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Trees regenerating in the understory respond to increased availability of light caused by gap formation by undergoing a range of morphological and physiological adjustments. These adjustments include the production of thick, sun-type leaves containing thicker mesophyll and longer palisade cells than in shade-type leaves. We asked whether in the shade-regenerating tree Acer pseudoplatanus, the increase in leaf thickness and expansion of leaf tissues are possible also in leaves that had been fully formed prior to the increase in irradiance, a response reported so far only for a handful of species. We acclimated potted seedlings to eight levels (from 1 to 100%) of solar irradiance and, in late summer, transferred a subset of them to full sunlight. Within 30 days, the shaded leaves increased leaf mass per area and became thicker mostly due to elongation of palisade cells, except for the most shaded individuals which suffered irreversible photo-oxidative damage. This anatomical acclimation was accompanied by partial degradation of chlorophyll and a transient decline in photosynthetic efficiency of PSII (Fv/FM). These effects were related to the degree of pre-shading. The Fv/FM recovered substantially within the re-acclimation period. However, leaves of transferred plants were shed significantly earlier in the fall, indicating that the acclimation was not fully effective. These results show that A. pseudoplatanus is one of the few known species in which mature leaves may re-acclimate anatomically to increased irradiance. This may be a potentially important mechanism enhancing utilization of gaps created during the growing season.

The commonly observed negative relationship between stomatal density (SD) and atmospheric CO2 has led to SD being proposed as an indicator of atmospheric CO2 concentration. The use of SD as a proxy for CO2 , however, has been hampered by an insufficient understanding of the intraspecific variation of this trait. We hypothesized that SD in Pinus sylvestris, a widely distributed conifer, varies geographically and that this variation is determined by major climatic variables. By sampling needles from naturally growing trees along a latitudinal range of 32.25°, equivalent to 13.7°C gradient of mean annual temperature (MAT) across Europe, we found that SD decreased from the warmest southern sites to the coldest sites in the north at a rate of 4 stomata per mm2 for each 1°C, with MAT explaining 44% of the variation. Additionally, samples from a provenance trial exhibited a positive relationship between SD and the MAT of the original localities, suggesting that high SD is an adaptation to warm temperature. Our study revealed one of the strongest intraspecific relationships between SD and climate in any woody species, supporting the utility of SD as a temperature, rather than direct CO2 , proxy. In addition, our results predict the response of SD to climate warming.

Trees regenerating in the understory respond to increased availability of light caused by gap formation by undergoing a range of morphological and physiological adjustments. These adjustments include the production of thick, sun-type leaves containing thicker mesophyll and longer palisade cells than in shade-type leaves. We asked whether in the shade-regenerating tree Acer pseudoplatanus, the increase in leaf thickness and expansion of leaf tissues are possible also in leaves that are already fully formed, a response reported so far only for a handful of species. We acclimated potted seedlings to eight levels (from 1 to 100%) of solar irradiance and, in late summer, transferred a subset of them to full sunlight. Within 30 days, the pre-shaded leaves increased leaf mass per area and became thicker mostly due to the elongation of palisade cells, except for the most shaded individuals which suffered irreversible photo-oxidative damage. This anatomical acclimation was accompanied by a transient decline in photosynthetic efficiency of PSII (Fv/FM), the magnitude of which was related to the degree of pre-shading. The Fv/FM recovered substantially within the re-acclimation period. However, leaves of transferred plants were shed earlier in the fall, indicating that the acclimation was not fully effective. These results show that A. pseudoplatanus is one of the few known species in which mature leaves may re-acclimate anatomically to increased irradiance. This may be an important mechanism enhancing utilization of gaps created during the growing season.

