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Experimental data published previously (Faiz and Weatherley, 1977) emphasized the existence of considerable hydraulic resistance in the perirhizal soil of rapidly transpiring plants. This was evident when soil water potential (ψs) in the root zone was as high as -2 or -3 bars. In a further paper (Faiz and Weatherley, 1978) the hypothesis was put forward that it is the soil-root interface which presents a high resistance to the flow of water through the soil-plant system. This resistance, it was thought, could increase as a result of contraction of stressed. roots, with the formation of vapour gaps between soil and root. In this paper we demonstrate that the root tissues may contract by as much as 25% of their turgid volume when the water potential of the leaves (ψl) falls to around -15 bars. Under such conditions the extensive formation of vapour gaps would be expected and a reduction of water stress should therefore follow if the gaps could be closed mechanically. Such closure was attempted by either squeezing or vibrating the soil mass containing the root system. Both of these treatments led to a temporary reduction in water stress in the plants and the existence of vapour gaps was thus supported. [ABSTRACT FROM AUTHOR]

• A previously published model of crop nitrogen (N) status based on intercepted photosynthetically active radiation ( Ri, mol per plant) suggested that plant organic N accumulation is related to Ri by a constant ratio, defined hereafter as the radiation use efficiency for N (NRUE). The aim of this paper was to compare the effects of N nutrition and CO2 enrichment on NRUE and RUE (radiation use efficiency for biomass accumulation). • In three unrelated glasshouse experiments, tomato plants ( Solanum lycopersicum) grown in hydroponics were fed for 28 d (exponential growth) with full solutions containing constant concentrations ([ ]) ranging from 0.05 to 15 mol m−3, both under ambient or CO2-enriched (1000 µl l−1) air. • Each experiment comprised five harvests. Low [ ] (< 0.3 mol m−3) limited growth via leaf area (LA) restriction and decreased light interception. CO2 enrichment enhanced dry weight and LA. RUE was not affected by [ ], but increased under CO2-enriched air. By contrast, NRUE was not affected by [ ] or CO2 enrichment. • It is suggested that the radiation efficiency for organic N acquisition (NRUE) did not depend on C or N nutrition for young plants grown under unstressed conditions. [ABSTRACT FROM AUTHOR]

• This paper establishes relationships between two aspects of ribosomal DNA (rDNA) biology: epigenetic silencing of rDNA loci; and homogenization leading to concerted evolution. • Here, we examined rDNA inheritance and expression patterns in three natural Nicotiana allopolyploids (closest living descendants of diploid parents are given), N. rustica ( N. paniculata ×  N. undulata), N. tabacum ( N. sylvestris ×  N. tomentosiformis) and N. arentsii ( N. undulata ×  N. wigandioides), and synthetic F1 hybrids and allopolyploids. • The extent of interlocus rDNA homogenization decreased in the direction N. arentsii > N. tabacum >  N. rustica. The persistence of parental rDNA units in one of the subgenomes was associated with their transcription inactivity and likely heterochromatization. Of synthetic hybrids and polyploids only N. paniculata ×  N. undulata showed strong uniparental transcriptional silencing of rDNA triggered already in F1. • Epigenetic patterns of expression established early in allopolyploid nucleus formation may render units susceptible or resistant to homogenization over longer time-frames. We propose that nucleolus-associated transcription leaves rDNA units vulnerable to homogenization, while epigenetically inactivated units, well-separated from the nucleolus, remain unconverted. [ABSTRACT FROM AUTHOR]

• This paper investigates the dependence of monoterpene emissions at the canopy scale on total leaf area and leaf distribution. Simulations were carried out for a range of hypothetical but realistic forest canopies of the evergreen Quercus ilex (holm oak). • Two emission models were applied that either did (SIM-BIM2) or did not (G93) account for cumulative responses to temperature and light. Both were embedded into a canopy model that considered spatial and temporal variations of foliage properties. This canopy model was coupled to a canopy climate model (CANOAK) to determine the micrometeorological conditions at the leaf scale. • Structural properties considerably impacted monoterpene emission. The sensitivities to changes in total leaf area and to leaf area distribution were found to be of similar magnitude. The two different models performed similarly on a whole-year basis but showed clear differences during certain episodes. • The analysis showed that structural indices have to be carefully evaluated for proper scaling of emission from leaves to canopy. Further research is encouraged on seasonal dynamics of emission potentials. [ABSTRACT FROM AUTHOR]

