Abstract

Freshwater ecosystems are increasingly threatened by interacting anthropogenic stressors such as nutrient enrichment and pollution, which can alter water chemistry and disrupt aquatic communities. In such environments, positive species interactions may help buffer the effects of environmental stress by modifying local abiotic conditions. Aquatic macrophytes, including duckweed (Lemnaceae), can influence physicochemical properties of freshwater systems through nutrient uptake and metabolic processes, potentially affecting other organisms inhabiting the same environment. Despite the extensive study of duckweed for applications such as bioremediation and biofuel, its indirect ecological effects on co-occurring organisms remain poorly understood. Whether duckweed influences the growth performance of aquatic insect larvae through modifications of water chemistry has not previously been tested. To address this, three laboratory experiments were conducted to examine how duckweed (Lemna minor) influences the growth of damselfly larvae (Ischnura verticalis) under different environmental conditions. The first experiment tested the effect of duckweed on pH, dissolved oxygen, and conductivity of the water. The second experiment examined how feeding (artemia input) influenced these parameters. The third experiment tested the effect of duckweed on larval growth and survival under different temperature and water trophic status. Overall, duckweed had a positive effect on larval growth and no effect on survival. The effect of duckweed on water chemistry parameters was stronger under significant organic matter input (feeding). These findings highlight the importance of considering indirect species interactions in freshwater ecosystems and suggest that the ecological effects of duckweed may depend strongly on environmental context.