Breakdown Of Organic Matter Research Articles

Organic matter breakdown in streams in a region of contrasting anthropogenic land use

Streams provide ecosystem services to humans that depend on ecosystem functions, such as organic matter breakdown (OMB). OMB can be affected by land use-related disturbance. We measured OMB in 29 low-order streams in a region of contrasting land use in south-west Germany to quantify land use effects on OMB. We deployed fine and coarse mesh leaf bags in streams of forest, agricultural, vinicultural and urban catchments to determine the microbial and invertebrate-mediated OMB, respectively. Furthermore, we monitored physicochemical, geographical and habitat parameters to explain potential differences in OMB among land use types and sites. Only microbial OMB differed between land use types. Microbial OMB was negatively correlated with pH and invertebrate-mediated OMB was positively correlated with tree cover. Generally, OMB responded to stressor gradients rather than directly to land use. Therefore, the monitoring of specific stressors may be more relevant than land use to detect effects on ecosystem functions, and to extrapolate effects on functions, e.g. in the context of assessing ecosystem services.

Soil-foraging animals alter the composition and co-occurrence of microbial communities in a desert shrubland.

Animals that modify their physical environment by foraging in the soil can have dramatic effects on ecosystem functions and processes. We compared bacterial and fungal communities in the foraging pits created by bilbies and burrowing bettongs with undisturbed surface soils dominated by biocrusts. Bacterial communities were characterized by Actinobacteria and Alphaproteobacteria, and fungal communities by Lecanoromycetes and Archaeosporomycetes. The composition of bacterial or fungal communities was not observed to vary between loamy or sandy soils. There were no differences in richness of either bacterial or fungal operational taxonomic units (OTUs) in the soil of young or old foraging pits, or undisturbed soils. Although the bacterial assemblage did not vary among the three microsites, the composition of fungi in undisturbed soils was significantly different from that in old or young foraging pits. Network analysis indicated that a greater number of correlations between bacterial OTUs occurred in undisturbed soils and old pits, whereas a greater number of correlations between fungal OTUs occurred in undisturbed soils. Our study suggests that digging by soil-disturbing animals is likely to create successional shifts in soil microbial and fungal communities, leading to functional shifts associated with the decomposition of organic matter and the fixation of nitrogen. Given the primacy of organic matter decomposition in arid and semi-arid environments, the loss of native soil-foraging animals is likely to impair the ability of these systems to maintain key ecosystem processes such as the mineralization of nitrogen and the breakdown of organic matter, and to recover from disturbance.

Evolving insights to understanding mycorrhizas

Evolving insights to understanding mycorrhizas

Sedimentary phosphate and associated fossil bacteria in a Paleoproterozoic tidal flat in the 1.85 Ga Michigamme Formation, Michigan, USA

Phosphorus is a nutrient fundamental to life and when it precipitates in modern environments bacteria are intimately involved in its release, concentration, and mineralization. Preserved fossil bacteria in phosphate crusts and grains from the ca. 1850 million-year-old Bijiki Iron Formation Member of the Michigamme Formation, Michigan provide insight into the longevity and nature of this relationship. The Michigamme Formation accumulated near the end of the Earth's initial phosphogenic episode (ca. 2.2 and 1.8Ga) to produce one of the first granular phosphorites. Phosphatic lithofacies consist of fine- to medium-sand-sized francolite peloids concentrated on bedding surfaces in peritidal facies. Granular beds are up to 2cm thick and peloids are often partially to completely replaced by dolomite and chert. The grains contain organic matter and pyrite framboids that suggest bacterial breakdown of organic matter and bacterial sulfate reduction.The peritidal nature of phosphorite in the Michigamme Formation is in sharp contrast to Phanerozoic phosphogenic environments in deeper coastal upwelling settings. Peritidal settings were well suited for phosphogenesis under the very low oxygen and low dissolved sulfate levels of the Paleoproterozoic as cyanobacteria produced oxygen in shallow water and evaporation led to increased sulfate concentrations. Such concomitant processes helped establish focused redox interfaces in the sediment that chemosynthetic bacterial communities (sulfur oxidizers, reducers, forms that concentrate P, and possibly iron oxidizers) could exploit. Phosphate released from organic matter by heterotrophic bacteria and Fe-redox pumping was further concentrated by these chemotrophs; a process that forms late Neoproterozoic to Phanerozoic phosphorites but on a much larger scale.This early example of a granular phosphorite demonstrates that, like their Phanerozoic counterparts, Paleoproterozoic phosphorites are the concentrated indirectly biomineralized products of bacterial communities. But unlike younger analogs, which accumulated across subtidal shelves and shelf margins, these ancient deposits formed only in tidal flat settings where phosphogenic redox processes could be established in the sediment. From this early beginning, the zone of phosphogenesis likely migrated into deeper water settings as oxygen and sulfate levels rose, expanding the zone of chemosynthetic bacterial and associated phosphogenesis across the shelf.

