How Past and Present Influence the Foraging of Clonal Plants?

Clonal plants spreading horizontally and forming a network structure of ramets exhibit complex growth patterns to maximize resource uptake from the environment. They respond to spatial heterogeneity by changing their internode length or branching frequency. Ramets definitively root in the soil but stay interconnected for a varying period of time thus allowing an exchange of spatial and temporal information. We quantified the foraging response of clonal plants depending on the local soil quality sampled by the rooting ramet (i.e. the present information) and the resource variability sampled by the older ramets (i.e. the past information). We demonstrated that two related species, Potentilla reptans and P. anserina, responded similarly to the local quality of their environment by decreasing their internode length in response to nutrient-rich soil. Only P. reptans responded to resource variability by decreasing its internode length. In both species, the experience acquired by older ramets influenced the plastic response of new rooted ramets: the internode length between ramets depended not only on the soil quality locally sampled but also on the soil quality previously sampled by older ramets. We quantified the effect of the information perceived at different time and space on the foraging behavior of clonal plants by showing a non-linear response of the ramet rooting in the soil of a given quality. These data suggest that the decision to grow a stolon or to root a ramet at a given distance from the older ramet results from the integration of the past and present information about the richness and the variability of the environment

Can Land Managers Control Japanese Knotweed? Lessons from Control Tests in Belgium

Japanese knotweed Fallopia japonica is an extremely abundant invasive plant in Belgium and surrounding countries. To date, no eradication method is available for land managers facing the invasion of this rhizomatous plant. We tested different chemical herbicides with two application methods (spraying and stem injection), as well as mechanical treatments, on knotweed clones throughout southern Belgium. The tested control methods were selected to be potentially usable by managers, e.g., using legally accepted rates for herbicides. Stem volume, height and density reduction were assessed after one or two years, depending on the control method. Labor estimations were made for each control method. No tested control method completely eradicated the clones. Stem injection with glyphosate-based herbicide (3.6 kg ha-1 of acid equivalent glyphosate) caused the most damage, i.e., no sprouting shoots were observed the year following the injection. The following year, though, stunted shoots appeared. Among the mechanical control methods, repeated cuts combined with native tree transplanting most appreciably reduced knotweed development. The most efficient methods we tested could curb knotweed invasion, but are not likely to be effective in eradicating the species. As such, they should be included in a more integrated restoration strategy, together with prevention and public awareness campaigns

Extensive physiological integration in Carex arenaria and Carex disticha in relation to potassium and water availability

Physiological integration between ramets is beneficial when acquiring heterogeneously distributed resources, and is hypothesized to occur when the benefits of resource sharing outweigh the costs. Our aim was to investigate if resource availability affected physiological integration in Carex arenaria and Carex disticha. Ramet systems were grown in high potassium and high water (K+ W+), high K and low water (K+ W-), or low K and high water (K- W+) for 1 month. Thereafter, water and K transport were traced with erythrosin and rubidium, respectively. Carex arenaria and C. disticha transported erythrosin over seven ramet generations and rubidium throughout the whole ramet system, but C. arenaria exported 20% more rubidium from the labelled shoot than C. disticha. A detailed analysis of subset of plants suggested that C. disticha in low K abundance shared more rubidium than in high K abundance, and that C. arenaria ramets in both K+ W- and K- W+ shared more resources than K+ W+ ramets. We demonstrated long-distance resource transport for K and water in C. arenaria and C. disticha. The distance of integration was not affected by resource availability in C. arenaria or C. disticha, but local concentrations of K showed marked and contrasting responses to nutrient and water treatment in both species