Dissolved Primary Production and the Strength of Phytoplankton? Bacterioplankton Coupling in Contrasting Marine Regions

Abstract

We analyzed the strength of phytoplankton-bacterioplankton coupling by comparing the rate of particulate (PPP) and dissolved primary production (DPP) with bacterial carbon demand (BCD) in four contrasting marine regions: offshore and coastal waters of the Southern Ocean, a coastal area of the NE Atlantic, and a coastal-offshore transect in the NW Mediterranean. We measured bacterial heterotrophic production (BHP) and estimated BCD from a literature model. Average phytoplanktonic percent extracellular release [PER = DPP/(DPP + PPP)] was 18-20% in the Antarctic (offshore and coastal, respectively), 16% in the NW Mediterranean, and 7% in the NE Atlantic. A significant inverse relationship was found between PER and total system productivity with pooled data. On average BHP amounted to <5% of total primary production in all regions. However, the strength of phytoplankton-bacterioplankton coupling, estimated as the potential importance of DPP in meeting BCD, differed greatly in the four regions. DPP was highly correlated to BCD in offshore Antarctic waters and was sufficient to meet BCD. In contrast, BCD exceeded DPP and bore no significant relationship in the remaining regions. The data suggest that a strong dependence of bacteria on algal extracellular production is only expected in open-ocean environments isolated from coastal inputs of DOC.

Towards a better understanding of microbial carbon flux in the sea*

“…Given the uncertainties in deriving empirical production estimates described herein, an independent and objective approach is needed to model realistic bacterial utilization and BP rates, consistent with observations of other plankton processes such as primary production, grazing and DOC release (Morán et al 2002). One approach is the combination of flexiblestoichiometry, multielement (C, N, P) models of plankton biogeochemistry (Y. Luo & H. Ducklow unpubl.…”

“…The formerly accepted constancy in the percentage of primary production released as extracellular DOM (Baines & Pace 1991) does not hold, and oligotrophic planktonic ecosystems release a higher percentage of the total primary production than nutrient-richer ecosystems. For example, Teira et al (2001) and Morán et al (2002) documented release of up to 35%. Heterotrophic bacteria can also generate DOM by processes such as viral lysis or autolysis.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…The release of DOM by phytoplankton is a significant driver of secondary production by heterotrophic prokaryotes. Generally, DOM release by phytoplankton is considered insufficient to support the observed heterotrophic bacterial growth (Baines & Pace, 1991;Nagata, 2000;Morán et al, 2002b;Teira et al, 2003b). In addition, processes such as viral lysis and sloppy feeding contribute a significant amount of the phytoplankton DOM that is utilized by bacteria.…”

“…Baines & Pace (1991) concluded that the DOC released by phytoplankton supports less than 50% of bacterial carbon requirements, based on a review of data from freshwater, estuarine and coastal environments, and modelling. Recent work has challenged this general assumption: DOC released by phytoplankton is sufficient to support the observed bacterial growth in the Southern Ocean (Morán et al, , 2002bMorán & Estrada, 2002) and in an area of coastal upwelling off the Iberian Peninsula in the Atlantic (Teira et al, 2003b).…”

Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton–bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes

“…It has also been demonstrated that UVR exposure in the upper layers of the water column can increase the proportion of photosynthate released as exudates (Carrillo et al, 2008;Korbee al., 2012), which would stimulate the growth of UVR-resistant bacteria (Xenopoulos and Schindler, 2003) and give rise to a coupled phytoplankton-bacteria relationship in clear oligotrophic lakes . Coupling between phytoplankton and bacterioplankton has been defined as the capacity of the carbon (C) released by phytoplankton to support the bacterial carbon requirement (Morán et al, 2002) and will therefore differ depending on (i) the availability of alternative (allochthonous or autochthonous) carbon sources (Gasol et al, 2009) and (ii) the supply of inorganic nutrients (Medina-Sánchez et al, 2010;López-Sandoval et al, 2011). Although the bacterial dependence on C released by phytoplankton is a well-established paradigm in aquatic microbiology (Cole et al, 1988), it is currently under renewed debate.…”