Winter variation in physiological status of cold stored and freshly lifted semi-evergreen Quercus nigra seedlings

? Water oak (Quercus nigra L.) is a tardily deciduous species commonly planted in afforestation projects in the Lower Mississippi River Alluvial Valley, USA. Field performance is often marked by low survival rates and top dieback, which may be associated with poor physiological quality of planting stock.

? We investigated physiological status of cold stored (2–4 °C; CS) and freshly lifted (FL) seedlings during the period between lifting and planting (December — February). In mid-February, seedlings were transplanted into a controlled greenhouse environment for 90 d to evaluate post-transplant growth performance.

? Net photosynthetic rates were positive until late January (generally greater in CS seedlings) and became negative thereafter. FL seedlings generally had lower LT₅₀ values from freeze-induced electrolyte leakage (FIEL), reflecting greater cold hardiness. FIEL of foliage provided the best indicator of physiological status, though terminal buds may serve as a suitable substitute. All seedlings experienced top dieback following transplant; CS seedlings had less relative root-collar diameter, height, and root volume increments.

? Cold storing seedlings did not appear to prolong dormancy, increase stress resistance, or hold promise as a means to improve outplanting success. Regardless of storage regime, seedlings appeared to be most cold hardy and perhaps stress resistant until late January.

     

Fall fertilization of Pinus resinosa seedlings: nutrient uptake, cold hardiness, and morphological development

? Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored.

? Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH₄NO₃) at 0, 11, 22, 44, or 89 kg N ha^?1. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season.

? Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha^?1 attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at ?40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season.

? Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels.

     

Effects of organic residue management and legume cover on growth of pine seedlings, nutrient leaching and soil properties

? The short-term effect of organic residue management on the growth and nutrition of Pinus pinaster Ait. seedlings, and on nutrient leaching and chemical properties of an acid soil was assessed through a lysimeter experiment. Treatments included absence, placement on the soil surface, and incorporation into the soil (with and without legume cover cropping) of organic residues (forest floor litter or forest floor litter plus harvest residues).

? Residues placed on the soil surface enhanced seedling growth. Organic residues reduced nutrient losses (NO ₃ ^? , Ca and Mg) and resulted in nutrient accumulation in the soil. Harvest residues positively affected K seedling nutrition status and enhanced K soil accumulation.

? Legume cover cropping reduced soil nutrient losses (N, Ca, Mg and K) during the early stage of seedling growth; it also improved seedling nutrition status (N and P), but without any effect on growth.

? Harvest residues plus forest floor litter placed on the soil surface was the most appropriate management to both reduce nutrient losses through leaching and increase height of seedlings at the end of the experimental period (two years).

     

Intraspecific variation in growth and allocation patterns in seedlings of Pinus pinaster Ait. submitted to contrasting watering regimes: can water availability explain regional variation?

? Interpopulation variation in key functional traits of Pinus pinaster Ait. is well recognized. However, the relative importance of drought tolerance to explain this regional variation in the species remains elusive.

? Here, we raise the question whether water availability constitutes a likely driver of regional variation in biomass allocation, growth and morphological traits of ten populations that cover the distribution range of P. pinaster. We carried out an experiment where seedlings of five families per population were submitted to two contrasting watering treatments.

? The effects of water availability and population were significant for relative diameter and height growth rate, biomass allocation and number of lateral stems and dwarf shoots. Total dry mass significantly differed between watering treatments but it did not among populations. Populations could be clustered into four main groups. Root mass fraction explained most of the variation and significantly correlated to altitude but not to aridity.

? The geographical pattern of genetic variation found in morphology and biomass allocation did not translate into population differences in drought tolerance or phenotypic plasticity to water availability, indicating that water availability is not a likely driver of the regional variation observed in the studied traits of P. pinaster at the seedling stage.