Plant Protection Development in Tea Plantations of South India in the Last Five Decades

The excessive use of chemicals in agriculture has resulted in several environmental problems like ozone layer depletion, poor soil health, due to the decline in natural microflora and acidification of water. To overcome these problems, application of biocontrol agents and biofertilizers has been found to be effective. Generally, these are beneficial microorganisms involved in the breakdown of organic matter, nitrogen fixation and secretion of growth promoting substances. They also supply nutrients to the plants, control diseases and maintain the soil structure in cultivable fields. Intensive research has been done to find out the usefulness of this aspect in the tea plantations. Certain groups of bacteria and fungi are considered as efficient biofertilizers and biocontrol agents in tea which are freely available in top soil, usually associated with plants with symbiotic relationship. These organisms receive nutrients from plant tissues and in turn supply the required nitrogen and phosphorus to the plants. In the present review article, the performance of Plant Pathology and Microbiology Division during the last five decade and the challenges ahead have been discussed.

Management options for water-repellent soils in Australian dryland agriculture

Water-repellent (‘non-wetting’) soils are a major constraint to agricultural production in southern and south-west Australia, affecting >10 Mha of arable sandy soils. The major symptom is dry patches of surface soil, even after substantial rainfall, directly affecting agricultural production through uneven crop and pasture germination, and reduced nutrient availability. In addition, staggered weed germination impedes effective weed control, and delayed crop and pasture germination increases the risk of wind erosion. Water repellency is caused by waxy organic compounds derived from the breakdown of organic matter mostly of plant origin. It is more prevalent in soils with a sandy surface texture; their low particle surface area : volume ratio means that a smaller amount of waxy organic compounds can effectively cover a greater proportion of the particle surface area than in a fine-textured soil. Water repellency commonly occurs in sandy duplex soils (Sodosols and Chromosols) and deep sandy soils (Tenosols) but can also occur in Calcarosols, Kurosols and Podosols that have a sandy surface texture. Severity of water repellency has intensified in some areas with the adoption of no-till farming, which leads to the accumulation of soil organic matter (and hence waxy compounds) at the soil surface. Growers have also noticed worsening repellency after ‘dry’ or early sowing when break-of-season rains have been unreliable. Management strategies for water repellency fall into three categories: (i) amelioration, the properties of surface soils are changed; (ii) mitigation, water repellency is managed to allow crop and pasture production; (iii) avoidance, severely affected or poorly producing areas are removed from annual production and sown to perennial forage. Amelioration techniques include claying, deep cultivation with tools such as rotary spaders, or one-off soil inversion with mouldboard ploughs. These techniques can be expensive, but produce substantial, long-lasting benefits. However, they carry significant environmental risks if not adopted correctly. Mitigation strategies include furrow-seeding, application of wetting agents (surfactants), no-till with stubble retention, on-row seeding, and stimulating natural microbial degradation of waxy compounds. These are much cheaper than amelioration strategies, but have smaller and sometimes inconsistent impacts on crop production. For any given farm, economic analysis suggests that small patches of water repellency might best be ameliorated, but large areas should be treated initially with mitigation strategies. Further research is required to determine the long-term impacts of cultivation treatments, seeding systems and chemical and biological amendments on the expression and management of water repellency in an agricultural context.

Earthworms: 'Soil and Ecosystem Engineers' – a Review

Earthworms can alter the soil environment by changing soil properties. They have great potentiality to enhance soil physical properties like bulk density, infiltrability, hydraulic conductivity, porosity, aggregate stability. Due to this ability they are only species which plays significant role in pedoturbation. Similarly, their role in nutrient cycling and organic matter breakdown is of unique interest. Earthworm cast fortified with the microbial population. Increasing microbial activity in soil, increases the nutrient mineralization and release. Earthworm activity enhances root distribution so that immobile macro nutrients like phosphorous and other micronutrients, which are absorbed by plant through root interception, are easily available to the plants. Hence, earthworms play important role in bioturbation, they are considered as 'soil engineer.' However, their activity differs with the agroecosystems. Their population density is more in reduced tillage system than conventional tillage system, aerobic condition than anaerobic conditions, grasslands than forest. Low population of earthworm was found in dry land agroecosystems. But earthworm presence in extreme environment is not studied well yet. So, this paper was reviewed to explore the role of earthworm as soil and ecosystem engineer. This was already established fact but main aim of this paper is to collect the related information and conclude the future research prospects to strengthen the earthworm role as soil and ecosystem engineer.

When, where and how does microbial community composition matter?

When, where and how does microbial community composition matter?

