Differentiation along a gradient of environmental productivity and predictability in populations of Hordeum spontaneum Koch: multilevel selection analysis

A contextual analysis combined with path analysis was applied to detect ecotype-specific past selection in hierarchically structured populations of wild barley, Hordeum spontaneum . In our analysis a multiple regression model incorporated several individual and ecotype-level unmeasured (derived) traits obtained by factor analysis from 20 measured morphological and phenological traits. Under favourable conditions (high water and nutrients) both individual and ecotype plant size (RF1) were significant predictors of individual plant fitness, estimated by either reproductive biomass or yield. Both individual and ecotype size of reproductive structures (RF2) were significantly related to individual reproductive biomass. Individual yield, however, significantly correlated with ecotype RF2 only. Transition to reproduction (RF3) correlated with neither reproductive biomass nor yield at individual level, but correlated with two estimates of fitness at ecotype level. In all cases, selection at the individual and ecotype levels was in opposition. We interpret the observed effect of ecotype identity on individual fitness not as a current group selection, but as a constraining effect of ecotype-specific past selection. The four ecotypes went through an environmentally specific selection process in their own environments with the optimal strategy evolved. Consequently, this strategy may have a constraining effect on plant performance in other environments. Under conditions of either low water or low nutrients the ecotype level did not contribute to individual fitness. The latter may suggest that a mechanism for plant responses to stress is largely independent of plant origin, with a difference between ecotypes under stressful conditions due entirely to the difference in amount, not architecture, of plasticity. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 313–318.     

Differentiation in populations of Hordeum spontaneum along a gradient of environmental productivity and predictability: life history and local adaptation

Reciprocal introduction of seeds and seedlings of wild barley, Hordeum spontaneum , originating in four different environments of Israel was used to: (1) test for local adaptation, (2) make inferences about environmental effects on life‐history and reproductive traits, and (3) identify trait combinations with recognizable ‘strategies’. The four populations examined represented the following environments: (1) desert ? low productivity and predictability, drought stress; (2) semi‐steppe batha ? moderate productivity and predictability; (3) grassland ? high productivity and predictability; and (4) mountain ? high productivity and predictability but with severe frost stress. Significant genotype‐by‐environment interactions were observed for yield and reproductive biomass, seedling biomass and percentage germinated and survived seeds, suggesting local ecotype adaptation. Increasing productivity and predictability of environment in respect to rainfall, without concomitant frost stress, was found to select for high reproductive biomass and large seeds, a high fraction of germinating seeds and high vigour of seedlings. The optimal strategy changes with increasing productivity and predictability and involves a trade‐off between seed size and number, with reduced yield but increased seed mass, consistent with competition selection (or K‐selection sensu MacArthur & Wilson (1967 )) type. No specific life‐history adaptations to predictable frost stress were detected for the mountain ecotype, but there was higher survival of seedlings in their indigenous (mountain) environment compared with other ecotypes. The latter appears to be a physiological adaptation to frost, which is consistent with selection for stress tolerance (or S‐selection sensu Grime (1977 )) type. The other stress factor, drought, which is very unpredictable in deserts, was associated with high seed dormancy, small seed size and low vigour of seedlings, but relatively high yield, which is consistent with a stress‐escape bet‐hedging strategy. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 479–490.     

Plasticity and ontogenetic drift of biomass allocation in response to above- and below-ground resource availabilities in perennial herbs: a case study of <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis>