     

Drying and soaking pretreatments affect germination in pedunculate oak

? Pedunculate oak (Quercus robur L.) acorns are recalcitrant so they are difficult to store. Therefore, deterioration in quality during storage may reduce seedling yield and quality. In an attempt to address this, the effects of drying and soaking treatments on acorn germination were assessed.

? After harvesting on two occasions in October, the moisture content (MC) of acorns were adjusted using the following treatments: (1) fresh state or control (46–48% MC); (2) soaked in fresh state (46–48%); (3) dried (40–42%) (standard method); and (4) dried and then soaked (46–48%). The treated acorns were allowed to germinate at 15 °C, both before and after storage at ?3 °C.

? Treatment effects were generally consistent for each harvest date. Compared to the untreated controls, soaking alone and drying followed by soaking significantly increased germination both before and after storage. Storage reduced germination, except for the dried and soaked acorns.

? The results confirmed that drying and soaking improved acorn germination, but this was not mediated through an effect on acorn MC. In a separate nursery experiment, acorns given this treatment resulted in higher seedling yields and better quality plants than those given the standard treatment (dried to 40–42% MC).

     

Effects of atmospheric and climate change at the timberline of the Central European Alps

? This review considers potential effects of atmospheric change and climate warming within the timberline ecotone of the Central European Alps. After focusing on the impacts of ozone (O₃) and rising atmospheric CO₂ concentration, effects of climate warming on the carbon and water balance of timberline trees and forests will be outlined towards conclusions about changes in tree growth and treeline dynamics.

? Presently, ambient ground-level O₃ concentrations do not exert crucial stress on adult conifers at the timberline of the Central European Alps. In response to elevated atmospheric CO₂ Larix decidua showed growth increase, whereas no such response was found in Pinus uncinata. Overall climate warming appears as the factor responsible for the observed growth stimulation of timberline trees.

? Increased seedling re-establishment in the Central European Alps however, resulted from invasion into potential habitats rather than upward migration due to climate change, although seedlings will only reach tree size upon successful coupling with the atmosphere and thus loosing the beneficial microclimate of low stature vegetation.

? In conclusion, future climate extremes are more likely than the gradual temperature increase to control treeline dynamics in the Central European Alps.

     

Elastic parameters of poplar wood with end-cracks

? In this study, longitudinal specific modulus of elasticity along the grain (specific MOE_L = MOE_L/ρ) as well as radial and tangential shear moduli (G _LR and (G _LT ) of Populus Deltoides wood were examined in free flexural vibration in a free-free bar method, where end-cracks produced manually in LT plane along and parallel to annual rings in four different sizes.

? The effects of four different crack sizes (0, 6, 12, and 18 cm) on elastic parameters of the bars were examined for their vibration properties based on Timoshenko bar equations, in order to find a procedure to make a confident choice of a clear specimen among the cracked ones, considering three initial modes of vibration.

? Based on research findings, a significant correlation existed between radial and tangential shear moduli of the clear bars as G _LR was approximately 15 percents higher than (G _LT . After making the shortest crack sizes, however, this correlation entirely faded. Statistically for 6 cm crack, decreases in specific MOE _L for measurement on the tangential impact were not significant though they were for longer cracks.

? It was also revealed that in specimen under the study if longitudinal specific modulus of elasticity from both LR and LT flexural vibrations were almost equal and G _LR was slightly larger than (G _LT , the user could be confident enough to consider the specimen without severe longitudinal cracks.

     

Forest floor contribution to phosphorus nutrition: experimental data

? Although accumulation of decomposing litter temporarily removes nutrients from active circulation, it creates a medium that is more suitable for nutrient uptake where soil conditions are unfavorable.

? A pot experiment was conducted using labeling of isotopically exchangeable phosphate ions of the soil and applying the dilution principle to accurately assess the contribution of the forest floor to P nutrition of maritime pine seedlings (Pinus pinaster Aït.). Three-week-old maritime pine seedlings were planted in pots containing either mineral soil (MS) or mineral soil covered with a forest floor layer (MS+FF).

