海拔对高山栎光合气体交换和叶性状的影响

理解影响植物分布的式样及过程是生态学研究的中心内容之一,但对许多物种而言,限制其分布的原因还不清楚。为了认识高山栎分布与生理生态特性的关系,我们在不同海拔的4个观测点研究了帽斗栎的光合气体交换、叶氮含量、叶绿素含量和比叶重。由于高的水气压亏缺和气温,帽斗栎的光合作用和蒸腾作用在午间表现出明显的降低现象。帽斗栎的饱和光合速率、水分利用效率、最大羧化速率、最大电子传递速率和氮利用效率在海拔中部比低海拔或高海拔处的为高。不同海拔的叶氮含量在5月份有差异,8月份则没有明显不同。叶片厚度随海拔增加,但叶绿素含量及光合最适温度随海拔升高而降低。帽斗栎光合作用的海拔变化与叶片的生化效率和氮含量有关,而与比叶重无关。研究结果说明,温度的海拔变化对高山栎的光合作用和叶性状有明显影响,最适宜帽斗栎光合碳获取及生长的海拔范围是3180～3610m。     

海拔对高山栎光合气体交换和叶性状的影响

理解影响植物分布的式样及过程是生态学研究的中心内容之一,但对许多物种而言,限制其分布的原因还不清楚。为了认识高山栎分布与生理生态特性的关系,我们在不同海拔的4个观测点研究了帽斗栎的光合气体交换、叶氮含量、叶绿素含量和比叶重。由于高的水气压亏缺和气温,帽斗栎的光合作用和蒸腾作用在午间表现出明显的降低现象。帽斗栎的饱和光合速率、水分利用效率、最大羧化速率、最大电子传递速率和氮利用效率在海拔中部比低海拔或高海拔处的为高。不同海拔的叶氮含量在5月份有差异,8月份则没有明显不同。叶片厚度随海拔增加,但叶绿素含量及光合最适温度随海拔升高而降低。帽斗栎光合作用的海拔变化与叶片的生化效率和氮含量有关,而与比叶重无关。研究结果说明,温度的海拔变化对高山栎的光合作用和叶性状有明显影响,最适宜帽斗栎光合碳获取及生长的海拔范围是3180~3610m。     

长白山红松臭冷杉光谱反射随海拔的变化

为了研究红松、臭冷杉光谱反射率随海拔梯度的变化,本研究使用光谱仪测量了长白山两种主要的针叶树种红松、臭冷杉不同海拔针叶的光谱反射率,分别对比了两个树种不同海拔间光谱反射率、光谱指数的差异,这些特征可以反映植物叶片色素组成和色素含量等信息。结果表明：两种针叶树在不同海拔的光谱反射率变化明显,光谱指数也有显著差异,证明相关生理状况发生明显变化。对比各海拔光谱反射率发现,1279m处红松、臭冷杉针叶的色素总含量较高,叶绿素指数反映出748m处红松、臭冷杉针叶叶绿素含量显著高于1040m和1279m处,Car：Chl指数的差异说明红松、臭冷杉均在748处受到较弱的胁迫,臭冷杉在1040m受到较强的胁迫,对比各波段反射率随海拔的变化,发现红松、臭冷杉针叶色素含量都随海拔变化有明显的变化,而且臭冷杉的叶片水分含量、叶片结构也可能容易受到海拔影响。     

Light adaptation and the role of autotrophic epiphytes in primary production of the temperate seagrass, Zostera marina L.

Photosynthetic features of Zostera marina L. and its autotrophic epiphyte community were investigated in a population inhabiting a shallow (1.3 m depth) water meadow in Great Harbor, Woods Hole, MA (U.S.A.). Photosynthesis versus irradiance (P-I) relationships were measured with respect to leaf age determined by the leaf position in the shoot bundle and by location of the tissue along the leaf axis. Therefore both age and light intensity gradients along the leaf axis were considered. The maximum photosynthesis (P_max) per dm² typically increased nearly two-fold along the leaf axis from leaf bases to apices. Photosynthetic rate on a chlorophyll (Chl) basis did not increase as dramatically along the leaf axis, and rates were usually lowest in tissues with the highest Chl content. The P-I relationships of leaves of different ages did not reveal photoinhibition even at light intensities > 1400 μE • m⁻² • s ⁻¹. Furthermore, no photoinhibition was observed in tissues from leaf blade bases, which never experienced high light levels (> 500 μE • m ⁻² • s⁻¹) in situ in Great Harbor. The initial slopes of the P-I curves and light compensation and saturation values varied along the leaf axis in relation to in situ light intensity gradients and in relation to leaf or tissue age. It appeared that leaf and/or tissue age was more important than light environment in determining P-I responses. The contribution of the autotrophic epiphyte community on Z. marina leaves to total photosynthesis per dm² was between 27 and 50%, and between 10 and 44% per mg chlorophyll. These levels of epiphyte photosynthesis can double the primary production of Z. marina leaves. No detrimental effects of epiphyte cover were realized in leaf maximal photosynthesis or P-I relationships. Non-epiphytized leaves and leaves from which epiphytes were removed showed essentially identical photosynthetic features. Light intensity and age gradients along the leaf axis control both the photosynthetic performance of the leaves and epiphyte biomass and photosynthesis.     

