Abstract
Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles. More than 96% of the marine DOM resists microbial degradation for thousands of years. The composition of this refractory DOM (RDOM) exhibits a molecular signature ubiquitously detected in the deep oceans. Surprisingly efficient microbial transformation of labile into stable forms of DOM has been shown previously, implying that microorganisms apparently produce far more RDOM than needed to sustain the global pool. Here we show, by assessing the microbial formation and transformation of DOM in unprecedented molecular detail for 3 years, that most of the microbial DOM is different from RDOM in the ocean. Only <0.4% of the net community production is channelled into a form of DOM that is undistinguishable from oceanic RDOM. Our study provides a molecular background for global models on the production, turnover and accumulation of marine DOM.
Highlights
Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles
The question remains whether the ‘refractory’ DOM detected in experimental studies is truly equal to oceanic refractory DOM (RDOM), having the potential to be preserved for thousands of years
The molecular similarity with oceanic RDOM is extended towards the level of molecular structures and especially abundance patterns, a very different picture emerges
Summary
Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles. More than 96% of the marine DOM resists microbial degradation for thousands of years The composition of this refractory DOM (RDOM) exhibits a molecular signature ubiquitously detected in the deep oceans. The question remains whether the ‘refractory’ DOM detected in experimental studies is truly equal to oceanic RDOM, having the potential to be preserved for thousands of years. We propose the term ‘pseudo-RDOM’ for the fraction of DOM that survives multiple years of microbial decomposition, but that does not fully match oceanic RDOM in its molecular composition. For this assessment, we combined conventional molecular analysis targeting amino acids and carbohydrates with non-targeted ultra-high-resolution FT–ICR–MS. Our results indicate that RDOM, as found in the deep ocean, is generated by diverse microbial communities, but at much lower efficiency than previously assumed based on experimental approaches
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