Nature vs nurture in the leaf morphology of Southern beech, Nothofagus cunninghamii (Nothofagaceae)

Proteomic and physiological signatures of altitude adaptation in a Myrsine coriacea population under common garden conditions

Plants exhibit phenotypic plasticity in response to environmental variations, which can lead to stable genetic and physiological adaptations if exposure to specific conditions is prolonged. Myrsine coriacea demonstrates this through its ability to thrive in diverse environments. The objective of the article is to investigate potential differences in protein accumulation and physiological responses of M. coriacea by cultivating plants from seeds collected from four populations at different altitudes in a common garden experiment. Additionally, we aim to evaluate whether these differences exhibit genetic fixation. Through integrated physiological and proteomic analyses, we identified 170 differentially accumulated proteins and observed significant physiological differences among the populations. The high-altitude population (POP1) exhibited a unique proteomic profile with significant down-regulation of proteins involved in carbon fixation and energy metabolism, suggesting a potential reduction in photosynthetic efficiency. Physiological analyses showed lower leaf nitrogen content, net CO2 assimilation rate, specific leaf area, and relative growth rate in stem height for POP1, alongside higher leaf carbon isotopic composition (δ13C) and leaf carbon (C) content. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriacea and underscore the importance of local adaptations. SIGNIFICANCE: We investigate the adaptive responses of M. coriacea, a shrub with a broad phenotypic range, by cultivating plants from seeds collected at four different altitudes in a common garden experiment. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriacea and underscore the importance of local adaptations in the face of climate change. This study contributes to advancing our understanding of the influence of altitude-specific selection pressures on the molecular biology and physiology of plants in natural populations. Our findings provide valuable insights that enhance our ability to predict and comprehend how plants respond to climate change.

Genomic insights into local adaptation and vulnerability of Quercus longinux to climate change

BACKGROUND

Climate change is expected to alter the factors that drive changes in adaptive variation. This is especially true for species with long life spans and limited dispersal capabilities. Rapid climate changes may disrupt the migration of beneficial genetic variations, making it challenging for them to keep up with changing environments. Understanding adaptive genetic variations in tree species is crucial for conservation and effective forest management. Our study used landscape genomic analyses and phenotypic traits from a thorough sampling across the entire range of Quercus longinux, an oak species native to Taiwan, to investigate the signals of adaptation within this species.

RESULTS

Using ecological data, phenotypic traits, and 1,933 single-nucleotide polymorphisms (SNPs) from 205 individuals, we classified three genetic groups, which were also phenotypically and ecologically divergent. Thirty-five genes related to drought and freeze resistance displayed signatures of natural selection. The adaptive variation was driven by diverse environmental pressures such as low spring precipitation, low annual temperature, and soil grid sizes. Using linear-regression-based methods, we identified isolation by environment (IBE) as the optimal model for adaptive SNPs. Redundancy analysis (RDA) further revealed a substantial joint influence of demography, geology, and environments, suggesting a covariation between environmental gradients and colonization history. Lastly, we utilized adaptive signals to estimate the genetic offset for each individual under diverse climate change scenarios. The required genetic changes and migration distance are larger in severe climates. Our prediction also reveals potential threats to edge populations in northern and southeastern Taiwan due to escalating temperatures and precipitation reallocation.

CONCLUSIONS

We demonstrate the intricate influence of ecological heterogeneity on genetic and phenotypic adaptation of an oak species. The adaptation is also driven by some rarely studied environmental factors, including wind speed and soil features. Furthermore, the genetic offset analysis predicted that the edge populations of Q. longinux in lower elevations might face higher risks of local extinctions under climate change.

Seedling age of Abies georgei var. smithii reveals functional trait coordination in high-altitude habitats in southeast tibet

Functional trait-based plant ecology is often used to study plant survival strategies and growth processes. In this work, the variation regularity of functional traits and their correlations were studied in Abies georgei var. smithii seedlings of different seedling ages found along the altitude gradient (3,800–4,400 m) in Sejila Mountain, Southeast Tibet. The following functional traits of seedlings in five age classes were determined: above-ground functional traits∼leaf thickness (T), leaf area (LA), specific leaf area (SLA), and leaf dry matter content (LDMC); below-ground functional traits∼specific stem length (SSL), specific root length (SRL), specific root surface area (SRA), root tissue density (RTD), and root dry matter content (RDMC). Results showed that (1) except for LDMC, most of the functional traits of the seedlings at different altitudes showed a regular change trend over time. The changes in traits caused by seedling age had significant effects on other traits (p < 0.05). Altitude only had significant effects on T, LA, SLA, SRA, RTD, and RDMC (p < 0.05). (2) The correlation between the above- and below-ground traits was more significant in 5-6-year-old seedlings than in other age classes (p < 0.05). Principal component analysis (PCA) results showed that LA and SLA were the dominant traits of fir seedlings in five age categories Pearson correlation analysis indicated a correlation between RTD and above-ground traits, thus validating the correlation between the above- and below-ground traits of seedlings of Abies georgei var. smithii of different ages. (3) Available potassium, total potassium, and total organic carbon (TOC) had the greatest influence on the traits of 5-6-year-old seedlings. This study revealed that the functional traits of Abies georgei var. smithii seedlings at different altitudesdynamically change with seedling age. The findings help in understanding the growth strategies of seedlings during early development. Future research on the combination of soil factors and seedling traits will provide a theoretical basis for artificial cultivation and protection of native vegetation.

