Consumption Of Organic Matter Research Articles

Alpha-glucans from bacterial necromass indicate an intra-population loop within the marine carbon cycle

Phytoplankton blooms provoke bacterioplankton blooms, from which bacterial biomass (necromass) is released via increased zooplankton grazing and viral lysis. While bacterial consumption of algal biomass during blooms is well-studied, little is known about the concurrent recycling of these substantial amounts of bacterial necromass. We demonstrate that bacterial biomass, such as bacterial alpha-glucan storage polysaccharides, generated from the consumption of algal organic matter, is reused and thus itself a major bacterial carbon source in vitro and during a diatom-dominated bloom. We highlight conserved enzymes and binding proteins of dominant bloom-responder clades that are presumably involved in the recycling of bacterial alpha-glucan by members of the bacterial community. We furthermore demonstrate that the corresponding protein machineries can be specifically induced by extracted alpha-glucan-rich bacterial polysaccharide extracts. This recycling of bacterial necromass likely constitutes a large-scale intra-population energy conservation mechanism that keeps substantial amounts of carbon in a dedicated part of the microbial loop.

Redox potential model for guiding moderate oxidation of polycyclic aromatic hydrocarbons in soils

In-situ chemical oxidation is an important approach to remediate soils contaminated with persistent organic pollutants, e.g., polycyclic aromatic hydrocarbons (PAHs). However, massive oxidants are added into soils without an explicit model for predicting the redox potential (Eh) during soil remediation, and overdosed oxidants would pose secondary damage by disturbing soil organic matter and acidity. Here, a soil redox potential (Eh) model was first established to quantify the relationship among oxidation parameters, crucial soil properties, and pollutant elimination. The impacts of oxidant types and doses, soil pH, and soil organic carbon contents on soil Eh were systematically clarified in four commonly used oxidation systems (i.e., KMnO4, H2O2, fenton, and persulfate). The relative error of preliminary Eh model was increased from 48–62% to 4–16% after being modified with the soil texture and dissolved organic carbon, and this high accuracy was verified by 12 actual PAHs contaminated soils. Combining the discovered critical oxidation potential (COP) of PAHs, the moderate oxidation process could be regulated by the guidance of the soil Eh model in different soil conditions. Moreover, the product analysis revealed that the hydroxylation of PAHs occurred most frequently when the soil Eh reached their COP, providing a foundation for further microorganism remediation. These results provide a feasible strategy for selecting oxidants and controlling their doses toward moderate oxidation of contaminated soils, which will reduce the consumption of soil organic matter and protect the main structure and function of soil for future utilization. Environmental implicationsThis study provides a novel insight into the moderate chemical oxidation by the Eh model and largely reduces the secondary risks of excessive oxidation and oxidant residual in ISCO. The moderate oxidation of PAHs could be a first step to decrease their toxicity and increase their bioaccessibility, favoring the microbial degradation of PAHs. Controlling the soil Eh with the established model here could be a promising approach to couple moderate oxidation of organic contaminants with microbial degradation. Such an effective and green soil remediation will largely preserve the soil’s functional structure and favor the subsequent utilization of remediated soil.

Sediment microbial fuel cell monitoring repeated Cr(VI) shocks in different wetlands for a year: Performance and mechanism

Cr(VI) is a major heavy metal contaminant that poses great threats to aquatic ecosystems and human health. To guarantee the safety of water quality, the development of in-situ and online sensors for monitoring Cr(VI) contamination events is crucial. In this work, sediment microbial fuel cell (SMFC) based sensors using floating cathode as sensing element were operated in outdoor environment for one year to monitor repeated Cr(VI) shocks in wetlands constructed with coastal alkaline soil (YC), paddy of acidic soil (YT), and paddy of neutral soil (NJ). K2CrO4 solutions were added to the cathode four times in January, March, June, and September, respectively. Results showed that each Cr(VI) addition triggered a voltage peak and the voltage increments were linearly correlated with Cr(VI) concentrations within the range of 5–120 mg L−1 Cr(VI). The highest sensitivity was observed for YC (1.2 mV L mg−1) and YT (1.4 mV L mg−1) in June and for NJ (1.2 mV L mg−1) in September. XPS analysis demonstrated the reduction reaction of Cr(VI) to Cr(III) on the cathode might contribute to the generation of voltage peaks. Despite repeated shocks, Cr(VI) was immobilized in the soil and completely reduced to low-toxic Cr(III) with the consumption of soil organic matter, and the diversity and abundance of exoelectrogenic bacteria-associated genera were not inhibited. As a result, stable operation of the SMFC sensors was ensured. The SMFC sensors exhibited great potential for in-situ and online monitoring of Cr(VI) contamination events across various wetlands.

