Abstract
The shifts among bloom-forming cyanobacteria have attracted increasing attention due to the reductions in nitrogen and phosphorus during the eutrophication mitigation process. However, knowledge is limited regarding the pattern and drivers of the shifts among these cyanobacterial genera. In this study, we performed a 7-year long, monthly investigation in Lake Chaohu, to analyze the interannual and seasonal shifts between Microcystis and Dolichospermum. Our results showed that Microcystis was the dominant cyanobacterium in the western lake region in summer, whereas Dolichospermum was dominant in the other regions and seasons. The Microcystis biomass and ratio were driven primarily by total phosphorus and temperature. The sensitivity of Dolichospermum to nutrients and temperature was relatively weak compared to that of Microcystis. The shifts between Microcystis and Dolichospermum might be led by Microcystis. If the temperature and phosphorus level were relatively high, then Microcystis grew rapidly, and competitively excluded Dolichospermum. If the nutrient level, especially the phosphorus level, was low, then the exclusive power of Microcystis was weak, and Dolichospermum maintained its dominance, even in summer. The key temperature (~17 °C) determined the dominance of the two cyanobacteria. Microcystis never dominated, while Dolichospermum was always dominant below the key temperature. Microcystis and Dolichospermum had different means of responding to the interaction of temperature, nitrogen and phosphorus. The Dolichospermum biomass was sensitive to the variation in nitrogen level, and the sensitivity depended on temperature. While the Microcystis biomass was sensitive to the variation in phosphorus level, and the sensitivity depended on temperature and total nitrogen. The different ways might contribute to the succession of the two cyanobacteria. Our findings will be helpful for improving the understanding of the shift process between Microcystis and Dolichospermum.
Highlights
Cyanobacteria often dominate a phytoplankton community, and even form harmful algal blooms in eutrophic freshwaters, such as lakes, reservoirs and estuaries
Microcystis grew rapidly and Dolichospermum in Lake Chaohu might be mostly led by Microcystis
We found that the Microcystis ratio increased, and the Dolichospermum ratio decreased, with increasing temperature and phosphorus levels, which was consistent with the previous findings that high temperature and phosphorus levels favor Microcystis dominance [13,14]
Summary
Cyanobacteria often dominate a phytoplankton community, and even form harmful algal blooms in eutrophic freshwaters, such as lakes, reservoirs and estuaries. The bloom-forming cyanobacteria are principally gas-vacuolate species. They are distributed across a number of genera, and vary in form and size from small filaments, such as Dolichospermum or Oscillatoria, to large globular colonies, such as Microcystis [1]. The most common bloom-forming cyanobacteria in these water bodies are Microcystis, Dolichospermum (Anabaena) and Aphanizomenon [2]. Different bloom-forming cyanobacteria can co-occur or successively dominate at an intra-annual scale in a specific water body [3,4]. The temporal and spatial dynamics of bloom-forming cyanobacteria is considered to be a
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