Importance Of Particulate Organic Matter Research Articles

Growth and feeding in the sponge Agelas tubulata from shallow to mesophotic depths on Grand Cayman Island

AbstractOn Caribbean coral reefs, sponges are important members of the benthic community and play multiple roles in ecosystem structure and function. They have an important role in benthic‐pelagic coupling, consuming particulate organic matter (POM) and dissolved organic matter (DOM) and in turn providing food in the form of sponge biomass or the release of detritus for a variety of coral reef organisms. Throughout the Caribbean, sponges show consistent increases in their abundance and growth rates as depth increases into the mesophotic zone (30–150 m). This has been hypothesized to be driven by bottom‐up forces, particularly the increased supply of nitrogen‐rich POM in mesophotic coral reef ecosystems (MCEs). Here, we tested the hypothesis that the sponge, Agelas tubulata, exhibits increased growth rates on MCEs relative to shallow reefs on Grand Cayman Island and that this is driven by bottom‐up forcing. We observed increased growth rates in mesophotic A. tubulata, compared with shallow conspecifics, despite variability in feeding on both POM and DOM. Mesophotic sponges, however, were consistently exposed to greater amounts of POM, which was seasonally variable unlike DOM. Changes in stable isotopic signatures, and higher feeding rates with increasing depth, were consistent with increasing rates of growth in sponges as depth increases. These observations support the hypothesis that mesophotic sponges have higher growth rates due to increased POM availability and consumption over time. The results of this study illustrate the crucial role that bottom‐up forcing has in the structuring of sponge communities on both shallow and mesophotic Caribbean coral reefs and the importance of POM as a source of nitrogen in sponge diets.

Earthworms act as biochemical reactors to convert labile plant compounds into stabilized soil microbial necromass

Earthworms co-determine whether soil, as the largest terrestrial carbon reservoir, acts as source or sink for photosynthetically fixed CO2. However, conclusive evidence for their role in stabilising or destabilising soil carbon has not been fully established. Here, we demonstrate that earthworms function like biochemical reactors by converting labile plant compounds into microbial necromass in stabilised carbon pools without altering bulk measures, such as the total carbon content. We show that much of this microbial carbon is not associated with mineral surfaces and emphasise the functional importance of particulate organic matter for long-term carbon sequestration. Our findings suggest that while earthworms do not necessarily affect soil organic carbon stocks, they do increase the resilience of soil carbon to natural and anthropogenic disturbances. Our results have implications for climate change mitigation and challenge the assumption that mineral-associated organic matter is the only relevant pool for soil carbon sequestration.

Photochemical production of singlet oxygen from particulate organic matter.

Dissolved organic matter is established as one of the most relevant photosensitizers in aquatic environments, producing singlet oxygen (1O2) alongside other photochemically produced reactive intermediates. While the production of 1O2 from DOM has been well studied, the relative importance of particulate organic matter (POM) to the overall 1O2 production is less well understood. POM is known to play an important role in pollutant fate through the sorption and transport of hydrophobic pollutants. If POM is directly involved in 1O2 production, sorbed molecules would be expected to undergo enhanced photodegradation. In this work, synthetic POM was prepared by coating silica particles with commercial humic acid. The photochemical behavior of these POM samples was compared to dissolved commercial humic acids (DOM). Suspended natural sediment was also studied to test the environmental relevance of the synthetic POM model. Synthetic POM particles appear to simulate well the 1O2-production of suspended sediment. The 1O2 concentrations experienced by POM-sorbed probe molecules was up to 30% higher than experienced by DOM-sorbed ones, even though the aqueous concentration of 1O2 in irradiated POM suspensions was much lower than the analogous DOM solutions. These results were interpreted with a reaction-diffusion model, which suggested that the production rate of 1O2 by POM is lower than DOM, but the loss of 1O2 from the POM-phase is also lower than DOM. Based on the experimental results of this study, calculations were conducted to estimate the impact of removing POM on 1O2-mediated processes. These calculations indicate that compounds with a log Koc value near 4 will be most affected by removal of POM and that the magnitude of the effect is proportional to the fraction of the total organic matter represented by POM. This study demonstrates that particles can play an important role in the degradation of organic compounds via aquatic photochemistry.

