Influence of wind loading on root system development and architecture in oak (Quercus robur L.) seedlings.

The effect of wind loading on seedlings of English oak (Quercus robur L.) was investigated. Instead of using a traditional wind tunnel, an innovative ventilation system was designed. This device was set up in the field and composed of a rotating arm supporting an electrical fan, which emitted an air current similar to that of wind loading. Oaks were sown from seed in a circle around the device. A block of control plants was situated nearby, and was not subjected to artificial wind loading. After 7 months, 16 plants from each treatment were excavated, and root architecture and morphological characteristics measured using a 3D digitiser. The resulting geometrical and topological data were then analysed using AMAPmod software. Results showed that total lateral root number and length in wind stressed plants were over two times greater than that in control trees. However, total lateral root volume did not differ significantly between treatments. In comparing lateral root characters between the two populations, it was found that mean root length, diameter and volume were similar between the two treatments. In trees subjected to wind loading, an accentuated asymmetry of root distribution and mean root length was found between the windward and leeward sides of the root system, with windward roots being significantly more numerous and longer than leeward roots. However, no differences were found when the two sectors perpendicular to the wind direction were compared. Mean tap root length was significantly higher in control samples compared to wind stressed plants, whilst mean diameter was greater in the latter. Wind loading appears to result in increased growth of lateral roots at the expense of the tap root. Development of the lateral root system may therefore ensure better anchorage of young trees subjected to wind loading under certain conditions.     

Inheritance and molecular variations of PCR-SSCP fragments in pedunculate oak (Quercus robur L.)

Single-strand conformaiton polymorphism (SSCP) profiles of six PCR-amplified fragments (250–800 bp) were analyzed in three full-sib families of pedunculate oak (Quercus robur L.) and their parents. Among the six fragments, four were polymorphic and one exhibited complex patterns that were not changed by varying the SSCP conditions. The number of bands for the analyzed fragments varied between two and four among individuals regardless of fragment size. As shown by segregation data, the variation in the number of bands between trees could only be attributed to the allelic composition (homozygotes vs heterozygotes): a genotype that exhibited two bands was presumptively homozygous, wheras a genotype exhibiting three or four bands was heterozygous. Mendelian proportions were observed in all crosses for each polymorphic fragment. In one cross, we could clearly identify a null allele due to a possible mutation at a primer site. Single-base mutations and short insertion-deletions were shown to be the molecular causes of the SSCP polymorphism observed between different alleles. The use of SSCP as a technique to identify co-dominant markers of PCR fragments (up to 800 bp) is recommended for gene diversity studies or for gene mapping.     

Interactive effects of mycorrhization and elevated carbon dioxide on growth of young pedunculate oak (Quercus robur L.) trees

Pedunculate oak (Quercus robur L.) was germinated and grown at ambient CO₂ level and 650 ppmv CO₂ in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 6 month under nutrient non-limiting conditions. Mycorrhization and elevated atmospheric CO₂ each supported the growth of the trees. Stem height, stem diameter, and dry matter accumulation of pedunculate oak were increased by mycorrhization. Elevated atmospheric CO₂ enhanced stem height, stem diameter, fresh weight and dry weight, as well as lateral root formation of the trees. In combination, mycorrhization and elevated atmospheric CO₂ had a more than additive, positive effect on tree height and biomass accumulation, and further improved lateral root formation of the trees. From these findings it is suggested that the efficiency of the roots in supporting the growth of the shoot is increased in mycorrhized oak trees at elevated atmospheric CO₂.Abbreviations DW dry weight - FW fresh weight - RWC relative water content     

Transport of organic sulfur and nitrogen in the roots of young mycorrhizal pedunculate oak trees (Quercus robur L.)

