The effect of shoot architecture on hydraulic conductance in beech (Fagus sylvatica L.)

 Shoot hydraulic conductance was measured in beech (Fagus sylvatica L.) that had previously been exposed to high levels of nitrogen input. Whole-shoot hydraulic conductance, conductance per unit pressure gradient and leaf specific conductance were negatively correlated with the number of bud scars per unit length, a morphological parameter of tree decline. We propose a negative feedback mechanism by which stress induced alterations in shoot morphology can cause a lasting reduction of tree vigour. Received: 2 July 1997 / Accepted: 25 June 1998     

Differences in the leaf functional traits of six beech (Fagus sylvatica L.) populations are reflected in their response to water limitation

Patterns of intraspecific variation in functional traits have been widely studied across plant species to find out what general suites of traits provide functional advantage under specific environmental conditions. Much less is known about this variation within tree species and, in particular, about its relationship with performance variables such as photosynthetic rates under water deficit. Nevertheless, this knowledge is fundamental to understand the adaptive potential of drought sensitive tree species to increased aridity as predicted in the context of climate change.Intraspecific variation in photosynthetic performance and other leaf functional traits in response to water availability were examined in a glasshouse experiment using seedlings of six European beech populations. The physiological response of seedlings to a “water stress” treatment was compared to a “control” treatment along an experimental cycle of progressive soil water deficit and recovery. We found evidence of intraspecific variation in beech's photosynthetic performance and other leaf functional traits in response to water availability. We also detected intraspecific variation in leaf-level tolerance of water deficit and phenotypic plasticity to water availability suggesting a pattern shaped by both regional and local scale effects. The Swedish population was particularly sensitive to water deficit, being the only population showing impaired photochemical efficiency under the experimental water deficit. Leaf-level tolerance of water deficit was related to PNUE, but not to other functional traits, such as WUE, SLA or leaf nitrogen content, that have been described to vary across species in adaptation to drought tolerance. Our results support the idea that general trends for variation in functional traits across species do not necessarily reflect a similar pattern when observed at the intraspecific level. The observed functional variation between beech populations reaffirms the importance of local adaptation to water deficit in the context of climate change.     

Stem hydraulic conductance of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) grown in elevated CO2

Over two seasons in c. 600 ppm CO₂, oak had lower stomatal conductancein CO₂-enriched compared to amblent air. Beech showed no responseto CO₂ concentration on sunny days. Mirroring this pattern,exposure to elevated CO₂ reduced whole-shoot hydraulic conductanceper unit leaf area in oak, but not in beech. Key words: Climate change, Fagaceae, gas exchange, trees, water relations     

Factors toxic to beech (Fagus sylvatica L.) seedlings in acid soils

The effects of highly and moderately acid soils on total biomass, biomass partitioning, fine root characteristics and nutritional status of beech seedlings (Fagus sylvatica L.) were studied in a growth chamber experiment. In Haplic Arenosols seedlings grew slowly but equally well without damage symptoms in a highly acid and a moderately acid soil horizon. The moderately acid A_h+B_w-horizon of a Eutric Cambisol was favourable to seedling growth. The fine root development was reduced in the highly acid A+B_w-horizon of a Dystric Cambisol and in the A_h+E-horizon of a Haplic Podzol, the latter of which also caused increased mortality. Seedling growth in the B₂-horizon of the Haplic Podzol was vigorous, in spite of a higher level of extractable Al and lower base saturation as compared with the A_h+E-horizon. These results are interpreted in relation to soil acidity, soil Al and nutritional status of the seedlings. We conclude that neither Al-toxicity nor nutrient deficiency cause the damage symptoms observed in the A_h+E-horizon of a Haplic Podzol and the fine root reduction in the A+B_w-horizon of a Dystric Cambisol. The damage symptoms of the PZh_A treatment seems to be more the result of H-toxicity or H-related factors other than nutrient shortage or Al-toxicity. Other pH-related toxic factors are discussed.     

High chloroplast haplotype diversity in Greek populations of beech (Fagus sylvatica L.)