Influence of altitude on local adaptation in upland tree species from central Argentina

• Steep climatic gradients boost morphological and physiological adjustments in plants, with consequences on performance. The three principal woody species of the Sierras Grandes Mountains of central Argentina have marked differences in sapling performance along their altitudinal distribution. We hypothesize that the steep gradient of climatic conditions across the species’ altitudinal distribution promotes trait differences between populations of different altitudes that are inherited by the following generation.
• Seeds from different altitudes were exposed to three temperature regimes to assess differential germination responses. Saplings were then transplanted to a greenhouse to assess possible variations in attributes and performance after 18 months.
• The three species showed differences in germination responses to temperature among altitudes and/or in sapling attributes and performance. In Maytenus boaria and Escallonia cordobensis, germination success was higher under high temperatures for the highest‐altitude, whereas lower temperatures boosted germination of the lowest altitudes. Polylepis australis showed no differences in germination among temperature treatments. In the greenhouse, saplings of the three species from intermediate altitudes showed high performance, whereas the upper and lower populations seemed to be adjusted to tolerating more stressful conditions (i.e., lower temperatures at the upper end and water stress at the lower end), showing lower performance toward both altitudinal limits.
• These patterns agree with those described for saplings growing under field conditions, suggesting adjustments in response to environmental changes undergone by populations along the altitudinal range. The marked adjustments of populations to the local environment suggest a potentially high impact of climatic change on species distribution.

     

Variation in invertebrate–bryophyte community structure at different spatial scales along altitudinal gradients

Aim This study assessed changes in diversity and assemblage composition in bryophytes and their associated invertebrates along altitudinal gradients in Australia and New Zealand. The importance of altitude in shaping these communities and for the diversity of both invertebrates and bryophytes was examined at different spatial scales, including local, altitudinal, regional and biogeographical. Location Samples were taken from four Australasian mountain ranges between 42° and 43°S: Mt Field and Mt Rufus, Tasmania, Australia, and Otira Valley and Seaward Kaikoura Mountains, South Island, New Zealand. Methods On both Tasmanian mountains, five altitudes were assessed (250, 500, 750, 1000 and 1250 m). At each location (mountain/altitude combination) two sites were chosen and six samples were taken. Six altitudes were assessed on New Zealand mountains (Otira: 250, 500, 750, 1000, 1250 and 1500 m; Kaikoura: 1130, 1225, 1325, 1425, 1525 and 2000 m). Bryophyte substrate was collected, and all samples were stored in 70% ethanol. Invertebrates were extracted from bryophytes using kerosene‐phase separation and all invertebrates were identified to family. At each location in Tasmania, all bryophyte species within six 25‐cm² grids per site were collected and identified to species. Bryophytes from New Zealand were identified to species from the invertebrate sample substrate because of sampling constraints. Results Altitude did have a significant effect on diversity, however, no general trend was found along the altitudinal gradient on the four mountains. There were distinct differences in diversity between biogeographical regions, mountains, altitudes and sites. In Tasmania, Mt Field had the highest diversity in invertebrates and bryophytes at 750 m. In contrast, Mt Rufus had consistent low invertebrate and bryophyte diversity along the entire altitudinal gradient. There were also distinctive differences between locations in the composition of invertebrate and bryophyte communities in Tasmania. Along the two altitudinal gradients in New Zealand, Otira had highest diversity for both invertebrates and bryophytes at low altitudes, whereas Kaikoura had highest invertebrate and lowest bryophyte diversity at the highest altitude. Main conclusions There was an effect of altitude, however, there were no consistent changes in diversity or composition on the four different mountains. There was considerable local and regional variation, and, despite a strong sampling design, no underlying altitudinal trends were detectable. This study demonstrates the importance of examining a range of spatial scales if patterns in community structure along altitudinal gradients are to be studied. The implications of this study are discussed with reference to survey design, taxonomic resolution, climate change and conservation of habitat.     