? After 130 d, P uptake was still insignificant in the MS treatment while the P content of the seedlings in the MS+FF treatment increased tenfold with respect to the initial P content. In the latter treatment, the forest floor contributed 99.1% of the P supply to pine seedlings.

? The higher P uptake from the forest floor than from the mineral soil may be explained by its lower ability to retain inorganic P, which enabled a higher concentration of inorganic P to be maintained in solution.

     

Mycorrhization, growth and nutrition of Pinus halepensis seedlings fertilized with different doses and sources of nitrogen

? Although fertilization is commonly used in nurseries, the effects of high level of nitrogen on Pinus halepensis mycorrhization are still unknown.

? The effect of fertilization at different N levels (low-LN: 35 mg/plant; medium-MN: 60 mg/plant; high-HN: 120 mg/plant), differing N sources (ammonium-(NH₄)₂SO₄; nitrate-HNO₃; ammonium+nitrate-NH₄NO₃) and inoculation with Pisolithus tinctorius and Lactarius deliciosus on the mycorrhization, growth and nutrient status of P. halepensis has been studied.

? P. tinctorius 3SR showed higher mycorrhizal ability (100% of mycorrhizal seedlings) than L. deliciosus (nearer to 50%). The application of increasing doses of N resulted in a significant reduction of mycorrhizal seedlings but no differences were observed between NH₄ and NO₃as N source at the 60 mg N/plant dose applied. The effects of fertilization on growth were mainly observed in uninoculated plants. The use of NH₄ increased growth in non-mycorrhized plants. Nutrient status was similar in all cases except for K concentration, which was higher in plants mycorrhized with P. tinctorius. Interactions between inoculation and fertilization were found, mycorrhizal effects appearing only at LN fertilization.

? It is advisable to avoid high doses of N fertilization in order to produce mycorrhizal P. halepensis seedlings.

     

Genetic variation for carbon isotope composition in Juglans regia L.: relationships with growth, phenology and climate of origin

? Among the traits of breeding interest for the common walnut tree Juglans regia L., characteristics such as timing of budbreak and leaf fall, water-use efficiency and growth performance are regarded as being of utmost relevance in Mediterranean conditions.

? The authors evaluated intraspecific variation in δ¹³C (carbon isotope composition, surrogate of intrinsic water-use efficiency, WUE_i) for 22 J. regia families grown in a progeny test under supplementary irrigation, and investigated whether such variation correlated with climatic indicators of native habitats. The genetic relationships between δ¹³C, growth and phenology were also assessed during two consecutive years.

? Overall, the most water-use-efficient families (i.e. with higher δ¹³C), which originated mainly from drought-prone provenance regions which have a high vapour pressure deficit and low rainfall, exhibited less height growth and smaller DBH. Using a stepwise regression procedure, δ¹³C was included as the main explanatory variable of genotypic variation in growth traits, together with growing season duration (for DBH in both years) and flushing (for height in 2007).

? It was concluded that WUE_i is largely unconnected to phenology effects in the explanation of growth performance for J. regia, therefore suggesting the opportunity of simultaneously selecting for low WUE_i and extended growing period to maximise productivity in non-water-limited environments.

     

Interactive responses of Quercus suber L. seedlings to light and mild water stress: effects on morphology and gas exchange traits

? The combined effect of water stress and light on seedlings of forest species is a key factor to determine the best silvicultural and afforestation practices in the Mediterranean area.

? The aims of this work was (1) to determine the optimal light level for the early development of cork oak seedlings under mild water stress and (2) to test if the combined effect of water stress and light followed the trade-off, the facilitation or the orthogonal hypothesis.

? Shade reduced instantaneous photosynthetic rates and water use efficiency in cork oak. However, seedlings grown under moderate shade (15% of full sunlight) were capable to accumulate similar amount of biomass than those grown under more illuminated environments by increasing their specific leaf area. Absolute differences in net photosynthesis between light treatments were higher in well watered than in water stressed seedlings. However, the impact of both factors on overall growth was orthogonal.