Key message Juniperus communis males are better adapted than females to changing, seasonal environmental conditions due to their higher photosynthetic capacity and the higher concentration of photosynthetic pigments in their needles. Males cope with ROS more efficiently than females having greater carotenoids concentration in needles. Abstract In dioecious woody plants, females often exhibit greater reproductive effort than male plants and as a result, they can be more vulnerable to different stressors. We hypothesized that female plants of J. communis L. could have a lower photochemical capacity and a higher level of antioxidant enzyme activity and that these differences between males and females would be more pronounced under conditions where nutrient availability is limited. We also assume that additional stressors connected with different seasons would increase those differences. Male and female plants of J. communis growing in fertilized or non-fertilized soils were used to test this hypothesis. The effect of fertilization and sex on photochemical parameters derived from chlorophyll a fluorescence light curves, and on the concentrations of photosynthetic pigments in needles, was determined in different seasons within 2 years. To assess the tolerance of male and female plants to the nutrient deficit, antioxidant enzyme activity, and the level of reactive oxygen species (ROS) were determined. Results revealed sex-related differences in photochemical parameters, level of antioxidant enzyme activity, H2O2 levels, the concentration of photosynthetic pigments, and in the leaf mass-to-area ratio. This indicates that J. communis males could be better adapted than females to changing, seasonal environmental conditions due to their higher photosynthetic capacity, as reflected by their higher ETRmax, and a higher concentration of photosynthetic pigments in their needles. The sex-related differences concerning photosynthetic capacity and stress response found in our study are constitutive traits of each sex and are genetically based as they occurred independently of fertilization.

The commonly observed negative relationship between stomatal density (SD) and atmospheric CO

Background and Aims The reliance on external support by lianas has been hypothesized to imply a reduction in the biomass cost of stem construction and root anchorage, and an increased investment in leaves, relative to self-supporting plants. These evolutionary trade-offs have not been adequately tested in an ontogenetic context and on the whole-plant scale. Moreover, the hypothesis may be extended to other potentially limiting resources, such as nitrogen (N.) Methods Plants belonging to five con-familiar pairs of temperate liana/shrub species were cultivated in 120 L barrels and sequentially harvested over up to three growing seasons. To account for the ontogenetic drift, organ biomass and nitrogen fractions were adjusted for plant biomass and N pool, respectively. Key Results Lianas invested, on average, relatively less biomass in the root fraction in comparison with shrubs. This was offset by only insignificant increases in leaf or stem investment. Even though liana stems and roots showed higher N concentration in comparison with shrubs, plant N distribution was mostly driven by, and largely matched, the pattern of biomass distribution. Lianas also showed a greater relative growth rate than shrubs. The differences between the growth forms became apparent only when ontogenetic drift was controlled for. These results were confirmed regardless of whether reproductive biomass was included in the analysis. Conclusions Our results suggest that temperate lianas, in spite of their diverse, species-specific resource distribution patterns, preferentially allocate resources to above-ground organs at the expense of roots. By identifying this trade-off and demonstrating the lack of a general trend for reduction in stem investment in lianas, we significantly modify the prevailing view of liana allocation strategies and evolutionary advantages. Such a resource distribution pattern, along with the cheap unit leaf area and stem unit length construction, situates lianas as a group close to the fast acquisition/rapid growth end of the life strategy spectrum.

Trees regenerating in the understory respond to increased availability of light caused by gap formation by undergoing a range of morphological and physiological adjustments. These adjustments include the production of thick, sun-type leaves containing thicker mesophyll and longer palisade cells than in shade-type leaves. We asked whether in the shade-regenerating tree Acer pseudoplatanus, the increase in leaf thickness and expansion of leaf tissues are possible also in leaves that had been fully formed prior to the increase in irradiance, a response reported so far only for a handful of species. We acclimated potted seedlings to eight levels (from 1 to 100%) of solar irradiance and, in late summer, transferred a subset of them to full sunlight. Within 30 days, the shaded leaves increased leaf mass per area and became thicker mostly due to elongation of palisade cells, except for the most shaded individuals which suffered irreversible photo-oxidative damage. This anatomical acclimation was accompanied by partial degradation of chlorophyll and a transient decline in photosynthetic efficiency of PSII (F

(1) The focus on floral functional traits and their variability has been significantly lower than when compared to other plant organs. Here, we focused on the variability of four novel floral chemical traits. We aimed to assess the level of interspecific variability of total non-structural carbohydrates (TNC) and total phenolic compounds (TPh) in the flowers of woody species. (2) We collected data on 70 species of temperate trees and shrubs. We also assessed the intraspecific level of variability by collecting flowers from the high-light and low-light parts of the crown. (3) We found a phylogenetic signal in the variability of starch and TPh. We did not observe statistically significant differences or biologically significant trends between the high-light and low-light parts of the crown. We detected a low impact of light availability on the intraspecimen variability of the TNC and TPh contents. (4) Low intraspecimen variability allows for a more reliable extrapolation of measurements in cases of interspecific comparisons and can be used to better describe the reproductive strategies of different woody species.