Patterns of Leaf Morphological Traits of Beech (Fagus sylvatica L.) along an Altitudinal Gradient

Broadleaved tree species in mountainous populations usually demonstrate high levels of diversity in leaf morphology among individuals, as a response to a variety of environmental conditions associated with changes in altitude. We investigated the parameters shaping leaf morphological diversity in 80 beech individuals (Fagus sylvatica L.), in light and shade leaves, growing along an elevational gradient and under different habitat types on Mt. Paggeo in northeastern Greece. A clear altitudinal pattern was observed in the morphological leaf traits expressing lamina size and shape; with increasing altitude, trees had leaves with smaller laminas, less elongated outlines, and fewer pairs of secondary veins. However, this altitudinal trend in leaf morphology was varied in different habitat types. Furthermore, the shade leaves and light leaves showed differences in their altitudinal trend. Traits expressing lamina shape in shade leaves were more related to altitude, while leaf size appeared to be more influenced by habitat type. While the altitudinal trend in leaf morphology has been well documented for numerous broadleaved tree species, in a small spatial scale, different patterns emerged across different habitat types. This morphological variability among trees growing in a mountainous population indicates a high potential for adaptation to environmental extremes.

Evaluation of environmental factors affecting the genetic diversity, genetic structure, and the potential distribution of Rhododendron aureum Georgi under changing climate

Understanding genetic variation and structure, adaptive genetic variation, and its relationship with environmental factors is of great significance to understand how plants adapt to climate change and design effective conservation and management strategies. The objective of this study was to (I) investigate the genetic diversity and structure by AFLP markers in 36 populations of R. aureum from northeast China, (Ⅱ) reveal the relative contribution of geographical and environmental impacts on the distribution and genetic differentiation of R. aureum, (Ⅲ) identify outlier loci under selection and evaluate the association between outlier loci and environmental factors, and (Ⅳ) exactly calculate the development trend of population of R. aureum, as it is confronted with severe climate change and to provide information for designing effective conservation and management strategies. We found high genetic variation (I = 0.584) and differentiation among populations (ΦST  = 0.703) and moderate levels of genetic diversity within populations of R. aureum. A significant relationship between genetic distance and environmental distance was identified, which suggested that the differentiation of different populations was caused by environmental factors. Using BayeScan and Dfdist, 42 outlier loci are identified and most of the outlier loci are associated with climate or relief factors, suggesting that these loci are linked to genes that are involved in the adaptability of R. aureum to the environment. Species distribution models (SDMs) showed that climate warming will cause a significant reduction in suitable areas for R. aureum, especially under the RCP 85 scenario. Our results help to understand the potential response of R. aureum to climatic changes and provide new perspectives for R. aureum resource management and conservation strategies.

Reconstructing leaf area from fragments: testing three methods using a fossil paleogene species

PREMISE

Fossil leaf traits can enable reconstruction of ancient environments and climates. Among these, leaf size has been particularly studied because it reflects several climatic forcings (e.g., precipitation and surface temperature) and, potentially, environment characteristics (e.g., nutrient availability, local topography, and openness of vegetation). However, imperfect preservation and fragmentation can corrupt its utilization. We provide improved methodology to estimate leaf size from fossil fragments.

METHODS

We apply three methods: (1) visually reconstructing leaf area based on taxon-specific gross morphology; (2) estimating intact leaf area from vein density based on a vein scaling relationship; and (3) a novel complementary method, determining intact leaf length based on the tapering of the midvein in the fragment. We test the three methods for fossils of extinct Eotrigonobalanus furcinervis (Fagaceae) from two lignite horizons of the middle and late Eocene of central Germany respectively (~45/46 and 35/36 Ma).

RESULTS

The three methods, including the new one, yield consistent leaf size reconstructions. The vein scaling method showed a shift to larger leaf size, from the middle to the late Eocene.

CONCLUSIONS

These methods constitute a toolbox with different solutions to reconstruct leaf size from fossil fragments depending on fossil preservation. Fossil leaf size reconstruction has great potential to improve physiognomy-based paleoenvironmental reconstructions and the interpretation of the fossil record.

Leaf size variations in a dominant desert shrub, Reaumuria soongarica, adapted to heterogeneous environments

The climate in arid Central Asia (ACA) has changed rapidly in recent decades, but the ecological consequences of this are far from clear. To predict the impacts of climate change on ecosystem functioning, greater attention should be given to the relationships between leaf functional traits and environmental heterogeneity. As a dominant constructive shrub widely distributed in ACA, Reaumuria soongarica provided us with an ideal model to understand how leaf functional traits of desert ecosystems responded to the heterogeneous environments of ACA. Here, to determine the influences of genetic and ecological factors, we characterized species-wide variations in leaf traits among 30 wild populations of R. soongarica and 16 populations grown in a common garden. We found that the leaf length, width, and leaf length to width ratio (L/W) of the northern lineage were significantly larger than those of other genetic lineages, and principal component analysis based on the in situ environmental factors distinguished the northern lineage from the other lineages studied. With increasing latitude, leaf length, width, and L/W in the wild populations increased significantly. Leaf length and L/W were negatively correlated with altitude, and first increased and then decreased with increasing mean annual temperature (MAT) and mean annual precipitation (MAP). Stepwise regression analyses further indicated that leaf length variation was mainly affected by latitude. However, leaf width was uncorrelated with altitude, MAT, or MAP. The common garden trial showed that leaf width variation among the eastern populations was caused by both local adaptation and phenotypic plasticity. Our findings suggest that R. soongarica preferentially changes leaf length to adjust leaf size to cope with environmental change. We also reveal phenotypic evidence for ecological speciation of R. soongarica. These results will help us better understand and predict the consequences of climate change for desert ecosystem functioning.