Uptake and xylem loading of organic sulfur and nitrogen were analyzed in detached mycorrhizal (Laccaria laccata L.) roots of pedunculate oak (Quercus robur L.) seedlings using radiolabeled reduced glutathione (GSH) and glutamine (Gln) for transport analyses. The experiments showed for the first time that GSH is taken up by plant roots from the nutrient solution and is partially allocated to the shoot. Apparently, GSH produced during mineralization processes in the soil can be used by plant roots as a sulfur source. GSH uptake into the roots showed biphasic kinetics within the concentration range studied (0–500 M) with maximum transport velocities (v _max) and substrate affinities (K _m) that were similar to the kinetics of Gln uptake. GSH uptake kinetics were also in the same range as previously reported for sulfate uptake by mycorrhizal roots of pedunculate oak. It may therefore be assumed that GSH and sulfate uptake can be of comparable significance for sulfur nutrition, provided both sulfur sources are available at similar concentrations at the sites of uptake. Xylem loading of GSH and Gln showed monophasic transport kinetics with v _max significantly lower than observed for the two respective uptake systems and, as indicated by the K _m-values, a substrate affinity between the high and the low affinity uptake systems. The possible nature of the transport systems for GSH and Gln is discussed.     

The alpha-tocopherol content of leaves of pedunculate oak (Quercus robur L.)--variation over the growing season and along the vertical light gradient in the canopy

This study was performed in order to investigate whether the actual requirement for defence against photo-oxidative stress is reflected by the alpha-tocopherol (alpha-Toco) content in leaves of pedunculate oak (Quercus robur L.). Antioxidants and pigments were quantified in leaves that were collected on six days between May and September 2000 in a mixed pine/oak forest at canopy positions differing in light environment. Pools of hydrophilic antioxidants and photo-protective xanthophyll cycle pigments (V + A + Z) reflected the anti-oxidative demand, as these pools increased with the average light intensity to which the leaves were acclimated. The photo-protective demand was not the determinant of the alpha-Toco content of oak leaves, as (1) foliage of a young oak, exposed to low light levels in the understorey, contained higher amounts of this lipophilic antioxidant than leaves sampled from semimature oaks at canopy positions with a similar light environment, and (2) a strong increase in the alpha-Toco content over the growing season was detected at each investigated crown position, whereas the V + A + Z pool did not show a concomitant accumulation during leaf ageing. The rate of alpha-Toco accumulation differed distinctly between samples taken at different canopy positions.     

Structure and identification of root bark of Quercus robur L.

The root bark structure of Quercus robur L. was analysed at different stages of root development and compared to the structure of stem bark. Root bark thickness varied considerably between different roots. Sclereid quantity decreased with increasing distance from the stem, which means it increased with age. Visible growth increments diminished with increasing distance from the stem. In lateral roots crystal quantity decreased with increasing distance from the stem. In lateral roots secondary phloem fibre length, sieve tube member length, and sieve tube diameter showed no regular trend. There were only a few basic structural differences between root and stem bark. The zone of cell differentiation (cell expansion, lignification) was wider in root bark; sieve tube collapse was delayed. In lateral root bark fewer sclereids were formed. The first-formed periderm often originated from deeper cell layers. Thus, primary elements were lacking after periderm formation. In root bark the phellem cell walls were of equal thickness. Thus, phellem lacked visible growth increments. Root bark phellem cells were slightly larger. The root phelloderm was more distinct. The secondary phloem fibres were slightly shorter than those in stem bark. Sieve tube members of stem and root bark were of similar length and diameter. The qualitative bark anatomical characters of oak root bark are suitable for root identifications. Due to minor structural differences between root and stem bark the characters must be used with care.     

Detection of microsatellite instability during somatic embryogenesis of oak (Quercus robur L.)

Five microsatellite loci (QpZAG1/5, QpZAG9, QpZAG36, MSQ4, MSQ13) were used to test for genetic stability of three somatic embryogenic culture lines of Quercus robur L. and plantlets derived therefrom. DNA variation was detected among somatic embryos within all embryogenic lines, whereas no genetic instability was found among the regenerated plants. Two microsatellite loci revealed variation, and a locus-dependent instability was observed. The most polymorphic and useful microsatellite locus for detecting genetic variation was QpZAG9, with 28.5% of the investigated loci being variable.     