Harsh environmental conditions affect both leaf structure and root traits. However, shoot growth in high-latitude systems is predominately under photoperiod control while root growth may occur for as long as thermal conditions are favorable. The different sensitivities of these organs may alter functional relationships above- and belowground along environmental gradients. We examined the relationship between absorptive root and foliar traits of Scots pine trees growing in situ along a temperate-boreal transect and in trees grown in a long-term common garden at a temperate latitude. We related changes in foliar nitrogen, phosphorus, specific leaf area, needle mass and 13 C signatures to geographic trends in absorptive root biomass to better understand patterns of altered tree nutrition and water balance. Increased allocation to absorptive fine roots was associated with greater uptake of soil nutrients and subsequently higher needle nutrient contents in the northern provenances compared with more southern provenances when grown together in a common garden setting. In contrast, the leaf δ13 C in northern and southern provenances were similar within the common garden suggesting that higher absorptive root biomass fractions could not adequately increase water supply in warmer climates. These results highlight the importance of allocation within the fine-root system and its impacts on needle nutrition while also suggesting increasing stomatal limitation of photosynthesis in the context of anticipated climatic changes.

In some lianas the use of trellis modifies within-plant biomass allocation and stimulates growth, however in other species trellis use may negatively affect growth indicating a cost associated with climbing. In order to improve access to light, lianas use other plants as climbing trellises. Whereas in shaded lianas climbing a trellis may enhance biomass gain by increasing leaf-level irradiance, we suspected that trellis use may also stimulate growth by triggering modifications in whole-plant allocation of biomass and nitrogen. We evaluated responses to trellis in three temperate lianas: Hedera helix, Celastrus orbiculatus and Wisteria floribunda. Lianas were grown outdoors in 120-L barrels and with ample space, with and without trellises. Biomass and nitrogen accumulation, distribution patterns and total stem length were determined after three and four seasons. Responses were adjusted for individual plant biomass. Liana responses to trellises were species-specific. In W. floribunda trellis use enhanced growth, consistently with the increased leaf mass fraction and leaf area ratio while biomass distribution to roots was reduced. Biomass distribution to stems and total stem length were increased by trellis use. In contrast, growth and biomass distribution in C. orbiculatus were not altered by trellis use. In H. helix growth was reduced in plants climbing on trellises in comparison with plants creeping on the ground, but biomass distribution pattern was not altered. Moreover, supported H. helix plants accumulated less nitrogen than did unsupported plants, suggesting a less efficient uptake of this nutrient. The ability to plastically modify growth and allocation patterns in response to trellis found in some lianas may constitute an important aspect of their ecological strategy. In other species, however, the switch to climbing may incur physiological costs resulting in lower growth.

Climate change has likely altered high-latitude forests globally, but direct evidence remains rare. Here we show that throughout a ≈1000-km transect in Scots pine (Pinus sylvestris L.) forests in Sweden, mature trees in ≈2015 had longer needles with shorter lifetimes than did trees in ≈1915. These century-scale shifts in needle traits were detected by sampling needles at 74 sites from 2012 to 2017 along the same transect where needle traits had been assessed at 57 sites in 1914–1915. Climate warming of ≈1 °C all along the transect in the past century has driven this temporal shift in foliage traits known to be physiologically critical to growth and carbon cycling processes. These century-scale changes in Scandinavian Scots pine forests represent a fingerprint of climate change on a fundamental biological element, the leaf, with repercussions for productivity and sensitivity to future climate, which are likely to be mirrored by similar changes for evergreen conifers across the boreal biome. (Less)