Changes in plant biomass allocation in response to varying resource availabilities may result from ontogenetic drift caused by allometric growth (i.e., apparent plasticity), a true adjustment of ontogenetic trajectories (true plasticity) or both (complex plasticity). Given that the root allocation of annual species usually decreases during the growth, the developmentally explicit model predicts that annual herbs will exhibit true plasticity in root allocation under above-ground resource limitation and apparent plasticity for moderate stress of below-ground resource. For perennial species, the root allocation of which increases during growth, the reverse patterns would be expected. In this study, we tested the developmentally explicit model with a perennial weed, Alternanthera philoxeroides (Mart.) Griseb. We report its adaptive changes and ontogenetic drift of root allocation in response to different resource levels (i.e., light, water and nutrient availability) by comparing root allocation on both an age and a size basis. The root allocation of A. philoxeroides increased with the size (i.e., ontogenetic drift) during the growth, and exhibited significant changes in response to different resource availabilities. Furthermore, the root allocation in response to water or nutrient availability exhibited typical complex plasticity, while the light stress only slowed down the growth, with the ontogenetic trajectory unchanged (apparent plasticity). The contrasting responses to above-ground and below-ground stresses were consistent with the prediction of the developmentally explicit model.     

Trait convergence and plasticity among native and invasive species in resource-poor environments

? Premise of study: Functional trait comparisons provide a framework with which to assess invasion and invasion resistance. However, recent studies have found evidence for both trait convergence and divergence among coexisting dominant native and invasive species. Few studies have assessed how multiple stresses constrain trait values and plasticity, and no study has included direct measurements of nutrient conservation traits, which are critical to plants growing in low-resource environments. ? Methods: We evaluated how nutrient and water stresses affect growth and allocation, water potential and gas exchange, and nitrogen (N) allocation and use traits among a suite of six codominant species from the Intermountain West to determine trait values and plasticity. In the greenhouse, we grew our species under a full factorial combination of high and low N and water availability. We measured relative growth rate (RGR) and its components, total biomass, biomass allocation, midday water potential, photosynthetic rate, water-use efficiency (WUE), green leaf N, senesced leaf N, total N pools, N productivity, and photosynthetic N use efficiency. ? Key results: Overall, soil water availability constrained plant responses to N availability and was the major driver of plant trait variation in our analysis. Drought decreased plant biomass and RGR, limited N conservation, and led to increased WUE. For most traits, native and nonnative species were similarly plastic. ? Conclusions: Our data suggest native and invasive biomass dominants may converge on functionally similar traits and demonstrate comparable ability to respond to changes in resource availability.     

Biomass partitioning in response to resources availability: A comparison between native and invaded ranges in the clonal invader Carpobrotus edulis

Identifying the mechanism underlying plant invasiveness is a fast-moving research topic in current ecology. Phenotypic plasticity has been pointed out as a trait that can contribute to plant invasiveness. This experiment examines the presence of rapid adaptive evolution favoring plastic biomass partitioning during the invasion process. With that aim, we tested differences in patterns of biomass allocation between populations of Carpobrotus edulis from South Africa (native area) and the Iberian Peninsula (invaded area) growing under different nutrient, water and light availabilities in a common garden experiment. Here we demonstrate that biomass partitioning in response to nutrient availability in C. edulis differs between populations from native and invaded ranges, indicating that this trait could be under selection during the invasion process. Thus, nutrient shortage significantly increased the proportional production of roots in populations from the invaded range, but not in populations from the native area. This plastic root-foraging response may contribute to the optimization of nutrient uptake by plants, and therefore could be considered as an adaptive strategy. Understanding the ecological implications of rapid evolution for plastic biomass partitioning is important in determining processes of plant adaptation to new environments, and contributes to disentangling the mechanisms underlying plant invasiveness.     

Phenotypic Plasticity in Response to the Social Environment: Effects of Density and Sex Ratio on Mating Behaviour Following Ecotype Divergence

