Macrophytes moderate the taxonomic and functional composition of phytoplankton assemblages during a nutrient loading experiment

Abstract

Ponds and shallow lakes are sensitive to eutrophication, which often increases turbidity and produces toxic algal blooms. Previous research has found that the presence of macrophytes in shallow water bodies can mitigate the effects of nutrient loading by promoting water clarity and inhibiting phytoplankton growth. However, there is still little known about how macrophyte abundance modifies the response of phytoplankton taxonomic assemblages, particularly their functional composition, to nutrient loading. We investigated how macrophyte abundance altered phytoplankton assemblages using experimental ponds that were treated with a nutrient press. Natural communities of phytoplankton, zooplankton, and fish were seeded in ponds with one of three levels of macrophyte abundance that received weekly nutrient additions. A total of nine ponds (each treatment in triplicate) were monitored for 76 days. Analyses of Shannon's diversity and functional dispersion revealed significant variation in phytoplankton assemblage composition among macrophyte treatments and through time. Phytoplankton biovolume, community metrics, and the dominant traits were generally more stable in the high macrophyte treatment ponds. Although nutrient loading did not induce a regime change to a turbid, phytoplankton‐dominated state, phytoplankton assemblages did shift to a dominance of larger, inedible taxa and metaphyton became more abundant in ponds with macrophytes and zooplankton assemblages shifted to smaller species. Our study demonstrates how functional traits and functional diversity metrics can provide richer insights into the dynamics and causes of shifts in shallow freshwater ecosystems. Macrophyte densities clearly played a significant role in shaping phytoplankton assemblages. Based on the functional traits of phytoplankton distinguished among treatments, we inferred that competition for light, grazing, and, probably, allelochemicals were mechanisms through which macrophytes mediated changes in phytoplankton assemblages.

The combined effects of filter-feeding bivalves (Cristaria plicata) and submerged macrophytes (Hydrilla verticillate) on phytoplankton assemblages in nutrient-enriched freshwater mesocosms

“…The submerged macrophyte H. verticillate , has been reported to produce and release allelochemicals that has inhibitory effects on Chlorella cell membrane ( Zhang et al., 2012 ) and cyanobacteria ( Wang et al., 2006 ; Gao et al., 2011 ). Over 32 days, SMs suppressed overall cyanobacteria biomass ( Table 2 ), concurring with findings from other experimental studies ( Lürling et al., 2006 ; Barrow et al., 2019 ; Amorim and Moura, 2020 ). Further, factors such as light and nutrient competition likely interacted with allelopathic controls in the mesocosms and led to the competitive exclusion of cyanobacteria.…”

“…In addition, SMs can facilitate nutrient uptake from the water column and sediment ( Sand-Jensen and Borum, 1991 ) and reduce sediment resuspension ( Horppila and Nurminen, 2003 ). Earlier studies involving small-scale experiments ( Barrow et al., 2019 ; Amorim and Moura, 2020 ) and natural aquatic ecosystems ( Chao et al., 2022 ; Peng et al., 2022 ) have repeatedly reported that the restoration of SMs decreases the phytoplankton abundance and increases water clarity. Thus, usage of SMs is a prospective tool for the elimination of algal blooms ( Jeppesen et al., 2007b ).…”

Optimization of Combined Submerged Macrophyte Planting Conditions for Inhibiting Algae by Response Surface Methodology

“…H. verticillata has a competitive advantage in shading, as the light crowns form rapidly. It can also reproduce readily via fragmentation and tubers, which increases its ability to uptake nutrients [38][39][40]. Thus, it can control algal biomass by limiting the external conditions required for algal growth [7].…”

Responses of Functional and Taxonomic Phytoplankton Diversity to Environmental Gradients in Subtropical and Tropical Reservoirs

“…The functional phytoplankton composition based on biovolume changed more than 200 km downstream in a tropical river, suggesting that damming can filter species by their traits Graco-Roza et al (2020). An experimental study (Barrow et al, 2019) showed the influence of the macrophyte abundance in shaping phytoplankton functional diversity, based on density/biovolume; it indicated that competition for light, grazing, and probably, allelochemicals were mechanisms through which macrophytes mediated changes in the phytoplankton community. A recent experimental study accessed the relative effects of spatial overlap, grazing, and the physical environment on multiple dimensions of phytoplankton diversity (functional and taxonomical).…”