Solid phases as important electron acceptors in freshwater organic sediments

Ferric iron in particulate iron (oxyhydr–) oxides and quinone moieties in dissolved organic matter (DOM) are well-established terminal electron acceptors (TEA) in heterotrophic anaerobic microbial respiration. The importance of particulate organic matter (POM) as TEA is, however, much less studied and understood despite the fact that POM is more abundant than DOM in many soils and sediments. Here, we studied the microbial reduction of POM and Fe(III)-containing phases in freshwater sediments. We present an electrochemical approach that can be used to assess the combined contributions of POM and Fe(III) to the TEA pools of soils and sediments. Following oxidation and drying of sediments from two carbonate–buffered freshwater lakes in air, wetting re–initiated anaerobic microbial respiration in the sediment samples as evidenced from electron transfer to solid–phase electron acceptors over three weeks of anoxic incubations. The microbial reduction of POM and mineral-associated ferric iron was directly quantified by mediated electrochemical analysis. We estimate that the POM from the analyzed sediments provided a capacity to accept or donate electrons of about 650 µmol e− (g organic carbon)−1. Our work substantiates earlier studies that suggested that the reduction of redox–active moieties in POM is an important contributor to anaerobic microbial respiration and might be responsible for the competitive suppression of methanogenesis in organic matter rich wetland soils. Our results further indicate that microbial reduction of POM must be accounted for to close respiration balances in (temporary) anoxic freshwater systems and peatlands.

Variability of heterotrophic metabolism in small stream corridors of an early successional watershed

[1] Metabolic activity in stream corridors is regulated by a complex combination of factors that are difficult to disentangle in mature ecosystems. Chicken Creek in Germany, an experimentally created watershed in an early successional stage, offers the opportunity to assess the spatiotemporal variation in metabolic activity in a simplified system. We measured microbial respiration in soils and sediments along the hydrologic flow path from upland terrestrial to ephemeral to perennial sites of three stream corridors. Dry soils and sediments were rewetted before respiration measurements to mimic periods of activity during and after rainfall. Respiration rates and organic matter contents of soil and sediment were generally low. The presence of algae and accretion of vascular plant fragments in the perennial stream reaches increased respiration rates, pointing to the importance of particulate organic matter. Contrary to expectation, respiration rates of rewetted soil and sediment from dry stream channels were similar to rates measured with sediments collected in the perennial channel sections. This suggests that permanent water availability was not a main factor determining metabolic potential in the early successional Chicken Creek watershed. Carbon turnover in perennial channels was fourfold to eightfold higher than in ephemeral channels and terrestrial sites, as water was permanently available. However, this magnitude was insufficient for perennial channels to compensate for the large surface area of terrestrial soils: extrapolated to a year and the whole watershed, stream channels contributed only 5% to total carbon turnover, 95% being due to soils during and after rainfall events.

Habitat structure determines resource use by zooplankton in temperate lakes

While the importance of terrestrial linkages to aquatic ecosystems is well appreciated, the degree of terrestrial support of aquatic consumers remains debated. Estimates of terrestrial contributions to lake zooplankton have omitted a key food source, phytoplankton produced below the mixed layer. We used carbon and nitrogen stable isotope data from 25 Pacific Northwest lakes to assess the relative importance of particulate organic matter (POM) from the mixed layer, below the mixed layer and terrestrial detritus to zooplankton. Zooplankton and deep POM were depleted in ¹³C relative to mixed layer POM in lakes that can support deep primary production. A Bayesian stable isotope mixing model estimated that terrestrial detritus contributed <5% to zooplankton production, and confirms the role of lake optical and thermal properties; deep POM accounted for up to 80% of zooplankton production in the clearest lakes. These results suggest terrestrial support of lake zooplankton production is trivial.