The ability to express phenotypically plastic responses to environmental cues might be adaptive in changing environments. We studied phenotypic plasticity in mating behaviour as a response to population density and adult sex ratio in a freshwater isopod (Asellus aquaticus). A. aquaticus has recently diverged into two distinct ecotypes, inhabiting different lake habitats (reed Phragmites australis and stonewort Chara tomentosa, respectively). In field surveys, we found that these habitats differ markedly in isopod population densities and adult sex ratios. These spatially and temporally demographic differences are likely to affect mating behaviour. We performed behavioural experiments using animals from both the ancestral ecotype (“reed” isopods) and from the novel ecotype (“stonewort” isopods) population. We found that neither ecotype adjusted their behaviour in response to population density. However, the reed ecotype had a higher intrinsic mating propensity across densities. In contrast to the effects of density, we found ecotype differences in plasticity in response to sex ratio. The stonewort ecotype show pronounced phenotypic plasticity in mating propensity to adult sex ratio, whereas the reed ecotype showed a more canalised behaviour with respect to this demographic factor. We suggest that the lower overall mating propensity and the phenotypic plasticity in response to sex ratio have evolved in the novel stonewort ecotype following invasion of the novel habitat. Plasticity in mating behaviour may in turn have effects on the direction and intensity of sexual selection in the stonewort habitat, which may fuel further ecotype divergence.     

Responses to simulated winter conditions differ between threespine stickleback ecotypes

Abiotic factors can act as barriers to colonization and drive local adaptation. During colonization, organisms may cope with changes in abiotic factors using existing phenotypic plasticity, but the role of phenotypic plasticity in assisting or hindering the process of local adaptation remains unclear. To address these questions, we explore the role of winter conditions in driving divergence during freshwater colonization and the effects of plasticity on local adaptation in ancestral marine and derived freshwater ecotypes of threespine stickleback (Gasterosteus aculeatus). We found that freshwater‐resident stickleback had greater tolerance of acute exposure to low temperatures than marine stickleback, but these differences were abolished after acclimation to simulated winter conditions (9L:15D photoperiod at 4 °C). Plasma chloride levels differed between the ecotypes, but showed a similar degree of plasticity between ecotypes. Gene expression of the epithelial calcium channel (ECaC) differed between ecotypes, with the freshwater ecotype demonstrating substantially greater expression than the marine ecotype, but there was no plasticity in this trait under these conditions in either ecotype. In contrast, growth (assessed as final mass) and the expression of an isoform of the electroneutral Na⁺/H⁺ exchanger (NHE3) exhibited substantial change with temperature in the marine ecotype that was not observed in the freshwater ecotype under the conditions tested here, which is consistent with evolution of these traits by a process such as genetic assimilation. These data demonstrate substantial divergence in many of these traits between freshwater and marine stickleback, but also illustrate the complexity of possible relationships between plasticity and local adaptation.     

Host environment and local genetic adaptation determine phenotype in parasitic Rhinanthus angustifolius

Plants have a remarkable capacity to adapt to local environmental conditions, which can result in ecotypic differentiation. Patterns of differentiation can, however, also be influenced by the extensive phenotypic plasticity exhibited by many plant species. In this study, we evaluated the distinctness of two putative ecotypes of the parasitic herb Rhinanthus angustifolius. We compared population means of characters commonly used to distinguish between the putative ecotypes after growing individuals of R. angustifolius with a variety of host species in a common garden. Resulting data were also pooled over environments to study how phenotypic plasticity affects the distinctness of ecotypes and individual populations. Except for node number, most of the characters were plastic. The pattern of differentiation was consistent with the existence of two, or possibly three, habitat‐related groups of populations; however, we observed considerable overlap in flowering time and morphological characters after pooling data across host environments. The results show that the complex phenological and morphological variation in R. angustifolius is caused by a combination of genetically determined ecotypic differentiation and plastic responses to the host environment and other factors. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 89–103.     

Changing water use and adaptive strategies along rainfall gradients in Mediterranean lupins

