Sulfur and primary production in aquatic environments: an ecological perspective

Abstract

Sulfur is one of the critical elements in living matter, as it participates in several structural, metabolic and catalytic activities. Photosynthesis is an important process that entails the use of sulfur during both the light and carbon reactions. Nearly half of global photosynthetic carbon fixation is carried out by phytoplankton in the aquatic environment. Aquatic environments are very different from one another with respect to sulfur content: while in the oceans sulfate concentration is constantly high, freshwaters are characterized by daily and seasonal variations and by a wide range of sulfur concentration. The strategies that algal cells adopt for energy and resource allocation often reflect these differences. In the oceans, the amount and chemical form of sulfur has changed substantially during the course of the Earth's history; it is possible that sulfur availability played a role in the evolution of marine phytoplankton communities and it may continue to have appreciable effects on global biogeochemistry and ecology. Phytoplankton is also the main biogenic source of sulfur; sulfur can be released into the atmosphere by algal cells as dimethylsulfide, with possibly important repercussions on global climate. These and related matters are discussed in this review.

Nitrogen and sulfur assimilation in plants and algae

“…The extant oceanic sulfate concentrations are probably the highest ever reached, with an average value of 28 mM, although, of course spatial and short-term temporal variations do occur, especially in coastal waters. In today's freshwater habitats, sulfate availability is usually much lower than in the ocean and variability is much greater; values between 0.01 and 1 mM sulfate characterize most freshwaters environments (Holmer and Storkholm, 2001;Giordano et al, 2005c;Norici et al, 2005). This also fits with the greater contribution of green algae to primary productivity in these environments as compared to the oceans.…”

“…Sulfur deficiency occasionally restricts growth of terrestrial plants (Andrew et al, 1952), especially in intensive cultivation of higher yield crops where N-fertilizers are used, and after SO 2 emission have been reduced by the 1979 Oslo protocol (Hell and Hillebrand, 2001 and references therein). In today's aquatic environments, S limitation is rare (Giordano et al, 2005c;Norici et al, 2005), although this has most likely not always been the case, since S concentration have been increasing (although not monotonically) in the ocean over the long term to reach a maximum after the Mesozoic era (Ratti et al, 2011). However, the Oslo protocol caused a decrease of sulfate also in freshwaters of Europe and, to a minor extent, of North America (Giordano et al, 2005c); hence, hints of S being limiting or nearly limiting have emerged in some Cumbrian (Maberly and Giordano, unpublished) and African lakes (Moss, 1969).…”

Evidence that sulfur metabolism plays a role in microcystin production by Microcystis aeruginosa

“…Sulfur plays an important role in aquatic environments (Norici et al, 2005) but, despite a plethora of studies examining the effects of environmental conditions on MC production, sulfur supply has rarely been considered with respect to cyanobacterial toxin production. Only recently has sulfate starvation been shown to negatively impact on the production of the cyanobacterial polyketide-derived alkaloid hepatotoxin, cylindrospermopsin, in Aphanizomenon ovalisporum (Bá csi et al, 2006).…”

“…Nonetheless, sulfur availability is likely to be variable in freshwater environments (Norici et al, 2005) and it may therefore play an important role in regulation of MC content of toxic blooms. The information presented in this study provides further understanding of the physiology of MC production and the role sulfur may play in its synthesis and could thus provide insights into management of toxin production.…”

Uptake, Distribution and Subcellular Transport of Sulfate

“…In spite of these early studies and the clear ecological importance of algae in the aquatic environment (Norici et al 2005) little further molecular characterization of the transporters has occurred with the exception of Chlamydomonas rheinhardtii. In this species a gene family of seven sulfate transporters of the SulP type has been identified (Pollock et al 2005) but not further characterized, and there is a detailed characterization of a chloroplast transporter of the ABC-type (see section V).…”