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.     

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.     

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.     

Comparison of pollen gene flow among four European beech (Fagus sylvatica L.) populations characterized by different management regimes

The study of the dispersal capability of a species can provide essential information for the management and conservation of its genetic variability. Comparison of gene flow rates among populations characterized by different management and evolutionary histories allows one to decipher the role of factors such as isolation and tree density on gene movements. We used two paternity analysis approaches and different strategies to handle the possible presence of genotyping errors to obtain robust estimates of pollen flow in four European beech (Fagus sylvatica L.) populations from Austria and France. In each country one of the two plots is located in an unmanaged forest; the other plots are managed with a shelterwood system and inside a colonization area (in Austria and France, respectively). The two paternity analysis approaches provided almost identical estimates of gene flow. In general, we found high pollen immigration (~75% of pollen from outside), with the exception of the plot from a highly isolated forest remnant (~50%). In the two unmanaged plots, the average within-population pollen dispersal distances (from 80 to 184 m) were higher than previously estimated for beech. From the comparison between the Austrian managed and unmanaged plots, that are only 500 m apart, we found no evidence that either gene flow or reproductive success distributions were significantly altered by forest management. The investigated phenotypic traits (crown area, height, diameter and flowering phenology) were not significantly related with male reproductive success. Shelterwood seems to have an effect on the distribution of within-population pollen dispersal distances. In the managed plot, pollen dispersal distances were shorter, possibly because adult tree density is three-fold (163 versus 57 trees per hectare) with respect to the unmanaged one.     

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.     

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     

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.     

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.     

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     

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).     

Drought-driven growth reduction in old beech (Fagus sylvatica L.) forests of the central Apennines, Italy

Productivity of old‐growth beech forests in the Mediterranean Basin was measured by average stem basal area increment (BAI) of dominant trees at two mountain sites in the Italian Apennines. Both forests could be ascribed to the old‐growth stage, but they differed markedly with regard to elevation (1000 vs. 1725 m a.s.l.), soil parent material (volcanic vs. calcareous), mean tree age (less than 200 years vs. 300 years), and stand structure (secondary old‐growth vs. primary old‐growth forest). Drought at the two sites was quantified by the self‐calibrated Palmer Moisture Anomaly Index (Z‐index), and by the self‐calibrating Palmer Drought Severity Index (PDSI) for summer (June through August) and the growing season (May through September). Dendroclimatological analyses revealed a moisture limitation of beech BAI at interannual (water availability measured by Z‐index) and decadal scales (water availability measured by PDSI). Both BAI and water availability increased from 1950 to 1970, and decreased afterwards. Trees were grouped according to their BAI trends in auxological groups (growth‐type chronologies), which confirmed that growth of most trees at both sites declined in recent decades, in agreement with increased drought. Because BAI is not expected to decrease without an external forcing, the patterns we uncovered suggest that long‐term drought stress has reduced the productivity of beech forests in the central Apennines, in agreement with similar trends identified in other Mediterranean mountains, but opposite to growth trends reported for many forests in central Europe.     

Effects of drought on photoprotective mechanisms in European beech (Fagus sylvatica L.) seedlings from different provenances

The effects of drought on photoprotection mechanisms of three beech provenances from three contrasting climatic origins have been studied. Morphology differed among provenances, with a lower leaf area/fine roots ratio in the xeric populations (Moncayo). This characteristic allowed this provenance to respond later than the others to a drought-stress treatment. However, in desiccating leaves the stability of PSII was higher in the plants from the stressful climate of the Pyrenees (Belagoa). Drought resulted in a reduction in pigment content (except in Belagoa) with simultaneous increases in antheraxanthin, zeaxanthin and tocopherol pools. These molecules play an important photoprotective role and reached similar values in stressed leaves from the three provenances. These antioxidants also protected the leaves from paraquat-induced oxidation. It is concluded that drought tolerance in the studied xeric ecotype is based to a greater extent on morphological characteristics than on a better photoprotective system.     

Temperature dependency of bark photosynthesis in beech (Fagus sylvatica L.) and birch (Betula pendula Roth.) trees

Temperature dependencies of stem dark respiration (R(d)) and light-driven bark photosynthesis (A(max)) of two temperate tree species (Fagus sylvatica and Betula pendula) were investigated to estimate their probable influence on stem carbon balance. Stem R(d) was found to increase exponentially with increasing temperatures, whereas A(max) levelled off or decreased at the highest temperatures chosen (35-40 degrees C). Accordingly, a linear relationship between respiratory and assimilatory metabolism was only found at moderate temperatures (10-30 degrees C) and the relationship between stem R(d) and A(max) clearly departed from linearity at chilling (5 degrees C) and at high temperatures (35-40 degrees C). As a result, the proportional internal C-refixation rate also decreased non-linearly with increasing temperature. Temperature response of photosystem II (PSII) photochemistry was also assessed. Bark photochemical yield (Delta F/F(m)') followed the same temperature pattern as bark CO(2) assimilation. Maximum quantum yield of PSII (F(v)/F(m)) decreased drastically at freezing temperatures (-5 degrees C), while from 30 to 40 degrees C only a marginal decrease in F(v)/F(m) was found. In in situ measurements during winter months, bark photosynthesis was found to be strongly reduced. Low temperature stress induced an active down-regulation of PSII efficiency as well as damage to PSII due to photoinhibition. All in all, the benefit of bark photosynthesis was negatively affected by low (<5 degrees C) as well as high temperatures (>30 degrees C). As the carbon balance of tree stems is defined by the difference between photosynthetic carbon gain and respiratory carbon loss, this might have important implications for accurate modelling of stem carbon balance.     

Fine root biomass in a beech (Fagus sylvatica L.) stand on Paiko Mountain,NW Greece

Abstract

Fine roots represent a small proportion of total plant biomass however they represent the most dynamic component of the root systems of woody plants. There is limited information on the beech fine root production in Mediterranean ecosystems and especially in Greece. We measured live, dead and total fine root biomass (d<2 mm) (LFRB, DFRB and TFRB, respectively) over a growing season in a beech (Fagus sylvatica L.) stand on Paiko mountain, NW Greece, in order to contribute to the generally scarce knowledge of the fine root biomass of beech stands. It was found that TFRB and LFRB increased from May to July and then decreased. LFRB decreased with soil depth while there was no pattern at the change of DFRB with soil depth.     

Root respiration and its importance for the carbon balance of beech saplings (Fagus sylvatica L.) in a montane beech forest

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Solling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5–9.8 nmol CO₂ gDW^–1 s^–1 at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p<0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p<0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO₂ gDW^–1 s^–1 were reached in the middle of July. Due to low light intensities in the under storey, daily net CO₂ assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO₂ assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.