• There is growing interest in harnessing the genetic and adaptive diversity of crop wild relatives to improve drought resilience of elite cultivars. Rainfall gradients exert strong selection pressure on both natural and agricultural ecosystems. Understanding plant responses to these facilitates crop improvement.
• Wild and domesticated narrow‐leafed lupin (NLL) collected along Mediterranean terminal drought stress gradients was evaluated under contrasting reproductive phase water supply in controlled field, glasshouse and cabinet studies. Plant phenology, growth and productivity, water use and stress responses were measured over time.
• There is an integrated suite of adaptive changes along rainfall gradients in NLL. Low rainfall ecotypes flower earlier, accumulate lower seed numbers, biomass and leaf area, and have larger root:shoot ratios than high rainfall ecotypes. Water‐use is lower and stress onset slower in low compared to high rainfall ecotypes. Water‐use rates and ecotypic differences in stress response (Ψleaf decline, leaf loss) are lower in NLL than yellow lupin (YL). To mitigate the effects of profligate water use, high rainfall YL ecotypes maintain higher leaf water content over declining leaf water potential than low rainfall ecotypes. There is no evidence for such specific adaptation in NLL.
• The data suggests that appropriate phenology is the key adaptive trait to rainfall gradients in NLL because of the flow‐on effects on biomass production, fitness, transpiration and stress onset, and the lack of physiological adaptations as in YL. Accordingly, it is essential to match phenology with target environment in order to minimize risk and maximize yield potential.

     

Local adaptation of switchgrass drives trait relations to yield and differential responses to climate and soil environments

Switchgrass, a potential biofuel crop, is a genetically diverse species with phenotypic plasticity enabling it to grow in a range of environments. Two primary divergent ecotypes, uplands and lowlands, exhibit trait combinations representative of acquisitive and conservative growth allocation strategies, respectively. Whether these ecotypes respond differently to various types of environmental drivers remains unclear but is crucial to understanding how switchgrass varieties will respond to climate change. We grew two upland, two lowland, and two intermediate/hybrid cultivars of switchgrass at three sites along a latitudinal gradient in the central United States. Over a 4-year period, we measured plant functional traits and biomass yields and evaluated genotype-by-environment (G × E) interaction effects by analyzing switchgrass responses to soil and climate variables. We found substantial evidence of G × E interactions on biomass yield, primarily due to deviations in the response of the southern lowland cultivar Alamo, which produced more biomass in hotter and drier environments relative to other cultivars. While lowland cultivars had the highest potential for yield, their yields were more variable year-to-year compared to other cultivars, suggesting greater sensitivity to environmental perturbations. Models comparing soil and climate principal components as explanatory variables revealed soil properties, especially nutrients, to be most effective at predicting switchgrass biomass yield. Also, positive correlations between biomass yield and conservative plant traits, such as high stem mass and tiller height,  became stronger at lower latitudes where the climate is hotter and drier, regardless of ecotype. Lowland cultivars, however, showed a greater predisposition to exhibit these conservative traits. These results suggest switchgrass trait allocation trade-offs that prioritize aboveground biomass production are more tightly associated in hot, dry environments and that lowland cultivars may exhibit a more specialized strategy relative to other cultivars. Altogether, this research provides essential knowledge for improving the viability of switchgrass as a biofuel crop.     

Phenotypic plasticity closely linked to climate at origin and resulting in increased mortality under warming and frost stress in a common grass

Phenotypic plasticity is important for species responses to global change and species coexistence. Phenotypic plasticity differs among species and traits and changes across environments. Here, we investigated phenotypic plasticity of the widespread grass Arrhenatherum elatius in response to winter warming and frost stress by comparing phenotypic plasticity of 11 geographically and environmentally distinct populations of this species to phenotypic plasticity of populations of different species originating from a single environment. The variation in phenotypic plasticity was similar for populations of a single species from different locations compared to populations of functionally and taxonomically diverse species from one environment for the studied traits (leaf biomass production and root integrity after frost) across three indices of phenotypic plasticity (RDPI, PIN, slope of reaction norm). Phenotypic plasticity was not associated with neutral genetic diversity but closely linked to the climate of the populations’ origin. Populations originating from warmer and more variable climates showed higher phenotypic plasticity. This indicates that phenotypic plasticity can itself be considered as a trait subject to local adaptation to climate. Finally, our data emphasize that high phenotypic plasticity is not per se positive for adaptation to climate change, as differences in stress responses are resulting in high phenotypic plasticity as expressed by common plasticity indices, which is likely to be related to increased mortality under stress in more plastic populations.     

