Effect of CO₂ concentration on C:N:P ratio in marine phytoplankton: A species comparison

Abstract

The effect of variable concentrations of dissolved molecular carbon dioxide, [CO 2,aq ], on C : N : P ratios in marine phytoplankton was studied in batch cultures under high light, nutrient-replete conditions at different irradiance cycles. The elemental composition in six out of seven species tested was affected by variation in [CO 2,aq ]. Among these species, the magnitude of change in C : N : P was similar over the experimental CO 2 range. Differences in both cell size and day length-dependent growth rate had little effect on the critical CO 2 concentration below which a further decrease in [CO 2,aq ] led to large changes in C : N : P ratios. Significant CO 2 -related changes in elemental ratios were observed at [CO 2,aq ] Ͻ 10 mol kg Ϫ1 and correlated with a CO 2 -dependent decrease in growth rate. At [CO 2,aq ] typical for ocean surface waters, variation in C : N : P was relatively small under our experimental conditions. No general pattern for CO 2 -related changes in the elemental composition could be found with regard to the direction of trends. Either an increase or a decrease in C : N and C : P with increasing [CO 2,aq ] was observed, depending on the species tested. Diurnal variation in C : N and C : P, tested in Skeletonema costatum, was of a similar magnitude as CO 2 -related variation. In this species, the CO 2 effect was superimposed on diurnal variation, indicating that differences in elemental ratios at the end of the photoperiod were not caused by a transient buildup of carbon-rich storage compounds due to a more rapid accumulation of carbohydrates at high CO 2 concentrations. If our results obtained under high light, nutrient-replete conditions are representative for natural phytoplankton populations, CO 2 -related changes in plankton stoichiometry are unlikely to have a significant effect on the oceanic carbon cycle.

Increased carbon dioxide availability alters phytoplankton stoichiometry and affects carbon cycling and growth of a marine planktonic herbivore

“…Similar results to the ones in our study with regard to changes in nutrient stoichiometry have been reported from terrestrial plants and previous experimental studies with aquatic primary producers (Urabe et al 2003;Riebesell et al 2000Riebesell et al , 2007Burkhardt et al 1999). To our knowledge, only two previous studies exist on the potential food chain effects of increased CO 2 availability in a stoichiometric context (Urabe et al 2003;Urabe and Waki 2009).…”

“…Most likely, changes in CO 2 availability will affect primary producers directly, although this appears to be highly species dependent and may not be the case for all organisms (Nielsen et al 2010;Gervais and Riebesell 2001;Burkhardt et al 1999;Urabe and Waki 2009;Urabe et al 2003). The high CO 2 availability to primary producers may affect their quality as food for herbivorous consumers, as the increasing carbon availability has the potential to change the balance (stoichiometry) of nutrients in primary producers thus possibly leading to limitations in other essential nutrients, such as nitrogen and phosphorus.…”

Build-up and decline of organic matter during PeECE III

“…Their natural habitats, the Southern Ocean and the subarctic Pacific, will become undersaturated with respect to their CaCO 3 (aragonite) shells at increasing CO 2 levels (Orr et al, 2005). Marine phytoplankton have also been shown to change their elemental composition (C/N/P) in response to changing [CO 2 ] (Burkhardt and Riebesell, 1997;Burkhardt et al, 1999b). But again, opposite sign.…”

Significant contribution of dissolved organic matter to seawater alkalinity

“…[6] Strains of three phytoplankton species (Prorocentrum minimum, Skeletonema costatum, and Chaetoceros curvisetus) were collected from Jangmok Bay, Korea (34.6°N,128.5°E ) [Burkhardt et al, 1999]. In our experiment a low light intensity was used to extend the growth period.…”