Thermally initiated solvent-free radical modification of beech (Fagus sylvatica) wood

A procedure for rapidly modifying beech wood using a thermally initiated solvent-free grafting system was examined. In the modification, butyl acrylate and butyl methacrylate were used as vinyl monomers. Free radicals were generated from 2,2′-azobis(2-methylpropionitrile) or benzoyl peroxide at 103 and 180 °C by contact heating of the modified material. Chemical changes in the material were investigated by FTIR and X-ray photoelectron spectroscopies. The modification resulted in decreased surface wetting of the material manifested by increased water contact angles. The hardness of the resultant material decreased, while its color changed by the effect of temperature. It was shown that the approach allowed for efficient thermal-initiated modification of wood with rapid contact heating.     

Seasonal time-course of the above ground biomass production efficiency in beech trees (Fagus sylvatica L.)

Key message

In order to record the seasonal changes in aboveground biomass production (trunk and branches) in a forest, changes in wood density must be taken into account. A 60-year-old beech forest displayed a large intra-annual variability in its aboveground woody biomass production efficiency. This variation followed a seasonal trend with a maximum during the summer while gross primary production was rather low.

Context

In the current context of land use and climate change, there is a need to precisely quantify the carbon (C) balance of forest ecosystems, and more specifically, of C allocation to tree compartments.

Aims

We quantified the seasonal changes in the aboveground biomass production (aBP) of a beech forest growing on two different soils: an alocrisol and a calci-brunisol. In addition, for the alocrisol ecosystem, we assessed the existence and degree of intra-annual variability in the ratio of wood aBP to gross primary production (GPP), i.e., the wood aBP efficiency.

Methods

The study site is a 60-year-old beech forest in northeastern France. An eddy covariance tower records continuously net ecosystem exchange. To investigate the temporal changes in aBP, mini-cores were drilled and diameter at breast height measurements were taken on a monthly basis from 45 trees for both stands studied over 2014.

Results

A clear difference in aBP was observed between the two soils with the alocrisol being more productive than the calci-brunisol. For the alocrisol, both woody aBP and GPP changed over the course of the year, reaching peak values during June (6 and 12.5 gC m^?2 day^?1, respectively). Wood applied bias photon-to-current efficiency aboveground Biomass Production Efficiency (aBPE) also showed important intra-annual variations, ranging from 0.09 in September to 0.58 in July. Wood density varied throughout the year, and not taking it into account would have led to an overestimation of aBP by as much as 20% in April and May.

Conclusion

Our study highlights the importance of taking wood density into account for intra-annual studies of aBP. Wood aBPE cannot be considered as constant as it fluctuated from 0.09 to 0.58 throughout the year for an annual value of 0.34. The potential error in wood aBPE stemming from not taking these changes into account amounts to 15%.

     

Radial distribution of carbohydrate reserves in the trunk of declining European beech trees (Fagus sylvatica L.)

Context

European beech (Fagus sylvatica L.) is considered threatened by anticipated climate change, but the physiological causes of potential beech decline or mortality remains poorly understood.

Aims

The purpose of the present study was to fuel debate about the assumption that carbohydrate depletion is involved in the decline of mature European beech.

Methods

The health status of beech trees from a severely declining stand was visually assessed by examining their crown condition. Content and radial distribution of non-structural carbohydrates (starch and soluble carbohydrate) were analyzed in the trunks and compared to those reported earlier in trunks of healthy beech trees.

Results and discussion

The distribution of carbohydrate in the beech trunks recorded here seemed affected by decline. We found a stronger radial decrease of starch content than those reported earlier for healthy beech trees. Carbohydrate reserves appear partially maintained in the outermost rings while starch depletion occurred in older wood rings in declining trees that may be able to mobilize carbohydrate reserves from older wood rings in response to successive climatic constraints.     

