Even though sediment macrofauna are widespread in the global seafloor, the influence of these fauna on microbial communities that drive sediment biogeochemical cycles remains poorly understood. ...According to recent field investigations, macrofaunal activities control bacterial and archaeal community structure in surface sediments, but the inferred mechanisms have not been experimentally verified. Here we use laboratory microcosms to investigate how activities of two major polychaete guilds, the lugworms, represented by
Abarenicola pacifica
, and the clamworms, represented by
Nereis vexillosa
, influence microbial communities in coastal sediments.
A. pacifica
treatments show >tenfold increases in microbial cell-specific consumption rates of oxygen and nitrate, largely due to the strong ventilation activity of
A. pacifica
. While ventilation resulted in clearly elevated percentages of nitrifying archaea (
Nitrosopumilus
spp.) in surface sediments, it only minorly affected bacterial community composition. By comparison, reworking – mainly by deposit-feeding of
A. pacifica
– had a more pronounced impact on microorganismal communities, significantly driving down abundances of Bacteria and Archaea. Within the Bacteria, lineages that have been linked to the degradation of microalgal biomass (e.g., Flavobacteriaceae and Rhodobacteraceae), were especially affected, consistent with the previously reported selective feeding of
A. pacifica
on microalgal detritus. In contrast,
N. vexillosa
, which is not a deposit feeder, did not significantly influence microbial abundances or microbial community structure. This species also only had a relatively minor impact on rates of oxygen and nitrogen cycling, presumably because porewater exchanges during burrow ventilation by this species were mainly restricted to sediments immediately surrounding the burrows. Collectively our analyses demonstrate that macrofauna with distinct bioturbation modes differ greatly in their impacts on microbial community structure and microbial metabolism in marine sediments.
Plastic pollution poses a threat to terrestrial ecosystems, even impacting soils from remote alpine and arctic areas. Biodegradable plastics are a promising solution to prevent long-term accumulation ...of plastic litter. However, little is known about the decomposition of biodegradable plastics in soils from alpine and polar ecosystems or the microorganisms involved in the process. Plastics in aquatic environments have previously been shown to form a microbial community on the surface of the plastic distinct from that in the surrounding water, constituting the so-called ‘plastisphere’. Comparable studies in terrestrial environments are scarce. Here, we aimed to characterize the plastisphere microbiome of three types of plastics differing in their biodegradability in soil using DNA metabarcoding. Polylactic acid (PLA), polybutylene adipate terephthalate (PBAT) and polyethylene (PE) were buried in two different soils, from the Swiss Alps and from Northern Greenland, at 15°C for eight weeks. While physico-chemical characteristics of the polymers only showed minor (PLA, PBAT) or no (PE) changes after incubation, a considerably lower α-diversity was observed on the plastic surfaces and prominent shifts occurred in the bacterial and fungal community structures between the plastisphere and the adjacent bulk soil not affected by the plastic. Effects on the plastisphere microbiome decreased with greater biodegradability of the plastics, from PLA to PE. Copiotrophic taxa within the phyla Proteobacteria and Actinobacteria benefitted the most from plastic input. Especially taxa with a known potential to degrade xenobiotics, including Burkholderiales, Caulobacterales, Pseudomonas, Rhodococcus and Streptomyces, thrived in the plastisphere of the Alpine and Arctic soils. In addition, Saccharimonadales (superphylum Patescibacteria) was identified as a key taxon associated with PLA. The association of Saccharibacteria with plastic has not been reported before, and pursuing this finding further may shed light on the lifestyle of this obscure candidate phylum. Plastic addition affected fungal taxa to a lesser extent since only few fungal genera such as Phlebia and Alternaria were increased on the plastisphere. Our findings suggest that the soil microbiome can be strongly influenced by plastic pollution in terrestrial cryoenvironments. Further research is required to fully understand microbial colonization on plastic surfaces and the biodegradation of plastic in soils.
Through a process called “bioturbation,” burrowing macrofauna have altered the seafloor habitat and modified global carbon cycling since the Cambrian. However, the impact of macrofauna on the ...community structure of microorganisms is poorly understood. Here, we show that microbial communities across bioturbated, but geochemically and sedimentologically divergent, continental margin sites are highly similar but differ clearly from those in nonbioturbated surface and underlying subsurface sediments. Solidand solute-phase geochemical analyses combined with modeled bioturbation activities reveal that dissolved O₂ introduction by burrow ventilation is the major driver of archaeal community structure. By contrast, solid-phase reworking, which regulates the distribution of fresh, algal organic matter, is the main control of bacterial community structure. In nonbioturbated surface sediments and in subsurface sediments, bacterial and archaeal communities are more divergent between locations and appear mainly driven by sitespecific differences in organic carbon sources.
Intertidal sands are global hotspots of terrestrial and marine carbon cycling with strong hydrodynamic forcing by waves and tides and high macrofaunal activity. Yet, the relative importance of ...hydrodynamics and macrofauna in controlling these ecosystems remains unclear. Here, we compare geochemical gradients and bacterial, archaeal, and eukaryotic gene sequences in intertidal sands dominated by subsurface deposit-feeding worms (
) to adjacent worm-free areas. We show that hydrodynamic forcing controls organismal assemblages in surface sediments, while in deeper layers selective feeding by worms on fine, algae-rich particles strongly decreases the abundance and richness of all three domains. In these deeper layers, bacterial and eukaryotic network connectivity decreases, while percentages of clades involved in degradation of refractory organic matter, oxidative nitrogen, and sulfur cycling increase. Our findings reveal macrofaunal activity as the key driver of biological community structure and functioning, that in turn influence carbon cycling in intertidal sands below the mainly physically controlled surface layer.
PDF