Effect of water stress on monoterpene emissions from young potted holm oak (Quercus ilex L.) trees

We investigated the effects of a short period of water stress on monoterpene emissions from Quercus ilex, a common oak species of the Mediterranean vegetation and a strong emitter of monoterpenes. The experiment was carried out on two young saplings with a branch enclosure system under semi-controlled conditions. Under unstressed conditions, small qualitative (cis--ocimene, trans--ocimene, -caryophyllene and 1,8-cineol) and large quantitative (as much as 40% for the main compounds emitted) differences were observed between the two apparently similar trees. Nevertheless these differences did not affect the short-and long-term responses to temperature and water stress. Daily courses of emissions and gas exchanges were similar before and after the stress. During the most severe stress, emissions were reduced by a factor of two orders of magnitude and the log-linear relationship between emissions and temperature no longer existed. Photosynthesis and transpiration rates decreased as soon as the soil started to dry, whereas monoterpene emissions slightly increased for few days and then dropped when the daily CO₂ balance approached zero. We concluded that under water stress monoterpene emissions were highly limited by monoterpene synthesis resulting from a lack of carbon substrate and/or ATP. After rewatering, both emissions and gas exchanges recovered immediately, but to a level lower than the pre-stress level. These results have many implications for monoterpene emission modelling in the Mediterranean area, since the dry period generally extends from May to August. If our results are confirmed by field experiments, water stress could lead to a large overestimation of the emissions under summer conditions, when the algorithms based on light and temperature would give high emission rates.     

Radial distribution of Ni in stemwood of Quercus ilex L. trees grown on serpentine and sandy loam (umbric leptosol) soils of NE-Portugal

Concentrations of Ni were determined in xylem and phloem of Quercus ilex trees growing on serpentine and sandy loam soils of northeast Portugal. Radial distribution patterns of Ni in stemwood were compared to variations in annual growth increments of the trees.Concentrations of Ni in xylem and phloem were higher in Q. ilex from serpentine soil, when compared with Q. ilex of a sandy loam soil.The radial distributions of Ni showed large variations among the trees, although they all grew in the same area within a short distance from each other. These differences can be caused by small-scale spatial variations in the soil. Therefore, the use of such radial Ni distributions for a retrospective biomonitoring of the Ni pollution of larger areas appears questionable.     

Heartwood and sapwood development within maritime pine (<Emphasis Type="Italic">Pinus pinaster </Emphasis>Ait.) stems

Heartwood and sapwood development in maritime pine (Pinus pinaster Ait.) is reported based on 35 trees randomly sampled in four sites in Portugal. It was possible to model the number of heartwood rings with cambial age. The heartwood initiation age was estimated to be 13 years and the rate of sapwood transformation into heartwood was 0.5 and 0.7 rings year^–1 for ages below and above 55 years, respectively. Reconstruction of heartwood volume inside the tree stem was made by visual identification by image analysis in longitudinal boards along the sawn surfaces. This volume was integrated into the 3D models of logs and stems developed for this species representing the external shape and internal knots. Heartwood either follows the stem profile or shows a maximum value at 3.8 m in height, on average, while sapwood width is greater at the stem base and after 3 m remains almost constant up the stem. Up to 50% of tree height heartwood represents 17% of stem volume, in 83-year-old trees and 12–13% in 42 to 55-year-old trees. Tree variables such as stem diameter, DBH and tree total height were found to correlate significantly with the heartwood content.     

Stem annual increments as ecobiological indicators in Turkey oak (Quercus cerris L.)

In recent decades, the biostatistical analysis of relationships among tree growth and macroclimatic factors has developed remarkably. In this discipline, the parametrisation of tree growth is generally based on the records of annual ring widths measured on breast height transverse sections of tree stems (ARI). The present research enables the stem volume annual increment (AVI) to be evaluated as a dendroclimatic indicator in comparison with ARI. The research is a part of a broader investigation into the ecobiological characteristics of Turkey oak in the Gargano region (southern Italy). The results indicate that AVI is no better than ARI as a means of highlighting expressive relationships among the examined macroclimatic factors (monthly precipitation and monthly averages of temperature daily maxima and minima) and the Turkey oak annual stem growth. In the examined stands, the most growthinfluencing factors are the autumn and spring rainfalls. Regarding the stem breast height radial increment, the most effective temperature factors are the June averages of daily minima and maxima.     

Clonal effects in propagating oak trees via in vitro culture

Shoot growth, shoot multiplication in vitro, and rooting of shoots were compared in 6 clones derived from adult trees originating from a single plot in a french forest and in 16 clones derived from seedlings originating in the NE of France or in the Netherlands. The results showed strong within-provenance variations affecting shoot growth, multiplication factor, number of subcultures that could be achieved and, for the clones from adult trees only, frequency of shoots that rooted. In contrast, significant between-provenance differences could not be shown.     