Heterologous Expression of Poplar WRKY18/35 Paralogs in Arabidopsis Reveals Their Antagonistic Regulation on Pathogen Resistance and Abiotic Stress Tolerance via Variable Hormonal Pathways

WRKY transcription factors (WRKY TFs) are one of the largest protein families in plants, and most of them play vital roles in response to biotic and abiotic stresses by regulating related signaling pathways. In this study, we isolated two WRKY TF genes PtrWRKY18 and PtrWRKY35 from Populustrichocarpa and overexpressed them in Arabidopsis. Expression pattern analyses showed that PtrWRKY18 and PtrWRKY35 respond to salicylic acid (SA), methyl JA (MeJA), abscisic acid (ABA), B. cinereal, and P. syringae treatment. The transgenic plants conferred higher B. cinerea tolerance than wild-type (WT) plants, and real-time quantitative (qRT)-PCR assays showed that PR3 and PDF1.2 had higher expression levels in transgenic plants, which was consistent with their tolerance to B. cinereal. The transgenic plants showed lower P. syringae tolerance than WT plants, and qRT-PCR analysis (PR1, PR2, and NPR1) also corresponded to this phenotype. Germination rate and root analysis showed that the transgenic plants are less sensitive to ABA, which leads to the reduced tolerance to osmotic stress and the increase of the death ratio and stomatal aperture. Compared with WT plants, a series of ABA-related genes (RD29A, ABO3, ABI4, ABI5, and DREB1A) were significantly down-regulated in PtrWRKY18 and PtrWRKY35 overexpression plants. All of these results demonstrated that the two WRKY TFs are multifunctional transcription factors in plant resistance.

Strong intraspecific trait variation in a tropical dominant tree species along an elevational gradient

Functional trait variation of plant species includes both inter- and intraspecific variation; however, trait-based plant ecology generally considers only interspecific variation while ignoring intraspecific variation. One reason for this neglect is that intraspecific variation may be negligible when compared to interspecific variation; however, direct comparisons between inter- and intraspecific variation of plant species are lacking, especially in tropical forests. Here we investigated intraspecific leaf trait variation (leaf area, specific leaf area, leaf thickness, leaf density, leaf chlorophyll content) of Pittosporopsis kerrii Craib (Icacinaceae), the most abundant tree species in the Xishuangbanna tropical seasonal rainforest in southwestern China, along an elevational gradient (703-824 m). We found a substantial range of intraspecific variation in P. kerrii that was never less than 22.1% of range of the interspecific variation among 462 tree species reported before in the same community. Moreover, with increased elevation, both leaf thickness and density increased and specific leaf area decreased significantly. It could be more important for the individuals of P. kerrii to produce thicker and denser leaves to tolerate environmental stress (e.g. soil water availability) rather than having high growth rates at the places with higher elevation in the Xishuangbanna tropical seasonal rainforest.

Transcriptome analysis reveals plasticity in gene regulation due to environmental cues in Primula sikkimensis, a high altitude plant species

BACKGROUND

Studying plasticity in gene expression in natural systems is crucial, for predicting and managing the effects of climate change on plant species. To understand the contribution of gene expression level variations to abiotic stress compensation in a Himalaya plant (Primula sikkimensis), we carried out a transplant experiment within (Ambient), and beyond (Below Ambient and Above Ambient) the altitudinal range limit of species. We sequenced nine transcriptomes (three each from each altitudinal range condition) using Illumina sequencing technology. We compared the fitness variation of transplants among three transplant conditions.

RESULTS

A large number of significantly differentially expressed genes (DEGs) between below ambient versus ambient (109) and above ambient versus ambient (85) were identified. Transcripts involved in plant growth and development were mostly up-regulated in below ambient conditions. Transcripts involved in signalling, defence, and membrane transport were mostly up-regulated in above ambient condition. Pathway analysis revealed that most of the genes involved in metabolic processes, secondary metabolism, and flavonoid biosynthesis were differentially expressed in below ambient conditions, whereas most of the genes involved in photosynthesis and plant hormone signalling were differentially expressed in above ambient conditions. In addition, we observed higher reproductive fitness in transplant individuals at below ambient condition compared to above ambient conditions; contrary to what we expect from the cold adaptive P. sikkimensis plants.

CONCLUSIONS

We reveal P. sikkimensis's capacity for rapid adaptation to climate change through transcriptome variation, which may facilitate the phenotypic plasticity observed in morphological and life history traits. The genes and pathways identified provide a genetic resource for understanding the temperature stress (both the hot and cold stress) tolerance mechanism of P. sikkimensis in their natural environment.