A test of the "flexible stem" model of evolution: ancestral plasticity, genetic accommodation, and morphological divergence in the threespine stickleback radiation

If an ancestral stem group repeatedly colonizes similar environments, developmental plasticity specific to that group should consistently give rise to similar phenotypes. Parallel selection on those similar phenotypes could lead to the repeated evolution of characteristic ecotypes, a property common to many adaptive radiations. A key prediction of this "flexible stem" model of adaptive radiation is that patterns of phenotypic divergence in derived groups should mirror patterns of developmental plasticity in their common ancestor. The threespine stickleback radiation provides an excellent opportunity to test this prediction because the marine form is representative of the ancestral stem group, which has repeatedly given rise to several characteristic ecotypes. We examined plasticity of several aspects of shape and trophic morphology in response to diets characteristic of either the derived benthic ecotype or the limnetic ecotype. When marine fish were reared on alternative diets, plasticity of head and mouth shape paralleled phenotypic divergence between the derived ecotypes, supporting the flexible stem model. Benthic and limnetic fish exhibited patterns of plasticity similar to those of the marine population; however, some differences in population means were present, as well as subtle differences in shape plasticity in the benthic population, indicating a role for genetic accommodation in this system.     

Experimental ecology of Dryas octopetala ecotypes

Summary Growth, survival and reproduction of adult plants from three reciprocally-transplanted populations of Dryas octopetala were followed over a seven year period, from 1979 to 1986. The two most different ecotypes, from snowbed and fellfield environments, were strongly selected against in extreme foreign environments via differential growth, survival, and reproduction. The more phenotypically-plastic ecotype from the snowbed experienced rapid, early mortality on the fellfield, prior to morphological adjustment, but no mortality in the last five years of the experiment. The less plastic fellfield ecotype showed no mortality for the first three years followed by a steady decline in numbers for the next four years. The ecotypic difference in plasticity may account for the contrasting mortality patterns. A population of plants with intermediate morphology was intermediate in fitness in extreme environments, but showed no superiority in its home site, suggesting that it is not a locally-adapted population. Natural selection maintains genetic differences between snowbed and fellfield populations in the face of gene flow. However, based on the response of intermediates, there appear to be limits to the degree to which selection can fine-tune adaptation along environmental gradients.     

Ecotypes of wild rooibos (Aspalathus linearis (Burm. F) Dahlg., Fabaceae) are ecologically distinct

Aspalathus linearis (Burm. F) Dahlg., Fabaceae is cultivated by small- and large-scale commercial farmers of the Cederberg and Bokkeveld Plateau in the Cape Floristic Region of South Africa, for the production of an herbal beverage called ‘rooibos’ or ‘rooibos tea’. Small-scale farmers also harvest A. linearis from the wild and market the tea as an organic and fair-trade certified product. However, little is known about the apparent ecotypes of wild A. linearis. We hypothesized that 1) rooibos ecotypes are ecologically distinct (occurring in different plant communities defined by environmental variables); 2) rooibos ecotypes are functionally distinct due to variance in water use efficiency; and 3) rooibos ecotypes are associated with threatened vegetation types/species, making populations of wild rooibos ecotypes worthy of conservation. Ecotypes of wild rooibos were identified based on plant habit and local knowledge. Plant communities were classified using Twinspan, environmental factors were tested as predictors of ecotype distribution and water use efficiency of ecotypes growing across a rainfall gradient was determined from foliar natural abundance of ¹³C. Wild rooibos was not generally associated with endangered vegetation types but was associated with plant species having endangered status. Wild rooibos occurred in four plant communities and comprised five wild rooibos ecotypes: shrub, tree, upright, salignus and prostrate types. Although some ecotypes clearly co-occurred, evidence is provided for habitat preference between the ecotypes: Prostrate and upright ecotypes occurred at higher elevations (> 400-600 m). Shrub ecotypes occurred at lower rainfall sites (< 200 mm p.a.) and the salignus ecotype occurred at higher rainfall sites (> 500 mm p.a.). Foliar ¹³C indicated greater water use efficiencies by ecotypes in relatively drier areas. The extent to which this is a plastic or inherent response requires further investigation. Considering that wild rooibos ecotypes differ both ecologically and possibly also functionally and genetically, it is concluded that populations of wild rooibos ecotypes should be considered as distinct and worthy of conservation. This distinctness should be considered when farmers apply for both harvesting and ploughing rights on land with wild rooibos ecotypes.     

