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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The decline in above-ground net primary productivity (Pa) that is usually observed in forest stands has been variously attributed to respiration, nutrient or hydraulic limitations. A novel model is proposed to explain the phenomenon and the co-occurring changes in the balance between foliage, conducting sapwood and fine roots. The model is based on the hypothesis that a functional homeostasis in water transport is maintained irrespective of age: hydraulic resistances through the plant must be finely tuned to transpiration rates so as to avoid extremely negative water potentials that could result in diffuse xylem embolism and foliage dieback, in agreement with experimental evidence. As the plant grows taller, allocation is predicted to shift from foliage to transport tissues, most notably to fine roots. Higher respiration and fine root turnover would result in the observed decline in Pa. The predictions of the model have been compared with experimental data from a chronosequence of Pinus sylvestris stands. The observed reduction in Pa is conveniently explained by concurrent modifications in leaf area index and plant structure. Changes in allometry and shoot hydraulic conductance with age are successfully predicted by the principle of functional homeostasis.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science, Ltd
    Plant, cell & environment 26 (2003), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plant hydraulic conductance, namely the rate of water flow inside plants per unit time and unit pressure difference, varies largely from plant to plant and under different environmental conditions. Herein the main factors affecting: (a) the scaling between whole-plant hydraulic conductance and leaf area; (b) the relationship between gas exchange at the leaf level and leaf-specific xylem hydraulic conductance; (c) the short-term physiological regulation of plant hydraulic conductance under conditions of ample soil water, and (d) the long-term structural acclimation of xylem hydraulic conductance to changes in environmental conditions are reviewed. It is shown that plant hydraulic conductance is a highly plastic character that varies as a result of multiple processes acting at several time scales. Across species ranging from coniferous and broad-leaved trees to shrubs, crop and herbaceous species, and desert subshrubs, hydraulic conductance scaled linearly with leaf area, as expected from first principles. Despite considerable convergence in the scaling of hydraulic properties, significant differences were apparent across life forms that underlie their different abilities to conduct gas exchange at the leaf level. A simple model of carbon allocation between leaves and support tissues explained the observed patterns and correctly predicted the inverse relationships with plant height. Therefore, stature appears as a fundamental factor affecting gas exchange across plant life forms. Both short-term physiological regulation and long-term structural acclimation can change the levels of hydraulic conductance significantly. Based on a meta-analysis of the existing literature, any change in environmental parameters that increases the availability of resources (either above- or below-ground) results in the long-term acclimation of a less efficient (per unit leaf area) hydraulic system.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Hydraulic resistance to water flow was measured in branches and stems of Scots pine trees ranging from 7 to 59 years of age in Thetford (East Anglia, UK). On the basis of these measurements, tree above-ground conductance was calculated and related to the amount of leaf area sustained by each tree. Branches at the crown bottom had a lower proportion of sapwood area and a lower total hydraulic conductance than branches of the same diameter at the tree top. Within branches, most of the hydraulic resistance was located near the needles. Tree above-ground conductance was positively related to tree diameter and inversely related to tree height. Compared with young trees, mature trees had about 4 times less above-ground conductance per unit of leaf area. Apparently, the increase in pathway length associated with tree height growth could be only partially compensated for by the increase in conductive capacities resulting from diameter growth. We argue that this reduction may account for reported decreases of stomatal conductance with tree age. It is suggested that the increase in branchiness associated with tree maturation may represent a compensation mechanism to reduce the overall resistance to water flow in the crowns.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Stomatal response to leaf water status was experimentally manipulated by pressurizing the soil and roots of potted common bean plants enclosed in a custom-built root pressure chamber. Gas exchange was monitored using a whole-plant cuvette and plant water status using in situ leaf psychrometry. Bean plants re-opened their stomata upon pressurization, but the extent of re-opening was strongly dependent on the time of day when the soil was pressurized, with maximum re-opening in the morning hours and limited re-opening in the afternoon. Neither leaf nor xylem abscisic acid concentrations could explain the reduced response to pressurization in the afternoon. The significance of this phenomenon is discussed in the context of circadian rhythms and of other recent findings on the ‘apparent feed-forward response’ of the stomata of some species to vapour pressure deficit.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The role of leaf water potential in controlling stomatal conductance (gs) was examined in the desert subshrub Hymenoclea salsola. For plants operating at high irradiance, stomatal closure in response to high leaf-air humidity gradient (D) was largely reversed by soil pressurization. Stomatal re-opening eliminated, on average, 89% of the closure normally induced by high D. Transpiration rates (E) reached under these conditions were far higher than maximal rates normally observed at any point of the D response. In situ stem psychrometry indicated that water flux at all times conformed to a simple Ohm’s-law analogy. Under conditions of high D, E increased substantially in response to soil pressurization. Stomatal regulation did not constrain E during this treatment, but did result in nearly constant minimum leaf water potentials.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 102 (1995), S. 164-168 