The distribution of chloroplast DNA (cpDNA) variations in Greek beech ( Fagus sylvatica L.) populations was studied using chloroplast microsatellite markers. Thirteen haplotypes were identified from 40 populations by combining three different primers. Most of the cpDNA variation was distributed among populations, but a considerable variation was also observed within populations. The total diversity was very high for all regions. The N_st/G_st comparison was significant, indicating phylogenetic subdivision, but no strong spatial structure was detected, suggesting complex post-glacial migration patterns. Possible scenarios explaining this diversity pattern include the existence of several separated refugia in the region, the recolonisation of mountains by different beech lineages and the formation of an introgression zone between two different beech subspecies in the eastern part of the country.     

Potential risks for European beech (Fagus sylvatica L.) in a changing climate

Over large areas of Europe, coniferous monocultures are being transformed into mixed forests by the re-introduction of broadleaf tree species belonging to the potential natural vegetation. One important species of interest in this changing forest policy is European beech (Fagus sylvatica). However, at present, this forest management directive has ignored potential adverse effects of global climate change on wide-spread re-introduction of beech to these areas. Average global surface temperatures have risen by approx. 0.8°C in the period between 1861 and 2005 and are expected to continue to increase until the end of this century by 1.5–5.8°C above the 1990 value. To estimate the climate change in the southern part of central Europe in future, we reviewed calculations from regional climate models. Temperature increase for the southern part of central Europe is projected to be up to 2°C within the next 40 years. In contrast, the annual precipitation will most likely remain constant over the same time period, but will experience significant changes in seasonal patterns. Rising intensities of individual precipitation events may result in increasing number and intensities of flooding events and reduced precipitation during the growing season in a higher frequency of summer droughts. Growth and competitive ability of European beech will not, necessarily, respond to increasing CO₂ concentrations but may be strongly impacted by intensive drought that occurs during the growing season. Seedlings as well as adult trees may suffer from xylem embolism, restricted nutrient uptake capacity and reduced growth under limited water availability. However, it remains uncertain to what extent other environmental factors (e.g. soil properties, competitive interactions) may modify the drought response of beech, thus either enhancing susceptibility or increasing drought tolerance and resilience potential. Water-logged soils, predicted during the spring for several regions due to higher than average precipitation, could negatively impact nutrient uptake and growth of beech. Whereas other dominant species as, e.g. oak are well adapted to that environmental stress, beech is known to be sensitive to water-logging and flooding. Thus, the competitive capacity of beech might—depending on the other environmental conditions—be reduced under the expected future climate conditions. Silvicultural practices must be aware today of the potential risks which a changing climate may impose on sustainable forest development.     

A contribution to understanding the internal nitrogen budget of beech (Fagus sylvatica L.)

Summary The seasonal variation in the total nitrogen content of the xylem sap of the lower trunk section was investigated for two middle aged beech tree stands in northern Hessen each containing 130 trees. In addition seasonal changes in the percentage of nitrate in the total nitrogen content are described. The median values of the total nitrogen content of the xylem sap during the spring mobilization period reached 175 and 250 mg/l. During the summer about 35% of the total nitrogen in the xylem sap is in the form of nitrate. Finally, the distribution of NO₃ in the xylem sap along the trunk height was studied for two sample trees for each of the four seasons (n = 8).     

Growth and nutrient dynamics of beech (Fagus sylvatica L.) seedlings in acid soils

The relative uptake rates of N, P, K, S, Ca, Mg, Fe, Mn, Zn, Cu, and Al were estimated in beech seedlings pot cultured in the field in six acid soils (treatments). The relative uptake rates were compared with the relative growth rates. The relative uptake rates of N, K and Ca agreed well with the growth rates of the seedlings irrespective of widely differing soil conditions (acid sand-clayey till, pH 4–6). The relative uptake rates of P, Fe, and Al differed from that predicted by the growth rate. The uptake rates of Fe and Al were highest at the lowest growth rates, and the P uptake rate was lower than the growth rate in these treatments. Thus the P availability probably limited growth in an eluvial (E) horizon of a podzol, and possibly in the illuvial (B) horizon of a podzol and in an acid clayey till (Dystric Cambisol). Low P uptake was associated with a tendency towards higher relative root growth rates. In terms of the concept of steady state nutrition the high relative root growth rate in some treatments may be interpreted as an acclimation to low P supply. The P limitation seemed to be related to interactions among Fe, Al and organic compounds of the soil solution.FAX no: +4646104423     

