Large Plankton Enhance Heterotrophy Under Experimental Warming in a Temperate Coastal Ecosystem

• Published in: Ecosystems (New York) Vol. 21; no. 6; pp. 1139 - 1154
• Main Authors: Huete-Stauffer, Tamara Megan, Arandia-Gorostidi, Nestor, González-Benítez, Natalia, Díaz-Pérez, Laura, Calvo-Díaz, Alejandra, Morán, Xosé Anxelu G.
• Format: Journal Article
• Language: English
• Published: New York Springer Science + Business Media 01.09.2018; Springer US; Springer; Springer Nature B.V
• Subjects: Bacteria; Biomedical and Life Sciences; Carbon; Coastal ecosystems; Coastal environments; Coastal waters; Ecology; Environmental Management; Fluxes; Geoecology/Natural Processes; Heterotrophy; Hydrology/Water Resources; Life Sciences; Marine ecosystems; Microorganisms; Nutrient deficiency; Original Articles; Plankton; Plant Sciences; Primary production; Respiration; Substrates; Summer; Temperature effects; Zoology; microbial plankton; carbon flux; global warming; metabolic balance; NE Atlantic; coastal ocean
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-017-0208-y

Microbes are key players in oceanic carbon fluxes. Temperate ecosystems are seasonally variable and thus suitable for testing the effect of warming on microbial carbon fluxes at contrasting oceanographic conditions. In four experiments conducted in February, April, August and October 2013 in coastal NE Atlantic waters, we monitored microbial plankton stocks and daily rates of primary production, bacterial heterotrophic production and respiration at in situ temperature and at 2 and 4°C over ambient values during 4-day incubations. Ambient total primary production (TPP) exceeded total community respiration (< 200 μm, TR) in winter and fall but not in spring and summer. The bacterial contribution to ecosystem carbon fluxes was low, with bacterial production representing on average 6.9 ± 3.2% of TPP and bacterial respiration (between 0.8 and 0.2 μm) contributing on average 35 ± 7% to TR. Warming did not result in a uniform increase in the variables considered, and most significant effects were found only for the 4°C increase. In the summer and fall experiments, under warm and nutrient-deficient conditions, the net TPP/TR ratio decreased by 39 and 34% in the 4°C treatment, mainly due to the increase in respiration of large organisms rather than bacteria. Our results indicate that the interaction of temperature and substrate availability in determining microbial carbon fluxes has a strong seasonal component in temperate planktonic ecosystems, with temperature having a more pronounced effect and generating a shift toward net heterotrophy under more oligotrophic conditions as found in summer and early fall.