title: Cylindrospermopsis raciborskii dominates under very low and high nitrogen-to-phosphorus ratios.
abstract: In freshwater ecosystems, a variety of factors mediate phytoplankton community structure, including herbivore community structure, light availability, temperature, mixing, and absolute and relative nutrient concentrations (total nitrogen (TN), total phosphorus (TP)). Ecological stoichiometry examines how the nutrient content of organisms and their environment may mediate population-, community-, and ecosystem-level processes. The manipulation of N:P ratios is a widely regarded tool for managing phytoplankton species composition given that nitrogen-fixing cyanobacteria should dominate algal communities under relatively low N:P (<64:1, by atoms) given their ability to convert dissolved dinitrogen gas into organic nitrogen. However, due to the physiological expense of nitrogen fixation, diazotrophs should be outcompeted by non-nitrogen fixing phytoplankton under higher N:P when other environmental factors are similar. We tested this hypothesis in a field experiment using 2500-L limnocorrals installed in a eutrophic lake (ambient N:P ∼40:1 (by atoms); TN ∼1360 μgL(-1); TP ∼75 μgL(-1)). At the start of the experiment, we randomly assigned limnocorrals among the ambient (40:1) and low (7:1) or high (122:1) N:P treatments (n = 4 replicates/treatment), which were established by adding P or N at the start of the experiment, respectively. The phytoplankton community in the enclosures at the start of the experiment was diverse (i.e., 18 phytoplankton genera) and dominated by chlorophytes (including Coelastrum and Scenedesmus (30% and 13% of total biomass, respectively)) and cyanobacteria (including Anabaena and Cylindrospermopsis (23% and 17% of total biomass, respectively)). In contrast to predictions based on ecological stoichiometry, the phytoplankton community in all N:P treatments increased in abundance and was almost entirely composed of the nitrogen-fixing cyanobacterium, Cylindrospermopsis raciborskii, by the conclusion of the study. Moreover, concentrations of the cyanobacterial neurotoxin, saxitoxin, were enhanced under the two highest N:P conditions. The ability of C. raciborskii to dominate phytoplankton communities under such extreme N:P shows that short-term management of nutrient stoichiometry through fertilization is not likely to be effective for controlling blooms of this noxious cyanobacterium and may help to explain the rapid expansion of this invasive species to temperate latitudes.
authors: Department of Fisheries and Allied Aquacultures, Auburn University, 203 Swingle Hall, Auburn, AL 36849, USA.
authors: Michael F
authors: MF
authors: Chislock
authors: Center for Coastal Studies, Texas A&M University - Corpus Christi, 3600 Ocean Drive, Corpus Christi, TX 78412, USA.
authors: Katherine L
authors: KL
authors: Sharp
authors: Department of Fisheries and Allied Aquacultures, Auburn University, 203 Swingle Hall, Auburn, AL 36849, USA. Electronic address: wilson@auburn.edu.
authors: Alan E
authors: AE
authors: Wilson
mesh_terms: D018533:Biomass; D046891:Cylindrospermopsis / Q000187:drug effects* / Q000254:growth & development*; D052998:Microcystins / Q000633:toxicity; D009584:Nitrogen / Q000494:pharmacology*; D010758:Phosphorus / Q000494:pharmacology*; D010839:Phytoplankton / Q000187:drug effects / Q000254:growth & development; D012530:Saxitoxin / Q000633:toxicity; D013696:Temperature; D014867:Water
chemical_list: D052998:Microcystins; D014867:Water; D010758:Phosphorus; D012530:Saxitoxin; C078588:microcystin; D009584:Nitrogen
keywords: Cylindrospermopsin; Eutrophication; Harmful algal blooms (HABs); Management; Microcystin; Microcystis; Saxitoxin; Toxic cyanobacteria