An increase in population density may result in the spatial and temporal heterogeneity of resources at scales smaller than an individual, inducing different modular responses at different positions of a plant, or architectural plasticity. To better understand how plants respond to density via architectural plasticity, we conducted a field experiment on an annual species, Abutilon theophrasti. Plants were subjected to three densities and harvested at 50 and 70 days, when each individual plant was separated into different layers vertically from bottom to top with an inter‐layer distance of 10 or 20 cm, before we measured a series of traits per layer and analyzed variations in them among layers, densities, and stages. Increased density reduced variation of traits among layers and had different effects on different layers of modular traits: it increased stem mass in the third to fifth layers (L3–L5) and increased stem diameter in the top layer, leading to an increase in stem density in lower layers and a decrease in stem density in the top layer. In addition, there was an increase in petiole length and mass, lamina size, and leaf number in upper layers, while they decreased in lower layers. Results suggested trade‐offs between upper and lower layers in stem density and leaf traits for plants in a dense population, which were important for keeping most leaves at higher positions to acquire light resources, while saving energy, in concert with the effort of extra stem elongation and the complex plasticity in branch traits.
Phenotypic integration and developmental canalization have been hypothesized to constrain the degree of phenotypic plasticity, but there is little evidence for the relationships among the three processes in different environments, especially for plants under natural conditions. To address this issue, we conducted a field experiment by subjecting plants of Abutilon theophrasti to low, medium and high densities, under infertile and fertile soil conditions, measured a variety of traits and analyzed canalization (coefficient of variation [CV]), integration (coefficient of integration [CI] and the number of significant correlations of a trait with other traits [NC]), and plasticity (REL RDPIs and ABS RDPIs) in these traits and their relationships at two stages of plant growth. Our results showed an increase in mean CV, NC and ABS RDPIs of traits with density, and the positive correlations between trait NC and ABS RDPIs became stronger with higher densities but weaker over time in fertile soil, while correlations among trait CV, NC and ABS RDPIs became stronger over time in infertile soil. Results suggested shared or cooperation mechanisms among phenotypic integration, canalization and plasticity. Soil conditions and growth stage may affect responses of these correlations to density via modifying plant size and competition strength. The attenuated canalization and enhanced integration may be helpful for the production of plasticity, especially under intense competition.
Temporally heterogeneous environments may drive rapid and continuous plastic responses, leading to highly variable plasticity in traits. However, direct experimental evidence for such meta‐plasticity due to environmental heterogeneity is rare. Our objective was to investigate the effects of early experience with temporally heterogeneous water availability on the subsequent plasticity of plant species in response to water conditions. We subjected eight plant species from three habitats, four exotic and four native to North America, to initial exposure to either a first round of alternating drought and inundation treatment (Ehet, temporally heterogeneous experience) or a consistently moderate water supply (Ehom, homogeneous experience), and to a second round of drought, moderate watering or inundation treatments. Afterwards the performance in a series of traits of these species, after the first and second rounds of treatments, was measured. Compared with Ehom, Ehet increased final mean total mass of all species considered together but did not affect mean mortality. Ehet relative to Ehom, decreased the initial total mass of native species as a group, but increased the mass of exotic species or species from hydric habitats; Ehet also increased the late growth of natives, but did not for exotics, and increased the late growth of mesic species more than xeric and hydric species. Our results suggest that previous exposure to temporal heterogeneity in water supply may be not beneficial immediately, but can be beneficial for plant growth and response to water stress later in a plant's lifetime. Heterogeneous experiences may not necessarily enhance the degree of plasticity but may improve the expression of plasticity in terms of better performance later, effects of which differ for different groups of species, suggesting species‐specific strategies for dealing with fluctuating abiotic environments. Synthesis. Previous temporally heterogeneous experience can benefits plant growth later in life though modulating the expression of plasticity, leading to adaptive meta‐plasticity. Studies of meta‐plasticity may improve our understanding not only on the importance of variable plasticity in relation to how plants cope with environmental challenges but also on the costs versus benefits of plastic responses and its limits over the long term.
Developmental stability, canalization, and phenotypic plasticity are the most common sources of phenotypic variation, yet comparative studies investigating the relationships between these sources, specifically in plants, are lacking. To investigate the relationships among developmental stability or instability, developmental variability, canalization, and plasticity in plants, we conducted a field experiment with Abutilon theophrasti, by subjecting plants to three densities under infertile vs. fertile soil conditions. We measured the leaf width (leaf size) and calculated fluctuating asymmetry (FA), coefficient of variation within and among individuals (CV intra and CV inter ), and plasticity (PI rel ) in leaf size at days 30, 50, and 70 of plant growth, to analyze the correlations among these variables in response to density and soil conditions, at each of or across all growth stages. Results showed increased density led to lower leaf FA, CV intra , and PI rel and higher CV inter in fertile soil. A positive correlation between FA and PI rel occurred in infertile soil, while correlations between CV inter and PI rel and between CV inter and CV intra were negative at high density and/or in fertile soil, with nonsignificant correlations among them in other cases. Results suggested the complexity of responses of developmental instability, variability, and canalization in leaf size, as well as their relationships, which depend on the strength of stresses. Intense aboveground competition that accelerates the decrease in leaf size (leading to lower plasticity) will be more likely to reduce developmental instability, variability, and canalization in leaf size. Increased developmental instability and intra-and interindividual variability should be advantageous and facilitate adaptive plasticity in less stressful conditions; thus, they are more likely to positively correlate with plasticity, whereas developmental stability and canalization with lower developmental variability should be beneficial for stabilizing plant performance in more stressful conditions, where they tend to have more negative correlations with plasticity.
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