Phenotypic plasticity in response to mechanical stress: hydrodynamic performance and fitness of four aquatic plant species

Abstract

Summary• Plastic responses of plants exposed to mechanical stress can lead to modified, performance-enhancing, morphologies, sometimes accompanied by costs to reproduction. The capacity to present short-term plastic responses to current stress, the resulting performance (expected lower mechanical forces), and the costs of such responses to reproduction were tested for four aquatic plant species.• Two ramets of the same genet were submitted to running vs standing water treatment. Traits describing the morphology, hydrodynamic performance and reproduction (sexual and vegetative) were measured.• For one species, plastic responses led to reduced hydrodynamic forces, without apparent costs to reproduction, indicating that the plastic response could be beneficial for plant maintenance in stressful habitats. For two species, plastic responses were not associated with variations in performance and reproduction, possibly because of the low hydrodynamic forces experienced, even for morphologies produced under standing conditions. For one species, plastic responses were associated with a sharp decrease in sexual reproduction, without variations in performance, revealing the negative impact of currents over a short time scale.• Species maintenance is linked to the capacity of individuals to tolerate mechanical forces. The contrasting responses to currents may be a key element for predicting community dynamics.

Plant resistance to mechanical stress: evidence of an avoidance–tolerance trade‐off

“…Whether this correlation is observed across species of other plants, and particularly terrestrial ones, remains to be seen. On the individual scale, plastic responses to mechanical stress (thigmomorphogenesis) can result in improved avoidance or tolerance (Puijalon et al, 2008) and it is possible that these responses are constrained by the same negative correlation identified in the present study for aquatic plants (i.e. enhanced avoidance ability is balanced by reduced tolerance and vice versa).…”

“…In the present study, both avoidance and tolerance may incur significant costs. The principal traits underlying avoidance are a reduced area exposed to flow, a streamlined canopy and a high capacity for reconfiguration (Sand-Jensen, 2003;Puijalon et al, 2005Puijalon et al, , 2008. Small-sized or stunted morphologies leading to reduced area may incur direct costs because various components of plant fitness are positively related to plant size (Shipley & Dion, 1992).…”

“…A small area can be achieved either through the production of a small growth form or through reconfiguration, at high fluid velocity, of the canopy in a compact form (Speck, 2003;Rudnicki et al, 2004;Puijalon et al, 2005). The main traits that reduce the force encountered for a given area are linked to the shape of the stems and leaves and, more generally, of the canopy (for example, its streamlining; Telewski & Jaffe, 1986b;Sand-Jensen, 2003;Puijalon et al, 2008). Concerning tolerance, the force required to break a plant structure (e.g.…”

“…Avoidance entails traits that enable plants to resist adverse conditions by preventing the deleterious effects of these conditions whereas tolerance consists in traits that enable plants to endure adverse conditions (Fitter & Hay, 2002;Schulze et al, 2005). In the case of exposure to mechanical forces, plant resistance relies either New Phytologist Research on minimizing the forces encountered, which by analogy can be regarded as an avoidance strategy, or on maximizing their resistance to breakage, which can be regarded as a tolerance strategy (Puijalon et al, 2008). The magnitude of the mechanical forces encountered by plants exposed to moving fluids (air or water) depends on several parameters, some of them being linked to plant morphology, particularly size and shape (Fig.…”

Fertile sediment and ammonium enrichment decrease the growth and biomechanical strength of submersed macrophyte Myriophyllum spicatum in an experiment

“…Moreover, submersed macrophytes under high-nutrient stress have small size, i.e. shorter shoots and fewer branches, which suggests a reduction in hydraulic forces encountered by plants (Schutten et al, 2004;Puijalon et al, 2005Puijalon et al, , 2008. Finally, nutrient availability regulates root biomass and morphology (Linkohr et al, 2002), and thus changes root anchorage strength (Schutten et al, 2004(Schutten et al, , 2005Puijalon et al, 2005).…”