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Phenotypic plasticity enables plants to buffer against environmental stresses and match their phenotypes to local conditions. However, consistent conclusive evidence for adaptive plasticity has only been obtained for a few traits. More studies on a wider variety of plant functional traits and environmental factors are still needed to further understand the adaptive significance of plasticity. We grew 21 genotypes of the stoloniferous clonal plant Duchesnea indica under different light and nutrient conditions, and used selection gradient analyses to test the adaptive value (benefits) of morphological and physiological plasticity responding to variation in light and nutrient availability. Plants grown in shade exhibited lower values for fitness measures (fruit number, ramet number and biomass), shortened thinner internode length and decreased adult leaf chlorophyll content, but higher petiole length, specific leaf area and old leaf chlorophyll content, than plants grown without shade. Plants grown in the low nutrient condition had shorter petiole length, thicker and smaller leaf area, lower chlorophyll content, but higher fruit number and root:shoot ratio than plants grown under the high nutrient condition. Selection gradient analyses revealed that plasticity of petiole length and old leaf chlorophyll content in response to light variation was adaptive, and plasticity of old and adult leaf chlorophyll content in response to nutrient variation was adaptive. Therefore, the adaptive value of plasticity in different traits depends on the specific ecological context. Our findings contribute to understanding the adaptive significance of phenotypic plasticity of clonal plants in response to environmental variation.

Epigenetic mechanisms such as DNA methylation are considered as an important pathway responsible for phenotypic responses and rapid acclimation of plants to different environments. To search for empirical evidence that DNA methylation is implicated in stress-responses of non-model species, we exposed genetically uniform, experimental populations of the wetland clonal plant

Invasive aquatic plants have the potential to threaten ecosystem stability and biodiversity in non-native ranges; it is therefore necessary to prevent and control such invasions. While environmental heterogeneity might drive functional trait variation in plant species across different spatial scales, the drivers of trait variation over a large spatial scale are not well understood for aquatic invasive plants. Understanding functional trait variation across space and potential environmental drivers might improve our understanding of habitable conditions for predicting where an invasive plant species might be found. Here, we studied Hydrocotyle vulgaris (Araliaceae) in Zhejiang Province, China, and propose that environmental spatial heterogeneity might drive functional trait variation of this invasive aquatic plant over a large scale. The investigation was conducted across 99 plots at 7 sites with H. vulgaris. We found significant variation in functional traits over a large scale, and these functional traits were significantly different across a variety of environmental conditions. Specifically, there were significant relationships between environmental factors (i.e. temperature, precipitation, solar radiation, and water vapor pressure) and functional traits, including specific leaf area, interval length, and specific interval length, indicating that spatial environmental heterogeneity might drive the variation in functional traits (especially leaf and clonal traits) of H. vulgaris, over a large spatial scale. Our study thus provides new insights into understanding the invasiveness of H. vulgaris.

The ability to tolerate novel herbivores is widely considered to influence plant invasion success. For clonal plants that have reduced capacity to evolve in response to novel herbivores, legacy effects of herbivory on parental plants might be translated to offspring ramets, resulting in pre-adaptation to tolerate herbivory for new vegetative growth. Using the invasive clonal plant Alternanthera philoxeroides, we first exposed plants to herbivory by Planococcus minor, a widespread and generalist piercing-sucking insect. Herbivory decreased above- and below-ground plant biomass by approximately 50% with a concomitant 134% increase in root N concentration but no changes in concentrations of soluble sugars, starch or non-structural carbohydrates related to herbivory tolerance. Offspring ramets were then exposed to herbivory by three different herbivore species: (1) P. minor, (2) the specialist leaf-beetle Agasicles hygrophila, and (3) the stenophagous tortoise-beetle Cassida piperata. There was no evidence of interactive effects between herbivory on parental plants and herbivory on offspring plants on growth, biomass allocation patterns, or physiological responses, suggesting that pre-adaptation to herbivory did not occur in A. philoxeroides with these herbivores. There were, however, species-specific herbivore tolerance responses. In the offspring generation, herbivory by A. hygrophila strongly suppressed growth and biomass allocation, but patterns were generally weaker for other herbivores. Tolerance effects could be explained by stimulatory effects of grazing by C. piperata and P. minor on taproot biomass along with idiosyncratic increases of starch and non-structural carbohydrate concentration in some storage organs. Our results highlight the importance of A. hygrophila in controlling the aboveground spread of A. philoxeroides. However, herbivory by other species was largely tolerated and accompanied by increased allocation to underground storage organs and altered physiological reserves, both of which could allow this invasive plant to tolerate herbivory and successfully invade new areas in the face of new herbivore pressure.

The evolution of phenotypic plasticity of plant traits may be constrained by costs and limits. However, the precise constraints are still unclear for many traits under different ecological contexts. In a glasshouse experiment, we grew ramets of 12 genotypes of a clonal plant Hydrocotyle vulgaris under the control (full light and no flood), shade and flood conditions and tested the potential costs and limits of plasticity in 13 morphological and physiological traits in response to light availability and flood variation. In particular, we used multiple regression and correlation analyses to evaluate potential plasticity costs, developmental instability costs and developmental range limits of each trait. We detected significant costs of plasticity in specific petiole length and specific leaf area in response to shade under the full light condition and developmental range limits in specific internode length and intercellular CO2 concentration in response to light availability variation. However, we did not observe significant costs or limits of plasticity in any of the 13 traits in response to flood variation. Our results suggest that the evolution of phenotypic plasticity in plant traits can be constrained by costs and limits, but such constraints may be infrequent and differ under different environmental contexts.

Heritable epigenetic modifications may occur in response to environmental variation, further altering phenotypes through gene regulation, without genome sequence changes. However, epigenetic variation in wild plant populations and their correlations with genetic and phenotypic variation remain largely unknown, especially for clonal plants. We investigated genetic, epigenetic and phenotypic variation of ten populations of an introduced clonal herb Hydrocotyle vulgaris in China. Populations of H. vulgaris exhibited extremely low genetic diversity with one genotype exclusively dominant, but significantly higher epigenetic diversity. Both intra- and inter-population epigenetic variation were related to genetic variation. But there was no correlation between intra-/inter-population genetic variation and phenotypic variation. When genetic variation was controlled, intra-population epigenetic diversity was related to petiole length, specific leaf area, and leaf area variation, while inter-population epigenetic distance was correlated with leaf area differentiation. Our study provides empirical evidence that even though epigenetic variation is partly under genetic control, it could also independently play a role in shaping plant phenotypes, possibly serving as a pathway to accelerate evolution of clonal plant populations.