Carbon dioxide regulation of nitrogen and phosphorus in four species of marine phytoplankton

Abstract

The concentration of carbon dioxide in seawater may affect phytoplankton physiology and ecology and their role in marine biogeochemical cycles. In order to assess the effects of CO 2 on the elemental composition of marine phytoplankon, carbon, nitrogen, and phosphorus quotas were measured in 4 species of marine phytoplankton acclimated to 150 to 1500 ppm CO 2 (5 to 50 µM) in semi-continuous cultures. Nitrogen quotas declined steeply with increasing CO 2 in the centric diatoms Thalassiosira pseudonana and T. weissflogii acclimated to 150 to 380 ppm (5 to 13 µM), but more slowly as the CO 2 increased from 380 to 1500 ppm (13 to 50 µM). Nitrogen demand varied little with CO 2 in the pennate diatom Phaeodactylum tricornutum, but was positively correlated with CO 2 over the range of 150 to 770 ppm in the prymnesiophyte Isochrysis galbana. Based on the nitrogen−CO 2 trends in centric diatoms, relief from carbon−nitrogen colimitation could lead to 2-fold larger cells as CO 2 increases from 150 to 380 ppm, but only 15% larger cells from 380 to 770 ppm CO 2 . Phosphorus quotas in the 3 diatoms decreased as CO 2 increased from 150 to 380 ppm. As previously observed in these and other species, C:N, C:P, and N:P ratios increased with increasing CO 2 , but the present results show that much of this variation was due to differences in nitrogen and phosphorus rather than carbon quotas. Marine phytoplankton could provide a negative feedback against increasing CO 2 over the pCO 2 range of 150 to 380 ppm by supporting larger cells or higher biomass, but would support a smaller carbon sink as atmospheric CO 2 rises above 380 ppm. KEY WORDS: Nitrogen · Phosphorus · Carbon dioxide · PhytoplanktonResale or republication not permitted without written consent of the publisher

Elevated CO 2 and Phosphate Limitation Favor Micromonas pusilla through Stimulated Growth and Reduced Viral Impact

“…However, in our study, the FSC of M. pusilla, which may be used as an indicator of cell size (51), did not show significant differences between the pCO 2 treatments. The in- creased abundances of M. pusilla under high pCO 2 and P-limiting conditions in our study were accompanied by higher ratios of cellular C:N and C:P. A similar decoupling of the uptake of C, N, and P under P limitation has been described by several authors (52)(53)(54), where the enhanced cellular C:N and C:P ratios were a combination of increased POC and decreased PON and POP. Under P-limiting conditions, the demand for M. pusilla for both P and N seems to decline under high pCO 2 , leading to increased abundances and cellular C:N and C:P ratios.…”

“…Under future pCO 2 conditions, less N would be needed for proteins such as RuBisCO and carbonic anhydrase. The demand for P would lower because of reduced rRNA or phospholipids or a lower energy demand for the functioning of carbon-concentrating mechanisms (CCMs) (48,53,54). Intact polar lipid (IPL) analysis did not show a change in IPL composition between the pCO 2 treatments in our study (data not shown).…”

Effects of CO2 on growth rate, C:N:P, and fatty acid composition of seven marine phytoplankton species

“…2A). Previously published growth rate responses to CO 2 are in agreement for T. pseudonana (no response; Clark & Flynn 2000, Roberts et al 2007a, Crawfurd et al 2011, Reinfelder 2012, Yang & Gao 2012, Wynn-Edwards et al 2014 and T. weissflogii (higher growth rate at elevated CO 2 ; Burkhardt et al 1999, Shi et al 2010, Wu et al 2014. In the case of T. weissflogii (CCMP2599 and CCMP1010), specific growth rate is limited only under the lowest CO 2 treatment (<100 ppm pCO 2 ) and apparently at maximal present-day pCO 2 (~350 to 380 ppm) and at pCO 2 representative of future projections and the geological past.…”

“…Knowing that C, N, and P are re quired for basic cell functions associated with growth (proteins, amino acids, RNA, phospholipids, etc.) and that bulk measurements constitute an integration of a multitude of cell functions, it remains a challenge to predict how elemental requirements (either absolute or as ratios) might change in re sponse to growth rate and/or CO 2 availability (Burk hardt et al 1999, Reinfelder 2012.…”

“…Laboratory experiments investigating the effects of high CO 2 /low pH have revealed potentially negative impacts on the physiological and morphological properties of calcifying marine phytoplankton (Riebesell et al 2000, Orr et al 2005. The effects of elevated pCO 2 upon phytoplankton also include higher cellular carbon quotas (Burkhardt et al 1999, Riebesell et al 2007, Hutchins et al 2009, King et al 2011, Reinfelder 2012) and changes in phytoplankton species composition and succession (e.g. Tortell et al 2002).…”