Microbial processing of sedimentary organic matter at a shallow LTER site in the northern Adriatic Sea: an 8-year case study

Abstract

Benthic prokaryotes are the key-players in C-cycling at the sediment-seawater interface, one of the largest biologically active interfaces on Earth. Here, microbial-mediated processes, such as the degradation of organic matter and the incorporation of mobilized C into microbial biomass, depend on several factors such as environmental temperature and substrate availability, especially in shallow sediments at mid-high latitudes where seasonal fluctuations of these variables occur. In the present study, four degradative activities (β-glucosidase, lipase, chitinase and aminopeptidase), Heterotrophic C Production (HCP), Total Organic C (TOC), Total Nitrogen (TN) and Biopolymeric C (BPC) were investigated seasonally from April 2010 to April 2018 in the surface sediments of a shallow Long-Term Ecological Research (LTER) station of the northern Adriatic Sea. Significant temperature-dependences were described by Arrhenius-type equations for HCP and each of the degradative activities tested with the exception of aminopeptidase. The relatively low apparent Activation Energies suggested that these microbial-mediated processes were enhanced by the availability of palatable substrates over the study period. Nevertheless, a clear and tight dependence from such substrates was detected only for aminopeptidase, the most pronounced degradative activity observed. TN was identified by the stepwise multiple regression analysis as the environmental variable that mainly drove this exoenzymatic activity. Enhanced aminopeptidase rates mirrored peaks of TN that seemed, in turn, linked to the seasonal proliferation of benthic microalgae. By supplying prokaryotes with promptly available substrates, these autotrophs, represented mainly by diatoms, seemed to play an important role in the C-cycling regulation at the studied LTER station.

Seamless integration of the coastal ocean in global marine carbon cycle modeling

“…Temperature-dependent degradation rates were also reported for the upper sediment, derived from in-situ measurements, diagenetic modeling, and laboratory incubation experiments (Arndt et al, 2013;Franzo et al, 2019). Consistent with the Q10 approach in the water column, we extended the temperature-dependence of the degradation of particulate organic matter and opal to the sediment.…”

Sediment Features and Human Activities Structure the Surface Microbial Communities of the Venice Lagoon

“…Furthermore, approximately 4.5% of genes (KEGG annotation) in the metagenomes were addressed to peptide degradation. Proteolysis is in fact the fastest hydrolytic activity within surface brackish and coastal sediments, aiming to provide prokaryotes with both organic C and N via amino acids, as highlighted by direct measurements (e.g., Cibic et al, 2012;Franzo et al, 2019). Together with carbohydrates, proteins and lipids are indeed the major constituents of the labile organic matter in the sediments (Pusceddu et al, 1999) and microbes are adapted to utilize these compounds heterotrophically (Oni et al, 2015), thus supporting the concept of sediments as hot spots for organic matter degradation (Lipka et al, 2018).…”

Seamless Integration of the Coastal Ocean in Global Marine Carbon Cycle Modeling

“…Temperature‐dependent degradation rates were also reported for the upper sediment, derived from in‐situ measurements, diagenetic modeling, and laboratory incubation experiments (Arndt et al., 2013; Franzo et al., 2019). Consistent with the Q10 approach in the water column, we extended the temperature‐dependence of the degradation of particulate organic matter and opal to the sediment.…”