• Attenuated total reflectance (ATR) spectra of plant leaves display complex absorption features related to organic constituents of leaf surfaces. The spectra can be recorded rapidly, both in the field and in the laboratory, without special sample preparation. • This paper explores sources of ATR spectral variation in leaves, including compositional, positional and temporal variations. Interspecific variations are also examined, including the use of ATR spectra as a tool for species identification. • Positional spectral variations generally reflected the abundance of cutin and the epicuticular wax thickness and composition. For example, leaves exposed to full sunlight commonly showed more prominent cutin- and wax-related absorption features compared with shaded leaves. Adaxial vs. abaxial leaf surfaces displayed spectral variations reflecting differences in trichome abundance and wax composition. Mature vs. young leaves showed changes in absorption band position and intensity related to cutin, polysaccharide, and possibly amorphous silica development on and near the leaf surfaces. • Provided that similar samples are compared (e.g. adaxial surfaces of mature, sun-exposed leaves) same-species individuals display practically identical ATR spectra. Using spectral matching procedures to analyze an ATR database containing 117 individuals, including 32 different tree species, 83% of the individuals were correctly identified. [ABSTRACT FROM AUTHOR]

• Conifer foliage structures affect branch and bud temperature by altering the development and convective resistance of the thermal boundary layer. This paper examines foliage effects on forced convection in branches and buds of Picea glauca (Moench) Voss and Pinus contorta Dougl. Ex. Loud., two species that represent the range of variation in foliage structure among conifers. • Forced convection is characterized by a power law relating Nusselt (heat transfer) and Reynolds (boundary layer development) numbers. Data were collected in a laminar flow wind tunnel for free stream velocities of 0.16–6.95 m s−1. Scaling parameters were compared against literature values for silver cast branch replicas, a bed of real foliage, cylinders, and tube banks. • Foliage structures reduced Nusselt numbers (heat transfer) relative to cylinders, which are typically used to approximate leafless branches and buds. Significantly different scaling relationships were observed for all foliage structures considered. • Forced convection scaling relationships varied with foliage structure. The scaling relationships reported here account for variation within populations of branches and buds and can be used to characterize forced convection in a forest canopy. [ABSTRACT FROM AUTHOR]

• The emergence of a regular phyllochron from the dynamic processes of leaf initiation, leaf elongation and whorl construction suggests causal relationships between leaf elongation and leaf emergence. This paper presents a hypothesis as to how the ontogeny of the growth zone of leaves is triggered by emergence events, and implements it in a dynamic model of leaf elongation.• Two different experiments, presenting two contrasted cases of relationships between leaf emergence and kinetics of leaf elongation, were analysed and interpreted with the model in terms of the functioning of the growth zone.• Analysis of elongation kinetics revealed that the hypothesis allows for several contrasted elongation patterns that were observed, and for a regular phyllochron emerging from the variable dynamic of elongation. The model was able to simulate these patterns, and helped to identify the mechanisms underlying the key points of the analysis.• The hypothesis is not demonstrated, but its coherence and robustness are established, which should inform a renewal of the modelling of leaf elongation in architectural models.New Phytologist(2005)doi: 10.1111/j.1469-8137.2005.01371.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

Numerous authors have attempted to quantity the physical properties of leaves in relation to aspects of leaf ecology, including decomposition, sclerophylly, herbivory, and leaf function and longevity. This paper examines the relative merits of the punch-and-die, tearing and shearing tests for assessing leaf physical properties. We conducted a series of these three mechanical tests on leaves of Solanum laciniatum, and determined the effect of various test parameters on the measurement of fracture properties. For the punch-and-die test, the parameters considered were machine speed, clearance between the punch and the die, edge definition of the punch, and area of the punch. Aspects of the tearing test examined were notch length, and effects, and length-to width requirements of t est strips, and for shearing tests the effects of blade proximity, angle and sharpness were investigated. All the test parameters investigated were found significantly to affect the assessment of leaf-fracture properties. In addition, fracture properties were found to vary significantly within leaves. Some general principles for designing and implementing tests are outlined. This study suggests that while punching and shearing tests are useful means of quantifying leaf fracture properties, the value of the tearing test may be reduced as it is most constrained by the biological nature of the test material. [ABSTRACT FROM AUTHOR]

Leaf anatomical parameters such as leaf mass per area (LMA) and biochemical composition can be used as indicators of leaf photosynthetic capacity. The aims of this study are to evaluate the potential of reflectance spectroscopy of fresh leaves for assessing and predicting Various parameters, anatomical (LMA and tissue thickness) and biochemical (nitrogen concentration). This paper describes results obtained with fresh leaves of holm oak (Quercus ilex), an evergreen oak that is widely distributed from mesic to xeric habitats in the Mediterranean. Fresh leaves (560) were collected over 3 yr at six different sites, from the top to the bottom of the canopy. The reflectance of each leaf was obtained within 1 h of sampling with an NIRSystems 6500 spectrophotometer over the range 400-2500 nm. LMA was determined for all samples; biochemical and anatomical measurements were conducted over representative subsample populations of 92 and 87 leaves, respectively. Stepwise regression calibrations and partial least squares (PLS) calibrations were developed and compared with different spectral regions and mathematical treatments. Calibration equations had high coefficients of determination (r2 ranging from 0.94 for nitrogen to 0.98 for LMA and tissue thickness). The PLS regressions gave better results than stepwise regressions for all parameters studied. Compared with regressions calculated on raw spectral data, calculations on second derivatives of spectra improved results in all cases. The use of scatter corrections also improved results. These results show that visible and near-infra red reflectance can he used for accurately predicting anatomical parameters and the nitrogen concentration of fresh holm oak leaves. The results support the suggestion that high spectral resolution imaging spectrometry can be a useful tool for assessing functional processes in forest ecosystems. [ABSTRACT FROM AUTHOR]

