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• Increasing atmospheric concentrations of phytotoxic ozone (O(3) ) can constrain growth and carbon sink strength of forest trees, potentially exacerbating global radiative forcing. Despite progress in the conceptual understanding of the impact of O(3) on plants, it is still difficult to detect response patterns at the leaf level. • Here, we employed principal component analysis (PCA) to analyse a database containing physiological leaf-level parameters of 60-yr-old Fagus sylvatica (European beech) trees. Data were collected over two climatically contrasting years under ambient and twice-ambient O(3) regimes in a free-air forest environment. • The first principal component (PC1) of the PCA was consistently responsive to O(3) and crown position within the trees over both years. Only a few of the original parameters showed an O(3) effect. PC1 was related to parameters indicative of oxidative stress signalling and changes in carbohydrate metabolism. PC1 correlated with cumulative O(3) uptake over preceding days. • PC1 represents an O(3) -responsive multivariate pattern detectable in the absence of consistently measurable O(3) effects on individual leaf-level parameters. An underlying effect of O(3) on physiological processes is indicated, providing experimental confirmation of theoretical O(3) response patterns suggested previously.

Six photosynthesis-dependent stomatal models were tested and compared against twig cuvette gas exchange data for adult common beech ( Fagus sylvatica L.). The models differed in the use of (1) either leaf surface CO 2 concentration ( C s ) or leaf intercellular CO 2 concentration ( C i ), and of (2) either measured environmental humidity variables or a crudely calculated leaf water potential to simulate the effect of drought stress on stomatal conductance. The models applying C s performed slightly better than the models applying C i . The models based on environmental humidity variables performed distinctly better than the models applying a calculated leaf water potential. Several explanations for the observed performance differences between models applying C s or C i were brought forward and discussed.

We present a mechanistic model of wood tissue development in response to changes in competition, management and climate. The model is based on a refinement of the pipe theory, where the constant ratio between sapwood and leaf area (pipe theory) is replaced by a ratio between pipe conductivity and leaf area. Simulated pipe conductivity changes with age, stand density and climate in response to changes in allocation or pipe radius, or both. The central equation of the model, which calculates the ratio of carbon (C) allocated to leaves and pipes, can be parameterized to describe the contrasting stem conductivity behavior of different tree species: from constant stem conductivity (functional homeostasis hypothesis) to height-related reduction in stem conductivity with age (hydraulic limitation hypothesis). The model simulates the daily growth of pipes (vessels or tracheids), fibers and parenchyma as well as vessel size and simulates the wood density profile and the earlywood to latewood ratio from these data. Initial runs indicate the model yields realistic seasonal changes in pipe radius (decreasing pipe radius from spring to autumn) and wood density, as well as realistic differences associated with the competitive status of trees (denser wood in suppressed trees).

The effects of changes in solar UV-B on the growth and pigmentation of six grass species from cold-temperate grasslands (Lolium perenne, Lolium multiflorum, Festuca arundinacea, Festuca rubra, Phleum pratense and Dactylis glomerata) in spring and summer were studied. The grasses were grown in greenhouses with different foils, resulting in three treatments: no UV-B, 80% of ambient and 90% of ambient UV-BBE.(biologically effective UV-B). The results indicated important effects of ambient UV-B levels on grass, but the different species reacted in very different ways. Both morphology and biomass production were influenced by UV-B in some species. However, changes in biomass production did not necessarily occur within the same species as changes in morphology. The grasses were more sensitive in summer. Overall, only F. rubra was positively influenced by UV-B under all circumstances. The biomass of D. glomerata and L. perenne was reduced by UV-B in spring and summer. Morphological changes included reduced height and increased tillering. The sensitivity of the different species was partially explained by their ability to reduce their specific leaf area in response to UV-B. Only the more sensitive species showed increased production of protective pigments. Overall, there were important differences between the effect of a low level of UV-B, and the further increase in UV-B, indicating that several mechanisms are operating at different light levels.

To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of rye (Secale cereale L.) to increased UV-B levels, plants were grown under eight different light treatments. In the control series (at ambient levels of UV-B), UV-B and visible light were decreased in parallel, resulting in four different total irradiation treatments with the same UV-B/photosynthetically active radiation (PAR) ratios. A second series with a 30% increase in UV-B irradiation at each PAR level was used to investigate the effect of UV-B under the varying total irradiance levels. The different total irradiance levels resulted in significant differences in total dry weight, specific leaf weight, photosynthesis-light response and pigment concentrations. A 30% increase in UV-B resulted in equal reductions in total dry weight (from 20.0 to 28.6%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the leaves was stimulated by PAR and even more by UV-B, except at the highest UV-B irradiation, where a small decrease was noted. These results indicate that rye plants are able to adapt to changes in the natural light environment as long as the ratio UV-B/PAR is constant.

