Phytoplankton cell size: intra- and interspecific effects of warming and grazing.

Decreasing body size has been suggested as the third universal biological response to global warming after latitudinal/altitudinal range shifts and shifts in phenology. Size shifts in a community can be the composite result of intraspecific size shifts and of shifts between differently sized species. Metabolic explanations for the size shifts dominate in the literature but top down effects, i.

No stimulation of nitrogen fixation by non-filamentous diazotrophs under elevated CO in the South Pacific.

Nitrogen fixation by diazotrophic cyanobacteria is a critical source of new nitrogen to the oligotrophic surface ocean. Research to date indicates that some diazotroph groups may increase nitrogen fixation under elevated pCO . To test this in natural plankton communities, four manipulation experiments were carried out during two voyages in the South Pacific (30-35 S).

Direct and Indirect Costs of Dinitrogen Fixation in Crocosphaera watsonii WH8501 and Possible Implications for the Nitrogen Cycle.

The recent detection of heterotrophic nitrogen (N(2)) fixation in deep waters of the southern Californian and Peruvian OMZ questions our current understanding of marine N(2) fixation as a process confined to oligotrophic surface waters of the oceans. In experiments with Crocosphaera watsonii WH8501, a marine unicellular diazotrophic (N(2) fixing) cyanobacterium, we demonstrated that the presence of high nitrate concentrations (up to 800 μM) had no inhibitory effect on growth and N(2) fixation over a period of 2 weeks. In contrast, the environmental oxygen concentration significantly influenced rates of N(2) fixation and respiration, as well as carbon and nitrogen cellular content of C.

STOICHIOMETRIC RESPONSES OF PHYTOPLANKTON SPECIES TO THE INTERACTIVE EFFECT OF NUTRIENT SUPPLY RATIOS AND GROWTH RATES(1).

Three species of phytoplankton, Rhodomonas sp., Phaeodactylum tricornutum Bohlin, and Isochrysis galbana Parke, were cultivated in semicontinuous culture to analyze the response of carbon (C):nitrogen (N):phosphorus (P) stoichiometry to the interactive effect of five N:P supply ratios and four growth rates (dilution rates). The relationship between cellular N and P quotas and growth rates fits well to both the Droop and Ågren's functions for all species.