Interaction of lignin and polysaccharides in beech wood (Fagus sylvatica) during drying processes

Summary ¹³C CP MAS NMR spectroscopy was used to characterize the structural changes of cell wall polymers in beech wood Fagus sylvatica during drying processes. The analysis of five wood samples, namely, untreated, untreated dried, pre-treated by steam and/or NaOH subjected to drying showed partial depolymerization of lignin component as well as the change of the ratio of the crystalline and of the amorphous parts of cellulose as the consequence of wood pre-treatment. In addition, T_1ρ(¹H) relaxation times were determined in beech wood sample pre-treated with steam at 135 °C and the lignin isolated from this sample. The magnitudes of the relaxation times were found comparable in both samples as well as in the lignin-cellulose model compound. These unique T_1ρ (¹H) values indicate that spin diffusion is complete and homogeneous due to spatial proximity of spins and confirmed the formation of lignin-cellulose complex during thermal treatment of wood. Received 30 June 1997     

Seasonal changes in the axial distribution of peroxidase activity in the xylem sap of beech (Fagus sylvatica L.) trees

Xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by water displacement. Peroxidase activity was analyzed in xylem saps collected in different phases of the yearly growth cycle and from different heights up the trunks (up to 14 m). The xylem saps contained two major peroxidase isozymes with acidic isoelectric points of 4.1 and 4.6, respectively. Mean peroxidase activity was low during the emergence of the new leaves and high in summer and in winter. In the cold season, peroxidase activity decreased from the stem base to the top, whereas significant gradients were not observed during the vegetative period.     

Morphological and physiological responses of beech (Fagus sylvatica) seedlings to grass-induced below ground competition

We examined morphological and physiological responses of beech (Fagus sylvatica L.) seedlings to grass-induced below ground competition in full-light conditions. Two-year-old beech seedlings were grown during two growing seasons in 160-l containers in bare soil or with a mixture of five grass species widely represented in semi-natural meadows of central France. At the end of the second growing season, beech seedlings in the presence of grass showed significant reductions in diameter and height growth, annual shoot elongation, and stem, root and leaf biomass, but an increase in root to shoot biomass ratio. Grasses greatly reduced soil water availability, which was positively correlated with daily seedling diameter increment. Beech seedlings seemed to respond to water deficit by anticipating stomatal closure. There was evidence of competition for nitrogen (N) by grasses, but its effect on seedling development could not be separated from that of competition for water. By labeling the plants with 15N, we showed that beech seedlings absorbed little N when grasses were present, whereas grasses took up more than 97% of the total N absorbed in the container. We conclude that, even if beech seedlings display morphological and physiological adaptation to below ground competition, their development in full-light conditions may be strongly restricted by competition from grass species.     

Genetic diversity and bark physiology of the European beech (Fagus sylvatica): a coevolutionary relationship with the beech scale (Cryptococcus fagisuga)

In 1994 and 1995, the degree of infestation by the beech scale (Cryptococcus fagisuga Lind.) was recorded on 120 beech trees (Fagus sylvatica L.) in the Pless Forest near G?ttingen, Germany. Simultaneously, the trees were characterized genetically and compounds of primary and secondary metabolism of beech bark were analyzed. A correlation was established between beech scale infestation and the genotype of the host trees, based on gene locus A of isocitrate dehydrogenase (IDH-A). The fraction of infested beech trees was higher in the heterozygous genotype A2A3 group than in the homozygous genotype A2A2 and A3A3 groups, whereas the fraction of beech trees with decreasing infestation from one year to the next was lower in the heterozygous genotype A2A3 group than in the homozygous genotype A2A2 and A3A3 groups. Concentrations of soluble carbohydrates, protein amino acids and proanthocyanidins were determined in the inner and outer bark of trees with differing degrees of infestation. The results indicate that the defense reaction of beech against infestation by beech scale comprises multiple processes in which nutrient availability to the beech scale is reduced by concentration shifts and by the formation of inhibiting compounds.     

