Reply to comment: Controls on turnover of marine dissolved organic matter—testing the null hypothesis of purely concentration‐driven uptake

Abstract

Our recent bioassay experiments indicate that molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean. This finding is questioned by Lennartz and Dittmar who modeled our experiments and concluded that our observations could be largely explained by concentration-driven uptake independent from molecular properties. We suggest the authors' models are deficient for establishing the relative roles of molecular properties and concentration-driven uptake. Our conclusion is consistent with earlier and recent experimental results and biogeochemical observations, supporting a unified theory with molecular properties as a more prominent control than concentration-driven uptake on marine organic carbon accumulation.

Experimental Insight into the Enigmatic Persistence of Marine Refractory Dissolved Organic Matter

“…RDOM can persist in the ocean interior for millennia, forming a long-lived carbon pool that plays an important role in carbon sequestration and in the regulation of the global climate. , To date, the recalcitrance mechanisms and fate of the oceanic RDOM are unclear. , Two major mechanisms have been proposed to explain the biological recalcitrance of RDOM: − the dilution hypothesis, which proposes that labile molecules are biologically inaccessible due to low concentrations; and the intrinsic recalcitrance hypothesis, which attributes the recalcitrance of DOM to intrinsic chemical properties in a specific environmental context, for example, a DOM molecule has a complex structure and is recalcitrant in the absence of microbes with the specific encoding genes to utilize it. Although which mechanism leads to the recalcitrance of RDOM has been studied for decades, − this topic is still under debate. Therefore, experimental evidence is vital to clarify this uncertainty.…”

Carbon Sequestration in the Form of Recalcitrant Dissolved Organic Carbon in a Seaweed (Kelp) Farming Environment

“…DOC has a complex molecular composition. The characteristics of the DOC molecular composition determine their stability or bioavailability in a certain environment . Here, using FT-ICR MS, we found that there was a very big difference in the molecular composition of DOC between the kelp mariculture and nonmariculture areas.…”

“…13 However, at present, it is unclear which and how much of the DOC molecules released by macroalgae can remain in the ocean as RDOC and function as carbon sequestration. To address this question, it is vital to determine the molecular components contained in the macroalgae-derived DOC and their stability, 14 and how much of the DOC molecules is RDOC, which is the main purpose of this study.…”

Linking Microbial Population Succession and DOM Molecular Changes in Synechococcus -Derived Organic Matter Addition Incubation

“…The bioavailability of DOM is related to its intrinsic chemical molecular properties ( 7 , 31 , 46 ). We found that DOM molecules with lower AI mod and higher NOSC were more easily degraded by prokaryotes (Fig.…”