? We concluded that cork oak development is impaired under deep shade (5% of full sunlight) but it can be optimal under moderate shade (15% of full sunlight) even under moderate water stress. Implications of these patterns on regeneration, cultivation and afforestation of cork oak are discussed.

     

Drought susceptibility and recovery of transplanted Quercus rubra seedlings in relation to root system morphology

? Transplant shock, implicated by depressed seedling physiological status associated with moisture stress immediately following planting, limits early plantation establishment. Large root volume (Rv) has potential to alleviate transplant shock because of higher root growth potential and greater access to soil water.

? We investigated impacts of drought and transplant Rv on photosynthetic assimilation (A), transpiration (E), stomatal conductance (g _s ), predawn leaf xylem water potential (Ψ_L), and growth of northern red oak (Quercus rubra L.) seedlings to explain mechanisms associated with susceptibility to transplant shock. One year-old barerooot seedlings were graded into four Rv categories and either well watered or subjected to drought consisting of low, medium, or high moisture stress by discontinuing irrigation at 22-day intervals for 3 months. Thereafter, all treatments were re-watered to examine recovery.

? Transplant shock was signified by reduced A, E, g _s, and Ψ_L, which generally increased with increasing moisture stress and Rv. Physiological status improved during recovery, though stress was still evident in seedlings exposed to medium or high moisture stress and in larger Rv seedlings. Growth declined with increasing moisture stress but was generally similar among Rv treatments, likely reflecting greater A at the whole plant level and/or reliance upon stored reserves in large Rv seedlings.

? The most effective drought avoidance mechanisms were root growth, stomatal regulation, reduced leaf area, and higher growth allocation to roots relative to shoots. Our results suggest that large initial Rv does not enhance drought avoidance during the first season after transplant in northern red oak seedlings.

     

Extending sapwood — Leaf area relationships from stems to roots in Coast Douglas-fir

? Studies of allometric relationships between leaf area and the cross-sectional area (CSA) of sapwood in the stem have shed light on the structural and functional relationships between water-conducting and photosynthetic tissues.

? The purpose of this study was to test whether sapwood-leaf area relationships could be extended from stems to roots in coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Twelve trees were felled, their stumps were excavated, and the CSA of sapwood and heartwood were estimated for individual roots, entire root systems, and stem section.

? Root sapwood CSA was greater than sapwood CSA throughout the stem, and the ratio of leaf area to sapwood CSA (A _l :A _s ) was accordingly lower for root sapwood. The relationship between sapwood CSA and leaf area was more variable in roots and at groundline compared to crown base. Root A _l :A _s decreased with relative tree height (tree height/mean stand height).

? The strong allometric relationship between leaf area and the CSA of sapwood in the stem generally holds when extended to roots. The greater CSA of sapwood in roots versus stems may reflect differences in their roles in supporting the tree.

     

Summer temperature affects the ratio of radial and height growth of Scots pine in northern Finland

? Radial and height growth chronologies from 150-year-old and 50-year old Scots pine stands, both located near to the northern timberline in Laanila, Finland (68° 30′ N, 27° 28′ E), were cross-correlated with each other and with mean temperatures of various temperature periods defined as months, days or growing-degree-days.

? The height-growth chronology correlates significantly with radial growth at lags 1 and 2, and radial growth with height growth at lag 2 when the effect of temperature is omitted. On average, low and high growth years represent cool and warm average growing seasons. The summer temperatures (June, July and August) affect most on growth, but height and radial growth do have a different set of effective temperature periods. Furthermore, July temperature variation affects stronger height than radial growth.

? Those years with low height/radial-growth ratio, i.e. relatively higher current year’s radial than next year’s height growth, do have lower growth and cooler-than-average July temperature whereas those years with high height/radial-growth ratio do have clearly warmer mid-summer temperatures.

     

Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings?