Polyester microfiber impacts on coastal sediment organic matter consumption

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function.

A theory for context-dependent effects of mammalian trampling on ecosystem nitrogen cycling.

Large mammalian herbivores substantially impact ecosystem functioning. As their populations are dramatically altered globally, disentangling their consumptive and non-consumptive effects is critical to advance mechanistic understanding and improve prediction of effects over ecosystem and Earth-system spatial extents. Mathematical models have played an important role in clarifying potential mechanisms of herbivore zoogeochemistry, based mostly on their consumptive effects as primary consumers and recyclers of organic and inorganic matter via defecation and urination. Trampling is a ubiquitous effect among walking vertebrates, but the consequences and potential mechanisms of trampling in diverse environments remain poorly understood. We derive a novel mathematical model of large mammalian herbivore effects on ecosystem nitrogen cycling, focusing on how trampling and environmental context impact soil processes. We model herbivore trampling with a linear positive or negative additive effect on soil-mediated nitrogen cycling processes. Combining analytical and numerical analyses, we find trampling by large mammalian herbivores is likely to decrease nitrogen mineralisation rate across diverse environments, such as temperate grassland and boreal forest. These effects are mediated by multiple potential mechanisms, including trampling-induced changes to detritivore biomass and functioning (e.g. rate of organic matter consumption). We also uncover scenarios where trampling can increase nitrogen mineralisation rate, contingent on the environment-specific relative sensitivity of detritivore mineral-nitrogen release and detritivore mortality, to trampling. In contrast to some consumptive mechanisms, our results suggest the pace of soil nitrogen cycling prior to trampling has little influence over the direction of the trampling net effect on nitrogen mineralisation, but that net effects may be greater in slow-cycling systems (e.g. boreal forests) than in fast-cycling systems (e.g. grasslands). Our model clarifies the potential consequences of previously overlooked mechanisms of zoogeochemistry that are common to all terrestrial biomes. Our results provide empirically testable predictions to guide future progress in empirical and theoretical studies of herbivore effects in diverse environmental contexts. Resolving ecological contingencies around animal consumptive and non-consumptive effects will improve whole-ecosystem management efforts such as restoration and rewilding.

Effect of Adding Synbiotic Isolate Pediococcus Pentosaceus Strain N6 and Cassava Peel Flour on the Digestibility of Dry Matter and Organic Matter of Super Native Chickens

Effect of Adding Synbiotic Isolate Pediococcus Pentosaceus Strain N6 and Cassava Peel Flour on the Digestibility of Dry Matter and Organic Matter of Super Native Chickens

In situ arsenic immobilization by natural iron (oxyhydr)oxide precipitates in As–contaminated groundwater irrigation canals