The effect of elevational gradient on alpine gingers (Roscoea alpina and R. purpurea) in the Himalayas

There is currently enormous interest in how morphological and physiological responses of herbaceous plants may be affected by changing elevational gradient. Mountain regions provide an excellent opportunity to understand how closely related species may adapt to the conditions that rapidly change with elevation. We investigated the morphological and physiological responses of two Himalayan alpine gingers (Roscoea alpina and R. purpurea) along two different vertical transects of 400 m, R. purpurea between 2,174-2,574 m a.s.l and R. alpina between 2,675-3,079 m a.s.l. We measured the variables of plant height, leaf length, leaf area, specific leaf area, and stomata density at five plots, along the vertical transect at an elevational gap of ca. 100 m. Results revealed that with increased elevation plant height, and leaf area decreased while stomata density increased, whereas changes in specific leaf area, were not correlated with the elevation. Our results reveal that these alpine gingers undergo local adaptation by modifying their plant height, leaf area and stomata density in response to the varying selection pressure associated with the elevational gradient. Thus, the findings of this research provide valuable information on how a narrow range of elevational gradient affects the herbaceous plants at the alpine habitat of the Himalayas.

Digital Morphometrics of Two North American Grapevines (Vitis: Vitaceae) Quantifies Leaf Variation between Species, within Species, and among Individuals

Recent studies have demonstrated that grapevine (Vitis spp.) leaf shape can be quantified using digital approaches which indicate phylogenetic signal in leaf shape, discernible patterns of developmental context within single leaves, and signatures of local environmental conditions. Here, we extend this work by quantifying intra-individual, intraspecific, and interspecific variation in leaf morphology in accessions of North American Vitis riparia and V. rupestris in a common environment. For each species at least four clonal replicates of multiple genotypes were grown in the Missouri Botanical Garden Kemper Center for Home Gardening. All leaves from a single shoot were harvested and scanned leaf images were used to conduct generalized Procrustes analysis, linear discriminant analysis, and elliptical Fourier analysis. Leaf shapes displayed genotype-specific signatures and species distinctions consistent with taxonomic classifications. Leaf shape variation within genotypes and among clones was the result of pest and pathogen-induced leaf damage that alters leaf morphology. Significant trends in leaf damage caused by disease and infestation were non-random with respect to leaf position on the shoot. Digital morphometrics is a powerful tool for assessing leaf shape variation among species, genotypes, and clones under common conditions and suggests biotic factors such as pests and pathogens as important drivers influencing leaf shape.

Variation in Ecophysiological Traits and Drought Tolerance of Beech (Fagus sylvatica L.) Seedlings from Different Populations

Frequency and intensity of heat waves and drought events are expected to increase in Europe due to climate change. European beech (Fagus sylvatica L.) is one of the most important native tree species in Europe. Beech populations originating throughout its native range were selected for common-garden experiments with the aim to determine whether there are functional variations in drought stress responses among different populations. One-year old seedlings from four to seven beech populations were grown and drought-treated in a greenhouse, replicating the experiment at two contrasting sites, in Italy (Mediterranean mountains) and Germany (Central Europe). Experimental findings indicated that: (1) drought (water stress) mainly affected gas exchange describing a critical threshold of drought response between 30 and 26% SWA for photosynthetic rate and Ci/Ca, respectively; (2) the Ci to Ca ratio increased substantially with severe water stress suggesting a stable instantaneous water use efficiency and an efficient regulation capacity of water balance achieved by a tight stomatal control; (3) there was a different response to water stress among the considered beech populations, differently combining traits, although there was not a well-defined variability in drought tolerance. A combined analysis of functional and structural traits for detecting stress signals in beech seedlings is suggested to assess plant performance under limiting moisture conditions and, consequently, to estimate evolutionary potential of beech under a changing environmental scenario.

Determinants of the N content of Quercus wutaishanica leaves in the Loess Plateau: a structural equation modeling approach

Most terrestrial ecosystems are nitrogen (N)-limited. The elucidation of the multivariate relationships among environmental drivers, leaf morphological traits, and foliar N of dominant species which are critical to the functioning of forests remains a critical challenge for ecologists. We sampled leaves of Quercus wutaishanica across a broad natural gradient in the Loess Plateau, China, and employed structural equation modelling to evaluate the causal pathways and the relative importance of drivers of the foliar N per unit area (Narea) and per unit mass (Nmass). We found that (1) Nmass and Narea were primarily affected by leaf morphological traits instead of environmental variables and that leaf morphological traits accounted for most of their variations; (2) the total soil potassium and phosphorus and mean annual precipitation had different effects on Nmass and Narea via different pathways and path coefficients, whereas the mean annual temperature and total soil N had non-significant effects on Nmass and Narea. Our results demonstrated that variations in Nmass and Narea within Quercus wutaishanica were strongly linked to their leaf morphological traits and that the leaf N was also influenced by mean annual precipitation and soil phosphorus and potassium instead of soil N in the Loess Plateau, China.

Growth habit and leaf economics determine gas exchange responses to high elevation in an evergreen tree, a deciduous shrub and a herbaceous annual

Plant growth at high elevations necessitates physiological and morphological plasticity to enable photosynthesis (A) under conditions of reduced temperature, increased radiation and the lower partial pressure of atmospheric gases, in particular carbon dioxide (pCO2). Previous studies have observed a wide range of responses to elevation in plant species depending on their adaptation to temperature, elevational range and growth habit. Here, we investigated the effect of an increase in elevation from 2500 to 3500 m above sea level (a.s.l.) on three montane species with contrasting growth habits and leaf economic strategies. While all of the species showed identical increases in foliar δ(13)C, dark respiration and nitrogen concentration with elevation, contrasting leaf gas exchange and photosynthetic responses were observed between species with different leaf economic strategies. The deciduous shrub Salix atopantha and annual herb Rumex dentatus exhibited increased stomatal (Gs) and mesophyll (Gm) conductance and enhanced photosynthetic capacity at the higher elevation. However, evergreen Quercus spinosa displayed reduced conductance to CO2 that coincided with lower levels of photosynthetic carbon fixation at 3500 m a.s.l. The lower Gs and Gm values of evergreen species at higher elevations currently constrains their rates of A. Future rises in the atmospheric concentration of CO2 ([CO2]) will likely predominantly affect evergreen species with lower specific leaf areas (SLAs) and levels of Gm rather than deciduous species with higher SLA and Gm values. We argue that climate change may affect plant species that compose high-elevation ecosystems differently depending on phenotypic plasticity and adaptive traits affecting leaf economics, as rising [CO2] is likely to benefit evergreen species with thick sclerophyllous leaves.

