

ABSTRACT Cambial growth was modelled as a function of detailed levelled physiological processes for cell enlargement and water and sugar transport to the cambium. Cambial growth was described at the cell level where local sugar concentration and turgor pressure induce irreversible cell expansion and cell wall synthesis. It was demonstrated how transpiration and photosynthesis rates, metabolic and physiological processes and structural features of a tree mediate their effects directly on the local water and sugar status and influence cambial growth. Large trees were predicted to be less sensitive to changes in the transient water and sugar status, compared with smaller ones, as they have more water and sugar storage and were, therefore, less coupled to short-term changes in the environment. Modelling the cambial dynamics at the individual cell level turned out to be a complex task as the radial short-distance transport of water and sugars and control signals determining cell division and cessation of cell enlargement and cell wall synthesis had to be described simultaneously.

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    • "These approaches used a sap flow and storage methodology, where water potential is the driver for linking changes of stem diameter to water stored in the stem. More recent water storage and sap flow models have linked variations in stem radius to both water relations and cambial growth (De Schepper & Steppe, 2010, Hölttä et al., 2010, Steppe, De Pauw, Lemeur & Vanrolleghem, 2006) and changes in phloem osmotic concentration (Mencuccini et al., 2013). "
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    ABSTRACT: The quantification of cambial growth over short time periods has been hampered by problems to discern between growth and the swelling and shrinking of a tree stem. This paper presents a model, which separates cambial growth and reversible water-potential induced diurnal changes from simultaneously measured whole stem and xylem radial variations, from field-measured Scots pine trees in Finland. The modelled growth, which includes osmotic concentration changes, was compared to (direct) dendrometer measurements and microcore samples. In addition, the relationship of modelled growth and dendrometer measurements to environmental factors were analysed. Results showed that the water-potential induced changes of tree radius were successfully separated from stem growth. Daily growth predicted by the model exhibited a high correlation with the modelled daily changes of osmotic concentration in phloem, and a temperature dependency in early summer. Late summer growth saw higher dependency on water availability and temperature. Evaluation of the model against dendrometer measurements showed that the latter masked a true environmental signal in stem growth due to water-potential induced changes. The model provides better understanding of radial growth physiology and offers potential to examine growth dynamics and changes due to osmotic concentration, and how the environment affects growth. This article is protected by copyright. All rights reserved.
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    • "rtheless , it appears that the model ' s ability to predict cell volume was the key output explaining differences between modelled and observed density . Thus , future efforts should be focused on improving the repre - sentation of turgor dynamics in MuSICA by coupling water and carbon more intimately as shown in other models ( Drew et al . 2010 , Hölttä et al . 2010 ) . Prediction of cell volume was highly sensitive to cell enlarge - ment rate , which may implicate a genetic component in cell expansion . Cell enlargement rate is proportional to soil moisture in the model , yet biological constraints affect the extent of dependence of the cambial environment on the soil environ - ment . Xylem ontoge"
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    ABSTRACT: Process-based models that link seasonally varying environmental signals to morphological features within tree rings are essential tools to predict tree growth response and commercially important wood quality traits under future climate scenarios. This study evaluated model portrayal of radial growth and wood anatomy observations within a mature maritime pine (Pinus pinaster (L.) Aït.) stand exposed to seasonal droughts. Intra-annual variations in tracheid anatomy and wood density were identified through image analysis and X-ray densitometry on stem cores covering the growth period 1999–2010. A cambial growth model was integrated with modelled plant water status and sugar availability from the soil–plant–atmosphere transfer model MuSICA to generate estimates of cell number, cell volume, cell mass and wood density on a weekly time step. The model successfully predicted inter-annual variations in cell number, ring width and maximum wood density. The model was also able to predict the occurrence of special anatomical features such as intra-annual density fluctuations (IADFs) in growth rings. Since cell wall thickness remained surprisingly constant within and between growth rings, variations in wood density were primarily the result of variations in lumen diameter, both in the model and anatomical data. In the model, changes in plant water status were identified as the main driver of the IADFs through a direct effect on cell volume. The anatomy data also revealed that a trade-off existed between hydraulic safety and hydraulic efficiency. Although a simplified description of cambial physiology is presented, this integrated modelling approach shows potential value for identifying universal patterns of tree-ring growth and anatomical features over a broad climatic gradient.
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    • "rtheless , it appears that the model ' s ability to predict cell volume was the key output explaining differences between modelled and observed density . Thus , future efforts should be focused on improving the repre - sentation of turgor dynamics in MuSICA by coupling water and carbon more intimately as shown in other models ( Drew et al . 2010 , Hölttä et al . 2010 ) . Prediction of cell volume was highly sensitive to cell enlarge - ment rate , which may implicate a genetic component in cell expansion . Cell enlargement rate is proportional to soil moisture in the model , yet biological constraints affect the extent of dependence of the cambial environment on the soil environ - ment . Xylem ontoge"
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    ABSTRACT: Process-based models that link seasonally varying environmental signals to morphological features within tree rings are essential tools to predict tree growth response and commercially important wood quality traits under future climate scenarios. This study evaluated model portrayal of radial growth and wood anatomy observations within a mature maritime pine (Pinus pinaster (L.) Aït.) stand exposed to seasonal droughts. Intra-annual variations in tracheid anatomy and wood density were identified through image analysis and X-ray densitometry on stem cores covering the growth period 1999-2010. A cambial growth model was integrated with modelled plant water status and sugar availability from the soil-plant-atmosphere transfer model MuSICA to generate estimates of cell number, cell volume, cell mass and wood density on a weekly time step. The model successfully predicted inter-annual variations in cell number, ring width and maximum wood density. The model was also able to predict the occurrence of special anatomical features such as intra-annual density fluctuations (IADFs) in growth rings. Since cell wall thickness remained surprisingly constant within and between growth rings, variations in wood density were primarily the result of variations in lumen diameter, both in the model and anatomical data. In the model, changes in plant water status were identified as the main driver of the IADFs through a direct effect on cell volume. The anatomy data also revealed that a trade-off existed between hydraulic safety and hydraulic efficiency. Although a simplified description of cambial physiology is presented, this integrated modelling approach shows potential value for identifying universal patterns of tree-ring growth and anatomical features over a broad climatic gradient. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
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