Xylem sap composition of beech (Fagus sylvatica L.) trees: seasonal changes in the axial distribution of sulfur compounds

During different phases of the annual growth cycle, xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by the water displacement technique. Irrespective of the height of the trunk, both sulfate and reduced sulfur compounds were detected in the xylem sap throughout the year. Sulfate was the predominant sulfur compound in all samples analyzed. Its concentration in the xylem sap varied between 10 and 350 micro mol l(-1), with highest concentrations in April, shortly before bud break. In contrast to other tree species, cysteine and not glutathione was the predominant thiol transported in the xylem sap of beech trees. The cysteine concentration ranged between 0.1 and 1 micro mol l(-1). As observed for sulfate, maximum cysteine concentrations were found in April. Apparently, both sulfate and cysteine transport contribute to the sulfur supply of the developing leaves. Seasonal changes in the axial distribution of cysteine and sulfate differed, indicating differences in the source-sink relations of these sulfur compounds. High, but uniform, xylem sap sulfate concentrations in April may originate from balanced sulfate uptake by the roots, whereas high cysteine concentrations in April, increasing with increasing height of the trunk, may originate in part from protein breakdown in the trunk. Reversal of the axial distribution of xylem sap cysteine in late summer-early fall to higher concentrations in the lower part of the trunk than in the upper part of the trunk suggests that the upper part of the trunk becomes a sink for cysteine as a result of the synthesis of storage proteins at this time of the year.     

Hydraulic architecture correlates with bud organogenesis and primary shoot growth in beech (Fagus sylvatica)

In beech (Fagus sylvatica L.), the number of leaf primordia preformed in the buds determines the length and the type (long versus short) of annual growth units, and thus, branch growth and architecture. We analyzed the correlation between the number of leaf primordia and the hydraulic conductance of the vascular system connected to the buds. Terminal buds of short growth units and axillary buds of long growth units on lower branches of mature trees were examined. Buds with less than four and more than five leaf primordia formed short and long growth units, respectively. Irrespective of the type of growth unit the bud was formed on, the occurrence of a large number of leaf primordia was associated with high xylem hydraulic conductance. Xylem conductance was correlated to the area of the outermost annual ring. These results suggest that organogenesis and primary growth in buds correlates with secondary growth of the growth units and thus with their hydraulic architecture. Possible causal relationships between the variables are discussed.     

Genetic structure of populations of beech (Fagus sylvatica L.) in Denmark

The genetic structure in Danish indigenous and introduced provenances of beech (Fagus sylvatica L.) is described. Ten stands are analysed based on variation revealed by seven enzyme systems. The present study reveals significant allele frequency differences between populations with a small absolute amount of genetic differentiation, with no pattern related to geographic distance. The genetic differentiation between indigenous populations measured by Wright's F _ST‐statistic does not deviate significantly from zero, and only 2.9% of the total genetic variation in the foreign populations was due to interpopulation differences, The allele frequencies in relatively small and isolated populations do not differ from the frequencies found in larger areas with beech forest. The low genetic differentiation of isozyme level between indigenous and foreign populations was opposed by significant differences in foliation performance measured on three pairs of neighbouring stands. Foliation performance in adjacent stands of indigenous and introduced beech indicates that quantitative characteristics must be considered separately from neutral variation at single loci.     

Investigations on viruses from declining beech trees (Fagus sylvatica L.) in Rhineland and Westfalia,Federal Republic of Germany

Viruses of the Poty-, Potex- and Tobamo-virus groups, and presumably Nepoviruses could be isolated from degenerating beech trees (Fagus sylvatica L.) in West-Germany. They are discussed as predisposing factors of tree decline.     