Influences of environmental factors on leaf morphology of Chinese jujubes

Rainfall and temperature are the primary limiting factors for optimum quality and yield of cultivated jujube (Ziziphus jujuba Mill.). Adaptation to arid and cool environments has been and remains an important goal of many jujube improvement programs. This study summarized the survey results of 116 Chinese jujube varieties grown at 33 sites in China. The objective was to identify the environmental factors that influence leaf morphology, and the implications for breeding and introduction of new jujube varieties. Jujube leaf morphological traits were evaluated for their potential relationships with mean annual temperature (MAT) and mean annual precipitation (MAP). The results showed that many leaf morphological traits had a strong linear relationship with local precipitation and temperature. Longer veins per unit area (VLA) and reduced leaf area and leaf perimeter were typical of arid areas. VLA was inversely related to MAT and MAP at the centers of origin of jujube. There was a positive relationship between leaf shape (perimeter2/area) and both MAT and MAP. These results indicated that leaf vein traits of Chinese jujubes might have resulted from their adaptation to environmental factors in the course of long-term evolution. Principal component analysis allocated the 116 jujube varieties to three different groups, differentiated on the basis of morphological and physiological leaf characteristics. Jujube varieties from the Hebei, Shandong, Henan, southern Shanxi and central Shaanxi provinces were closely related, as were varieties from northwest Shanxi and northeast Shaanxi provinces, and varieties from the Gansu and Ningxia provinces. These close relationships were partially attributed to the frequent exchanges of varieties within each group. Leaf venation characteristics might be used as reference indices for jujube variety introduction between different locations.

Evolutionary divergence of leaf width and its correlates

•

PREMISE OF THE STUDY

The question why leaf dimensions vary so much between species has long puzzled ecologists. Presumably, variation arises from selective forces acting on leaf function but which selective forces and which leaf functions? This investigation assesses the consistency of divergence in plant traits and habitat variables in association with leaf width divergence in the flora of NSW, Australia.•

METHODS

More than 80 traits and habitat variables were measured for 25 independent evolutionary divergence events (PICs). Each PIC was represented by two related plant species that had diverged substantially in leaf width. Outgroup species provided indications of the direction of divergence. Most PICs were within genus, so divergences represent relatively recent evolutionary events.•

KEY RESULTS

No plant traits or habitat variables were 100% consistently associated with a divergence in leaf width, and surprisingly few diverged in a consistent direction significantly more than what might be expected by chance. This surprising lack of consistent divergence with leaf width contrasted with the result that many of these traits and habitat variables were correlated with leaf width across all species in our data set and in line with correlations reported from other studies. Subcategorizing PICs according to the probable direction of leaf width divergence did not improve consistency.•

CONCLUSIONS

These results indicate that evolutionarily recent leaf width divergence events are not tightly tied to divergences in other leaf traits or in environmental situations, despite the broad correlations that have been observed across many species. Rather, cross species correlations are underpinned by earlier divergence events in the phylogeny.

The roles of genetic drift and natural selection in quantitative trait divergence along an altitudinal gradient in Arabidopsis thaliana

Understanding how natural selection and genetic drift shape biological variation is a central topic in biology, yet our understanding of the agents of natural selection and their target traits is limited. We investigated to what extent selection along an altitudinal gradient or genetic drift contributed to variation in ecologically relevant traits in Arabidopsis thaliana. We collected seeds from 8 to 14 individuals from each of 14 A. thaliana populations originating from sites between 800 and 2700 m above sea level in the Swiss Alps. Seed families were grown with and without vernalization, corresponding to winter-annual and summer-annual life histories, respectively. We analyzed putatively neutral genetic divergence between these populations using 24 simple sequence repeat markers. We measured seven traits related to growth, phenology and leaf morphology that are rarely reported in A. thaliana and performed analyses of altitudinal clines, as well as overall QST-FST comparisons and correlation analyses among pair-wise QST, FST and altitude of origin differences. Multivariate analyses suggested adaptive differentiation along altitude in the entire suite of traits, particularly when expressed in the summer-annual life history. Of the individual traits, a decrease in rosette leaf number in the vegetative state and an increase in leaf succulence with increasing altitude could be attributed to adaptive divergence. Interestingly, these patterns relate well to common within- and between-species trends of smaller plant size and thicker leaves at high altitude. Our results thus offer exciting possibilities to unravel the underlying mechanisms for these conspicuous trends using the model species A. thaliana.

