Human-induced changes in external nutrient loading affect the phytoplankton community and abundance directly by changing the amount of nutrients available, but also indirectly through changes in the zooplankton (that is, grazer) community structure, mediated in part by changes in the fish community structure and biomass. Such shifts affect the species dynamics and community succession of lake phytoplankton communities, and they may ultimately influence community stability. However, the relative importance of different biotic mechanisms influencing the community stability of phytoplankton along nutrient and associated zooplankton grazing pressure gradients remains unclear. Here, we evaluated the importance of four potential stabilizing biotic metrics—taxon richness, synchrony, community dominance and biomass of phytoplankton to the seasonal stability over two decades of re-oligotrophication in 20 Danish lakes. We found no clear temporal patterns in seasonal stability across lakes but considerable variations in the individual lakes. Total phosphorus (TP) affected the seasonal stability of the phytoplankton communities either directly or indirectly through changes in community dominance. Total nitrogen (TN) influenced the seasonal stability indirectly via changes in phytoplankton taxon richness, synchrony, and community dominance. Grazer richness (that is, zooplankton taxa richness) impacted the seasonal stability indirectly through changes in phytoplankton taxon richness and synchrony. Grazing pressure, using the biomass ratio of zooplankton:phytoplankton as a proxy, had an indirect effect on seasonal stability via changes in synchrony and community dominance. Compensatory dynamics (as indicated by the synchrony of phytoplankton) exerted dominant control of phytoplankton seasonal stability at high TN and high grazer richness and pressure, while the portfolio effect (as indicated by taxon richness) contributed to phytoplankton seasonal stability at low TN and high grazer richness. However, a strongly negative selection effect (as indicated by community dominance of phytoplankton) was observed at high nutrient levels and low grazer richness. Grazer richness and grazing pressure had stronger stabilizing effects on the seasonal succession of the phytoplankton communities than did TP and TN. Our results highlight how various biotic mechanisms (for example, compensatory dynamics and portfolio effect) can change in their importance in maintaining the seasonal stability of phytoplankton communities subjected to nutrient and grazer control.

人为引起的外部养分负荷变化直接通过改变可用养分的数量来影响浮游植物群落和丰度，但也间接地通过浮游动物（即放牧者）群落结构的变化而间接地影响，而浮游动物（即放牧者）的群落结构的变化部分是由鱼类群落结构的变化所介导的和生物质。这种变化影响了湖泊浮游植物群落的物种动态和群落演替，最终可能影响群落的稳定性。然而，影响营养物质和相关浮游动物放牧压力梯度的浮游植物群落稳定性的不同生物机制的相对重要性仍然不清楚。在这里，我们评估了四个潜在的稳定生物指标的重要性-紫杉类丰富度，同步性，在20个丹麦湖泊中，浮游植物的群落优势度和浮游生物量在过去20年的再富营养化过程中的季节稳定性。我们发现湖泊之间的季节性稳定性没有明显的时间格局，但各个湖泊之间存在相当大的差异。总磷（TP）通过改变群落优势度直接或间接影响了浮游植物群落的季节稳定性。总氮（TN）通过浮游植物分类单元丰富度，同步性和群落优势度的变化间接影响季节稳定性。Grazer的丰富度（即浮游生物类群的丰富度）通过浮游植物类群丰富度和同步性的变化间接影响了季节的稳定性。以浮游动物：浮游植物的生物量比为代表的放牧压力，通过同步性和社区优势的变化间接影响了季节的稳定性。补偿动力学（如浮游植物的同步性所表明）在高TN，高放牧者丰富度和压力下对浮游植物的季节性稳定性起主要控制作用，而投资组合效应（如分类群丰富度）则在低TN和高放牧者中促进了浮游植物的季节性稳定性。丰富。然而，在高营养水平和低放牧者丰富度下，观察到强烈的负选择作用（如浮游植物的群落优势所表明）。与TP和TN相比，Grazer的丰富度和放牧压力对浮游植物群落的季节演替具有更强的稳定作用。我们的结果强调了各种生物机制（例如，