Over-mature beech trees (Fagus orientalis Lipsky) and close-to-nature forestry in northern Iran

Oriental Beech is the most important commercial tree species in northern Iran. In recent years wood production companies interested in felling large beech trees for profit have challenged advocates of close-to-nature silviculture who favor conservation. Our study objective was to assess the economic value of over-mature beech trees by relating tree diameter (DBH) to amount of decay. Based on the location of onset of decay, we categorized three types of decay as stump, stem, and crown decay. Trees of greater diameter (age) typically showed greater decay in the stem. Percent of decayed volume, diameter of decayed tissue, and length of decay in tree stems varied between 0.5%?64.3%, 15 cm?75 cm, and 2.0?19.5 m, respectively. With increasing trunk diameter, the proportion of truck decay increased. Red heart and dark red heart constituted 25% and 14.3% of sampled trees, respectively. However, we found no correlation between intensity of stem decay and morphological characteristics of trees. Seedlings were not abundant around the bases of over-mature trees, suggesting that the trees did not contribute to regeneration of the stand. Beech trees of diameter >1 m do not provide valuable round wood for industries and cause to raise wood production costs. We recommend that these trees >1 m DBH should be retained in forest stands because of their low commercial value but high ecological and conservational values such as maintaining biodiversity in forest ecosys-tems.     

Genetic structure and variability of phenological forms in the European beech (Fagus sylvatica L.)

? Microsatellite markers were used to describe the genetic structure and variability of early, intermediate and late phenological forms of European beech (Fagus sylvatica L.). Two hundred and seventy individuals from three populations located in southern Poland were divided into three forms according to the phenological criterion — bud burst, and analyzed for allelic variation at five highly polymorphic microsatellite loci.

? Population differentiation was moderate and differed significantly among phenological forms. Average values of F _ST and R _ST decreased across phenological forms and amounted to F _ST values of 0.135, 0.110 and 0.108 and R _ST values of 0.365, 0.231 and 0.098 for early, intermediate and late forms of beech, respectively.

? Analysis of Molecular Variance (AMOVA) revealed different genetic structures characteristic of respective phenological forms of beech. The amount of within-population variability increased with the delay of the beginning of vegetation and amounted to 64%, 77% and 90% of total variability, depending on phenological form. A similar trend was found in average pairwise genetic distance between individuals belonging to a given phenological form (11.78, 11.85 and 12.22, from early to late forms).

? Our results demonstrate the importance of late spring frosts as a factor influencing the genetic structure of beech, and as a cause of the decrease in genetic variability as well as the increase in population differentiation proportional to the degree of phenological earliness.

     

Vulnerability of spruce (Picea abies) and beech (Fagus sylvatica) forest stands to storms and consequences for silviculture

The form and magnitude of storm damage and stand disclosure patterns were assessed in 332 randomly chosen pure and regular stands of spruce (Picea abies L.) and beech (Fagus sylvatica L.) after storm lothar, within a region of the Swiss Midlands. This data was analysed in relation to maximal wind speed, measured with Doppler radar techniques and other influential factors such as relief, allometric characteristics, silvicultural history, and neighbourhood. In addition, storm damage, assessed from aerial photographs over an extended perimeter (about 70,000 ha) was considered. A storm of the magnitude of lothar (December 26 1999), with an average maximal wind speed of 45 m s⁻¹ (160 km h⁻¹) appears to have a highly chaotic wind field structure, with great spatial and temporal variation of wind gusts. Wind speeds were not a significant predictor for damage in spruce stands and only weakly influential for beech. The consequences of this high randomness were analysed to estimate the return time of such a storm at the stand level. It lies between 86 and 113 years for spruce, 357 and 408 for beech. Only a few independent variables were significant and the overall explanatory strength of the model was unexpectedly low (R ²=0.07 for spruce and 0.30 for beech). Among the more reliable predisposing factors were mixture and aspect combined with gradient. An admixture of 10% or more broadleaved tree species or wind-firm conifers like Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] significantly reduced the vulnerability of spruce stands (by a factor of more than three). On wind-exposed aspects, damage was more than twice the average. Steeper slopes caused a significant reduction in susceptibility (by a factor of six for slopes over 50%, in comparison to gentle slopes <20%). Other factors such as height to diameter ratio of trees or time since last thinning did not appear to be significant predictors.     

