Phytoplankton Community Stability Across Eutrophic Gradients: Insights From Annual and Monthly Timescales

ABSTRACT Exploring the response of natural community stability to anthropogenic environmental changes, such as eutrophication, is an important topic in current ecological research. Eutrophication directly affects species dynamics, abundance and succession in phytoplankton communities, potentially leading to shifts in ecological processes in these communities over multiple years. However, it remains unclear how the annual and monthly dynamics of phytoplankton communities shift along eutrophication gradients to maintain stability. We conducted an 8‐year survey in a large shallow lake, where the entire area exhibited a gradient of eutrophication. Using this dataset, we analysed three dynamic characteristics of phytoplankton communities: biomass stability (BS), composition stability (CS) and species rank‐abundance curve change (Curve_change). These variables were analysed at annual (from 2014 to 2021, with annual data collected at each sampling site) and monthly (extending to 96 months within the same period, with monthly data) scales to examine how they changed in response to the eutrophication gradient. Annual and monthly BS was only slightly affected by the eutrophication gradient, whereas monthly composition stability and changes in species rank‐abundance curves were significantly altered. BS correlated positively with CS but negatively with changes in the species rank‐abundance curve. This indicates that phytoplankton can maintain BS through specific adjustments in community structure over shorter timescales, with distinct mechanisms operating across the eutrophication gradient. At high nutrient concentrations, this stability is associated with shifts in the relative abundance of non‐dominant species, which buffer fluctuations in dominant species abundances and ensure functional redundancy. In contrast, at relatively low‐nutrient concentrations, BS is achieved through compensatory dynamics among dominant species, where declines in one species are offset by increases in another with similar ecological functions. However, this internal regulatory mechanism is less evident over longer timescales. These findings highlight the importance of timescales in studying the impact of eutrophication on phytoplankton community stability, providing important clues for assessing and predicting the response of lake ecosystems to future environmental changes.