Transgenerational plasticity to drought: contrasting patterns of non-genetic inheritance in two semiarid Mediterranean shrubs.

BACKGROUND AND AIMS: Intra- and transgenerational plasticity may provide substantial phenotypic variation to cope with environmental change. Since assessing the unique contribution of the maternal environment to the offspring phenotype is challenging in perennial, outcrossing plants, little is known about the evolutionary and ecological implications of transgenerational plasticity and its persistence over the life cycle in these species. We evaluated how intra- and transgenerational plasticity interplay to shape the adaptive responses to drought in two perennial Mediterranean shrubs. METHODS: We used a novel common garden approach that reduced within-family genetic variation in both the maternal and offspring generations by growing the same maternal individual in two contrasting watering environments, well-watered and drought, in consecutive years. We then assessed phenotypic differences at the reproductive stage between offspring reciprocally-grown in the same environments. KEY RESULTS: Maternal drought had an effect on offspring performance only in Helianthemum squamatum. Offspring of drought-stressed plants showed more inflorescences, less sclerophyllous leaves and higher growth rates in both watering conditions, and heavier seeds under drought, than offspring of well-watered maternal plants. Maternal drought also induced similar plasticity patterns across maternal families, showing a general increase in seed mass in response to offspring drought, a pattern not observed in the offspring of well-watered plants. In contrast, both species expressed immediate adaptive plasticity, and the magnitude of intragenerational plasticity was larger than the transgenerational plastic responses. CONCLUSIONS: Our results highlight that adaptive effects associated with maternal drought can persist beyond the seedling stage and provide evidence of species-level variation in the expression of transgenerational plasticity. Such differences between co-occurring Mediterranean species in the prevalence of this form of non-genetic inheritance may result in differential vulnerability to climate change.

Within-individual leaf trait variation increases with phenotypic integration in a subtropical tree diversity experiment.

Covariation of plant functional traits, that is, phenotypic integration, might constrain their variability. This was observed for inter- and intraspecific variation, but there is no evidence of a relationship between phenotypic integration and the functional variation within single plants (within-individual trait variation; WTV), which could be key to understand the extent of WTV in contexts like plant-plant interactions. We studied the relationship between WTV and phenotypic integration in c. 500 trees of 21 species in planted forest patches varying in species richness in subtropical China. Using visible and near-infrared spectroscopy (Vis-NIRS), we measured nine leaf morphological and chemical traits. For each tree, we assessed metrics of single and multitrait variation to assess WTV, and we used plant trait network properties based on trait correlations to quantify phenotypic integration. Against expectations, strong phenotypic integration within a tree led to greater variation across leaves. Not only this was true for single traits, but also the dispersion in a tree's multitrait hypervolume was positively associated with tree's phenotypic integration. Surprisingly, we only detected weak influence of the surrounding tree-species diversity on these relationships. Our study suggests that integrated phenotypes allow the variability of leaf phenotypes within the organism and supports that phenotypic integration prevents maladaptive variation.

Ecological drivers of fine-scale distribution of arbuscular mycorrhizal fungi in a semiarid Mediterranean scrubland.

BACKGROUND AND AIMS: Arbuscular mycorrhizal (AM) fungi enhance the uptake of water and minerals by the plant hosts, alleviating plant stress. Therefore, AM fungal-plant interactions are particularly important in drylands and other stressful ecosystems. We aimed to determine the combined and independent effects of above- and below-ground plant community attributes (i.e. diversity and composition), soil heterogeneity and spatial covariates on the spatial structure of the AM fungal communities in a semiarid Mediterranean scrubland. Furthermore, we evaluated how the phylogenetic relatedness of both plants and AM fungi shapes these symbiotic relationships. METHODS: We characterized the composition and diversity of AM fungal and plant communities in a dry Mediterranean scrubland taxonomically and phylogenetically, using DNA metabarcoding and a spatially explicit sampling design at the plant neighbourhood scale. KEY RESULTS: The above- and below-ground plant community attributes, soil physicochemical properties and spatial variables explained unique fractions of AM fungal diversity and composition. Mainly, variations in plant composition affected the AM fungal composition and diversity. Our results also showed that particular AM fungal taxa tended to be associated with closely related plant species, suggesting the existence of a phylogenetic signal. Although soil texture, fertility and pH affected AM fungal community assembly, spatial factors had a greater influence on AM fungal community composition and diversity than soil physicochemical properties. CONCLUSIONS: Our results highlight that the more easily accessible above-ground vegetation is a reliable indicator of the linkages between plant roots and AM fungi. We also emphasize the importance of soil physicochemical properties in addition to below-ground plant information, while accounting for the phylogenetic relationships of both plants and fungi, because these factors improve our ability to predict the relationships between AM fungal and plant communities.