Arsenic-contaminated groundwater is widely used in agriculture. To meet the increasing demand for safe water in agriculture, an efficient and cost-effective method for As removal from groundwater is urgently needed. We hypothesized that Fe (oxyhydr)oxide (FeOOH) minerals precipitated in situ from indigenous Fe in groundwater may immobilize As, providing a solution for safely using As-contaminated groundwater in irrigation. To confirm this hypothesis and identify the controlling mechanisms, we comprehensively evaluated the transport, speciation changes, and immobilization of As and Fe in agricultural canals irrigated using As-contaminated groundwater. The efficiently removed As and Fe in the canals accumulated in shallow sediment rather than subsurface sediment. Linear combination fitting (LCF) analysis of X–ray absorption near edge spectroscopy (XANES) indicated that As(V) was the dominant As species, followed by As(III), and there was no FeAsO4 precipitate. Sequential extraction revealed higher contents of amorphous FeOOH and associated As in shallower sediment than in the subsurface layer. Stoichiometric molar ratio calculations, SEM‒EDS, FTIR, and fluorescence spectroscopy collectively demonstrated that the microbial reductive dissolution of amorphous FeOOH proceeded via reactive dissolved organic matter (DOM) consumption in subsurface anoxic porewater environment facilitating high labile As, whereas in surface sediment, the in situ-generated amorphous FeOOH was stable and strongly inhibited As release via adsorption. In summary, groundwater Fe2+ can efficiently precipitate in benthic surface sediment as abundant amorphous FeOOH, which immobilizes most of the dissolved As, protecting agricultural soil from contamination. This field research supports the critical roles of the phase and reactivity of in situ-generated FeOOH in As immobilization and provides new insight into the sustainable use of contaminated water.

Environment-specific virocell metabolic reprogramming.

Viruses impact microbial systems through killing hosts, horizontal gene transfer, and altering cellular metabolism, consequently impacting nutrient cycles. A virus-infected cell, a "virocell", is distinct from its uninfected sister cell as the virus commandeers cellular machinery to produce viruses rather than replicate cells. Problematically, virocell responses to the nutrient-limited conditions that abound in nature are poorly understood. Here we used a systems biology approach to investigate virocell metabolic reprogramming under nutrient limitation. Using transcriptomics, proteomics, lipidomics, and endo- and exo-metabolomics, we assessed how low phosphate (low-P) conditions impacted virocells of a marine Pseudoalteromonas host when independently infected by two unrelated phages (HP1 and HS2). With the combined stresses of infection and nutrient limitation, a set of nested responses were observed. First, low-P imposed common cellular responses on all cells (virocells and uninfected cells), including activating the canonical P-stress response, and decreasing transcription, translation, and extracellular organic matter consumption. Second, low-P imposed infection-specific responses (for both virocells), including enhancing nitrogen assimilation and fatty acid degradation, and decreasing extracellular lipid relative abundance. Third, low-P suggested virocell-specific strategies. Specifically, HS2-virocells regulated gene expression by increasing transcription and ribosomal protein production, whereas HP1-virocells accumulated host proteins, decreased extracellular peptide relative abundance, and invested in broader energy and resource acquisition. These results suggest that although environmental conditions shape metabolism in common ways regardless of infection, virocell-specific strategies exist to support viral replication during nutrient limitation, and a framework now exists for identifying metabolic strategies of nutrient-limited virocells in nature.

Rainforest transformation reallocates energy from green to brown food webs

Terrestrial animal biodiversity is increasingly being lost because of land-use change1,2. However, functional and energetic consequences aboveground and belowground and across trophic levels in megadiverse tropical ecosystems remain largely unknown. To fill this gap, we assessed changes in energy fluxes across ‘green’ aboveground (canopy arthropods and birds) and ‘brown’ belowground (soil arthropods and earthworms) animal food webs in tropical rainforests and plantations in Sumatra, Indonesia. Our results showed that most of the energy in rainforests is channelled to the belowground animal food web. Oil palm and rubber plantations had similar or, in the case of rubber agroforest, higher total animal energy fluxes compared to rainforest but the key energetic nodes were distinctly different: in rainforest more than 90% of the total animal energy flux was channelled by arthropods in soil and canopy, whereas in plantations more than 50% of the energy was allocated to annelids (earthworms). Land-use change led to a consistent decline in multitrophic energy flux aboveground, whereas belowground food webs responded with reduced energy flux to higher trophic levels, down to −90%, and with shifts from slow (fungal) to fast (bacterial) energy channels and from faeces production towards consumption of soil organic matter. This coincides with previously reported soil carbon stock depletion3. Here we show that well-documented animal biodiversity declines with tropical land-use change4–6 are associated with vast energetic and functional restructuring in food webs across aboveground and belowground ecosystem compartments.