    ISSN: 1432-1939
    Keywords: Pinus sylvestris ; Hydraulic architecture ; Geographic variation ; Pipe theory ; Branchiness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Analysis of the branch area/stem area ratio of Scots pine growing in different climatic conditions in Europe and Siberia indicates that the branch area supported by a stem increases in warmer and drier conditions. The ratio was significantly correlated with several climatic variables, especially with potential evapotranspiration (E p). The ratio was negatively correlated with stand density (d s). A regression model combining E p and d s accounted for 85% of the total variation. These trends are believed to reflect hydraulic segmentation of trees and may represent a strategy to avoid cavitation in the tree, especially in the branches.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 98 (1999), S. 411-421 
    ISSN: 1432-2242
    Keywords: Key words AFLPs ; Diversity ; Phylogeny ; Olea europaea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Amplified fragment length polymorphism (AFLP) analysis was used to study the genetic variation within and among populations of genus Olea. A group of genotypes, all of them cultivated varieties of a single species, Olea europaea, was compared with wild olives and with a group of individuals belonging to different Olea species. Five primer combinations were used which produced about 290 polymorphic bands. The data obtained were elaborated with the Nei’s genetic similarity coefficient, applying different clustering methods and the Principal Coordinate Analysis. Cultivars, wild olives and North-West African species formed groups clustering together at a similarity level of 0.56, while the Olea species from East Africa and Asia grouped separately. Species from the Indian Ocean and Australia showed the highest diversity. We hypothesize that cultivars and wild plants are different forms of the same O. europaea species. The Olea from East Africa and Asia may be assigned to a different species, while the role of O. laperrini as well as that of O. maroccana as an intermediary form is confirmed.
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2015-04-30
    Print ISSN: 0829-318X
    Electronic ISSN: 1758-4469
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 9
    Publication Date: 2015-05-08
    Description: Growth models continue to be of importance in modern multi-functional forestry to provide forecasts. Bayesian calibrations allow both model structure and parameters to be assessed simultaneously in a probabilistic framework, providing a model with which forecasts and their uncertainty can be better understood and quantified using posterior probability distributions. A Bayesian calibration of a stand-level dynamic growth (SLeDG) model is carried out for both Sitka spruce and Scots pine in the UK for the first time. The calibration used the differential evolution Markov-Chain method to reduce the required number of iterations for inference. Two different model structures were considered for estimating local stand productivity: one using the measured height–age relationship, and one using estimated site yield class. The height–age relationship was shown to be more probable for both species in a Bayesian model comparison (total model probability $=$ 0.64 and 0.58 for Sitka spruce and Scots pine, respectively), although metrics of model performance were similar for both model structures ( $R^2 \geq 0.88$ in all variables). A complete calibration (using all data) of the more probable model structure was then completed, and excellent model fit was observed ( $R^2 〉 0.95$ for all variables in both species). Example forecasts using the output from the calibration were demonstrated, and are compatible with existing yield tables for both species. This method could be applied to other species or other model structures in the future.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 10
    Publication Date: 2012-02-11
    Description: The effects of site preparation practices (drainage, mounding and fertilization) on the fluxes from the soil surface of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) were studied on an organic-rich peaty gley soil at Harwood Forest, north-east England. Drained plots had significantly higher CO 2 fluxes but significantly lower CH 4 fluxes compared with undrained plots, while N 2 O emissions were not affected by drainage. Mounding caused significantly higher CH 4 emissions, while it significantly reduced N 2 O emissions. Fertilization caused significant increases in emissions of CO 2 , CH 4 and N 2 O. In terms of overall greenhouse warming potential, drainage and fertilization increased CO 2 -equivalent emissions by ~18–29 and 7–23 per cent, respectively, while mounding reduced CO 2 -equivalent emissions by ~8 per cent in year 1, but had no effect on emissions in year 2 of study. Soil temperature was the main environmental variable controlling CO 2 emissions, while CH 4 was controlled primarily by water table depth. Nitrous oxide emissions responded to changes in soil temperature and water table depth. In the short term, drainage and fertilization contributed to accelerating greenhouse gas emissions significantly, although their long-term effects are likely moderated by accelerating carbon accumulation in the tree biomass. Long-term studies are required to assess the cumulative impacts of site preparation practices during the whole rotation cycle.
    Print ISSN: 0015-752X
    Electronic ISSN: 1464-3626
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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