ReSurveyGermany: Vegetation-plot time-series over the past hundred years in Germany.

Vegetation-plot resurvey data are a main source of information on terrestrial biodiversity change, with records reaching back more than one century. Although more and more data from re-sampled plots have been published, there is not yet a comprehensive open-access dataset available for analysis. Here, we compiled and harmonised vegetation-plot resurvey data from Germany covering almost 100 years. We show the distribution of the plot data in space, time and across habitat types of the European Nature Information System (EUNIS). In addition, we include metadata on geographic location, plot size and vegetation structure. The data allow temporal biodiversity change to be assessed at the community scale, reaching back further into the past than most comparable data yet available. They also enable tracking changes in the incidence and distribution of individual species across Germany. In summary, the data come at a level of detail that holds promise for broadening our understanding of the mechanisms and drivers behind plant diversity change over the last century.

Effects of parental drought on offspring fitness vary among populations of a crop wild relative.

Transgenerational plasticity is a form of non-genetic inheritance that can reduce or enhance offspring fitness depending on parental stress. Yet, the adaptive value of such parental environmental effects and whether their expression varies among populations remain largely unknown. We used self-fertilized lines from climatically distinct populations of the crop wild relative Lupinus angustifolius. In the parental generation, full-siblings were grown in two contrasting watering environments. Then, to robustly separate the within-generation and transgenerational response to drought, we reciprocally assigned the offspring of parents to the same experimental treatments. We measured key functional traits and assessed lifetime reproductive fitness. Offspring of drought-stressed parents produced less reproductive biomass, but a similar number of lighter seeds, in dry soil compared to offspring of genetically identical, well-watered parents, an effect not mediated by differences in seed provisioning. Importantly, while the offspring of parents grown in the favourable environment responded to drought by slightly increasing individual seed mass, the pattern of plasticity of the offspring of drought-grown parents showed the opposite direction, and the negative effects of parental drought on seed mass were more pronounced in populations from cooler and moist habitats. Overall, our results show that parental effects may override immediate adaptive responses to drought and provide evidence of population-level variation in the expression of transgenerational plasticity.

Phenotypic integration does not constrain phenotypic plasticity: differential plasticity of traits is associated to their integration across environments.

Understanding constraints to phenotypic plasticity is key given its role on the response of organisms to environmental change. It has been suggested that phenotypic integration, the structure of trait covariation, could limit trait plasticity. However, the relationship between plasticity and integration is far from resolved. Using a database of functional plasticity to drought of a Mediterranean shrub that included 20 ecophysiological traits, we assessed environmentally-induced changes in phenotypic integration and whether integration constrained the expression of plasticity, accounting for the within-environment phenotypic variation of traits. Furthermore, we provide the first test of the association between differential trait plasticity and trait integration across an optimum and a stressful environment. Phenotypic plasticity was positively associated with phenotypic integration in both environments, but this relationship was lost when phenotypic variation was considered. The similarity in the plastic response of two traits predicted their integration across environments, with integrated traits having more similar plasticity. Such variation in the plasticity of traits partly explained the lower phenotypic integration found in the stressful environment. We found no evidence that integration may constitute an internal constraint to plasticity. Rather, we present the first empirical demonstration that differences in plastic responses may involve a major reorganization of the relationships among traits, and challenge the notion that stress generally induces a tighter phenotype.

Phylogeography of a gypsum endemic plant across its entire distribution range in the western Mediterranean.

