The Effect of Phosphorus Reduction and Competition on Invasive Lemnids: Life Traits and Nutrient Uptake

Joëlle Gérard,Ludwig Triest

doi:10.1155/2014/514294

Abstract

Introduction of invasive macrophytes often leads to competition with native species or with already established invasive species. Competition between invasive species in multiple-invaded systems is expected to be particularly high, especially when they share growth form and position in the water column. We performed indoor experiments between invasive free-floating Lemna minuta and Landoltia punctata in monocultures and mixtures under a phosphorus gradient concurring with hypereutrophic, eutrophic, mesotrophic, and oligotrophic conditions. Our results showed that a phosphorus reduction from hypereutrophic to eutrophic had important negative impacts on the relative growth rate (RGR) of both species. A further reduction to mesotrophic condition did not alter either species RGR. However, species strategies and nutrient uptake differed. Both intra- and interspecific interference occurred; however, the intensity differed between phosphorus concentrations. Difference in RGR (RGRD) showed L. minuta to gain at high phosphorus levels, while a reduction favoured L. punctata. In oligotrophic condition, either species hardly produced new daughter fronds. Our results are useful to (1) understand the effects of phosphorus and setting target values in the process of eutrophication reduction and (2) diminish the impacts of invasive lemnids since a water column phosphorus reduction would prevent large impacts.

Highlights

In the last 100 years, a variety of invasive aquatic plants have been introduced to Europe due to increasing travel and trade [1]
Our results showed that a phosphorus reduction from hypereutrophic to eutrophic had important negative impacts on the relative growth rate (RGR) of both species
Difference in RGR (RGRD) showed L. minuta to gain at high phosphorus levels, while a reduction favoured L. punctata

Summary

Introduction

In the last 100 years, a variety of invasive aquatic plants have been introduced to Europe due to increasing travel and trade [1]. These introductions often lead to competitive interactions with native species and with already established alien species [2]. Eutrophication of aquatic ecosystems is a second major threat to freshwater biodiversity It plays an important facilitating role in the invasion process [7, 8], since it can increase the invasibility of water bodies [9] and change the competitive balance between plant species leading to changes in species composition [10]. P is delivered to aquatic ecosystems as a mixture of these forms, but aquatic plants only take up P in inorganic form, primarily as orthophosphate [13]

Methods

Results

Discussion

Conclusion