Photosynthesis in three altitudinal populations of the Andean plant Espeletia schultzii (Compositae)

Photosynthesis was compared in three altitudinal populations of Espeletia schultzii: 3,100, 3,550 and 4,200 masl. The measured parameters were Rubisco activity (EC 4.1.139), chlorophyll, soluble protein and soluble sugars contents, and specific leaf area (SLA). The 4,200 m population had a higher Rubisco activity (at 4 degrees C) followed by those at 3,550 m and 3,100 m. There were no significant differences between populations at 3,100 m and 3,550 m (ANOVA), but their activities were different from those of the 4,200 m population. Chlorophyll a content decreased slightly with elevation, while chlorophyll b was constant; therefore, the Ra/b ratio decreased with elevation, but not significantly. The leaf soluble sugars content increased along the altitudinal gradient. Leaf protein content did not differ. The SLA decreased with altitude. The increase in Rubisco activity might reflect higher enzyme activation and not higher enzyme protein. The increase in soluble sugars is probably associated to Rubisco activity. Three out of the five measured parameters revealed differences with altitude, suggesting a compromise between a higher metabolic activity and a smaller cellular volume.     

武夷山不同海拔植物水分利用效率的变化及其与养分变化的关系

以武夷山不同海拔(600、900、1300、1500、1800、2000和2100 m)的乔木、灌木和草本3种生活型植物为研究对象,观测其水分利用效率和叶片氮、磷养分浓度随海拔的变化趋势,旨在探索海拔梯度间水分、养分变化与植物水分利用效率变化的关系.结果表明: 植物水分利用效率随海拔的增加呈显著上升趋势,乔木叶片δ¹⁸O随海拔变化不显著.总体上看,叶片氮浓度未观测到规律性的变化,高海拔地区的叶片磷浓度显著高于低海拔地区.水分利用效率与叶片磷浓度呈显著正相关,而与叶片氮浓度相关性不显著.不同海拔植物水分利用效率变化主要由光合速率的变化引起,水分状况对植物水分利用效率的影响不显著.海拔梯度间植物叶片磷浓度的差异对光合速率影响显著,进而影响水分利用效率.     

Contrasting patterns of genetic variation and structure in plant invasions of mountains

Aim To assess the population genetic consequences of the colonization of two species with contrasting mating systems, Solidago canadensis and Lactuca serriola, along altitudinal gradients in both their native and introduced ranges. Location Allegheny Mountains, West Virginia and Wallowa Mountains, Oregon, USA; Valais, southern Switzerland. Methods Leaf material was collected from populations along altitudinal gradients and genotyped at seven microsatellite loci for each species. Differences in variability between native and introduced areas and in relation to altitude were analysed using linear models. Differences in the genetic, geographical and altitudinal structure of populations between areas were analysed by AMOVA, cluster analysis and Mantel tests. Results Genetic variation within and across populations of S. canadensis was significantly reduced, while populations of L. serriola were significantly more variable, in the introduced area. Genetic diversity decreased significantly with altitude for S. canadensis but not L. serriola. Genetic structure of S. canadensis was similar in both areas, and populations were isolated by geographical but not altitudinal distance. By contrast, population structure of L. serriola was much weaker in the introduced area, and populations were not isolated by distance in either area. Main conclusions Solidago canadensis has experienced a strong genetic bottleneck on introduction to the Valais, but this has not prevented it from colonizing a wide altitudinal range. Variation in neutral markers is therefore not necessarily a good measure for judging the ecological behaviour of a species. By contrast, the greater variability of L. serriola in the introduced area, where it also occurs over a greater altitudinal range, can be explained by increased outcrossing among admixed populations. This suggests that the ecological amplitude of alien species might be enhanced after population admixture in the new range, especially for species with highly structured native populations. However, even genetically depauperate introduced populations can be expected to colonize the same environmental range that they occupy in the native area.     

