Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass Spartina densiflora

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

Trait responses of invasive aquatic macrophyte congeners: colonizing diploid outperforms polyploid

Understanding traits underlying colonization and niche breadth of invasive plants is key to developing sustainable management solutions to curtail invasions at the establishment phase, when efforts are often most effective. The aim of this study was to evaluate how two invasive congeners differing in ploidy respond to high and low resource availability following establishment from asexual fragments. Because polyploids are expected to have wider niche breadths than diploid ancestors, we predicted that a decaploid species would have superior ability to maximize resource uptake and use, and outperform a diploid congener when colonizing environments with contrasting light and nutrient availability. A mesocosm experiment was designed to test the main and interactive effects of ploidy (diploid and decaploid) and soil nutrient availability (low and high) nested within light environments (shade and sun) of two invasive aquatic plant congeners. Counter to our predictions, the diploid congener outperformed the decaploid in the early stage of growth. Although growth was similar and low in the cytotypes at low nutrient availability, the diploid species had much higher growth rate and biomass accumulation than the polyploid with nutrient enrichment, irrespective of light environment. Our results also revealed extreme differences in time to anthesis between the cytotypes. The rapid growth and earlier flowering of the diploid congener relative to the decaploid congener represent alternate strategies for establishment and success

Demography

Demographic data and calculated variables

Data from: Spatial pattern and scale influence invader demographic response to simulated precipitation change in an annual grassland community

It is important to predict which invasive species will benefit from future changes in climate, and thereby identify those invaders that need particular attention and prioritization of management efforts. Because establishment, persistence, and spread determine invasion success, this prediction requires detailed demographic information. Explicit study of the impact of pattern on demographic response is particularly important for species that are naturally patchy, such as the invasive grass, Aegilops triuncialis. In the northern California Coast Range, where climate change may increase or decrease mean annual rainfall, we conducted a field experiment to understand the interaction of climate change and local-scale patterning on the demography of A. triuncialis. We manipulated precipitation (reduced, ambient, or augmented), seed density, and seeding pattern. Demographic and environmental data were collected for three years following initial seeding. Pattern and scale figure prominently in the demographic response of A. triuncialis to precipitation manipulation. Pattern interacts with precipitation and seeding density in its influence on per-plant seed output. Although per-plot seed production was highest when seeds were not aggregated, per-plant seed output was higher in aggregated patches. Results suggest aggregation of invasive A. triuncialis reduces the detrimental impact of interspecific competition in its invaded community, and that interspecific competition per se has a stronger impact than intraspecific competitio

WaterContent

Volumetric water conten

Demographic response of <i>Aegilops triuncialis</i>.

<p>Mean (±SE) A) spikelet number per adult individual plant, B) spikelet number per treatment cell, and C) spikelet number per treatment sub-plot grouped by precipitation treatment, seeding density (low or high), and seeding pattern (non-aggregated or aggregated).</p

Mean (±SE) estimated net reproductive rate of <i>Aegilops triuncialis</i> grouped by year and seeding pattern (non-aggregated or aggregated).

<p>Mean (±SE) estimated net reproductive rate of <i>Aegilops triuncialis</i> grouped by year and seeding pattern (non-aggregated or aggregated).</p

Diagram of experimental seeding pattern and density.

<p>A) The aggregated (checkerboard) pattern seed distribution treatment in a 1 m × 1 m subplot. Each stippled cell represents seeding locations of <i>Aegilops triuncialis</i>. Cells labeled A-C represent sub-sample locations. B) Local densities in each treatment cell for low and high density seeding rates applied without pattern (“Non-agg”) or with pattern (“Agg”).</p

Results from a MANOVA, followed by protected repeated measure general linear models for five demographic response variables in <i>Aegilops triuncialis</i>: number of spikelets per plant (A), coefficient of variation for spikelets per plant (B), number of spikelets produced per cell (C), number of spikelets produced per sub-plot (D), net population growth rate (E).

<p>Results from a MANOVA, followed by protected repeated measure general linear models for five demographic response variables in <i>Aegilops triuncialis</i>: number of spikelets per plant (A), coefficient of variation for spikelets per plant (B), number of spikelets produced per cell (C), number of spikelets produced per sub-plot (D), net population growth rate (E).</p

Results from a repeated measure GLM for soil water content (%).

<p>Results from a repeated measure GLM for soil water content (%).</p