? Artificial defoliation is often used to simulate defoliation by herbivory and is usually considered a good indication of a plant’s response to a given type of damage. However, the findings of studies directly comparing the two defoliation types are inconsistent.

? Here, the short term effects of artificial and insect defoliation by larvae of Paropsisterna agricola on growth, biomass allocation and photosynthetic capacity of Eucalyptus globulus seedlings were compared in a glasshouse experiment. The artificial defoliation was carried out to closely resemble the spatial patterns observed for insect defoliation.

? Height and diameter increments were reduced as a result of insect defoliation, whereas artificial defoliation had no significant effect on height. Increased photosynthetic capacity was observed in response to both treatments, but the magnitude of this increase was larger in insect-than in artificially-defoliated seedlings. Significant reductions in foliar carbohydrate content and total biomass were noticeable in artificially-defoliated seedlings. Although the foliar carbohydrate levels also decreased across the crown zones following insect defoliation treatment, seedlings allocated a large amount of their biomass in the branches of the damaged zone.

? Despite our best endeavours to simulate insect defoliation in the artificial treatment, the latter may not reflect accurately the full strength of the effects. However, artificial and insect defoliation were similar in their direction of the responses they caused in E. globulus seedlings.

     

Spatial and temporal variability of natural regeneration in a temperate old-growth forest

? The natural regeneration of shade-tolerant tree species is characterized by large spatial heterogeneity and temporal variability. The mechanisms producing those patterns are still poorly understood and the knowledge of long-term fluctuations in regeneration processes is very limited.

? We used data from long-term study plots in an old-growth stand dominated by European beech and silver fir to address three questions: (1) Is a tendency towards clumping in seedlings associated with a particular spatial scale? (2) Are the spatial patterns in seedlings constant over time? (3) Is the distribution of seedlings related to light intensity?

? Over the study period the seedling density varied from 2.5 to 6 ind./m². Stronger fluctuations occurred at a fine scale. Seedlings were clumped at distances ranging from a few centimeters to a few meters. The distribution of places with high seedling densities was relatively constant over time, especially in beech. Positive but weak rank correlations were found between light intensity and densities of beech and fir seedlings.

? Despite large fluctuations in seedlings densities, caused by mast-seeding, a permanent seedling bank was maintained. Very pronounced clumping of tree seedlings found in this study was only partially explained by differences in light intensity.

     

Simplified and improved somatic embryogenesis of hybrid larches (Larix × eurolepis and Larix × marschlinsii). Perspectives for breeding

? Development of clonal propagation method, such as somatic embryogenesis, has numerous applications such as mass-production of genetically improved plants and the amenability of embryogenic cultures to cryogenic storage. Since the 90’s, researchers at INRA have engaged in research on somatic embryogenesis in Larix species (Larix × eurolepis, Larix × marschlinsii).

? The aim of this work was to improve and to simplify all steps of somatic embryogenesis and to apply this protocol to the new hybrid variety REVE-VERT.

? The somatic embryogenesis initiation frequency from immature zygotic embryos was high (65%) on a medium with reduced plant growth regulator concentrations (2.2 μM of 2.4-dichlorophenoxyacetic acid and 2.3 μM of 6-benzyladenine). Simplified cryopreservation method (no need of programmable freezer) of the embryonal masses resulted in 100% recovery of cryopreserved lines. Maturation of a large number of somatic embryos was greatly improved when embryonal masses were dispersed on filter paper placed on medium containing high concentration of gellan gum (8 g·L^?1). Under these conditions, 94% of the lines matured somatic embryos that developed into plantlets. Clearly ageing and cryopreservation did not reduce embryogenic potential of embryonal masses.

? Requirements for the effective integration of somatic embryogenesis into the larch breeding programme are discussed.

     

Changes in nitrogen level and mycorrhizal structure of Scots pine seedlings inoculated with Thelephora terrestris

? We investigated the influence of Thelephora terrestris, an ectomycorrhizal fungus, on the concentration of nitrogen in needles of Pinus sylvestris L. seedlings and their mycorrhizal structure within four seasons of growth.