Effects of Using Different Concentrate Supplementation Levels in Diets of Lambs Fed Tropical Aruana (Megathyrsus maximus) or Marandu (Brachiaria brizantha) Grass: Performance, Digestibility, and Costs of Production

In Brazil, grazing is the main or only source of food for livestock. The appropriate combination of supplementation with concentrate in a lamb’s diet on pasture is an alternative that can be explored to use natural resources to produce quality meat. The aim of the current study was to evaluate the effects of different supplementation levels (0%, 1.5%, and 3% of BW) on the intake, performance, and production costs of lambs grazing on Aruana (Megathyrsus maximus) and Marandu (Brachiaria brizantha) grasses. Thirty-six non-castrated male Suffolk lambs (22.54 ± 2.72 kg) were used. The lambs were evaluated for nutrient intake and digestibility, such as dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and consumption in relation to body weight (% BW), in addition to the average daily gain (ADG), body condition score (BCS), and hot carcass weight (HCW), as well as the rising production cost of each system. The dry matter of the green leaf blades was influenced by the pasture type (p < 0.05), producing 1503.6 vs. 2977.4 kg/ha of Aruana and Marandu grasses, respectively. The concentrate supplementation level influenced the type of pasture (p < 0.05). A higher consumption of DM, CP, NDF, and organic matter was registered for the supplemented animals (p < 0.05) and on Aruana grass. The intake in relation to body weight was significantly influenced by the concentrate levels (p < 0.05). The empty body weight and HCW were significantly influenced by the supplementation levels (p < 0.05). The ADG and feed conversion (FC; kg DM/ADG) were influenced by the supplementation levels and type of pasture. The BCSs differed between the concentrate levels (p < 0.05). The supplementation improved dry matter digestibility. The ADG and FC were superior in the supplemented animals, with an advantage for those grazing on Aruana grass. The slaughter ADG was also higher in the supplemented animals. The lambs’ pasture comprising Aruana grass with 1.5% BW of concentrate supplementation showed improved production and economic results.

Dry matter and organic matter digestibility of complete feed based on durian waste (Durio zibethinus Murr.) as local male sheep feed

Durian waste has the potential to be used as livestock feed, but it needs further processing to increase its nutritional value. The aim of this study was to examine the value of dry matter and organic matter digestibility of complete feed based on durian waste as local male sheep feed. Apart from that, this research also aims to create a sustainable agricultural system with zero waste. The design used a completely randomized design (CRD) 4x4. The treatment consisted of P0 = control; P1 = CF with 20% durian peel + 20% durian seed + 20% elephant grass; P2 = CF with 30% durian peel + 20% durian seed + 10% elephant grass; P3 = CF with 40% durian peel + 20% durian seed. The result showed that the use of durian waste in the complete feed had a significant (P<0.05) effect on the consumption and digestibility of dry matter and organic matter. The conclusion of this study is the utilization of durian peel and seeds in complete feed can increase the consumption and digestibility of dry matter and organic matter for local male sheep with the best dosage being 30% durian peel + 20% durian seed + 10% elephant grass.

Effect of block feed supplementation based on palm oil sludge for Bengkulu local cattle (Kaur Cattle) on the dry matter and organic matter digestibility of rations

The objective of this study was to evaluate dry matter (DM) and organic matter (OM) digestibility of the ration supplemented with block feed made from palm oil sludge (solid) to Kaur cattle. Palm oil sludge was substitute for rice bran in the commercial block feed fomula namely “Sakura Block”. Four treatments were arranged in Latin Square Design that were the solid level in block feed. The treatments consisted of P0 = “Sakura” block feed (28% bran), P1 = block feed (14% bran + 14% solid), P2 = block feed (7% bran + 21% solid), P3 = block feed (28% solid). The results showed that there were no difference on OM consumption and production of fecal DM and OM among treatments. For DM consumption and DM digestibility, P1 showed the lowest (P<0.05) but among P0, P2 and P3 were no diferrence (P>0.05). For the OM digestibility, there was no a significant difference (P>0.05) among treatment. Block feed P3 (28% solid) can increase the consumption and the DM digestibility of rations.