Alien phytophagous insects are often introduced along with their host plants, creating opportunities for troublesome invasions. Yet, not all of them are able to successfully colonize novel host plants. In this study, we investigated host selection by the alien leaf miner Phyllonorycter leucographella (Zeller, 1850) on both its original host and novel host plants in the insect's alien range. We predicted that this insect's percentage infestation of the original host would be positively related to its specific leaf area (SLA), because high-SLA leaves are nutritious and have thin cuticles, traits related to high offspring developmental success. We further hypothesized that this host selection process would apply in the selection of novel host plants. Our results show that this leaf miner selects leaves of its original host plant, Pyracantha coccinea, according to their SLA values. The SLA value was also positively related to the probability of P. leucographella infesting and successfully developing on novel host plants. The selection of high-SLA plants by the moth leads to a high developmental success on novel host plants in the first (summer) generation, but it is likely to be maladaptive in the second (overwintering) generation, because in temperate Europe, high SLA values are associated with deciduous plants that shed their leaves in autumn. It is likely that the apparent maladaptive selection of novel host plants by P. leucographella reduces the invasiveness of this pest by preventing its establishment on native plants.

Occupancy of cold habitats by evergreen species requires structural modification of photosynthetic organs for stress resistance and longevity. Such modifications have been described at interspecific level, while intraspecific variation has been underexplored. To identify structural and anatomical traits that may be adaptive in cold environments, we studied intraspecific variability of needles of Scots pine (Pinus sylvestris L.), a wide-ranging tree, along a 1,900 km temperate-boreal transect in Europe. Needles from 20 sites representing mean minimum winter temperatures between -4.0 and -19.9°C and mean annual temperatures between 8.3 and -1.7°C were sampled for measurements of leaf mass per area (LMA, g/m2), leaf density (LD, g/cm3) and 30 other morpho-anatomical traits. Needles from cold sites lived longer, were shorter, showed higher LMA and LD, had narrower and more collapse-resistant tracheids, thicker epidermal cells with thicker cell walls and wider resin ducts occupying larger fraction of needle volume in comparison to needles from warmer sites. Along the steep climatic gradient, needles presented a coordinated phenotypic spectrum of external and internal traits that are largely interpretable in functional, adaptive terms. This intraspecific pattern of covarying traits provides insight into the adaptive syndrome associated with stress tolerance and extended needle longevity under cold conditions of high latitudes. A plain language summary is available for this article. (Less)

Plant functional traits may be altered as plants adapt to various environmental constraints. Cold, low fertility growing conditions are often associated with root adjustments to increase acquisition of limiting nutrient resources, but they may also result in construction of roots with reduced uptake potential but higher tissue persistence. It is ultimately unclear whether plants produce fine roots of different structure in response to decreasing temperatures and whether these changes represent a trade-off between root function or potential root persistence. We assessed patterns of root construction based on various root morphological, biochemical and defense traits including root diameter, specific root length (SRL), root tissue density (RTD), C:N ratio, phenolic compounds, and number of phellem layers across up to 10 root orders in diverse populations of Scots pine along a 2000-km climatic gradient in Europe. Our results showed that different root traits are related to mean annual temperature (MAT) and expressed a pattern of higher root diameter and lower SRL and RTD in northern sites with lower MAT. Among absorptive roots, we observed a gradual decline in chemical defenses (phenolic compounds) with decreasing MAT. In contrast, decreasing MAT resulted in an increase of structural protection (number of phellem layers) in transport fine roots. This indicated that absorptive roots with high capacity for nutrient uptake, and transport roots with low uptake capacity, were characterized by distinct and contrasting trade-offs. Our observations suggest that diminishing structural and chemical investments into the more distal, absorptive roots in colder climates is consistent with building roots of higher absorptive capacity. At the same time, roots that play a more prominent role in transport of nutrients and water within the root system saw an increase in structural investment, which can increase persistence and reduce long-term costs associated with their frequent replacement.