? Seedlings were grown in four treatments: (I) inoculated + 0.030 g N, (II) inoculated + 0.045 g N, (III non-inoculated + 0.030 g N, (IV) non-inoculated + 0.045 g N under laboratory conditions and later planted in post-agricultural land.

? For inoculated treatments, statistically significant differences in N concentration of needles were observed for two- and four-year-old seedlings. The number of ectomycorrhizae and concentration of N in needles were negatively correlated. After four seasons of growth the greatest numbers of ectomycorrhizae were present on seedlings from treatment II, and the smallest on seedlings from treatment IV.

? Two-year-old seedlings had been colonized by at least six different fungal taxa, i.e. Cenococcum geophilum, Hebeloma crustuliniforme, Rhizopogon sp., Suillus bovinus, Thelephora terrestris and a non-identified one. Treatments I and II were dominated by the ectomycorrhizae of T. terrestris and their number was significantly greater than in treatments III or TV. On four-year-old seedlings ectomycorrhizae of T. terrestris were dominated in all treatments, while ectomycorrhizae of Hebeloma sp. were not found.

     

Compared effects of competition by grasses (Graminoids) and broom (Cytisus scoparius) on growth and functional traits of beech saplings (Fagus sylvatica)

? The effect of two weeds (grasses and broom, Cytisus scoparius) competition on the growth and functional traits of European beech saplings (Fagus sylvatica) was investigated in an experimental plantation in the French Massif central.

? We hypothesized that grasses would have a much more harmful effect than broom on beech growth through strong competition for soil water and nitrogen.

? A randomized block design was used with three separate blocks, each possessing three types of vegetation; grasses (mainly Agrostis capillaris, Holcus mollis and H. lanatus), broom, and bare soil as a control.

? Two years after plantation beech sapling growth was significantly greater in bare soil than with competition from grasses, and was intermediate on broom. Growth was positively correlated with beech leaf nitrogen content (N_m) and xylem water potential (Ψ_x). N and Ψ_x were dependent, with nitrogen uptake probably decreasing with increasing drought. There was no clear correlation between growth and light transmitted 10 cm below the apex of the saplings.

? Beech leaf mass on an area basis (LMA) was correlated with the three resource variables (water, nitrogen and light) and with growth, confirming that LMA is a sensitive functional trait integrating the degree of stress experienced by the saplings.

? The results suggest that broom is less competitive than grasses and, if properly managed on a sufficiently well-watered site, can generate satisfactory conditions for beech establishment and growth.

     

Cryopreservation of dormant orthodox seeds of forest trees: mazzard cherry (Prunus avium L.)

? The sensitivity of dormant seeds of mazzard cherry (Prunus avium L.) of Polish provenances to extreme desiccation and/or the ultra-low temperature of liquid nitrogen, LN (?196 °C), was investigated to identify the optimum seed water content (w.c.) at this temperature.

? Germination and seedling emergence tests in this study showed that there is no critical seed w.c. for deeply desiccated seeds (stone w.c. 1.6%), although such desiccated seeds were sensitive to the temperature of LN in the seedling emergence test. For seeds frozen in LN, the highest germinability was observed at w.c. of 9.0–16.9%, but seedling emergence was then significantly lower than in nonfrozen seeds. The 2-year of storage in LN of seeds desiccated to 7.8% w.c. did not decrease germinability after thawing, in comparison with 2-year of storage at ?3 °C. Storage in LN showed that if seeds were stored after breaking of their dormancy, germinability after storage was lower because of the necessity of seed desiccation to the lower level (～ 8%) of w.c. after stratification (before storage). Secondary dormancy was induced in seeds desiccated after stratification.

? The results of this study demonstrate the potential for long-term cryopreservation of mazzard cherry seeds in forest gene banks.