Altitudinal gradients, plant hybrid zones and evolutionary novelty

Altitudinal gradients are characterized by steep changes of the physical and biotic environment that present challenges to plant adaptation throughout large parts of the world. Hybrid zones may form where related species inhabit different neighbouring altitudes and can facilitate interspecific gene flow and potentially the breakdown of species barriers. Studies of such hybrid zones can reveal much about the genetic basis of adaptation to environmental differences stemming from changes in altitude and the maintenance of species divergence in the face of gene flow. Furthermore, owing to recombination and transgressive effects, such hybrid zones can be sources of evolutionary novelty. We document plant hybrid zones associated with altitudinal gradients and emphasize similarities and differences in their structure. We then focus on recent studies of a hybrid zone between two Senecio species that occur at high and low altitude on Mount Etna, Sicily, showing how adaptation to local environments and intrinsic selection against hybrids act to maintain it. Finally, we consider the potential of altitudinal hybrid zones for generating evolutionary novelty through adaptive introgression and hybrid speciation. Examples of homoploid hybrid species of Senecio and Pinus that originated from altitudinal hybrid zones are discussed.

Highly local environmental variability promotes intrapopulation divergence of quantitative traits: an example from tropical rain forest trees

BACKGROUND AND AIMS

In habitat mosaics, plant populations face environmental heterogeneity over short geographical distances. Such steep environmental gradients can induce ecological divergence. Lowland rainforests of the Guiana Shield are characterized by sharp, short-distance environmental variations related to topography and soil characteristics (from waterlogged bottomlands on hydromorphic soils to well-drained terra firme on ferralitic soils). Continuous plant populations distributed along such gradients are an interesting system to study intrapopulation divergence at highly local scales. This study tested (1) whether conspecific populations growing in different habitats diverge at functional traits, and (2) whether they diverge in the same way as congeneric species having different habitat preferences.

METHODS

Phenotypic differentiation was studied within continuous populations occupying different habitats for two congeneric, sympatric, and ecologically divergent tree species (Eperua falcata and E. grandiflora, Fabaceae). Over 3000 seeds collected from three habitats were germinated and grown in a common garden experiment, and 23 morphological, biomass, resource allocation and physiological traits were measured.

KEY RESULTS

In both species, seedling populations native of different habitats displayed phenotypic divergence for several traits (including seedling growth, biomass allocation, leaf chemistry, photosynthesis and carbon isotope composition). This may occur through heritable genetic variation or other maternally inherited effects. For a sub-set of traits, the intraspecific divergence associated with environmental variation coincided with interspecific divergence.

CONCLUSIONS

The results indicate that mother trees from different habitats transmit divergent trait values to their progeny, and suggest that local environmental variation selects for different trait optima even at a very local spatial scale. Traits for which differentiation within species follows the same pattern as differentiation between species indicate that the same ecological processes underlie intra- and interspecific variation.

Environmental and genetic variation in leaf anatomy among populations of Andropogon gerardii (Poaceae) along a precipitation gradient

PREMISE OF THE STUDY

Phenotypes of two Andropogon gerardii subspecies, big bluestem and sand bluestem, vary throughout the prairie ecosystem of North America. This study sought to determine the role of genetics and environment in driving adaptive variation of leaf structure in big bluestem and sand bluestem. •

METHODS

Four populations of big bluestem and one population of sand bluestem were planted in common gardens at four sites across a precipitation gradient from western Kansas to southern Illinois. Internal leaf structure and trichome density of A. gerardii were examined by light microscopy to separate genetic and environmentally controlled traits. Leaf thickness, midrib thickness, bulliform cells, interveinal distance, vein size, and trichome density were quantified. •

KEY RESULTS

At all planting sites, sand bluestem and the xeric population of A. gerardii had thicker leaves and fewer bulliform cells compared with mesic populations. Environment and genetic source population were both influential for leaf anatomy. Leaves from plants grown in mesic sites (Carbondale, Illinois and Manhattan, Kansas) had thicker midribs, larger veins, fewer trichomes, and a greater proportion of bulliform cells compared to plants grown in drier sites (Colby and Hays, Kansas). •

CONCLUSIONS

Water availability has driven adaptive variation in leaf structure in populations of A. gerardii, particularly between sand bluestem and big bluestem. Genetically based differences in leaves of A. gerardii indicate adaptive variation and evolutionary forces differentiating sand bluestem from big bluestem. Environmental responses of A. gerardii leaves suggest an ability to adjust to drought, even in populations adapted to mesic home environments.

Leaf traits in parental and hybrid species of Sorbus (Rosaceae)

PREMISE OF THE STUDY

Knowledge of functional leaf traits can provide important insights into the processes structuring plant communities. In the genus Sorbus, the generation of taxonomic novelty through reticulate evolution that gives rise to new microspecies is believed to be driven primarily by a series of interspecific hybridizations among closely related taxa. We tested hypotheses for dispersion of intermediacy across the leaf traits in Sorbus hybrids and for trait linkages with leaf area and specific leaf area.

METHODS

Here, we measured and compared the whole complex of growth, vascular, and ecophysiological leaf traits among parental (Sorbus aria, Sorbus aucuparia, Sorbus chamaemespilus) and natural hybrid (Sorbus montisalpae, Sorbus zuzanae) species growing under field conditions. A recently developed atomic force microscopy technique, PeakForce quantitative nanomechanical mapping, was used to characterize the topography of cell wall surfaces of tracheary elements and to map the reduced Young's modulus of elasticity.

KEY RESULTS

Intermediacy was associated predominantly with leaf growth traits, whereas vascular and ecophysiological traits were mainly parental-like and transgressive phenotypes. Larger-leaf species tended to have lower modulus of elasticity values for midrib tracheary element cell walls. Leaves with a biomass investment related to a higher specific leaf area had a lower density. Leaf area- and length-normalized theoretical hydraulic conductivity was related to leaf thickness.