The function of a leaf is photosynthesis, which requires the interception of light and access to atmospheric CO2 while controlling water loss. This paper examines the influence of leaf anatomy on both light capture and CO2 diffusion. As photosynthetic metabolism is spread between many chloroplasts, a leaf faces the challenge of matching light capture by a given chloroplast with the metabolic capacity of that chloroplast. Chloroplasts nearest the leaf surface receive the greatest irradiance and therefore absorb more light per unit chlorophyll than chloroplasts in the centre of a leaf. Electron transport and carbon fixation capacities per unit of chlorophyll decline with increasing depth in the leaf, to complexes in chloroplasts have nuclear encoded genetic information. Consequently, all chloroplasts within a given cell have a similar metabolic complement, which limits the potential gradient of photosynthetic capacity per unit chlorophyll across the leaf. A simple model couples light absorption through the leaf (based on the Beer-Lambert law) with the profile of chlorophyll through a leaf and the gradient in photosynthetic capacity. It is validated by comparison with 14CO2 fixation profiles through spinach leaves obtained in various studies. The model can account for published 14C fixation profiles obtained with blue, red and green light of different irradiances and white light applied in different combinations to the adaxial and abaxial surfaces of spinach leaves. The model confirms that spongy mesophyll increases the apparent extinction coefficient of chlorophyll compared to palisade tissue. The palisade tissue nearest the surface which received light facilitates the penetration of light to a greater depth, while spongy mesophyll promotes scattering to enhance light absorption, thus reducing the gradient in light absorbed per unit chlorophyll through a leaf CO2 fixation faces a diffusional limitation, which necessitates Rubisco to be spread evenly across the cell walls exposed to intercellular airspace. Mesophyll cell structure reflects the need to have a large cell surface per unit volume exposed to airspaces, The regular array of columnar cells in palisade tissue, or cell lobing in monocot leaves, results in greater exposed surface per unit tissue volume than spongy mesophyll. The exposed surface area per unit leaf area scales with photosynthetic capacity such that the difference in CO2 partial pressure surface area per unit leaf area scales with photosynthetic capacity such that the difference in CO2 partial pressure between substomatal cavities and the sites of carboxylation within chloroplasts is, on average, independent of photosynthetic capacity of the leaf. However, Rubisco specific activity declines as the Rubisco content per unit leaf area increases due to grater internal diffusional limitations. [ABSTRACT FROM AUTHOR]

Sclerophylly and synthesis of phenolic compounds are active responses of plants subjected to environmental stress (drought, low nutrient supply, u.v.-B radiation, ozone). Here we describe the morphological and histochemical alterations occurring in field-grown leaves of Fagus sylvatica L. from three sites located along an ecological gradient: from a site in cool and protected conditions to one located on a mountain ridge, where the trees grow on a thin layer of soil and are exposed to the wind and to intense solar radiation in summer. The morphological data show that, as the ecological conditions of the stand worsen, individual leaf surface decreases, while the thickness of the leaves and their specific d. wt (i.e. d. wt per unit leaf area) increases. Histochemical and ultrastructural tests show a marked increase of phenolics during the course of the year. These substances, present primarily in the leaves of trees growing in stress conditions, have been identified mainly as tannins. They accumulate in the vacuoles, especially those of the upper epidermal layer and the palisade mesophyll; at a later stage they appear to be solubilized in the cytoplasm and retranslocated, eventually impregnating the outer wall of the epidermal cells amidst the cellulose fibrils, where they cluster together and form an electron-opaque layer between the wall and the cuticle. Observation of the epidermal cells also reveals that the outer cell wall is thicker. The paper discusses the roles of secondary metabolites in protection and detoxification processes; the possible ecological significance of these alterations in the ecophysiology of beech trees. [ABSTRACT FROM AUTHOR]

