Competitive Interactions of Flowering Rush (Butomus umbellatus L.) Cytotypes in Submersed and Emergent Experimental Aquatic Plant Communities

Nathan E Harms

doi:10.3390/d12010040

Abstract

The ability to invade communities in a variety of habitats (e.g., along a depth gradient) may facilitate establishment and spread of invasive plants, but how multiple lineages of a species perform under varying conditions is understudied. A series of greenhouse common garden experiments were conducted in which six diploid and four triploid populations of the aquatic invasive plant Butomus umbellatus L. (Butomaceae) were grown in submersed or emergent conditions, in monoculture or in a multispecies community, to compare establishment and productivity of cytotypes under competition. Diploid biomass overall was 12 times higher than triploids in the submersed experiment and three times higher in the emergent experiment. Diploid shoot:root ratio was double that of triploid plants in submersed conditions overall, and double in emergent conditions in monoculture. Relative interaction intensities (RII) indicated that triploid plants were sixteen times more negatively impacted by competition under submersed conditions but diploid plants were twice as impacted under emergent conditions. Recipient communities were similarly negatively impacted by B. umbellatus cytotypes. This study supports the idea that diploid and triploid B. umbellatus plants are equally capable of invading emergent communities, but that diploid plants may be better adapted for invading in submersed habitats. However, consistently lower shoot:root ratios in both monoculture and in communities suggests that triploid plants may be better-adapted competitors in the long term due to increased resource allocation to roots. This represents the first examination into the role of cytotype and habitat on competitive interactions of B. umbellatus.

Highlights

IntroductionAquatic invasive species generate environmental and economic harm through their negative impacts on navigation [1], angling [2,3], water supply and alteration of historical hydrology [4], increased sedimentation [5], reduced habitat quality for wildlife [6,7], property values [8], and displacement of native species [1]
Aquatic invasive species generate environmental and economic harm through their negative impacts on navigation [1], angling [2,3], water supply and alteration of historical hydrology [4], increased sedimentation [5], reduced habitat quality for wildlife [6,7], property values [8], and displacement of native species [1]. Many of these impacts are expected to increase in the future with climate change [9,10]. Given their negative impacts on economies and environments, considerable and high-profile focus has been placed on quantifying such impacts [2,9,11,12], predicting future invaders through development of trait-based frameworks [13,14,15,16], preventing establishment and subsequent impacts through policy and regulatory actions [17,18,19], and developing effective management to contain or reverse negative impacts in recipient communities [20,21,22,23]
Butomus umbellatus colonizes a variety of wetland and aquatic habitats including shallow wetlands, slow-moving rivers, large reservoirs, ponds, and roadside ditches [60,61,62]

Summary

Introduction

Aquatic invasive species generate environmental and economic harm through their negative impacts on navigation [1], angling [2,3], water supply and alteration of historical hydrology [4], increased sedimentation [5], reduced habitat quality for wildlife [6,7], property values [8], and displacement of native species [1] Many of these impacts are expected to increase in the future with climate change [9,10]. Resident plant species can reduce the likelihood of plant invader success through direct or indirect competition, or spillover of herbivores or disease [31,32] Community characteristics such as species composition, functional and/or phylogenetic similarity or difference, diversity, productivity, and resident competitive traits may all be important in preventing or limiting negative impacts by plant invaders [28,33,34,35,36]. Spatial heterogeneity in biotic resistance may be considerable if the invader is phenotypically plastic in response to environmental conditions or potential competitors or natural enemies vary at multiple spatial scales [24,39,40,41,42]

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