Understanding marine dissolved organic matter production: Compositional insights from axenic cultures of Thalassiosira pseudonana

Abstract

Marine dissolved organic matter (DOM) is a key source of carbon and nutrients to microbial life in the oceans, but rapid biological utilization of labile DOM confounds its compositional characterization. In order to characterize potentially bioavailable DOM produced by phytoplankton, DOM from axenic cultures of Thalassiosira pseudonana cultivated in phosphorus (P) replete and low P conditions was extracted using high‐recovery electrodialysis (ED) techniques, which resulted in an average dissolved organic carbon (DOC) recovery of 76% ± 7% from all cultures. Low P concentrations resulted in greater cell‐normalized production of DOC relative to P replete culture controls at the same growth phase. Despite the different nutrient conditions, DOC composition and DOM molar ratios of carbon to nitrogen (C : N) were similar in all cultures. In contrast, low P concentrations influenced DOM molar carbon to phosphorus (C : P) ratios and dissolved organic phosphorus (DOP) composition. Under P replete and low P conditions, DOM C : P ratios were 130 (± 22) and 2446 (± 519), respectively. 31P Nuclear Magnetic Resonance (NMR) spectroscopy identified P esters (> 90% of DOP) as the dominant P species in DOM produced under P replete conditions, with small or negligible contributions from phosphonates or glycerol P and polyphosphates. However, based on direct fluorometric analysis, DOP from low P cultures was greater than 8 times enriched in dissolved polyphosphate compared to DOP from replete cultures, which is consistent with the growing evidence that polyphosphate is a dynamic component of total P in low P ocean regions.

Mini‐review: Phytoplankton‐derived polysaccharides in the marine environment and their interactions with heterotrophic bacteria

“…Thus, different biomes may harbour different hydrolytic potentials (Wietz et al, 2015). Furthermore, polysaccharides produced under phosphate limitation support a different microbial communities compared with polysaccharides produced under phosphate replete conditions (Saad et al, 2016). Accompanied with different microbial communities, polysaccharides exuded into phosphate-depleted conditions reveal a longer persistence if compared with nutrient replete conditions (Puddu et al, 2003).…”

Dissolved organic matter release by phytoplankton in the context of the Dynamic Energy Budget theory

“…To our knowledge no direct evidence exists for DOM excretion related either assimilation or maintenance. However, DOM can be excreted from growing cells in the exponential phase of culture (Myklestad, 2000;Urbani et al, 2005;Lomas et al, 2000;Saad et al, 2016) and the specific DOM release is proportional to the specific growth rate (Myklestad et al, 1989;Underwood et al, 2004). Therefore, we assume that the growth flux contributes to DOM production at a specific rate…”

Particulate polyphosphate and alkaline phosphatase activity across a latitudinal transect in the tropical Indian Ocean

“…Recent transcriptomic and genomic studies of marine plankton (Temperton et al 2011;Dyhrman et al 2012;Cruz de Carvalho et al 2016), and manipulative experiments with freshwater periphyton communities (Rier et al 2016) have further confirmed the ability of aquatic microbes to maintain significant polyP stores under acute P stress. Moreover, polyP appears to account for a significant fraction of the P pool even in P-replete environments, with quantitative estimates suggesting a contribution of around 10% of total P (Solrzano and Strickland 1968;Diaz et al 2008Diaz et al , 2016Orchard et al 2010;Young and Ingall 2010;Martin and Van Mooy 2013;Saad et al 2016). Laboratory culture experiments have confirmed that marine phytoplankton can have a high polyP content under a variety of culture conditions (Rhee 1973;Perry 1976).…”