Genetic variation of beech (Fagus sylvatica L.) in Rodopi (N.E. Greece)

The recent taxonomic classification of beech in Europe considers existence of one species (Fagus sylvatica L.) with two subspecies: F. sylvatica ssp. sylvatica and F. sylvatica ssp. orientalis. Four beech populations growing on the Greek part of the Rodopi Mountains were studied using morphological traits as well as DNA molecular markers (AFLPs and chloroplast DNA SSR). The aim of the study was to describe the variation patterns of beech in the Rodopi Mountains and to test the hypothesis of possible introgression between the beech subspecies’ sylvatica and orientalis in this area. Both morphological traits and gene markers revealed a possible influence of F. orientalis on the east side of Rodopi and at the low elevations, while characters resembling F. sylvatica were observed mainly on the western part of the mountains and in higher altitudes. There was a clinal increase of genetic diversity from the west to the east, reaching a level firstly reported for beech populations. These results can be explained either by the existence of a main refugial area for beech during the last glaciation or by the occurrence of a recent hybridization among the subspecies, which were spatially isolated during the last glaciation and came into reproductive contact during their postglacial remigration. These two scenarios are not necessarily mutually exclusive.     

Spatial and temporal variability of foliar mineral concentration in beech (Fagus sylvatica) stands in northeastern France

Foliar mineral concentration may provide a basis for monitoring the consequences of long-term environmental changes, such as eutrophication and acidification of soils, or increase in atmospheric CO(2) concentration. However, analytical drifts and inter-tree and year-to-year variations may confound environmental effects on long-term changes in foliar mineral concentration. We have characterized the relative effects of these potentially confounding factors on foliar carbon, nitrogen, phosphorus, calcium, potassium, magnesium and manganese concentrations in 118 pure beech (Fagus sylvatica L.) stands, sampled in 1969-71 and 1996-97. Interannual fluctuations of these elements were quantified in a subset of six beech stands monitored for 5 years. Intercalibration between the methods used at each sampling period for nitrogen and phosphorus analyses showed significant, but low, relative differences (0.8 and 3.3% for N and P, respectively). Based on inter-tree variability, elements could be arranged in four groups: C (constant), N and P (low variability), K and Ca (medium variability), Mn and Mg (high variability). Inter-tree coefficients of variation were 2, 6, 8, 15, 18, 22 and 27%, respectively. Year-to-year fluctuations increased in the order N, P, Mg, K, Ca, and Mn coefficients of variation of 4, 4, 7, 9, 11, 15 and 29%, respectively). Between the two sampling periods, foliar N concentration increased 12%, whereas decreases were observed for P (-23%), Mg (-38%) and Ca (-16%). Ratios of N/P, N/K and N/Mg increased by 42, 19 and 77%, respectively. These changes were larger than the interannual variations for P, Mg, N/P, N/Mg and Mg/Ca. Decreasing concentrations of P and cations were particularly marked for trees growing on acidic soils, whereas the positive N trend did not depend on soil type. Both increasing atmospheric CO(2) concentrations and acidification of forest soils could contribute to decreasing P and cation concentrations in foliage. The increase in foliar N concentration with time suggests a nitrogen deposition effect. Whatever the causes of these changes, the large shift in element ratios indicates an accelerating imbalance between nitrogen and cation status.     

DNA sequence variation and development of SNP markers in beech (Fagus sylvatica L.)

European beech (Fagus sylvatica L.) is one of the most important deciduous tree species in Central Europe. The potential of beech to adapt to climate change, higher temperatures, and less precipitation in the summer months is still unknown. Most studies in beech used microsatellite, AFLP (amplified fragment length polymorphism), or isozyme markers, which have only a restricted potential to analyze adaptation. Only few studies investigated genes probably involved in the adaptation to drought stress and bud phenology in beech. In this study, SNP (single nucleotide polymorphisms) markers were developed in order to analyze adaptation and their technical advantages compared to microsatellites and AFLPs were discussed. Partial sequences of ten candidate genes probably involved in drought stress and/or bud phenology were identified at the genomic level, and SNPs and indels (insertions/deletions) in coding and non-coding regions were analyzed. Plant material was sampled along a precipitation gradient in Germany. In total, 8,145?bp were sequenced and analyzed, 4,038?bp were located in exon and 4,107?bp in intron regions. 63 SNPs and 11 indels were detected, which are differently distributed over the studied gene regions. The nucleotide diversity ranged from 0 to 6.62 (π?×?10^?3) and is comparable to other tree species, whereas the mean nucleotide diversity (2.64) for F. sylvatica is comparatively low. These results will help to investigate the genetic basis of drought stress and bud burst and to conduct association mapping in natural populations. Furthermore, the detected SNPs can also be used for population genetic studies.     