Developmental and seasonal changes of stress responsiveness in beech leaves (Fagus sylvatica L.)

The development of beech leaves (Fagus sylvatica L.) was characterized by determination of the pigment and electrolyte concentrations as well as the accumulation of dry mass and specific leaf mass from bud break to senescence. To test the hypothesis that stress tolerance and responsiveness of defences show developmental and/or seasonal changes, leaf discs were either incubated in the absence (control) or presence of paraquat to induce oxidative stress. Controls displayed developmental changes in stress susceptibility ranging from less than 15% of maximum electrolyte leakage in mature leaves to more than 20% leakage in senescent and 36–46% in immature leaves. Paraquat concentrations were chosen to result in about 95% of maximum electrolyte conductivity within 24 h in all developmental stages. Paraquat accumulation was about two‐fold lower in senescent as compared with immature leaves, whereas stress susceptibility, as characterized by the kinetics of the increase in relative leakage, was similar in these developmental stages with 50% of maximum electrolyte conductivity (EC₅₀) = 6·5 h in immature and 7·5 h in senescent leaves. In mature leaves with intermediate paraquat accumulation rates, two classes of stress‐sensitivity were distinguished, namely stress‐resistant and stress‐susceptible leaves with EC₅₀= 9·5 and 5·2 h, respectively. Stress‐resistance of mature leaves was accompanied by a rapid, approximately two‐fold induction of superoxide dismutase activity. Stress‐sensitive mature leaves initially contained high superoxide dismutase activities but showed a rapid, more than six‐ fold loss in activity in 24 h. Correlation of meteorological data with leakage rates suggested that high air temperatures and low precipitation might have been predisposing for loss of resistance against oxidative stress in beech leaves.     

The response of European beech (Fagus sylvatica L.) seedlings from two Italian populations to drought and recovery

The response of gas exchange, leaf chlorophyll content, relative fluorescence to decreasing water potential and recovery was followed in European beech seedlings from two Italian populations, differing in their native precipitation amounts. A population from Sicily (southern Italy) was selected as representative of a xeric population while a population from central Italy, Abetone, represented a mesic one. Dry-matter partitioning, leaf area, hydraulic sufficiency and xylem embolism were evaluated in both well-watered control plants as well as in plants subjected to drought. With the onset of water stress, values of water potential, leaf relative water content, net photosynthesis, leaf conductance and leaf chlorophyll concentration decreased concurrently while relative fluorescence remained unchanged. The population from Sicily showed a delay in effects of the imposed drought. Within 5 days of rewatering, leaf conductance was not fully recovered while all of the other parameters recovered to control levels, in both populations. Total, shoot, stem and root dry weight tended to be higher in seedlings from Abetone, even though both populations had similar photosynthetic rates. The population from Sicily exhibited about 3% greater (even if not significant) allocation to roots than the population from Abetone. Seedlings from Abetone had higher, but not significant, leaf specific conductivity and per cent loss in hydraulic conductivity than seedlings from Sicily. Drought resulted in a reduction of hydraulic conductivity and hydraulic sufficiency in seedlings from both populations. Photosynthesis of water stressed plants from both populations appeared to be reduced primarily by carbon dioxide diffusion through stomata and perhaps secondarily by changes in chlorophyll concentration rather than by efficiency of photosystem II. The effect of hydraulic factors on gas exchange during drought and recovery was not clearly evident.     