PREMISE: Gypsum soils in the Mediterranean Basin house large numbers of edaphic specialists that are adapted to stressful environments. The evolutionary history and standing genetic variation of these taxa have been influenced by the geological and paleoclimatic complexity of this area and the long-standing effect of human activities. However, little is known about the origin of Mediterranean gypsophiles and the factors affecting their genetic diversity and population structure. METHODS: Using phylogenetic and phylogeographic approaches based on microsatellites and sequence data from nuclear and chloroplast regions, we evaluated the divergence time, genetic diversity, and population structure of 27 different populations of the widespread Iberian gypsophile Lepidium subulatum throughout its entire geographic range. RESULTS: Lepidium subulatum diverged from its nearest relatives ~3 million years ago, and ITS and psbA/matK trees supported the monophyly of the species. These results suggest that both geological and climatic changes in the region around the Plio-Pleistocene promoted its origin, compared to other evolutionary processes. We found high genetic diversity in both nuclear and chloroplast markers, but a greater population structure in the chloroplast data. These results suggest that while seed dispersal is limited, pollen flow may be favored by the presence of numerous habitat patches that enhance the movement of pollinators. CONCLUSIONS: Despite being an edaphic endemic, L. subulatum possesses high genetic diversity probably related to its relatively old age and high population sizes across its range. Our study highlights the value of using different markers to fully understand the phylogeographic history of plant species.

The role of root community attributes in predicting soil fungal and bacterial community patterns.

Roots are assumed to play a major role in structuring soil microbial communities, but most studies exploring the relationships between microbes and plants at the community level have only used aboveground plant distribution as a proxy. However, a decoupling between belowground and aboveground plant components may occur due to differential spreading of plant canopies and root systems. Thus, soil microbe-plant links are not completely understood. Using a combination of DNA metabarcoding and spatially explicit sampling at the plant neighbourhood scale, we assessed the influence of the plant root community on soil bacterial and fungal diversity (species richness, composition and ß-diversity) in a dry Mediterranean scrubland. We found that root composition and biomass, but not richness, predict unique fractions of variation in microbial richness and composition. Moreover, bacterial ß-diversity was related to root ß-diversity, while fungal ß-diversity was related to aboveground plant ß-diversity, suggesting that plants differently influence both microbial groups. Our study highlights the role of plant distribution both belowground and aboveground, soil properties and other spatially structured factors in explaining the heterogeneity in soil microbial diversity. These results also show that incorporating data on both plant community compartments will further our understanding of the relationships between soil microbial and plant communities.

Author Correction: The GenTree Dendroecological Collection, tree-ring and wood density data from seven tree species across Europe.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

High differentiation in functional traits but similar phenotypic plasticity in populations of a soil specialist along a climatic gradient.

BACKGROUND AND AIMS: Plants experiencing contrasting environmental conditions may accommodate such heterogeneity by expressing phenotypic plasticity, evolving local adaptation or a combination of both. We investigated patterns of genetic differentiation and plasticity in response to drought in populations of the gypsum specialist Lepidium subulatum. METHODS: We created an outdoor common garden with rain exclusion structures using 60 maternal progenies from four distinct populations that substantially differ in climatic conditions. We characterized fitness, life history and functional plasticity in response to two contrasting treatments that realistically reflect soil moisture variation in gypsum habitats. We also assessed neutral genetic variation and population structure using microsatellite markers. KEY RESULTS: In response to water stress, plants from all populations flowered earlier, increased allocation to root tissues and advanced leaf senescence, consistent with a drought escape strategy. Remarkably, these probably adaptive responses were common to all populations, as shown by the lack of population × environment interaction for almost all functional traits. This generally common pattern of response was consistent with substantial neutral genetic variation and large differences in population trait means. However, such population-level trait variation was not related to climatic conditions at the sites of origin. CONCLUSIONS: Our results show that, rather than ecotypes specialized to local climatic conditions, these populations are composed of highly plastic, general-purpose genotypes in relation to climatic heterogeneity. The strikingly similar patterns of plasticity among populations, despite substantial site of origin differences in climate, suggest past selection on a common norm of reaction due to similarly high levels of variation within sites. It is thus likely that plasticity will have a prevalent role in the response of this soil specialist to further environmental change.

The GenTree Dendroecological Collection, tree-ring and wood density data from seven tree species across Europe.