Quantitative trait loci controlling water use efficiency and related traits in Quercus robur L.

Genetic variation for intrinsic water use efficiency (W _i) and related traits was estimated in a full-sib family of Quercus robur L. over 3 years. The genetic linkage map available for this F1 family was used to locate quantitative trait loci (QTL) for W _i, as estimated by leaf carbon stable isotope composition (δ ¹³C) or the ratio of net CO₂ assimilation rate (A) to stomatal conductance to water vapour (g _w) and related leaf traits. Gas exchange measurements were used to standardize estimates of A and g _w and to model the sensitivity of g _w to leaf-to-air vapour pressure deficit (sg^VPD). δ ¹³C varied by more than 3‰ among the siblings, which is equivalent to 40% variation of W _i. Most of the studied traits exhibited high clonal mean repeatabilities (>50%; proportion of clonal mean variability in global variance). Repeatabilities for δ ¹³C, leaf mass per area (LMA) and leaf nitrogen content were higher than 70%. For δ ¹³C, ten QTLs were detected, one of which was detected repeatedly for all 3 years and consistently explained more than 20% of measured variance. Four genomic regions were found in which co-localizing traits linked variation in W _i to variations in leaf chlorophyll and nitrogen content, LMA and sg^VPD. A positive correlation using clonal means between δ ¹³C and A/g _w, as well as a co-localisation of QTL detected for both traits, can be seen as validation of the theoretical model linking the genetic architecture of these two traits.     

Distribution of Cd and Zn in annual xylem rings of young spruce trees [Picea abies (L.) Karst.] grown in contaminated soil

Concentrations and total amounts of Cd and Zn in individual annual xylem increments of 5-year-old spruce trees (Picea abies) were investigated after one growing season in contaminated soils. The plants had been potted in soils amended with different concentrations of Cd and Zn and kept in open air conditions. In the outer xylem rings formed during the treatment period lowest concentrations of Cd and Zn were found. In inner rings concentrations of both elements increased and were highest at the pith. Total amounts of both elements showed reversed distribution patterns with highest values in the outermost rings. The observed increase of total dry matter of the rings from pith towards the outer rings was stronger than the parallel increase in total element amounts in the rings. Thus, concentrations dropped in younger rings. The time of the soil contamination event cannot be inferred from element concentrations in annual rings. The results challenge the concept of monitoring historical trends in trace element pollution using analytical data of tree rings of conifers.     

Productivity and nutrient uptake in a holm oak (Quercus ilex L.) stand and during regeneration after clearcut

The effect of clearcutting on biomass production and nutrient consumption was examined during the two years in a clearcut and a mature Quercus ilex L. coppice. The comparison was limited to the leaf compartment and to the annual shoots, which were the only comparable compartments in the two situations. At the same time, the dynamics of the nutrient pool (N, P, K, Ca, Mg), monthly uptake and recycling from the foliage, were studied.The second year after cutting, the leaf production was roughly the same at the two sites. However, the photosynthates appear to be used differently: in the young stand the perennial wood production was greater than in the mature stand, where the maintenance costs are higher. This is corroborated by the patterns of nutrient use.     

Severe winter rings of oak trees (Quercus robur L.) from Central European Russia

Oak trees were sampled in a flood plain forest in the valley of the Zapadnaya Dvina (Daugava) river (Tver region, Russia). Annual rings of the time period from 1826 to 2010 were studied. Anatomically distinct rings with a stripe of small-sized cells in the innermost part and narrow earlywood vessels located in three to four rows occurred in 1861, 1862, 1929, 1940, 1942, 1956 and 1979. Deviations of earlywood development were associated with the drop of winter temperature below ?42 °C. The percentage of severe winter ring (SWR) occurrence depends upon tree age and decreases from 75.6 % in younger specimens (under 41 years old at the time of the severe winter) to 27.1 % in middle-aged ones (from 41 to 80 years) to 3.5 % in trees older than 80 years. Described anatomical features can be used in the reconstruction of severe winter frequency in the past.     