Study on the Effectiveness of Constructed Wetlands in Purifying Polluted Water from Rivers and Greenhouse Gas Emissions

In order to investigate the effect of different substrates of constructed wetlands on the purification of polluted water in rivers and their greenhouse gas emissions, this study designed three small-scale constructed wetland experimental systems with traditional gravel (CW-G), volcanic rock (CW-V) and biomass carbon (CW-B) as filler substrates to investigate the effect of different constructed wetland systems on the removal of COD and nitrogen pollutants and to further analyse their effect on greenhouse gas emissions. The results showed that the removal rates of organic matter in all three groups of constructed wetlands reached over 90%. and 49.29% to 58.71%, respectively, with CW-V and CW-B significantly improving the removal of NH4 + -N and NO3− -N compared to CW-G (P &lt; 0.05). A comparison of greenhouse gas emissions reveals that although CW-B resulted in the highest N2O emissions due to its better removal of NO3− -N, its share in nitrogen removal was still the smallest. In addition, the rapid consumption of organic matter in the influent water and the oxidation of some CH4 to CO2 resulted in no detectable CH4 in any of the three groups of constructed wetlands. The results of this study show that the differences in treatment effects and greenhouse gas emissions between the three types of substrate constructed wetlands are significant, and this study can provide some scientific reference for the construction and operation of wetlands for the purification of polluted water bodies in rivers.

Effect of Genetic Variation of Leptin Gene on Intake of Roughage and Concentrated Diet of Awassi Lambs

This research was carried out in the animal farm at the University of Baghdad’s College of Agricultural Engineering Sciences between January 22 and April 2, 2022. The purpose of this research is to examine how variations in the leptin gene may influence feed conversion ratio, roughage intake, and concentrated diet consumption. Here, forty Awassi lambs are put to use. The (40) Awassi lambs were randomly assigned to separate pens when they were selected at 4–5 months old with an average birth weight of 25.4 kilograms. 66.67, 30.56, and 2.7% were found to be SNP (G>A) variants; the differences between these three groups were statistically significant (P0.01). Roughage feed derived from dry matter, organic matter, crude protein, ether extract, croud fiber, ash g/day, and metabolic energy MJ/kg dry matter () showed no significant differences in leptin gene variation. The results also showed that genetic stress Leptin gene had no effect on organic dry matter consumption (g/day), crude protein consumption (g/day), ash consumption (g/day), fat extract consumption (g/day), crude fiber consumption (g/day), or the amount of soluble carbohydrates and metabolite energy (MJ/kg dry matter) consumed.

Drought-induced resource use efficiency responses in an alpine meadow ecosystem of northern Tibet

Drought is a threat universally faced by global terrestrial ecosystems under global climate change. The habitat of alpine ecosystems is harsh, and they necessitate to use the limited resources efficiently to survive. However, drought occurred frequently during the short growing season, which greatly affected their resource use efficiency (RUE). In this study, based on long-term flux and microclimate observations in a typical alpine meadow ecosystem in northern Tibet, the effects of drought on RUE, including water use efficiency (WUE), light use efficiency (LUE), and carbon use efficiency (CUE), were studied. The results indicate that droughts could change the driving paths of abiotic and biotic factors on carbon and water fluxes and hence affect RUE. When vegetation exhibits robust physiological activity, droughts could enhance the control effects of biotic factors. The droughts that occurred at different periods of the growing season showed divergent effects on RUE. In the early-growing season, the strong photosynthetic capacity of the nascent leaves facilitated enhancements in WUE and LUE in response to drought conditions. However, the CUE did not increase significantly due to the heightened consumption of organic matter by respiration. The mid-growing season droughts led to a sharp decrease in gross primary productivity (GPP), consequently leading to a decline in WUE, LUE and CUE. During the late-growing season, droughts together with the decomposition of chlorophyll reduced the photosynthetic capacity and led to a significant decrease in LUE. The diminished physiological activity of the senescent leaves led to insensitive responses of WUE and CUE to droughts. These findings indicate that RUE might primarily be regulated by factors affecting GPP rather than others. This study would be beneficial for assessing the responses and adaptation characteristics of alpine meadow ecosystems to future climate change and could help accurately predict their possible evolution trends.