The dataset presented here was collected by the GenTree project (EU-Horizon 2020), which aims to improve the use of forest genetic resources across Europe by better understanding how trees adapt to their local environment. This dataset of individual tree-core characteristics including ring-width series and whole-core wood density was collected for seven ecologically and economically important European tree species: silver birch (Betula pendula), European beech (Fagus sylvatica), Norway spruce (Picea abies), European black poplar (Populus nigra), maritime pine (Pinus pinaster), Scots pine (Pinus sylvestris), and sessile oak (Quercus petraea). Tree-ring width measurements were obtained from 3600 trees in 142 populations and whole-core wood density was measured for 3098 trees in 125 populations. This dataset covers most of the geographical and climatic range occupied by the selected species. The potential use of it will be highly valuable for assessing ecological and evolutionary responses to environmental conditions as well as for model development and parameterization, to predict adaptability under climate change scenarios.

Plant domestication disrupts biodiversity effects across major crop types.

Plant diversity fosters productivity in natural ecosystems. Biodiversity effects might increase agricultural yields at no cost in additional inputs. However, the effects of diversity on crop assemblages are inconsistent, probably because crops and wild plants differ in a range of traits relevant to plant-plant interactions. We tested whether domestication has changed the potential of crop mixtures to over-yield by comparing the performance and traits of major crop species and those of their wild progenitors under varying levels of diversity. We found stronger biodiversity effects in mixtures of wild progenitors, due to larger selection effects. Variation in selection effects was partly explained by within-mixture differences in leaf size. Our results indicate that domestication might disrupt the ability of crops to benefit from diverse neighbourhoods via reduced trait variance. These results highlight potential limitations of current crop mixtures to over-yield and the potential of breeding to re-establish variance and increase mixture performance.

Estimating belowground plant abundance with DNA metabarcoding.

Most work on plant community ecology has been performed above ground, neglecting the processes that occur in the soil. DNA metabarcoding, in which multiple species are computationally identified in bulk samples, can help to overcome the logistical limitations involved in sampling plant communities belowground. However, a major limitation of this methodology is the quantification of species' abundances based on the percentage of sequences assigned to each taxon. Using root tissues of five dominant species in a semi-arid Mediterranean shrubland (Bupleurum fruticescens, Helianthemum cinereum, Linum suffruticosum, Stipa pennata and Thymus vulgaris), we built pairwise mixtures of relative abundance (20%, 50% and 80% biomass), and implemented two methods (linear model fits and correction indices) to improve estimates of root biomass. We validated both methods with multispecies mixtures that simulate field-collected samples. For all species, we found a positive and highly significant relationship between the percentage of sequences and biomass in the mixtures (R2  = .44-.66), but the equations for each species (slope and intercept) differed among them, and two species were consistently over- and under-estimated. The correction indices greatly improved the estimates of biomass percentage for all five species in the multispecies mixtures, and reduced the overall error from 17% to 6%. Our results show that, through the use of post-sequencing quantification methods on mock communities, DNA metabarcoding can be effectively used to determine not only species' presence but also their relative abundance in field samples of root mixtures. Importantly, knowledge of these aspects will allow us to study key, yet poorly understood, belowground processes.

Population size, center-periphery, and seed dispersers' effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon.

The effect of population size on population genetic diversity and structure has rarely been studied jointly with other factors such as the position of a population within the species' distribution range or the presence of mutualistic partners influencing dispersal. Understanding these determining factors for genetic variation is critical for conservation of relict plants that are generally suffering from genetic deterioration. Working with 16 populations of the vulnerable relict shrub Cneorum tricoccon throughout the majority of its western Mediterranean distribution range, and using nine polymorphic microsatellite markers, we examined the effects of periphery (peripheral vs. central), population size (large vs. small), and seed disperser (introduced carnivores vs. endemic lizards) on the genetic diversity and population structure of the species. Contrasting genetic variation (HE: 0.04-0.476) was found across populations. Peripheral populations showed lower genetic diversity, but this was dependent on population size. Large peripheral populations showed high levels of genetic diversity, whereas small central populations were less diverse. Significant isolation by distance was detected, indicating that the effect of long-distance gene flow is limited relative to that of genetic drift, probably due to high selfing rates (FIS = 0.155-0.887), restricted pollen flow, and ineffective seed dispersal. Bayesian clustering also supported the strong population differentiation and highly fragmented structure. Contrary to expectations, the type of disperser showed no significant effect on either population genetic diversity or structure. Our results challenge the idea of an effect of periphery per se that can be mainly explained by population size, drawing attention to the need of integrative approaches considering different determinants of genetic variation. Furthermore, the very low genetic diversity observed in several small populations and the strong among-population differentiation highlight the conservation value of large populations throughout the species' range, particularly in light of climate change and direct human threats.