CONCLUSIONS

For the whole complex of examined leaf traits, hybrid microspecies were mosaics of parental-like, intermediate, and transgressive phenotypes. The high proportion of transgressive character expressions found in Sorbus hybrids implies that generation of extreme traits through transgressive segregation played a key role in the speciation process.

A critical framework for the assessment of biological palaeoproxies: predicting past climate and levels of atmospheric CO(2) from fossil leaves

This review uses proxies of past temperature and atmospheric CO(2) composition based on fossil leaves to illustrate the uncertainties in biologically based proxies of past environments. Most leaf-based proxies are geographically local or genetically restricted and therefore can be confounded by evolution, extinction, changes in local environment or immigration of species. Stomatal frequency proxies illustrate how genetically restricted proxies can be particularly vulnerable to evolutionary change. High predictive power in the modern world resulting from the use of a very narrow calibration cannot be confidently extrapolated into the past (the Ginkgo paradox). Many foliar physiognomic proxies of climate are geographically local and use traits that are more or less fixed for individual species. Such proxies can therefore be confounded by floristic turnover and biome shifts in the region of calibration. Uncertainty in proxies tends to be greater for more ancient fossils. I present a set of questions that should be considered before using a proxy. Good proxies should be relatively protected from environmental and genetic change, particularly through having high information content and being founded on biomechanical or biochemical principles. Some current and potential developments are discussed, including those that involve more mechanistically sound proxies and better use of multivariate approaches.

Intraspecific trait variation and covariation in a widespread tree species (Nothofagus pumilio) in southern Chile

• The focus of the trait-based approach to study community ecology has mostly been on trait comparisons at the interspecific level. Here we quantified intraspecific variation and covariation of leaf mass per area (LMA) and wood density (WD) in monospecific forests of the widespread tree species Nothofagus pumilio to determine its magnitude and whether it is related to environmental conditions and ontogeny. We also discuss probable mechanisms controlling the trait variation found. • We collected leaf and stem woody tissues from 30-50 trees of different ages (ontogeny) from each of four populations at differing elevations (i.e. temperatures) and placed at each of three locations differing in soil moisture. • The total variation in LMA (coefficient of variation (CV) = 21.14%) was twice that of WD (CV = 10.52%). The total variation in traits was never less than 23% when compared with interspecific studies. Differences in elevation (temperature) for the most part explained variation in LMA, while differences in soil moisture and ontogeny explained the variation in WD. Traits covaried similarly in the altitudinal gradient only. • Functional traits of N. pumilio exhibited nonnegligible variation; LMA varied for the most part with temperature, while WD mostly varied with moisture and ontogeny. We demonstrate that environmental variation can cause important trait variation without species turnover.

Stomatal index responses of Agrostis canina to CO2 and sulphur dioxide: implications for palaeo-[CO2] using the stomatal proxy

• Stomatal index values of fossil plants are widely used in reconstructing palaeo-[CO(2)]. This depends upon the assumption that the stomatal index is determined by the atmospheric concentration of CO(2) ([CO(2)]). This study investigates whether fumigation with, and resistance to, sulphur dioxide (SO(2)) induces a reduction in the stomatal index that may affect stomatal reconstructions of palaeo-[CO(2)] coinciding with episodes of global-scale volcanism. • Agrostis canina from Mefite di Ansanto, Italy, grow in atmospheres of elevated-[CO(2)], SO(2) and hydrogen sulphide (H(2)S). Mefite A. canina were compared with a control population in a 'common-garden' experiment and a controlled-environment study under elevated-[CO(2)] and SO(2) fumigation. • In A. canina, resistance to toxic volcanic gases is not associated with reduced stomatal index, and fumigation with SO(2) does not cause a decrease in stomatal initiation. The two populations of A. canina analyzed in this study exhibit different stomatal index-[CO(2)] 'responses', with control plants showing a reduction in stomatal index and Mefite plants showing no response. • Stomatal reconstructions of palaeo-[CO(2)] during past episodes of global-scale volcanism probably reflect atmospheric [CO(2)] and not [SO(2)]. The lack of a reduction in the stomatal index in response to elevated [CO(2)] in the Mefite plants, suggests that resistance to toxic gases and/or long-term growth at high [CO(2)] reduces, or negates, sensitivity of the stomatal index-[CO(2)] relationship, or that stomatal index-[CO(2)] in the Mefite plants is attuned to [CO(2)] fluctuations at much higher concentrations.

Phenotypic plasticity of leaf shape along a temperature gradient in Acer rubrum

Both phenotypic plasticity and genetic determination can be important for understanding how plants respond to environmental change. However, little is known about the plastic response of leaf teeth and leaf dissection to temperature. This gap is critical because these leaf traits are commonly used to reconstruct paleoclimate from fossils, and such studies tacitly assume that traits measured from fossils reflect the environment at the time of their deposition, even during periods of rapid climate change. We measured leaf size and shape in Acer rubrum derived from four seed sources with a broad temperature range and grown for two years in two gardens with contrasting climates (Rhode Island and Florida). Leaves in the Rhode Island garden have more teeth and are more highly dissected than leaves in Florida from the same seed source. Plasticity in these variables accounts for at least 6-19% of the total variance, while genetic differences among ecotypes probably account for at most 69-87%. This study highlights the role of phenotypic plasticity in leaf-climate relationships. We suggest that variables related to tooth count and leaf dissection in A. rubrum can respond quickly to climate change, which increases confidence in paleoclimate methods that use these variables.