长白山垂直自然带弹尾纲物种概况

以长白山弹尾纲为研究对象, 基于1758‒2022年度发表的分类学和生态学文献资料, 编制了长白山垂直自然带弹尾纲物种名录, 分析了首次发表物种的学者贡献、出版物、发表时间和各属沿海拔梯度的分布情况。本研究共梳理弹尾纲物种92种, 隶属于3目11科46属, 长角䖴目、原䖴目和愈腹䖴目的物种分别占比61%、31%和8%, 其中长角䖴目的等节䖴科(该类群物种数占总体比例, 26%)、长角䖴科(16%)和鳞䖴科(16%)、原䖴目的棘䖴科(26%)是该地区的主要类群。统计的92种长白山弹尾纲物种由36位学者首次定名和报道, 中国学者占主要贡献(33%), 其次为波兰(11%)、瑞典(11%)、俄罗斯(8%)和美国(8%); 相关论文多发表在国际期刊上, Zootaxa是发表的主要期刊。基于海拔梯度的统计发现, 鳞䖴属(Tomocerus)和符䖴属(Folsomia)的物种沿海拔梯度的分布范围最广(海拔800‒1,700 m), 分布在海拔800 m (15个物种)、1,100 m (20个物种)和1,400 m (14个物种)的物种最多。基于以上结果, 本文讨论了长白山弹尾纲分类学现状和发展前景。     

Unravelling genetics at the top: mountain islands or isolated belts?

Background and Aims

In mountain plant populations, local adaptation has been described as one of the main responses to climate warming, allowing plants to persist under stressful conditions. This is especially the case for marginal populations at their lowest elevation, as they are highly vulnerable. Adequate levels of genetic diversity are required for selection to take place, while high levels of altitudinal gene flow are seen as a major limiting factor potentially precluding local adaptation processes. Thus, a compromise between genetic diversity and gene flow seems necessary to guarantee persistence under oncoming conditions. It is therefore critical to determine if gene flow occurs preferentially between mountains at similar altitudinal belts, promoting local adaptation at the lowest populations, or conversely along altitude within each mountain.

Methods

Microsatellite markers were used to unravel genetic diversity and population structure, inbreeding and gene flow of populations at two nearby altitudinal gradients of Silene ciliata, a Mediterranean high-mountain cushion plant.

Key Results

Genetic diversity and inbreeding coefficients were similar in all populations. Substantial gene flow was found both along altitudinal gradients and horizontally within each elevation belt, although greater values were obtained along altitudinal gradients. Gene flow may be responsible for the homogeneous levels of genetic diversity found among populations. Bayesian cluster analyses also suggested that shifts along altitudinal gradients are the most plausible scenario.

Conclusions

Past population shifts associated with glaciations and interglacial periods in temperate mountains may partially explain current distributions of genetic diversity and population structure. In spite of the predominance of gene flow along the altitudinal gradients, local genetic differentiation of one of the lower populations together with the detection of one outlier locus might support the existence of different selection forces at low altitudes.     

苦竹叶片碳氮磷化学计量特征的海拔梯度效应

为揭示海拔梯度对苦竹林立竹叶片碳(C)、氮(N)、磷(P)化学计量特征的影响,该文以3个海拔梯度[低海拔,(200±10) m;中海拔,(400±10) m;高海拔,(800±10) m]苦竹林为研究对象,测定1至3年生立竹叶片C、N、P含量,分析其化学计量特征和异速增长关系。结果表明:(1)立竹年龄对苦竹叶片C、N、P含量及其化学计量特征影响明显,随立竹年龄的增大,苦竹叶片C、N、P含量和N∶P总体上均呈降低趋势,而C∶N、C∶P总体上呈升高趋势。(2)海拔对苦竹叶片C、N、P含量及其化学计量特征有重要影响,随海拔梯度升高,不同年龄立竹叶片C含量呈先升高后下降变化趋势,N、P含量总体上呈降低趋势,而C∶N、C∶P和N∶P均呈升高趋势。(3)不同海拔梯度苦竹林立竹叶片C、N、P含量和C∶N、C∶P差异显著,中、高海拔苦竹林立竹叶片N∶P无显著差异,均显著高于低海拔苦竹林;不同海拔梯度苦竹林立竹叶片C、N、P间呈显著的正异速增长关系,随海拔梯度的升高,C-N、C-P异速增长指数显著升高,而N-P异速增长指数显著下降。综上结果表明,高海拔苦竹林虽然N、P利用效率提高,但立竹叶片C含量较低,P限制性作用增强;中海拔苦竹林不但具有较高的N、P利用效率,而且立竹叶片C含量高,说明中海拔是苦竹林丰产培育的适宜海拔。     

Evidence for oxidative stress in sugar maple stands growing on acidic,nutrient imbalanced forest soils

