Interactive effects of light and snail herbivory rather than nutrient loading determine early establishment of submerged macrophytes

Abstract

Submerged macrophytes play a key role in maintaining a clear‐water phase and promoting biodiversity in shallow aquatic ecosystems. Since their abundance has declined globally due to anthropogenic activities, it is important to include them in aquatic ecosystem restoration programs. Macrophytes establishment in early spring is crucial for the subsequent growth of other warm‐adapted macrophytes. However, factors affecting this early establishment of submerged macrophytes have not been fully explored yet. Here, we conducted an outdoor experiment from winter to early spring using the submerged macrophytes Potamogeton crispus and Vallisneria spinulosa to study the effects of shading, nutrient loading, snail herbivory (Radix swinhoei), and their interactions on the early growth and stoichiometric characteristics of macrophytes. The results show that the effects strongly depend on macrophyte species. Biomass and number of shoots of P. crispus decreased, and internode length increased during low light conditions, but were not affected by nutrient loading. P. crispus shoot biomass and number showed hump‐shaped responses to increased snail biomass under full light. In contrast, the biomass of the plant linearly decreased with snail biomass under low light. This indicates an interaction of light with snail herbivory. Since snails prefer grazing on periphyton over macrophytes, a low density of snails promoted growth of P. crispus by removing periphyton competition, while herbivory on the macrophyte increased during a high density of snails. The growth of V. spinulosa was not affected by any of the factors, probably because of growth limitation by low temperature. Our study demonstrates that the interaction of light with snail herbivory may affect establishment and growth of submerged macrophytes in early spring. Macrophyte restoration projects may thus benefit from lowering water levels to increase light availability and making smart use of cold‐adapted herbivores to reduce light competition with periphyton.

Effects of Interactions between Light Intensity and Total Sediment Organic Matter Load on the Submerged Macrophyte Vallisneria natans

“…Understanding the responses of submerged macrophytes to environmental factors is essential for their successful restoration. However, previous studies have insufficiently revealed the effects of the interactions between multiple environmental factors [15,[17][18][19][20][21]. In this study, we investigated the interactions and the mechanisms by which light intensity and SOM load affect submerged macrophyte growth.…”

“…Light intensity and sediment organic matter (SOM) load are environmental factors that affect submerged macrophyte growth. Previous studies have established that light intensity is the primary factor that affects submerged macrophyte growth, as well as water depth, turbidity, number of epiphytes, total suspended matter, and chlorophyll concentration, which indirectly affect plant growth and distribution by influencing the light intensity available to the submerged macrophytes [15,[17][18][19]. As in terrestrial plants with root systems, the growth of submerged macrophytes is undoubtedly influenced by the physicochemical properties of the sediment.…”