Cross-realm assessment of climate change impacts on species' abundance trends.

Climate change, land-use change, pollution and exploitation are among the main drivers of species' population trends; however, their relative importance is much debated. We used a unique collection of over 1,000 local population time series in 22 communities across terrestrial, freshwater and marine realms within central Europe to compare the impacts of long-term temperature change and other environmental drivers from 1980 onwards. To disentangle different drivers, we related species' population trends to species- and driver-specific attributes, such as temperature and habitat preference or pollution tolerance. We found a consistent impact of temperature change on the local abundances of terrestrial species. Populations of warm-dwelling species increased more than those of cold-dwelling species. In contrast, impacts of temperature change on aquatic species' abundances were variable. Effects of temperature preference were more consistent in terrestrial communities than effects of habitat preference, suggesting that the impacts of temperature change have become widespread for recent changes in abundance within many terrestrial communities of central Europe.

Habitat Fragmentation Differentially Affects Genetic Variation, Phenotypic Plasticity and Survival in Populations of a Gypsum Endemic.

Habitat fragmentation, i.e., fragment size and isolation, can differentially alter patterns of neutral and quantitative genetic variation, fitness and phenotypic plasticity of plant populations, but their effects have rarely been tested simultaneously. We assessed the combined effects of size and connectivity on these aspects of genetic and phenotypic variation in populations of Centaurea hyssopifolia, a narrow endemic gypsophile that previously showed performance differences associated with fragmentation. We grew 111 maternal families sampled from 10 populations that differed in their fragment size and connectivity in a common garden, and characterized quantitative genetic variation, phenotypic plasticity to drought for key functional traits, and plant survival, as a measure of population fitness. We also assessed neutral genetic variation within and among populations using eight microsatellite markers. Although C. hyssopifolia is a narrow endemic gypsophile, we found substantial neutral genetic variation and quantitative variation for key functional traits. The partition of genetic variance indicated that a higher proportion of variation was found within populations, which is also consistent with low population differentiation in molecular markers, functional traits and their plasticity. This, combined with the generally small effect of habitat fragmentation suggests that gene flow among populations is not restricted, despite large differences in fragment size and isolation. Importantly, population's similarities in genetic variation and plasticity did not reflect the lower survival observed in isolated populations. Overall, our results indicate that, although the species consists of genetically variable populations able to express functional plasticity, such aspects of adaptive potential may not always reflect populations' survival. Given the differential effects of habitat connectivity on functional traits, genetic variation and fitness, our study highlights the need to shift the focus of fragmentation studies to the mechanisms that regulate connectivity effects, and call for caution on the use of genetic variation and plasticity to forecast population performance.

Limits to Future Adaptation in the Invasive Plant Polygonum cespitosum: Expression of Functional and Fitness Traits at Elevated CO2.

For organisms to adapt to future environments, they must both evolve appropriate functional responses and phenotypically express those responses under future climatic and CO2 conditions. We examined these 2 components of future adaptation in an invasive annual plant (Polygonum cespitosum) by performing a "resurrection" experiment under field conditions simulating a future environment. Resurrection experiments reveal recent evolution by comparing genotypes from natural populations sampled across a multigeneration interval. We collected genotypes from the same 3 North American populations in 1994 and 2005 and raised inbred lines from these collections under free air CO2 enrichment to examine functional and fitness traits expressed in hot, dry conditions at both ambient and elevated CO2 (N = 295 plants). The species has rapidly evolved in its introduced range to increase photosynthetic rate (collection year effect P ≤ 0.011) and delay senescence (P = 0.017) under full-sun, dry field conditions, but these adaptive changes were not expressed when the field environment included elevated CO2 (within-treatment year effect P ≥ 0.20 for both traits). Populations showed different levels of reproductive output and its genetic variance in these novel, stressful conditions. These findings illustrate constraints on evolutionary adaptation to predicted future conditions at both the species and population levels.