A twig blight of understorey European beech (Fagus sylvatica) caused by soilborne Phytophthora spp.

During and after prolonged periods of rainfall in late spring, blighted young twigs of European beech (Fagus sylvatica) were frequently observed in several beech stands in south‐western and southern Germany. Long and short shoots of young understorey trees or lower branches up to 1.5 m above the soil level were affected. Symptoms also occurred regularly on twigs in heights up to 2 m and more above the ground. Necroses usually expanded within the current year’s tissue and often also reached into the previous year’s wood. Ponding rain water in the stands or along forest roads or open soil seemed to promote the disease. Of a total of 54 symptomatic twigs collected in four stands, 37 revealed Phytophthora isolates, of which 33 were P. plurivora and four were P. cambivora. Both species caused extensive lesions on beech twigs in laboratory pathogenicity tests. Patterns of the disease indicated that these pathogens, generally considered soilborne species, in most cases are transmitted from the soil to above‐ground parts of the trees via rain splash. In larger heights, however, other vectors such as snails might be responsible for transmission. Although Phytophthora spp. are well known as causal agents of seedling blight as well as root and cambium rot and aerial bleeding cankers of mature beech, to our knowledge this is the first report of a twig blight in beech associated with soilborne Phytophthora spp. In particular in periods of high precipitation, this disease might pose an additional threat to Central European beech forests, especially endangering the success of artificial and natural regeneration of beech in affected stands.     

Uptake and distribution of calcium and phosphorus in beech (Fagus sylvatica) as influenced by aluminum and nitrogen

We studied the effects of excess nitrogen added as nitrate (NO(3) (-)) or ammonium (NH(4) (+)), or both, on mineral nutrition and growth of beech (Fagus sylvatica L.) plants grown at pH 4.2 in Al-free nutrient solution or in solutions containing 0.1 or 1.0 mM AlCl(3). A high external concentration of NH(4) (+) increased the concentration of nitrogen in roots, stems and leaves. The root/shoot dry weight ratio was less in plants grown in the presence of NH(4) (+) than in plants grown in the presence of NO(3) (-). The concentration of phosphorus in the roots was increased and the concentration of potassium in all parts of the plant was decreased by NH(4) (+). A high external concentration of NO(3) (-) caused a decrease in phosphorus concentrations of the root, stem and leaf. Uptake of (45)Ca(2+) by roots was reduced in the presence of high concentrations of NH(4) (+) or NO(3) (-), and a combination of high concentrations of nitrogen and aluminum further reduced the uptake of (45)Ca(2+). Uptake of phosphate ((32)P) and concentrations of phosphorus in root and shoot were increased when plants were grown in the presence of 0.1 mM Al. Exposure to 1.0 mM Al, however, reduced the concentration of phosphorus in roots and shoots and the reduction was greater when plants were grown in the presence of a high external NO(3) (-) concentration. Aluminum binds to roots, and plants grown in the presence of 1.0 mM Al had a slightly higher concentration of aluminum in roots than plants grown in the presence of 0.1 mM Al, whereas the concentration of Al in the shoot was increased 2 to 3 times in plants exposed to 1.0 mm Al. Furthermore, the effects of 1.0 mM Al on uptake of other macronutrients were quite different from the effects of 0.1 mM Al. We conclude that 0.1 mM Al facilitates uptake and transport of phosphorus in beech and that between 0.1 and 1.0 mM Al there is a dramatic change in the effects of Al on uptake and transport of divalent cations and phosphorus.