An indicator system for identification of sites of high conservation value for saproxylic oak (Quercus spp.) beetles in southern Sweden

The saproxylic beetle fauna on old oaks was sampled in four regions of southern Sweden using two methods: window and pitfall trapping. The aim was to test a way of finding indicator species which can be used to identify sites with high species number or that scored high on a conservation priority species index, based on occurrence of red-listed species. From 92 sites surveyed, in total 164 species of saproxylic beetles were identified. Different sets of indicator species were selected based upon 22 sites from a centrally located region. Predictions of species number and the index for 30 other sites from the same province were made. The correlation between observed and predicted species number and the index increased with increasing number of indicators. When comparing different treatment of species indata, the explanatory power of predictions was strongest for presence/absence data. Indicator sets of species effectively caught with pitfall traps gave overall the best predictions of both species number and the index. Predictions of species number and the index worked well within the same regions but gave varied result for the three other regions which shows that transferability of indicators between regions may be doubtful.     

Effect of cleaning and thinning on height growth and girth increment in holm oak coppices (Quercus ilex L.)

This article studies the influence of cleaning or thinning intensity and of coppice age at the time of silvicultural treatment, on the growth of shoots remaining on the stool, in Quercus ilex coppices.Two experimental designs were used to answer these questions. The first studied the effect of two cleaning intensities on 4, 8, 15, 20, and 25 year old coppices. The second studied the effect of 4 thinning intensities (26%, 42%, 58%, or 78% removal of the initial basal area) on 43 and 57 year old coppices. In both cases, control plots undergoing no silvicultural treatment were maintained for each age class.The results, 4 and 5 years after silvicultural treatment, concerned girth increment and height growth of coppice shoots.Cleaning or thinning consistently had a positive influence on girth increment. In young coppices, less than 25 years old, mean annual girth increment was approximately 6 mm in the controls and double that under heavy cleaning. In older coppices, girth increment was lower in controls (3 mm per year) but the effect of thinning was very positive and, under very heavy thinning, growth was more than 11 mm per year.Cleaning and thinning often modify height growth. This effect was found to be either positive or negative and no general trend could be defined which was valid for all the age classes.Silvicultural treatments also had a positive effect on the appearance and growth of epicormic shoots on the holm oak trunks.The results were also analysed at the stool level. The number or percentage of shoots removed had a positive effect on the individual growth of selected shoots.     

Tree-ring element analysis of Korean pine (Pinus koraiensis Sieb. et Zucc.) and Mongolian oak (Quercus mongolica Fisch. ex Turcz.) from Changbai Mountain,north-east China

Summary Tree-ring analysis of 17 elements (Pb, Cd, Cu, Zn, As, Cr, Ti, Ni, V, Mn, Fe, Al, Ca, Mg, K, Na and P) was performed on Korean pine (Pinus koraiensis Sieb. et Zucc.) and Mongolian oak (Quercus mongolica Fisch. ex Turcz.) specimens from Changbai Mountain, a remote nature reserve in north-east China. The radial distribution patterns of Pb, Cu, Cr, Ti, Ni, V, As and Fe for both Korean pine and Mongolian oak were similar: concentrations remained generally constant in tree-ring intervals spanning approximately 200 years. These temporal patterns were in accordance with the known stability of the local ecological environment during this period. However, the other elements showed characteristic distribution patterns that differed between Korean pine and Mongolian oak. These patterns can only be interpreted in terms of physiological results; specifically they appeared to be related to the sapwood-heartwood conversion.     

Organic matter distribution and fluxes within a holm oak (Quercus ilex L.) stand in the Etna volcano

Located at 1100 m above sea level, on the western site of the Etna volcano, the ecophysiology of the Mount Minardo holm oak coppice has been investigated for more then twenty years. In this stand, now 31 years old, the above ground biomass amounts to 15000 g m^-2 of organic material, including leaves and perennial woody material. During these 31 years, the mean annual production has been around 775 g m^-2. The yearly mean litterfall amounts to 310 g m^-2, including 200 g m^-2 of leaves, mostly two years old. The soil surface is covered by a litter layer amounting to 3150 g m^-2. Each year, following Jenny's decomposition rate and field measurements, 290 g m^-2 of the litter turns into CO₂, or becomes incorporated in the soil organic matter.