Trading offspring for survival: high duckweed cover decreases reproductive potential and stimulates elongation in the submerged macrophyte Chara globularis Thuillier

Abstract

Compact blankets of free-floating plants generate stressful aquatic environments. The response of submerged macrophytes remains largely elusive. Will they rush toward the light or rather speed up reproductive efforts and escape using propagules—the macrophyte equivalent of lifeboats? We studied the effects of complete duckweed (Lemna minor) cover on growth and reproductive fitness of macroalga Chara globularis in a pond mesocosm experiment. C. globularis growing in Lemna-covered plots lost biomass and developed longer internodes, indicating an elongative reflex to escape stress. Densities of reproductive organs per biomass unit evolved positively in open plots and negatively in covered plots, suggesting a trade-off between reproductive effort and vegetative elongation. Reproductive potential correlated significantly with incident radiation. Lemna cover, however, did not affect oospore rain—at least within the limited time span of propagule trapping. C. globularis thus displayed an ability to modify phenology in response to floating plant stress, allocating resources to internodes instead of gametangia. Nevertheless, duckweed dominance clearly suppressed the overall reproductive performance of C. globularis. The regenerative capacity of many submerged macrophytes will likely suffer from increased floating plant dominance due to global warming—unless efforts are made to reduce nutrient levels in vulnerable waterbodies.

Loring Pond Duckweed Abundance and Diversity Assessment Via By-Catch of Surface Skimming, and Suitability of Compost for Organic Gardens

“…Total Phosphorus concentration decreased slightly, and dissolved oxygen increased by 1019% from pre-removal period (Ronkainen, 2021). A study that focused on Chara globularis, a common, eutrophication-tolerant macroalga, found L. minor domination to inhibit growth of C. globularis and potentially lead to a gradual decline of its overall population (Van Onsem et al ., 2021).…”

Changing phenology of benthic primary producers in inland waters: Current knowledge and future directions

“…2e), notably through interspecific competition for light. For example, shading by the free‐floating duckweed in a mesocosm experiment modified submerged charophyte morphology and decreased reproductive capacity, resulting in an earlier peak of reproductive organ density (Van Onsem and Triest 2021). Conversely, increased light availability through changes in riparian vegetation canopy associated with stochastic weather events explained an increase in gross primary production by macroalgae in streams altering the overall growing season (Roberts et al 2007; Mulholland et al 2009).…”