Studies of heat and mass exchange between leaves and their local environment are central to our understanding of plant-atmosphere interactions. The transfer across aerodynamic leaf boundary layers is generally described by non-dimensional expressions which reflect largely empirical adaptations of engineering models derived for flat plates. This paper reviews studies on leaves, and leaf models with varying degrees of abstraction, in free and forced convection. It discusses implications of findings for leaf morphology as it affects - and is affected by - the local microclimate. Predictions of transfer from many leaves in plant communities are complicated by physical and physiological feedback mechanisms between leaves and their environment. Some common approaches, and the current challenge of integrating leaf-atmosphere interactions into models of global relevance, are also briefly addressed. [ABSTRACT FROM AUTHOR]

This paper reports a comparison of the effects of the same ozone exposure given at different stages of growth on a population major L., which is as sensitive to ozone as Bel-W3 tobacco. Plants were grown from seed for eight weeks in controlled environment chambers and exposed to 70 μl O3 l-1 7 h d-1 for the whole period or for 2-wk episodes during weeks 1+2, 3+4, 5+6 or 7+8. Controls had charcoal filtered air. Effects on leaf, flower, seed and dry matter production, and on relative growth rate of shot and root are given. At whatever time the ozone was given it altered relative growth rate, dry matter partitioning and seed output. The experiment supports the view that assessment of the sensitivity of a herbaceous species can be indicated by a short-term exposure of young plants, even though the nature of the response may change with development. Comparison of the effect of ozone on dry matter partitioning at different stages of growth suggested that at each stage in development, ozone relatively strengthened the currently dominant sink, therefore reducing allocation to subsidiary sinks. As a plant develops, the relative strengths of sources and sinks change so the effects of an ozone episode on allocation will depend upon the timing. It is concluded that the commonly held view that ozone tends to reduce root growth more than shoot may be an over-simplification. For native plants growing in the field, the timing of episodes in relation to development may be crucial to understanding ozone impact. On the ecosystem level we need knowledge of response and source - sink relationships at times of the year when episodes occur. [ABSTRACT FROM AUTHOR]

Recent data obtained in this laboratory have shown that a number of triazole fungicides induce in leaves of barley and Elodea densa an early release of solutes and an inhibition of H+ extrusion. This paper deals with the early effects of two triazoles, penconazole and flusilazol, on intracellular pH and plasmamembrane permeability in Elodea densa leaves. Different effects were found at low (0.1-0.15 mM) or at high (0.3-0.5 mM) triazole concentrations. At the low concentrations the triazoles induced a marked intracellular acidification (corresponding to an acidification of both the cytosol and the vacuole) as evaluated by the weak acid and weak base distribution method. For higher triazole concentrations (0.3-0.5 mM) the intracellular pH became very close to that of the external medium (pH 5.5), and cytosolic and vacuolar pH measurements became unreliable. Triazoles at concentrations higher than 0.1-0.15 mM induced an early and very marked increase in net efflux of K+ and Cl-. At these 'toxic' concentrations the sorbitol-permeable space (apparent free space) was increased from about 20% to more than 90%. These results suggest that triazoles at low 'sub-toxic' concentrations inhibit some mechanism involved in the regulation of intracellular pH (possibly the plasmalemma proton pump), whilst at higher concentrations they induce a non-specific increase in passive permeability of the plasmamembrane. [ABSTRACT FROM AUTHOR]

Plant growth analysis, demographic analysis and yield component analysis are three procedures used to study relationships underlying plant growth and development. Previously, it has been shown that demographic analysis is qualitatively different from plant growth analysis. This paper demonstrates how plant growth analysis and yield component analysis can be merged into a composite procedure, sequential plant growth analysis. The composite approach treats some of the traditional indices of plant growth, including leaf area ratio, leaf area index, unit leaf rate, relative growth rate, crop growth rate and harvest index, as yield components. Regression analysis is used to assess quantitatively the contributions of individual yield components to variations in growth and yield. Fitted curves and trends in coefficients of determination are both used to follow the time course of relationships during development. A study of vegetative growth in bean plants is used to illustrate the composite procedure. [ABSTRACT FROM AUTHOR]

The article discusses the life history variation in Thlaspi caerulescens. It has been identified as a key model species in which to research the phenomenon of hyperaccumulation, where a small number of species accumulate a few metals to extraordinary concentrations in their leaves and shoots. Populations of this species are known to store zinc, nickel and cadmium, and there have been many recent papers studying the biochemistry, molecular biology and physiology of zinc and cadmium hyperaccumulation in this material. The evolutionary advantage of hyperaccumulation has also attracted attention, specifically testing the hypothesis that the metals in the leaves act as an antifeedant, deterring a range of small invertebrate terrestrial herbivores.

This article presents an introduction of the special issue of the journal "New Phytologist." This Special issue of the journal explore the impacts of variation in leaf structure on processes occurring from the level of the leaf itself to that ecosystem and biomes. The introductory review by Vince Gutschick assesses the basic consequences of differences in leaf structure, and this is followed by both reviews and research papers that expand on this theme: providing up-to-date accounts of the environmental, genotypic and whole-plant controls over leaf structure.