Illustrating the importance of particulate organic matter to pelagic microbial abundance and community structure—an Arctic case study

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 40:217-227 (2005) - doi:10.3354/ame040217 Illustrating the importance of particulate organic matter to pelagic microbial abundance and community structure—an Arctic case study Lisa R. Hodges1,2, Nasreen Bano1, James T. Hollibaugh1, Patricia L. Yager1,* 1Department of Marine Sciences, University of Georgia, 220 Marine Sciences Building, Athens, Georgia 30602-3636, USA2Present address: Centers for Disease Control & Prevention, 1600 Clifton Road, Mail-Stop C16, Atlanta, Georgia 30333, USA *Corresponding author. Email: pyager@uga.edu ABSTRACT: The pelagic bacterial community composition of the summertime Chukchi Sea (coastal Alaskan Arctic) was investigated under varying particle concentrations. Free-living and wholecommunity assemblages were compared using PCR-amplified 16S rDNA with denaturing gradient gel electrophoresis (PCR/DGGE) alongside traditional geochemical and microbial inventories. Algal blooms were characterized by increased microbial abundance, decreased species richness, and decreased similarity between free-living and whole-community bacterial assemblages. Bacterial and viral abundance correlated positively with a bloom index identified by principle components analysis that included particulate organic carbon and nitrogen, total organic carbon, and chlorophyll a, but not dissolved organic carbon or inorganic nutrients. The species richness of the free-living community correlated negatively with microbial abundance; differences between free-living and whole-community assemblages correlated positively with viral abundance. Algal blooms may therefore increase microbial abundance while stimulating a succession of the bacterial assemblage to fewer free-living species and more specialized particle-associated bacteria. Such community-level shifts are very likely to impact the fate of carbon in high production and export regions like the coastal Arctic. We speculate about the importance of viral lysis to such a succession. KEY WORDS: Bacterioplankton · Virioplankton · Bacterial community composition · Particleassociated bacteria · Free-living bacteria · Psychrophiles · Arctic · Carbon fluxes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 40, No. 3. Online publication date: October 18, 2005 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2005 Inter-Research.

Nutrient dynamics of seagrass ecosystems: 15N evidence for the importance of particulate organic matter and root systems

The availability of nitrogen in sediment phytodetritus to seagrass was investigated in 5 tropical species (Thalassia hemprichii, Halodule uninervis, H. pinifolia, Halophila ovalis/ovata and Syringodium isoetifolium) from Indonesia. 15N-labeled phytodetritus was injected into the sediment and the appearance of 15N in the roots, the rhizomes and the leaves of the plants were measured after 1, 2, 4 and 8 d. The transfer of 15N from sediment phytodetritus to the plant tissues was very rapid (within 1 d) and continued over the 8 d period, indicating an efficient retention of the phytodetritus and a net mineralization of nitrogen rather than an immobilisation by bacteria. Relative enrichment of roots versus leaves indicated that 15N was taken up by the roots and then transferred to the leaves. The combined efficiency of seagrass canopy-induced trapping and retention of sestonic particles and root-uptake, results in the acquisition of nutrients released upon mineralization of particulate organic matter (POM), giving them a competitive advantage over other primary producers in oligotrophic environments. [KEYWORDS: Tropical seagrass ; Nutrient uptake ; Canopy ; 15N ; Mineralization ; Phytodetritus]

The Effect of Temporal Changes and Environmental Trophic Condition on the Isotopic Composition (ω13C and ω15N) of Atherina boyeri (Risso, 1810) and Gobius niger (L., 1758) in a Mediterranean Coastal Lagoon (Lake of Sabaudia): Implications for Food Web Structure

Abstract. ω13C and ω15N of organic matter sources and consumers were employed to analyse trophic differentiation between a benthic consumer, Gobius niger (L., 1758) (Pisces, Osteichthyes), and a pelagic consumer, Atherina boyeri (Risso, 1810) (Pisces, Osteichthyes) in a Mediterranean coastal lagoon (Lake of Sabaudia) in winter and summer 1999. Trophic differences between the two species throughout the two sampling periods were related to the environmental trophic condition (i. e. nutrient and phytopigment concentrations). Although these two fish have different habitats, they both exploited benthic organisms, above all in summer. When the nutrient and phytopigment concentrations were higher (summer), the most abundant benthic organisms were the main food sources for both species. In winter A. boyeri apparently shifted its feeding preferences to include zooplankton, confirming its opportunistic feeding strategy. Par‐ticulate organic matter and algae seemed to play the main trophic role in the food web structure. Benthic invertebrates used both sources, while zooplankton seemed to rely exclusively on the particulate fraction. The overlapping and very depleted signatures of sedimentary and particulate organic matter highlights a strong link between sediments and water column, rarely observed in other aquatic ecosystems using stable isotopes. Such a finding further substantiates the importance of particulate organic matter as a food source in the study area.