Microbial race to colonise leaf litter in a littoral‐lake environment and its relation to nutrient dynamics

Abstract Litter colonisation by fungi and bacteria is essential for decomposition. Although algae are not directly related to the decomposition process, in lentic environment, they usually colonise leaf litter rapidly and stimulate the activity of heterotrophs. We hypothesised that the timing of litter entering the water determines a rapid colonisation by algae, which affects fungal and bacterial colonisation, nutrient dynamics of leaf litter, and decomposition rates. We incubated two leaf litter species, Nothofagus antarctica and Potentilla anserina, in the littoral zone of a lake under two conditions: submerged from the beginning (aquatic: AQ) and near the shoreline (initially terrestrial: T‐A). The T‐A treatment was flooded on day 44, so the decomposition process continued in aquatic conditions. We estimated two decomposition rates, one before day 42 (k42) and one for the whole incubation period (ka), algal and fungal biomass, bacterial abundance, and nutrient (P and N) content in leaf litter throughout the experiment. The timing of litter entering the water affected decomposition rates, k42 and ka were faster in AQ than in T‐A conditions and only the ka was faster in P. anserina than in N. antarctica. Microbial colonisation was also affected. Algal biomass was always higher in the AQ treatment, but bacterial abundance differed between treatments and changed through the decomposition process. Fungal biomass depended on both the treatment and the litter species. Bacterial–algal and fungal–algal relationships in AQ treatment were synergistic and independent of time, while, with terrestrial exposure, microbial relationships depended on the stage of the decomposition process. Nutrient dynamics depended on the treatment and the species, but both species tended to gain or maintain nutrient content throughout the experiment. Fungi were related to N:P changes through the decomposition process. Our results suggest that the conspicuous growth of an autotrophic biofilm on some litter (in P. anserina) might retard decomposition but at the same time stimulate heterotrophic colonisation. Therefore, the study of decomposition in the littoral zone of lakes must include the autotrophic component of biofilms that grow on detritus, since it alters organic matter consumption by decomposers and nutrient dynamics.

Impacts of autochthonous dissolved organic matter on the accumulation of methylmercury by phytoplankton and zooplankton in a eutrophic coastal ecosystem

The bioaccumulation of methylmercury (MeHg) within the pelagic food webs is a crucial determinant of the MeHg concentration in the organisms at higher trophic levels. Dissolved organic matter (DOM) is recognized for its influence on mercury (Hg) cycling in the aquatic environment because of its role in providing metabolic substrate for heterotrophic organism and serving as a strong ligand for MeHg. However, the impact of DOM on MeHg bioaccumulation in pelagic food chains remain controversial. Here, we explored MeHg bioaccumulation within a pelagic food web in China, in the eutrophic Bohai Sea and adjacent seas, covering a range of DOM concentrations and compositions. Our findings show that elevated concentrations of dissolved organic carbon (DOC) and phytoplankton biomass may contribute to a reduction in MeHg uptake by phytoplankton. Moreover, we observe that a higher level of autochthonous DOM in the water may result in more significant MeHg biomagnification in zooplankton. This can be explained by alterations in the structure of pelagic food webs and/or an increase in the direct consumption of DOM and particulate organic matter (POM) containing MeHg. Our study offers direct field monitoring evidence of dual roles played by DOM in regulating MeHg transfers from water to phytoplankton and zooplankton in coastal pelagic food webs. A thorough understanding of the intricate interactions is essential for a more comprehensive evaluation of ecological risks associated with MeHg exposure in coastal ecosystems.