Population differentiation in a Mediterranean relict shrub: the potential role of local adaptation for coping with climate change.

Plants can respond to climate change by either migrating, adapting to the new conditions or going extinct. Relict plant species of limited distribution can be especially vulnerable as they are usually composed of small and isolated populations, which may reduce their ability to cope with rapidly changing environmental conditions. The aim of this study was to assess the vulnerability of Cneorum tricoccon L. (Cneoraceae), a Mediterranean relict shrub of limited distribution, to a future drier climate. We evaluated population differentiation in functional traits related to drought tolerance across seven representative populations of the species' range. We measured morphological and physiological traits in both the field and the greenhouse under three water availability levels. Large phenotypic differences among populations were found under field conditions. All populations responded plastically to simulated drought, but they differed in mean trait values as well as in the slope of the phenotypic response. Particularly, dry-edge populations exhibited multiple functional traits that favored drought tolerance, such as more sclerophyllous leaves, strong stomatal control but high photosynthetic rates, which increases water use efficiency (iWUE), and an enhanced ability to accumulate sugars as osmolytes. Although drought decreased RGR in all populations, this reduction was smaller for populations from the dry edge. Our results suggest that dry-edge populations of this relict species are well adapted to drought, which could potentially mitigate the species' extinction risk under drier scenarios. Dry-edge populations not only have a great conservation value but can also change expectations from current species' distribution models.

An ideal weed: plasticity and invasiveness in Polygonum cespitosum.

The introduced Asian plant Polygonum cespitosum has only recently become invasive in northeastern North America, spreading into sunny as well as shaded habitats. We present findings from a multiyear case study of this ongoing species invasion, drawing on field environmental measurements, glasshouse plasticity and resurrection experiments, and molecular genetic (microsatellite) data. We focus in particular on patterns of individual phenotypic plasticity (norms of reaction), their diversity within and among populations in the species' introduced range, and their contribution to its potential to evolve even greater invasiveness. Genotypes from introduced-range P. cespitosum populations have recently evolved to express greater adaptive plasticity to full sun and/or dry conditions without any loss of fitness in shade. Evidently, this species may evolve the sort of "general-purpose genotypes" hypothesized by Herbert Baker to characterize an "ideal weed." Indeed, we identified certain genotypes capable of extremely high reproductive output across contrasting conditions, including sunny, shaded, moist, and dry. Populations containing these high-performance genotypes had consistently higher fitness in all glasshouse habitats; there was no evidence for local adaptive differentiation among populations from sunny, shaded, moist, or dry sites. Norm of reaction data may provide valuable insights to invasion biology: the presence of broadly adaptive, high-performance genotypes can promote a species' ecological spread while providing the fuel for increased invasiveness to evolve.

Evidence for rapid ecological range expansion in a newly invasive plant.

Little is known about how an introduced species may expand its ecological range, i.e. the set of local environmental conditions in which it can successfully establish populations. Delimiting this range of conditions is a methodological challenge, because it is impossible to sample all potential field locations for any species in a given region. Developing approaches to track ecological range over time could substantially contribute to understanding invasion dynamics. In this study, we use a previously established sampling strategy to document apparent changes across a 15-year time interval in the ecological range of the Asian annual Polygonum cespitosum Blume in northeastern North America, where the species has recently become invasive. Using a structured sample drawn from a large set of field populations, we determined the range of light, soil moisture and soil nutrient conditions that the species currently occupies in this region and the proportional distribution of individuals in differing types of microsite, and compared them with field measurements that were similarly determined 15 years earlier. Although in 1994 the species was absent from both high-light and flooded habitats, in 2009 P. cespitosum occurred in open as well as shaded habitats, across a wide range of moisture conditions. In 2009 the species also occupied a greater proportion of high-light microsites within field sites than in 1994. These findings suggest an expanded ecological range that, intriguingly, is consistent with the recent evolution in North American P. cespitosum populations of adaptive plasticity in response to high light. Possible non-evolutionary explanations for the change in field distribution are also considered.