Soil acidification and the disruption of nutrient cycles appear to be important factors that weaken sugar maple resistance to both abiotic and biotic stresses and predispose it to decline symptoms. Although connections between edaphic stress and decline symptoms have been identified, very little is known about the physiological and biochemical mechanisms that underlie this relationship. In this study, we tested the hypothesis that foliar nutrient imbalances impair the photosynthetic apparatus of sugar maple through oxidative stress. We examined leaf nutrition, photosynthesis and antioxidant enzyme activity (a biomarker of oxidative stress) from early June to late August in three-paired overstory sugar maple stands on Pennsylvania’s Allegheny Plateau that contrast in soil nutrient availability according to slope position. Beginning in early June, trees on upper slopes (nutrient-poor) had significantly lower foliar Ca and Mg concentrations and significantly higher foliar Mn concentrations than trees on lower slopes. These differences increased throughout summer peaking in late August. Photosynthesis and antioxidant enzyme activity closely reflected changes in foliar nutrient status throughout the summer. In the latter half of the summer, leaf gas exchange and chlorophyll content were significantly lower and antioxidant enzyme activity was significantly higher in stands on upper slope soils. At the end of August, leaf nutrient imbalances corresponded with lower rates of photosynthesis and higher antioxidant enzyme activity, suggesting that foliar nutrient imbalances may impair sugar maple function through mechanisms of oxidative stress.     

Natural selection drives altitudinal divergence at the albumin locus in deer mice, Peromyscus maniculatus

In populations that are distributed across steep environmental gradients, the potential for local adaptation is largely determined by the spatial scale of fitness variation relative to dispersal distance. Since altitudinal gradients are generally characterized by dramatic ecological transitions over relatively short linear distances, adaptive divergence across such gradients will typically require especially strong selection to counterbalance the homogenizing effect of gene flow. Here we report the results of a study that was designed to test for evidence of adaptive divergence across an altitudinal gradient in a natural population of deer mice, Peromyscus maniculatus. We conducted a multilocus survey of allozyme variation across a steep altitudinal gradient in the southern Rocky Mountains that spanned several distinct biomes, from prairie grassland to alpine tundra. As a control for the effects of altitude, we also surveyed the same loci in mice sampled along a latitudinal transect through the prairie grassland that ran perpendicular to the east-west altitudinal transect. We used a coalescent-based simulation model to identify loci that deviated from neutral expectations, and we then assessed whether locus-specific patterns of variation were nonrandom with respect to altitude. Results indicated that the albumin locus (Alb) reflects a history of diversifying selection across the altitudinal gradient. This conclusion is supported by two main lines of evidence: (1) Alb was characterized by levels of divergence across the altitudinal transect that exceeded neutral expectations in two consecutive years of sampling (in contrast to the spatial pattern of variation across the latitudinal transect), and (2) levels of divergence at the Alb locus exhibited a positive association with altitudinal distance in both years (in contrast to the pattern observed at unlinked loci). We conclude that clinal variation at the Alb locus reflects a balance between gene flow and diversifying selection that results from elevational changes in fitness rankings among alternative genotypes.     

A genetic analysis of the photosynthetic properties of populations of Danthonia spicata that have different growth responses to light level

Summary Three populations of the grass Danthonia spicata were observed to have different rates of biomass accumulation when grown in common environment treatments. The populations were native to adjacent sites of different successional age and different levels of shading. Twelve individuals from each population were clonally replicated and two replicates were grown in each of two light treatments, 100% and 22% of unshaded sunlight. Following growth in the treatments the populations all exhibited the same mean light-saturated photosynthetic rate of 11.7 mol m^-2s^-1. This rate is intermediate for published values of sun and shade species and for species from along a successional gradient. There was no difference in photosynthetic rate among treatments. There was significant genetic variation for lightsaturated photosynthetic rate within populations but no significant differences among populations. The populations had similar leaf water potential values of-1.12 MPa in all treatments. There were significant differences among treatments and genotypes for specific leaf weight which resulted in significant differences among treatments and no significant differences among genotypes in light-saturated photosynthetic rate expressed on a leaf weight basis. Lightsaturated photosynthetic rate had a high heritability and low plasticity. We postulate that photosynthetic rate is under strong selection and that the observed rates permit populations of D. spicata to grow in a wide range of habitat light levels.     