Patterns of intraspecific trait variation along an aridity gradient suggest both drought escape and drought tolerance strategies in an invasive herb

Background and AimsIn water-limited landscapes, some plants build structures that enable them to survive with minimal water (drought resistance). Instead of making structures that allow survival through times of water limitation, annual plants may invoke a drought escape strategy where they complete growth and reproduction when water is available. Drought escape and resistance each require a unique combination of traits and therefore plants are likely to have a suite of trait values that are consistent with a single drought response strategy. In environments where conditions are variable, plants may additionally evolve phenotypically plastic trait responses to water availability. Invasive annual species commonly occur in arid and semi-arid environments and many will be subject to reduced water availability associated with climate change. Assessing intraspecific trait variation across environmental gradients is a valuable tool for understanding how invasive plants establish and persist in arid environments.MethodsIn this study, we used a common garden experiment with two levels of water availability to determine how traits related to carbon assimilation, water use, biomass allocation and flowering phenology vary in California wild radish populations across an aridity gradient.Key ResultsWe found that populations from arid environments have rapid flowering and increased allocation to root biomass, traits associated with both drought escape and tolerance. Early flowering was associated with higher leaf nitrogen concentration and lower leaf mass per area, traits associated with high resource acquisition. While trait values varied across low- and high-water treatments, these shifts were consistent across populations, indicating no differential plasticity across the aridity gradient.ConclusionsWhile previous studies have suggested that drought escape and drought resistance are mutually exclusive drought response strategies, our findings suggest that invasive annuals may employ both strategies to succeed in novel semi-arid environments. As many regions are expected to become more arid in the future, investigations of intraspecific trait variation within low water environments help to inform our understanding of potential evolutionary responses to increased aridity in invasive species.     

Local adaptation,genetic divergence,and experimental selection in a foundation grass across the US Great Plains’ climate gradient

Many prior studies have uncovered evidence for local adaptation using reciprocal transplant experiments. However, these studies are rarely conducted for a long enough time to observe succession and competitive dynamics in a community context, limiting inferences for long‐lived species. Furthermore, the genetic basis of local adaptation and genetic associations with climate has rarely been identified. Here, we report on a long‐term (6‐year) experiment conducted under natural conditions focused on Andropogon gerardii, the dominant grass of the North American Great Plains tallgrass ecosystem. We focus on this foundation grass that comprises 80% of tallgrass prairie biomass and is widely used in 20,000 km² of restoration. Specifically, we asked the following questions: (a) Whether ecotypes are locally adapted to regional climate in realistic ecological communities. (b) Does adaptive genetic variation underpin divergent phenotypes across the climate gradient? (c) Is there evidence of local adaptation if the plants are exposed to competition among ecotypes in mixed ecotype plots? Finally, (d) are local adaptation and genetic divergence related to climate? Reciprocal gardens were planted with 3 regional ecotypes (originating from dry, mesic, wet climate sources) of Andropogon gerardii across a precipitation gradient (500–1,200 mm/year) in the US Great Plains. We demonstrate local adaptation and differentiation of ecotypes in wet and dry environments. Surprisingly, the apparent generalist mesic ecotype performed comparably under all rainfall conditions. Ecotype performance was underpinned by differences in neutral diversity and candidate genes corroborating strong differences among ecotypes. Ecotype differentiation was related to climate, primarily rainfall. Without long‐term studies, wrong conclusions would have been reached based on the first two years. Further, restoring prairies with climate‐matched ecotypes is critical to future ecology, conservation, and sustainability under climate change.     

