Abstract

Two submerged Elodea species have small differences in their ecophysiological responses when exposed to individual environmental factors. However, field observations showed that under eutrophic conditions with low light availability, Elodea canadensis could be displaced by Elodea nuttallii. Here we investigated the combined effect of environmental factors on the ecophysiological response of the two species in order to explain the differences in their invasion successes. We cultivated the plants in aquaria containing five different nitrogen (N) concentrations and incubated at five different light intensities. For both species increasing nitrogen concentrations resulted in increased relative growth rate, chlorophyll concentration, and actual photochemical efficiency of photosystem II (ΦPSII), however, they produced less roots. Lowering light intensity resulted in a lower relative growth rate, root production, and nutrient removal. In contrast, chlorophyll concentration in the leaves, and ΦPSII increased. The main difference between the two Elodea species was that the light compensation point (Ic) and weight loss in the dark were significantly higher and photochemical efficiency and chlorophyll concentration were significantly lower for E. canadensis than for E. nuttallii, indicating that the latter can survive under much more shady and hypertrophic conditions. The change in nitrogen concentration of the media and in tissue concentration of the plants indicated that E. nuttallii has a higher nitrogen removal capacity. The ecophysiological differences between the two species can be an explanation for invasion success of E. nuttallii over E. canadensis and thus may explain why the latter is replaced by the first.

Highlights

  • Light and nutrient availability are key factors governing the distribution and growth of submerged macrophytes in aquatic ecosystems (Chambers, 1987; Chambers and Kalff, 1987; Best et al, 2001)

  • Growth seemed to be saturated above 80 μmol m−2 s−1 for E. nuttallii at all N concentrations except for the lowest one, and in contrast, light stimulated the growth of E. canadensis up to the highest light intensity (180 μmol m−2 s−1)

  • The relative growth rate (RGR) measured at the highest light intensity was significantly higher for E. canadensis than for E. nuttallii (MD 0.025 ± 0.002 Pairwise comparisons P < 0.001)

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Summary

Introduction

Light and nutrient availability are key factors governing the distribution and growth of submerged macrophytes in aquatic ecosystems (Chambers, 1987; Chambers and Kalff, 1987; Best et al, 2001). Rooted submerged plants grow under relatively low light conditions at the start of the growing season, and their growth is accelerated when temperature rises. Due to their apical elongation, they grow towards the water surface and become exposed to higher light levels which is favorable for photon capture (Kuni, 1982). Eutrophication opens the window of opportunity for submerged macrophytes that have those traits (James et al, 1999) Species with those traits invade new regions where they are more competitive than native species (Vilà and Weiner, 2004; Espinar et al, 2015)

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