Regenerating oak seedlings by different methods impacts taproot architecture, root-to-shoot allometry and, potentially, soil water use and plant growth under water limitations. In the present study, Quercus robur (L.) seedlings regenerated by four different methods – sowing (acorn-sown seedlings), sowing followed by shoot clipping (coppiced), sowing followed by root-pruning (root-pruned), and container planting with the root plug intact (containerized) – were subjected to four water-shortage regimes – full watering and 75, 50, and 25% of full watering. These treatments were used to test the hypotheses that root morphology, anatomy and biochemistry varied among regeneration methods, and, thus, differentially affected plant responses to water-shortages. For most traits, the response to water shortage of acorn-sown and containerized seedlings was similar, and opposite to that of coppiced and root-pruned seedlings. Water shortage did not change tree allocation to total root biomass among regeneration methods but altered the partitioning between absorptive and structural roots within the root system. Acorn-sown and containerized seedlings produced more pioneer roots, and coppiced and root–pruned seedlings more highly-branched fine roots with greater specific root length and specific root surface area under greater water shortage. Thus, acorn-sown and containerized oaks appeared to be primed for water foraging, and coppiced and root-pruned oaks for water absorption efficiency in response to water shortage. Water shortage caused a reduction in nonstructural carbohydrate concentrations in fine roots of acorn-sown and containerized seedlings and in the taproot of coppiced and root-pruned seedlings. Results generally indicated that seedling response to water limitation depended on the regeneration method, highlighting the importance of root–to–shoot allometry, taproot development, and carbon reserve mobilization for plant functioning under water shortage. Acorn-sown and containerized oaks seedlings might be more suitable for forest regeneration in sites characterized by severe water shortage periods. The reduction of taproot starch reserves under strong water shortage may render root-pruned oak trees more susceptible to topsoil water deficit than acorn-sown trees. This work contributes to understand drought acclimation and to identify the most adequate forestry regeneration practices to adapt forest ecosystems to ongoing climatic changes.

We hypothesized that female and male individuals of the dioecious tree species, Juniperus communis, exhibit different strategies of resource allocation when growing under stress conditions. To test this hypothesis, we performed a two-year pot experiment on plants exposed to different levels of nutrient availability. Analysis of the plants revealed a higher concentration of carbohydrates, carbon, and phenolic compounds in needles of female plants, indicating that females allocate more resources to storage and defense than males. This difference was independent of nutrient availability. Differences in carbohydrates levels between the sexes were most often significant in June, during the most intensive phase of vegetative growth in both sexes, but could also be attributed to female resources investment in cone development. A higher level of nitrogen and other macroelements was observed in males than in females, which may have been connected to the accumulation of resources (nitrogen) for pollen grain production in males or greater allocation of these elements to seeds and cones in females. The interaction between sex and soil fertilization for the C:N ratio may also indicate sex-specific patterns of resource allocation and utilization, which is impacted by their availability during specific periods of J. communis annual life cycle.

The correlations of phenotypic traits with environmental drivers suggest that variability of these traits is a result of natural selection, especially if such trait correlations are based on genetic variability. We hypothesized that in situ correlations of structural needle traits of Scots pine (Pinus sylvestris L) with minimal winter temperature (Tmin) reported previously from a temperate/boreal transect would be conserved when plants are cultivated under common conditions. We tested this hypothesis by analyzing needles from two common gardens located in the temperate zone, one including adult trees and the other juvenile seedlings. The majority of adult needle traits for which correlations with Tmin were found in the field turned out to be under environmental influence. In contrast, the majority of traits studied in juvenile needles were correlated with the original Tmin suggesting the role of past natural selection in shaping their variability. Juvenile needles thus appeared to be inherently less plastic than adult needles, perhaps reflecting the stronger selective pressure acting during juvenile, as compared with adult, ontogenetic stage. Genetically based cold-climate adaptation in either juvenile or adult needles, or both, involved an increase in leaf mass per area and leaf density, decrease in needle length, reduction in the amount of xylem and phloem, increase in thickness of epidermis, decrease in tracheid diameter and increase in tracheid density, and increase in diameter and volume fraction of resin ducts. We also show that at least some traits, such as transverse xylem and phloem areas and number of fibers, scale with needle length, suggesting that climate-related trait variation may also be mediated by changes in needle length. Moreover, slopes of these allometric relationships may themselves be plastically modified. The phenotypic syndrome typical of needles from cold environments may thus be under environmental, genetic and allometric control.

