Microbial-mediated contribution of kelp detritus to different forms of oceanic carbon sequestration

Abstract

Kelp is one of the most important primary producers in the coastal oceans. When it matures or begins to decay, a substantial amount of detritus sinks and is degraded by microorganisms. However, the fate of these detritus after long-term microbial degradation, which is closely related to their ultimate carbon sequestration function, is not yet clear. Here, by studying the long-term (210-day) microbial degradation dynamics of kelp detritus, we reveal that the bioavailable components of kelp detritus (when kept in the dark) persisted for over four months. This left a considerable amount (in total, ca. 8.85%) of different forms of stable carbon that could function in long-term carbon sequestration. Among them, recalcitrant dissolved organic carbon (RDOC), recalcitrant particulate organic carbon, dissolved inorganic carbon, particulate inorganic carbon, and residual large particulate carbon accounted for 1.27%, 0.12%, 6.00%, 0.04%, and 1.41% of the initial kelp detrital carbon, respectively. The remaining organic carbon resisted further degradation due to the high content of humic-like substances, polycyclic aromatics, and highly aromatic compounds. Microbial community structure showed obvious successional characteristics during the long-term degradation process, driving the gradual transformation of the detritus-derived organic carbon from labile to recalcitrant. Notably, microbial transformation of the bioavailable components of kelp detritus contributed 28.7% of the remaining RDOC molecular species. This study provides novel insights into the contribution of the microbial-mediated degradation of kelp detritus to different forms of carbon sequestration.