Weak seasonality in benthic food web structure within an Arctic inflow shelf region

The Arctic Ocean is characterized by pronounced seasonality in the quantity and quality of organic matter exported from the surface ocean. While it is well established that changes in food availability can alter the abundance, biomass and function of benthic organisms, the impact on food web structure is not well studied. We used bulk carbon and nitrogen stable isotope analysis to assess the quantity and quality of sediment organic matter and structure of the benthic food web in four seasons within the Northern Barents Sea (76°N − 82 °C). Despite a highly seasonal vertical flux, we found that the organic carbon and chlorophyll-a content of surface sediments was seasonally stable, suggesting a lack of seasonality in food availability at the seafloor. However, organic biomarkers indicate that the quality of sediment organic matter increased to a maximum in August and December, up to 6 months after the spring bloom. The seasonal stability of food quantity was mirrored in food-web structure (e.g., total isotopic range, number of trophic levels) which did not change significantly across sampling periods. We expected that suspension and deposit feeders would respond more readily to seasonal changes in food quality compared to predators. However, we observed no significant seasonal changes in the trophic levels or isotopic niche areas of benthic functional groups. The centroids of isotopic niches of all benthic functional groups shifted seasonally by <2 ‰ along the δ13C-axis, suggesting minimal shifts in carbon resource use. Because the northern Barents Sea experiences significant changes in seasonal sea ice cover, we expected that stable-isotope ratios of benthic organisms would show an increased consumption of sympagic-derived organic matter through less negative δ13C values in early spring and summer. However, only two taxa (the soft coral Gersemia spp. and bivalves in the family Yoldiidae) showed 13C-enrichment in spring or summer consistent with the assimilation of sympagic-derived organic matter, despite previous evidence suggesting widespread use of this carbon source. Overall, our results show that there is an apparent de-coupling in time between pelagic processes and benthic food-webs in which the accumulation and assimilation of high-quality organic matter occurs for benthos during the fall and early winter months when there is little to no fresh organic matter generated at the surface. This temporal mismatch highlights the importance of considering the timescales over which components of the marine ecosystem respond to short-term environmental changes and the methods employed to assess seasonality.

Contribution of holothuroids to the bioremediation and stimulation of the benthic microbial metabolism in aquaculture

The implementation of sustainable system designs in aquaculture comprises the biological treatment of pollutants. In order to test the potential of Holothuria (Roweothuria) poli as a candidate for bioremediation of aquaculture wastes, the effect of this species on the benthic microbial activity was studied. Two experimental treatments, with and without holothuroids, were allocated in two benthocosms, each one containing four replicate tanks with undisturbed sediment and a volume of water above it. It was anticipated that H. poli could affect the overall assimilative capacity of the aquaculture effluent system either through the consumption of particulate organic matter or through the stimulation of benthic microbial metabolism. Indeed, the results indicated that the microbial activity related to the mineralization of the N and C was significantly different between the treatments verifying our hypothesis that deposit-feeders that move above or inside the sediment matrix can accelerate the depletion of organic matter through bioturbation.

Warming promotes the decomposition of oligotrophic bacterial-driven organic matter in paddy soil

The ongoing global warming is causing paddy soil to come under threat by hitherto unseen levels of carbon and nitrogen loss. The mechanism of soil organic matter (SOM) components and microbial metabolism responding to increased temperature is complicated; for example, the temperature sensitivity (Q10) of SOM decomposition in rice topsoil and subsoil remains poorly understood. In this study, 0–30 cm columns of undisturbed paddy soil were collected and incubated at 5, 15, or 25 °C for 117 days to investigate the effect of temperature on SOM decomposition and microbial characteristics in different soil layers. Results showed that Q10 of subsoil (15–30 cm) was more than twice that of topsoil (0–15 cm), indicating that SOM mineralisation in subsoil was facilitated more by temperature than that in topsoil. Warming promoted the decomposition of recalcitrant SOM and reduced the fluorescent intensity of dissolved organic matter. Increased temperature exerted no significant effect on microbial biomass, but it did enhance the relative abundance of oligotrophic bacteria and promote anabolism. Therefore, recalcitrant SOM decomposition driven by oligotrophic bacteria was more sensitive to warming than labile organic matter consumption mediated by copiotrophic bacteria. Our findings revealed the underlying mechanisms by which elevating temperature promoted SOM mineralisation, thereby emphasising the need to remain vigilant regarding the threat to carbon dynamics in deep soil poised by global climate changes.