Plant invasions along mountain roads: the altitudinal amplitude of alien Asteraceae forbs in their native and introduced ranges

Studying plant invasions along environmental gradients is a promising approach to dissect the relative importance of multiple interacting factors that affect the spread of a species in a new range. Along altitudinal gradients, factors such as propagule pressure, climatic conditions and biotic interactions change simultaneously across rather small geographic scales. Here we investigate the distribution of eight Asteraceae forbs along mountain roads in both their native and introduced ranges in the Valais (southern Swiss Alps) and the Wallowa Mountains (northeastern Oregon, USA). We hypothesised that a lack of adaptation and more limiting propagule pressure at higher altitudes in the new range restricts the altitudinal distribution of aliens relative to the native range. However, all but one of the species reached the same or even a higher altitude in the new range. Thus neither the need to adapt to changing climatic conditions nor lower propagule pressure at higher altitudes appears to have prevented the altitudinal spread of introduced populations. We found clear differences between regions in the relative occurrence of alien species in ruderal sites compared to roadsides, and in the degree of invasion away from the roadside, presumably reflecting differences in disturbance patterns between regions. Whilst the upper altitudinal limits of these plant invasions are apparently climatically constrained, factors such as anthropogenic disturbance and competition with native vegetation appear to have greater influence than changing climatic conditions on the distribution of these alien species along altitudinal gradients.     

The dynamics of leaf extension in plants with diverse altitudinal ranges

Summary The dynamics of leaf extension in five species of Poa were studied with electronic auxanometers (LVDTs) along an elevational gradient from 600 to 3200 m in the Austrian Alps. Extension rates peak at midday at all elevations and rates at 20°C are almost twice as high at low elevation as compared with those from the highest sites. The low temperature threshold for leaf extension drops by 7 K over this range of elevation, with plants from the highest sites showing some extension around freezing point. Thus, there is a substantial adaptive adjustment in response of leaf extension to declining mean temperatures with increasing altitude, which is not paralleled by known altitudinal trends of photosynthetic responses in herbaceous plants.     

海拔梯度对长白山北坡岳桦水分利用效率的影响

以分布于长白山北坡海拔1800～2050 m的岳桦林为对象,以叶片碳稳定同位素(δ13C)值作为岳桦长期水分利用效率指示值,探讨海拔梯度对岳桦林水分利用效率的影响.结果表明:随海拔升高,岳桦林土壤体积含水量、比叶质量极显著增加,而叶片含水量和土壤温度显著降低;岳桦叶片δ13C值与海拔呈极显著正相关,增幅为1.013‰·(100 m)-1,与土壤体积含水量、比叶质量呈显著正相关,与生长季土壤平均温度、叶片含水量呈显著负相关.温度不是长白山林线的唯一限制性因子,海拔梯度上水热条件的差异及其交互作用可能造成岳桦生长期间的生理干旱.     

Sources of Variation in Leaf Shape among Two Populations of Achillea Lanulosa

Achillea lanulosa has complex, highly dissected leaves that vary in shape and size along an altitudinal gradient. Plants from a high and an intermediate altitude population were clonally replicated and grown in a controlled environment at warm and cool conditions under bright light. There were genetic differences among populations and among individuals within populations in leaf size and shape. Heritabilities for leaf size and shape characters were moderate. Leaves of the lower altitude population were larger and differed from the higher altitude plants in both coarse and fine shape. Plastic response to temperature of the growth environment paralleled the genetic differentiation between low and high altitude populations. There was no apparent trade-off between genetic control over morphology and the capacity for directional plastic response to the environment. Differences in leaf dissection and size at contrasting altitudes in this species are the result of both genetic divergence among populations and of acclimative responses to local environments.     

Adaptive responses for seed and leaf phenology in natural populations of sessile oak along an altitudinal gradient

We assessed the adaptive potential of seed and leaf phenology in 10 natural populations of sessile oak (Quercus petraea) sampled along two altitudinal transects using common garden experiments. Population differentiation for both phenological traits was observed with high-altitude populations germinating and flushing later than low altitude ones. However, high genetic variation and heritability values were also maintained within populations, despite slightly decreasing for dates of leaf unfolding with increasing altitude. We suggest that biotic and abiotic fluctuating selection pressures within populations and high gene flow are the main mechanisms maintaining high genetic variation for these fitness related traits. Moreover, changes in selection intensity and/or selection pressures along the altitudinal gradient can explain the reduction in genetic variation observed for leaf phenology. We anticipate that the maintenance of high genetic variation will be a valuable resource for future adaptation of sessile oak populations undergoing an upslope shift caused by climate change.