In evergreen plants, old leaves may contribute photosynthate to initiation of shoot growth in the spring. They might also function as storage sites for carbohydrates and nitrogen (N). We hence hypothesized that whole-plant allocation of carbohydrates and N to storage in stems and roots may be lower in evergreen than in deciduous species. We selected three species pairs consisting of an evergreen and a related deciduous species: Mahonia aquifolium (Pursh) Nutt. and Berberis vulgaris L. (Berberidaceae), Prunus laurocerasus L. and Prunus serotina Ehrh. (Rosaceae), and Viburnum rhytidophyllum Hemsl. and Viburnum lantana L. (Adoxaceae). Seedlings were grown outdoors in pots and harvested on two dates during the growing season for the determination of biomass, carbohydrate and N allocation ratios. Plant size-adjusted pools of nonstructural carbohydrates in stems and roots were lower in the evergreen species of Berberidaceae and Adoxaceae, and the slope of the carbohydrate pool vs plant biomass relationship was lower in the evergreen species of Rosaceae compared with the respective deciduous species, consistent with the leading hypothesis. Pools of N in stems and roots, however, did not vary with leaf habit. In all species, foliage contained more than half of the plant’s nonstructural carbohydrate pool and, in late summer, also more than half of the plant’s N pool, suggesting that in juvenile individuals of evergreen species, leaves may be a major storage site. Additionally, we hypothesized that concentration of defensive phenolic compounds in leaves should be higher in evergreen than in deciduous species, because the lower carbohydrate pool in stems and roots of the former restricts their capacity for regrowth following herbivory and also because of the need to protect their longer-living foliage. Our results did not support this hypothesis, suggesting that evergreen plants may rely predominantly on structural defenses. In summary, our study indicates that leaf habit has consequences for storage economics at the whole-plant level, with evergreen shrub species storing less carbohydrates (but not N) per unit plant biomass than deciduous species.

16 p., 1 mapa, tablas -- Postprint del artículo publicado en Diversity and Distributions. A Journal of Conservation Biogeopraphy. Versión revisada y corregida, [Aim] Scots pine is one of the dominant tree species in forest ecosystems of the temperate and boreal zones in Eurasia. Since the Tertiary, it has persisted also in the Mediterranean region, forming relict populations. In this study, we investigate range-wide genetic diversity of Scots pine, aiming to provide comprehensive information on the phylogeography and genetic resources of the species., [Location] Europe and Asia., [Methods] Thirteen paternally inherited chloroplast microsatellite (cpSSR) loci were used to investigate the genetic structure of 62 populations from Fennoscandia and 30 populations from the Mediterranean. We also surveyed variability of two maternally inherited mitochondrial DNA (mtDNA) regions and additionally included literature data from 156 populations (248 populations in total)., [Results] Scots pine retains an overall high genetic diversity in the chloroplast genome but, unexpectedly, the historically younger populations from Fennoscandia showed statistically higher mean intrapopulation diversity than the Mediterranean stands (0.807 and 0.750, respectively). The latter also contained a lower number of private cpSSR haplotypes. Population differentiation with respect to mtDNA was higher (GST = 0.628) than at cpSSR (GST = 0.015) indicating an efficient pollen-mediated gene flow among refugial populations of the species. One novel haplotype mtDNA was found, increasing the number of known mitotypes for the species from 4 to 5. The geographic distribution of mitotypes was structured into four groups corresponding to the main refugial areas of the species., [Main conclusions] Genetic impoverishment of the Mediterranean populations may enhance their vulnerability to future environmental changes. The spatial distribution of two mitotypes in Fennoscandia, featuring predominance of mitotype a in Norway and Sweden and mitotype b in Finland, gives strong support for dual colonization of that region from south-eastern (Finland) and south-western (Sweden) directions. These results thus provide new insights into both Holocene expansion of Scots pine and the present distribution of species' genetic resources., This study was supported by the National Science Centre (2011/02/A/NZ9/00108) and Institute of Dendrology, Polish Academy of Sciences.