Currently, the most important source of uncertainty in stomatal ozone flux (FO3) modelling is the stomatal conductance (g(st)) factor. Hence FO3 model accuracy will strongly depend on the g,t model being implemented. In this study the recently developed semi-empirical g(st) model of Dewar was coupled to the widely known biochemical photosynthesis (A(n)) model of Farquhar. The g(st) performance of this model combination was evaluated with a 4-month time series of beech (Fagus sylvatica L.) measurements. The g(st) model was hereto optimized in two steps to a 4-day and a 8-day period. A comparison between the modelled and measured g(st) to O-3 (g(stO3)) revealed a rather good overall performance (R-2 = 0.77). Errors between the model combination and the measurements are thought to be largely caused by a moderate performance of the A(n) model, due to poor parameterization. Two 2-day periods with distinctly differing soil and meteorological conditions were chosen to give a picture of the daily g, performance. Although instant relative differences between modelled and measured g(stO3) are sometimes high, the model combination is able to simulate the rough daily courses of g(stO3) and hence FO3 reasonably well. Further improvement on full parameterization of the g, model and a well-parameterized A, model to be linked to are needed to draw founded conclusions about its performance. Future efforts hereto are certainly justified since the model's mechanistic nature makes it a tool able to model g(st) variation in space and time, O-3 effects on g(st), and effective FO3.

Needle length and width at midpoint are often used to make estimates of needle surface area for conifers. For these estimates, Scots pine (Pinus sylvestris L.) fascicles are assumed to be cylindrical; thus, for a two-needle pine, the cross section of a needle within the fascicle is assumed to be hemicylindrical. The objectives of this study were to determine whether these assumptions lead to a good estimate of the actual surface area and how needles vary with tree age and crown position. We used a digital scanning microscope to measure needle width, thickness, and perimeter at 11 positions along 28 needles from different crown positions in different-aged trees and found that they varied with position within the individual needle as well as with tree age and crown position. Needle shape was relatively constant: needle width and perimeter both increased from the base to the needle midpoint and then decreased slightly to the needle tip, but needles were not hemicylindrical and actual perimeters were nearly 12% larger than predicted perimeters. The predicted surface areas based on measurements of width at the needle midpoint and length need to be reduced by 9% to account for the fact that needles taper and are not cylindrical. Furthermore, tree age and crown position must be considered when crown-level estimates are made.Key words: digital image analyzer, light microscope, needle width, needle thickness, needle perimeter, Pinus sylvestris.

The interaction between reduced UV-B radiation and elevated CO 2 on the growth, allocation and physiology of white clover ( Trifolium repens ) was studied in greenhouses of different UV-B transmittance (82 and 88% of ambient) with either ambient (371 ppm) or elevated (521 μmol mol −1 ) CO 2 concentration. The 88% UV-B levels in increased growth and flowering, indicating an important role for ambient UV-B levels in plant functioning and growth. High CO 2 increased growth significantly only under the 88% UV-B level. The interaction between UV-B and CO 2 effects on total biomass was significant. Allocation was affected significantly by both UV-B (increased root growth, increased flowering) and CO 2 (increased flowering, reduced stem weight). The results clearly indicate the importance of using UV-B transmittant greenhouse or open-top chamber when conducting CO 2 studies, or at least stating the reduction in UV-B within greenhouses.

The purpose of this study was to investigate whether differences in canopy architecture due to the investigated species (planophile versus erectophile, single versus mixed canopies) or to UV-B effects on plant morphology, lead to differences in UV-B and UV-B/PAR doses within canopies.

There are several very accurate methods to determine leaf angles in closed canopies. However, these are generally very time-consuming or require special equipment. Average canopy leaf angles were derived from simple height and blade length measurements. An exponential relationship between the height/length ratio and the average blade leaf angle was used. The method was tested for two grass species, Dactylis glomerata and Festuca arundinacea, grown under different UV-B levels. The results clearly show that the method is reasonably accurate and able to identify UV-B induced changes in leaf angle. To get these results only 50 measurements of leaf blade height and length were necessary to calculate the allometric relationship, after which 10 length and height measurements from a canopy were used to calculate the average canopy leaf angle.

We estimated daily use of stored water by Scots pine (Pinus sylvestris L.) trees growing in a temperate climate with the ANAFORE model (ANAlysis of FORest Ecosystems) and compared the simulation results with sap flow measurements. The original model was expanded with a dynamic water flow and storage model that simulates sap flow dynamics in an individual tree. ANAFORE was able to accurately simulate diurnal patterns of measured sap flow under microclimatic conditions that differ from those of the calibration period. Strong relationships were found between stored water use and several tree characteristics (diameter at breast height, sapwood area, leaf area), but not with tree height. Relative to transpiration, stored water use varied over time (between < 1% and 44% of daily transpiration). On days when transpiration was high, trees were more dependent on stored water, indicating that the contribution of internal water to transpiration is not a constant in the water budget of trees.