Photoprotection mechanisms in European beech (Fagus sylvatica L.) seedlings from diverse climatic origins

This study shows that beech leaves adapt to their light environment by inducing dramatic changes to antioxidant systems and pigment composition. Thus, ascorbate, tocopherol, glutathione, β-carotene and xanthophyll cycle pigments are much more concentrated in sun leaves, while α-carotene is much less concentrated than in shade leaves. These characteristics were used to identify the inherent potential of beech cotyledons from three contrasting climatic origins to tolerate light stress. The antioxidant content was initially different in the three provenances tested, but these initial differences tended to reduce with leaf ageing. The higher antioxidant and de-epoxidized xanthophyll content found in developing cotyledons indicated a superior potential for tolerance to photo-oxidative damage in those plants collected from the stressful climate of the Pyrenees. Nevertheless under an experimental high irradiation treatment no differences in light stress tolerance were observed between provenances. Received: 31 May 1999 / Accepted: 16 November 1999     

The variability of vessel size in beech (Fagus sylvatica L.) and its ecophysiological interpretation

The vessel areas of ten beech trees growing on a dry site were measured separately for all tree rings using automatic image analysis. These data were correlated with the monthly amount of precipitation from the July prior to the growing season until the August of the current growing season. It is evident that vessel formation at the beginning of cambial activity is mainly controlled by internal factors. The rainfall in the previous summer and autumn and in the contemporary May had only a slight influence. Vessel formation towards the end of the cambial activity is strongly influenced by the July rainfall and is thus determined to a greater degree by external factors. These results are discussed on the basis of hypotheses of tree physiology.     

Growth, photosynthesis and ozone uptake of young beech (Fagus sylvatica L.) in response to different ozone exposures

Beech seedlings (Fagus sylvatica L.) were exposed to episodes of O₃ in environmentally controlled growth chambers during one growing season. Three treatments were applied: charcoal-filtered air, charcoal-filtered air with the addition of 40 ppb O₃ for seven episodes of 5 days' duration (9000-1700 hours), and charcoal-filtered air with the addition of 100 ppb O₃ for seven episodes of 5 days' duration (9000-1700 hours). The accumulated exposure over a threshold of 40 ppb in the last treatment reached 13,911 ppb h. Throughout the growing season we measured growth as well as photosynthetic properties and related effects to external and calculated internal doses of O₃, using stomatal conductance (g_s) data. Growth, measured as diameter increment and biomass, was not significantly affected by the O₃ treatments. In the 100-ppb treatment, light-saturated CO₂ assimilation rates and chlorophyll content were significantly reduced, and the chlorophyll fluorescence parameter F_v/F_m was significantly reduced at times of high uptake rates and coincided with strong reductions of assimilation rates. O₃ uptake was lowered in the 100-ppb treatment due to reduced g_s. There was serious visible damage by the end of the exposure period in the 100-ppb treatment, while the treatment with 40 ppb O₃ did not seem to cause any significant changes.     

Identifying the pathways for foliar water uptake in beech (Fagus sylvatica L.): a major role for trichomes

Foliar water uptake (FWU), the direct uptake of water into leaves, is a global phenomenon, having been observed in an increasing number of plant species. Despite the growing recognition of its functional relevance, our understanding of how FWU occurs and which foliar surface structures are implicated, is limited. In the present study, fluorescent and ionic tracers, as well as microcomputed tomography, were used to assess potential pathways for water entry in leaves of beech, a widely distributed tree species from European temperate regions. Although none of the tracers entered the leaf through the stomatal pores, small amounts of silver precipitation were observed in some epidermal cells, indicating moderate cuticular uptake. Trichomes, however, were shown to absorb and redistribute considerable amounts of ionic and fluorescent tracers. Moreover, microcomputed tomography indicated that 72% of empty trichomes refilled during leaf surface wetting and microscopic investigations revealed that trichomes do not have a cuticle but are covered with a pectin‐rich cell wall layer. Taken together, our findings demonstrate that foliar trichomes, which exhibit strong hygroscopic properties as a result of their structural and chemical design, constitute a major FWU pathway in beech.