Flowering time plasticity in Arabidopsis thaliana: a reanalysis of Westerman & Lawrence (1970)

Environmental variation in temperature can have dramatic effects on plant morphology, phenology, and fitness, and for this reason it is important to understand the evolutionary dynamics of phenotypic plasticity in response to temperature. We investigated constraints on the evolution of phenotypic plasticity in response to a temperature gradient in the model plant Arabidopsis thaliana by applying modern analytical tools to the classic data of Westerman & Lawrence (1970). We found significant evidence for two types of constraints. First, we detected numerous significant genetic correlations between plastic responses to temperature and the mean value of a trait across all environments, which differed qualitatively in pattern between the set of ecotypes and the set of mutant lines in the original sample. Secondly, we detected significant costs of flowering time plasticity in two of the three experimental environments, and a net pattern of selection against flowering time plasticity in the experiment overall. Thus, when explored with contemporary methods, the prescient work of Westerman & Lawrence (1970) provides new insights about evolutionary constraints on the evolution of plasticity.     

Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass <Emphasis Type="Italic">Spartina densiflora</Emphasis>

Salinity and tidal inundation induce physiological stress in vascular plant species and influence their distribution and productivity in estuarine wetlands. Climate change-induced sea level rise may magnify these abiotic stressors and the physiological stresses they can cause. Understanding the potential of invasive plants to respond to predicted salinity increases will elucidate their potential niche breadth. To examine potential phenotypic plasticity and functional trait responses to salinity stress in the invasive cordgrass Spartina densiflora, we collected rhizomes from four invasive populations occurring from California to Vancouver Island, British Columbia on the Pacific Coast of North America. In a glasshouse common garden experiment, we measured plant traits associated with growth and allocation, photosynthesis, leaf pigments, and leaf chemistry and calculated plasticity indices across imposed salinity treatments. Fifteen of 21 leaf chemistry, pigment, morphological and physiological traits expressed plastic responses to salinity. When averaged across all measured traits, degree of plasticity did not vary among sampled populations. However, differences in plasticity among populations in response to salinity were observed for 9 of 21 measured plant traits. Leaf chemistry and adaxial leaf rolling trait responses demonstrated the highest degree of plasticity, while growth and allocation measures were less plastic. Phenotypic plasticity of leaf functional traits to salinity indicates the potential of S. densiflora to maintain invasive growth in response to rising estuarine salinity with climate change.     

Phenotypic plasticity in rice: responses to fertilization and inoculation with arbuscular mycorrhizal fungi

Aims Changes in the phenotype of crops (phenotypic plasticity) are known to play an important role in determining responses to nutrient availability, with the direction and magnitude of plasticity of individual traits being crucial for grain yields. Our study analysed the direction, magnitude and hierarchy of plastic responses of yield-related traits (i.e. biomass allocation and yield components) of rice (Oryza sativa L.) to nutrient availability. We estimated the effect of inoculation with arbuscular mycorrhizal fungi (AMF) on these characteristics of phenotypic plasticity.Methods A field experiment was carried out in northeast China, providing rice with six NPK fertilizer levels with or without inoculation with Glomus mosseae. At maturity, we quantified biomass allocation traits (shoot:root ratio and panicle:shoot ratio) and yield component traits (panicle number per hill, spikelet number per panicle, percentage of filled spikelets and seed weight). We also assessed the direction of change in each trait and the magnitude of trait plasticity.Important findings In non-inoculated plants, we found that biomass allocation and seed-number traits (i.e. panicle number per hill, spikelet number per panicle and percentage of filled spikelets) responded to fertilization in the same direction, increasing with rising fertilization. Panicle formation was the most plastic trait, while seed mass was the least plastic trait. AMF inoculation nullified the relationship between most biomass allocation and seed-number traits (except for that between panicle:shoot ratio and the percentage of filled spikelets) but increased the magnitude of plasticity in biomass allocation traits without altering the hierarchy of traits' plasticity. These results underscore the importance of plasticity of yield-related traits per se, and the impact of AMF on plasticity, for maintaining rice yields under low fertilization regimes.