Projections of future climates suggest that droughts (Ds) may become more frequent and severe in many regions. Genetic variation, especially within populations in traits related to D resistance, is poorly investigated in forest trees, but this knowledge is necessary to better understand how forests will respond to water shortages. In this study, we investigated variability among seven open-pollinated half-sib families of a single population and two population-level progenies of Norway spruce (Picea abies (L.) H. Karst.) in their gas exchange response to imposed D and xylem vulnerability to embolism. During their third growing season, saplings were subjected to three treatments-control (C), D (for 19 weeks) and broken drought (BD, 54 days without watering starting in mid-July, then well-watered). In response to D, all families reduced their stomatal conductance (gs) and light-saturated rates of photosynthesis (Amax) in a similar way. After rewatering, the xylem water potential (Ψ) recovered in the BD treatment, but gs and Amax remained lower than in C. Needle starch concentration was altered in both D treatments compared with C. Xylem of D-exposed trees was more vulnerable to embolism than in C. The minimum attained safety margin remained positive for all families, indicating that no catastrophic hydraulic failure occurred in stem xylem during D. Significant family variation was found for Ψ early in the D (midday Ψ between -1.2 and -1.8 MPa), and for needle damage, but not for sapling mortality. Family variation found at the initial stages of D, and not afterward, suggests that all families responded similarly to greater D intensity, exhibiting the species-specific response. Limited variation at the family level indicates that the response to D and the traits we examined were conservative within the species. This may limit breeding opportunities for increased D resistance in Norway spruce in light of expected climatic changes.

Establishment of the Nitrogen Fertilizer Factory in Pulawy, Poland (NFFP) in 1966 resulted in contamination of the environment with nitrogen and sulfur compounds. As a result, radial stem growth declined in Pinus sylvestris and increased in Quercus robur. In this study we explored possible causal agents responsible for differences in pollution response among P. sylvestris, Q. robur and Q. petraea species, including differential uptake of nitrogen oxide pollutants by foliage and nutrient imbalances. We compared trees growing in the vicinity of the NFFP and a control area and found that Q. robur leaves were characterized by a relatively smaller N increase than those of P. sylvestris. It is possible that relatively high accumulation of N by pine could cause metabolic dysfunction in that species. However, differences in the concentration of nitrogen or activity of nitrate reductase did not sufficiently explain observed growth differences among the studied species. It is likely that among the factors contributing to the increased growth of oaks after the establishment of NFFP there is the rapid decline and mortality of pollution-sensitive Scots pine trees, easing competition for light and nutrients in the remaining Quercus trees.

To evaluate the acclimative ability of current-year and previous-year needles of a shade tolerant conifer Taxus baccata L. to contrasting irradiance conditions, seedlings were raised under 27% solar irradiance and at 3 years of age they were transferred to an experimental garden and grown for one season under full irradiance (HL), 18% irradiance (ML) or 5% irradiance (LL). Whereas previous year needles did not change anatomically, current year needles in HL were thicker and had a thicker palisade and spongy mesophyll, and greater leaf mass per area than ML or LL needles. LL needles had greater nitrogen concentration than HL needles irrespective of age but only previous year LL needles also had an increased N per area content, thanks to their lack of reduction in LMA. Adjustment of chlorophyll and carotenoid content occurred in both needle age classes with LL and ML needles having much higher concentrations but, in current year needles, only slightly higher per area content than HL needles. Chlorophyll a/b ratio was not affected by age or irradiance. These modifications had no significant effect on photosynthetic capacities, which did not significantly differ between the age classes in HL or LL treatment and between treatments. On the other hand, high growth irradiance resulted in a greater photochemical yield, photochemical quenching, apparent electron transport rate and inducible non-photochemical quenching in needles formed in the current season. In previous year needles, however, only inducible NPQ was enhanced by high irradiance with other parameters remaining identical among treatments. To test sensitivity to photoinhibition, at the end of the summer plants from the three irradiance levels were transferred to a HL situation and F (v)/F (M) was determined over the following 18 days. Sensitivity to photoinhibition was negatively related to growth irradiance and previous year needles were less photoinhibited than current year needles. Thus, differences in acclimation ability between needle age classes were most pronounced at the level of anatomy and light reactions of photosynthesis, both of which showed almost no plasticity in previous year needles but were considerably modified by irradiance in current year needles.