Drought response in self-compatible species of tomato (Solanaceae)

Wild tomatoes occur in habitats from the extremely dry Atacama Desert to moist areas in the Andean highlands, which may have resulted in adaptation of populations or species to differences in soil moisture availability. However, when two accessions representing extremes in habitat water availability from each of the five self-compatible species were grown in a common garden, we observed no differences in leaf physiological responses to soil drought within or between species. All five species had drought avoidance characteristics with the same threshold soil moisture availability for decline of assimilation, stomatal conductance, and leaf water potential (Ψ(l)) in response to slowly decreasing soil moisture. After rewatering, all species rapidly recovered to near predrought Ψ(l), but bulk leaf solute potential after recovery did not indicate any osmotic adjustment. The lack of variation in shoot physiological traits during soil drought is unexpected as water deficit is commonly thought to have imposed selective pressure in the evolution of plant physiology. However, species did differ in assimilation under nonstressed conditions, which may contribute to differential soil water conservation and growth or survival during drought.

Sensitivity of leaf size and shape to climate within Acer rubrum and Quercus kelloggii

* Variation in the size and shape (physiognomy) of leaves has long been correlated to climate, and paleobotanists have used these correlations to reconstruct paleo-climate. Most studies focus on site-level means of largely nonoverlapping species sets. The sensitivity of leaf shape to climate within species is poorly known, which limits our general understanding of leaf-climate relationships and the value of intraspecific patterns for paleoclimate reconstructions. * The leaf physiognomy of two species whose native North American ranges span large climatic gradients (Acer rubrum and Quercus kelloggii) was quantified and correlated to mean annual temperature (MAT). Quercus kelloggii was sampled across a wide elevation range, but A. rubrum was sampled in strictly lowland areas. * Within A. rubrum, leaf shape correlates with MAT in a manner that is largely consistent with previous site-level studies; leaves from cold climates are toothier and more highly dissected. By contrast, Q. kelloggii is largely insensitive to MAT; instead, windy conditions with ample plant-available water may explain the preponderance of small teeth at high elevation sites, independent of MAT. * This study highlights the strong correspondence between leaf form and climate within some species, and demonstrates that intraspecific patterns may contribute useful information towards reconstructing paleoclimate.

Local adaptation and cogradient selection in the alpine plant, Poa hiemata, along a narrow altitudinal gradient

Alpine environments are particularly susceptible to environmental changes associated with global warming but there is potential for alpine plants to adapt to warming if local adaptation occurs and gene flow allows genotypes adapted to low altitudes to colonize higher altitude sites. Here we examine the adaptive potential of a common alpine grass, Poa hiemata, within the restricted alpine habitat of Australian mountains, across a narrow altitudinal gradient replicated in three areas. Grasses at high altitude sites had shorter leaf lengths and larger circumferences than those at lower sites. Transplant experiments with clonal material and plants grown from seed indicated that these differences were partly genetic, with environmental and genetic factors both contributing to the differences between altitudes. Differences in altitudinal forms were also evident in a common garden experiment. Plants showed a home-site advantage in terms of survival. A fitness analysis indicated that at high altitude sites, selection favored plants with short leaves and larger circumferences, whereas these traits were selected in the opposite direction at the low altitude sites. These findings indicate cogradient selection and potential for both plastic and genotypic shifts in response to climate change in P. hiemata.

The response of leaf morphology to irradiance depends on altitude of origin in Nothofagus cunninghamii

Leaf morphology varies reliably with increasing altitude in many species, and this is generally considered to be related to temperature. Changes in irradiance with elevation may confound any relationships between a morphological character and altitude, particularly if altitude of origin affects the response to irradiance. Here we describe the interaction between irradiance and altitude of origin on leaf morphology of Southern beech, Nothofagus cunninghamii. Cuttings from each of four altitudes were grown in a glasshouse under full sunlight or 50% shade, and leaf morphology was related to irradiance, altitude of origin and accession. There was a significant interaction between irradiance and altitude of origin for leaf length, width, thickness, area, weight, specific leaf area and stomatal density. There was no effect of altitude on leaf length to width ratio or stomatal index, nor was there an interaction between irradiance and altitude of origin for these variables. These results show that the altitude of origin of a plant has an overriding impact on the leaf morphological response to irradiance. This must be considered in climatic reconstructions.

Environmental signals from leaves--a physiognomic analysis of European vegetation

Leaf physiognomic traits vary predictably along climatic and environmental gradients. The relationships between leaf physiognomy and climate have been investigated on different continents, but so far an investigation based on European vegetation has been missing. A grid data set (0.5 degrees x 0.5 degrees latitude/longitude) has been compiled in order to determine spatial patterns of leaf physiognomy across Europe. Based on distribution maps of native European hardwoods, synthetic chorologic flora lists were compiled for all grid cells. Every synthetic chorologic flora was characterised by 25 leaf physiognomic traits and correlated with 16 climatic parameters. Clear spatial patterns of leaf physiognomy have been observed, which are statistically significant related to certain, temperature-related climate parameters. Transfer functions for several climatic parameters have been established, based on the observed relationships. The study provides evidence that synthetically generated floras represent a powerful tool for analysing spatial patterns of leaf physiognomy and their relationships to climate. The transfer functions from the European data set indicate slightly different relationships of leaf physiognomy and environment compared with results obtained from other continents.