Zooplankton carcasses stimulate microbial turnover of allochthonous particulate organic matter

Abstract

Carbon turnover in aquatic environments is dependent on biochemical properties of organic matter (OM) and its degradability by the surrounding microbial community. Non-additive interactive effects represent a mechanism where the degradation of biochemically persistent OM is stimulated by the provision of bioavailable OM to the degrading microbial community. Whilst this is well established in terrestrial systems, whether it occurs in aquatic ecosystems remains subject to debate. We hypothesised that OM from zooplankton carcasses can stimulate the degradation of biochemically persistent leaf material, and that this effect is influenced by the daphnia:leaf OM ratio and the complexity of the degrading microbial community. Fresh Daphnia magna carcasses and 13C-labelled maize leaves (Zea mays) were incubated at different ratios (1:1, 1:3 and 1:5) alongside either a complex microbial community (<50 µm) or solely bacteria (<0.8 µm). 13C stable-isotope measurements of CO2 analyses were combined with phospholipid fatty acids (PLFA) analysis and DNA sequencing to link metabolic activities, biomass and taxonomic composition of the microbial community. Our experiments indicated a significantly higher respiration of leaf-derived C when daphnia-derived OM was most abundant (i.e. daphnia:leaf OM ratio of 1:1). This process was stronger in a complex microbial community, including eukaryotic microorganisms, than a solely bacterial community. We concluded that non-additive interactive effects were a function of increased C–N chemodiversity and microbial complexity, with the highest net respiration to be expected when chemodiversity is high and the degrading community complex. This study indicates that identifying the interactions and processes of OM degradation is one important key for a deeper understanding of aquatic and thus global carbon cycle.

Network-based integration of omics, physiological and environmental data in real-world Elbe estuarine Zander

“…Proteinase K digestion in CTAB buffer was followed by chlorophorm-phenol extraction. Nucleic acids were precipitated in PEG 6000 using LPA-carrier and recovered and washed repeatedly with 95% and 70% ethanol before resuspension in water [51]. QC was performed via spectroscopy (Nanodrop, Thermo Fisher) and gel electrophoreses.…”

Reduced greenhouse gas emissions from particulate organic matter degradation in iron-enriched sediments

“…the internal structure of the material, and in accordance with previous studies investigating reactivities of allochthonous vs. autochthonous PM. 6,9 Allochthonous OM (e.g., terrestrial leaves) have more support tissues and are rich in complex structural compounds, e.g. lignin and cellulose, which are highly resistant to enzymatic breakdown by microorganisms, as specic, energetically expensive enzymes for microbial utilization are required.…”

“…[5][6][7] However, recent studies have also demonstrated that highly bioavailable OM such as aquatic plankton can enhance the microbial degradation of structurally complex OM; such as terrestrial substrates, which is described as 'positive priming'. 8,9 The 'priming effect' itself describes non-additive effects on OM degradation aer combining sources of contrasting bioavailability. 10,11 Physical breakdown of OM preceding biodegradation includes leaching, during which inorganic elements (Ca, K, Mg) and simple organic compounds are released.…”

Particulate Organic Matter in the Atacama Trench: Tracing Sources and Possible Transport Mechanisms to the Hadal Seafloor

“…POM varies in size and composition, ranging from phytodetritus (Rice et al., 1986), larvacean houses (Robison et al., 2005) and faecal pellets (Turner, 2002) to mucilaginous aggregates (Martín & Miquel, 2010). The downward flux of organic material is further affected by the regional and seasonal variability in export flux (de Melo Viríssimo et al., 2022; Lutz et al., 2007; Poff et al., 2021), the size, shape, and composition of the POM (De La Rocha et al., 2008; Kriest, 2002; Omand et al., 2020), the interaction with microbes and/or zooplankton (Cavan et al., 2021; Neubauer et al., 2021), physical processes of aggregation/disaggregation of particles (Burd & Jackson, 2009; Iversen & Ploug, 2010), and ventilation/advection through deep‐ocean circulation (Chunhui et al., 2020). According to biogeochemical models (e.g., Ichino et al., 2015), the export of sinking OM of photosynthetic origin to hadal depths (>6,000 m below sea level) is expected to be low.…”