Sediment-rooting affects growth and biomass allocation in Myriophyllum spicatum under varying growth conditions

Abstract

Abstract Myriophyllum spicatum L. is a widely distributed submerged aquatic plant species, which became a model species for different test systems using either unrooted or sediment-rooted plants. Here, we tested the response of unrooted and sediment-rooted M. spicatum to different combinations of temperature, light and CO2 conditions, respectively. Overall, the relative growth rates of rooted plants were higher than for unrooted plants, with sediment-rooted plants showing a stronger growth response to varying growth conditions. Relative growth rates based on dry mass and fresh mass strongly differed due to differences in dry matter contents. M. spicatum showed increased branching under elevated CO2 and high light conditions. Sediment-rooting caused higher biomass allocation to roots, but lower allocation to stems and leaves. The dry matter contents were higher in unrooted than in rooted plants and increased with increasing CO2 and light availability, while temperature had only a minor effect. Chlorophyll contents decreased with increasing dry matter contents, and were reduced under both high CO2 and high light conditions. We conclude that the responses to varying growth conditions should be considered in test systems using M. spicatum. Moreover, the selection of the analyzed growth parameters can strongly influence the outcome of studies. We further recommend that the growth conditions must be controlled, particularly the pH, which often change due to the photosynthetic carbon uptake of the plants.