CYANOBACTERIAL BUOYANCY REGULATION: THE PARADOXICAL ROLES OF CARBON¹

Abstract

In stratified lakes, dominance of the phytoplankton by cyanobacteria is largely the result of their buoyancy and depth regulation. Bloom‐forming cyanobacteria regulate the gas vesicle and storage polymer contents of their cells in response to interactive environmental factors, especially light and nutrients. While research on the roles of nitrogen and phosphorus in cyanobacterial buoyancy regulation has reached a consensus, evaluations of the roles of carbon have remained open to dispute. We investigated the various effects of changes in carbon availability on cyanobacterial buoyancy with continuous cultures of Microcystis aeruginosa Kuetz. emend. Elenkin (1924), a notorious bloom‐former. Although CO2 limitation of photosynthesis can promote buoyancy in the short term by preventing the collapse of turgor‐sensitive gas vesicles and/or by limiting polysaccharide accumulation, we found that sustained carbon limitation restricts buoyancy regulation by limiting gas vesicle as well as polysaccharide synthesis. These results provide an explanation for the positive effects of bicarbonate enrichment on cyanobacterial nitrogen uptake and bloom formation in lake experiments and may help to explain the pattern of cyanobacterial dominance in phosphorus‐enriched, low‐carbon lakes.

Cyanobacteria dominance: Quantifying the effects of climate change

“…2d) revealed enhanced biomass of Anabaena during longlasting stratified periods, whereas Microcystis was only found during short stratified periods of 1-2 weeks in duration. A decrease in buoyancy in several cyanobacteria genera, including Microcystis, under N and P limitation has been consistently reported from numerous studies (Konopka et al 1987;Klemer et al 1996). Thus, under Nlimiting conditions, such as those observed in Mü ggelsee (Wagner and Adrian 2009), N-fixing species such as Anabaena gain an advantage over non-N-fixing species of Microcystis.…”

Artificial mixing to control cyanobacterial blooms: a review

“…Chien et al 2013). Far fewer studies have concentrated on the nutrient response, and they report a consistent decrease in buoyancy under N and P limitation and a buoyancy increase under N and P replenishment (Klemer et al 1996;Brookes and Ganf 2001;Chu et al 2007). In natural conditions, Bormans et al (1999) combined field observations from several Australian systems with studies reported in the literature to show that no field studies reported evidence for population migration to sufficient depth to reach nutrients in stratified systems.…”

Effects of dissolved inorganic carbon on competition of the bloom-forming cyanobacteriumMicrocystis aeruginosawith the green algaChlamydomonas microsphaera

“…However, competition for inorganic carbon is conceptually and experimentally more complex. Although earlier studies suggested that the ability of cyanobacteria to thrive and become dominant at low DIC concentration can be attributed to their CCM and competitive advantage for CO 2 , experimental evidence for this is limited (Shapiro, 1990;Klemer et al, 1996;Badger et al, 2006). Nakano et al (2003) found that Microcystis spp.…”