Impact of water abstraction on storage and breakdown of coarse organic matter in mountain streams

Water abstraction is a prevalent impact in streams and rivers, which is likely to increase in the near future. Because abstraction reduces discharge, the dimensions of the wetted channel and water depth and velocity, it can have strong influence on stream ecosystem functioning. Although the impacts of large dams on stream and river ecosystems are pretty well known, the effects of diversion schemes associated with low dams are still poorly understood. Furthermore, the remote location of many diversion schemes and the lack of collaboration by power companies often make it difficult to know the volume of water diverted and its environmental consequences. To assess the impact of water abstraction on the storage and breakdown of coarse particulate organic matter in streams we compared reaches upstream and downstream from five low dams that divert water to hydropower plants in mountain streams in N Spain. We measured the storage of organic matter and the breakdown of alder leaves in winter and spring, and calculated the results at the patch (i.e., per square meter of bed) and at the reach scale (i.e., per lineal meter of channel). Water diversion significantly reduced discharge, and the width and depth of the wetted channel, but did not affect water quality. Diversion significantly reduced the storage and breakdown of organic matter in winter but not in spring. The number of shredders colonizing litter bags was also significantly reduced. The results point to an important effect of water abstraction on the storage and breakdown of organic matter in streams at least in some periods, which could affect downstream reaches, global carbon fluxes, and associated ecosystem services.

Bacterially mediated removal of phosphorus and cycling of nitrate and sulfate in the waste stream of a “zero-discharge” recirculating mariculture system

Simultaneous removal of nitrogen and phosphorus by microbial biofilters has been used in a variety of water treatment systems including treatment systems in aquaculture. In this study, phosphorus, nitrate and sulfate cycling in the anaerobic loop of a zero-discharge, recirculating mariculture system was investigated using detailed geochemical measurements in the sludge layer of the digestion basin. High concentrations of nitrate and sulfate, circulating in the overlying water (∼15 mM), were removed by microbial respiration in the sludge resulting in a sulfide accumulation of up to 3 mM. Modelling of the observed S and O isotopic ratios in the surface sludge suggested that, with time, major respiration processes shifted from heterotrophic nitrate and sulfate reduction to autotrophic nitrate reduction. The much higher inorganic P content of the sludge relative to the fish feces is attributed to conversion of organic P to authigenic apatite. This conclusion is supported by: (a) X-ray diffraction analyses, which pointed to an accumulation of a calcium phosphate mineral phase that was different from P phases found in the feces, (b) the calculation that the pore waters of the sludge were highly oversaturated with respect to hydroxyapatite (saturation index = 4.87) and (c) there was a decrease in phosphate (and in the Ca/Na molar ratio) in the pore waters simultaneous with an increase in ammonia showing there had to be an additional P removal process at the same time as the heterotrophic breakdown of organic matter.

Compostagem de biomassa de acácia com casca de pinheiro

Acacias are invasive Fabaceae species that can be composted to produce organic amendments and horticultural substrates. With this aim, big piles were set up with ground and screened acacia residues and pine bark, and managed with different turning frequency, to analyze the physicochemical characteristics during composting and to model the breakdown of acacia organic matter (OM). Temperatures were >60oC for several months, indicating pathogen inactivation, seed destruction and high amount of biodegradable OM (600-620 g kg-1 of initial OM). High temperature and high pH conditions promoted significant N losses (450-470 g kg-1 of initial N). Nevertheless, these were smaller compared to C losses and so the C/N ratio decreased from 56 at the beginning to 40-41 at the end of composting. This study indicates that composting acacia can produce organic amendments with high OM content, and low electrical conductivity (<0.7 dS m-1). However, a long period of composting is required to achieve advanced compost maturation.

Relationships between lake transparency, thermocline depth, and sediment oxygen demand in Arctic lakes

The burial of organic matter within lake sediments can be a significant component of landscape carbon cycling. Whether organic matter deposited in lake sediments is sequestered or mineralized depends on factors limiting the decomposition rate of organic matter, such as temperature and the availability of oxygen. In stratified lakes, the distribution of temperature and oxygen is determined by the depth of the thermocline, and therefore sediment organic matter burial should be sensitive to changes in thermocline depth. Using a survey of more than 30 lakes over 3 years in the Alaskan Arctic, we found that thermocline depth during the summer was positively correlated with water transparency. Furthermore, using sediment incubations from 3 lakes, we found that variation in sediment oxygen demand is primarily affected by variation in temperature and the availability of oxygen with limited effect of the source of the sediments. Because variation in temperature and oxygen concentration in stratified lakes is mainly determined by the depth of thermocline, these results indicate that changes in transparency can have indirect effects on the rate of organic matter mineralization in lakes. A reduction in thermocline depth that results from decreased lake transparency may decrease the breakdown of sediment organic matter and increase the storage of organic carbon in lake sediments.

Saltwater intrusion into tidal freshwater marshes alters the biogeochemical processing of organic carbon

Abstract. Environmental perturbations in wetlands affect the integrated plant-microbial-soil system, causing biogeochemical responses that can manifest at local to global scales. The objective of this study was to determine how saltwater intrusion affects carbon mineralization and greenhouse gas production in coastal wetlands. Working with tidal freshwater marsh soils that had experienced ~ 3.5 yr of in situ saltwater additions, we quantified changes in soil properties, measured extracellular enzyme activity associated with organic matter breakdown, and determined potential rates of anaerobic carbon dioxide (CO2) and methane (CH4) production. Soils from the field plots treated with brackish water had lower carbon content and higher C : N ratios than soils from freshwater plots, indicating that saltwater intrusion reduced carbon availability and increased organic matter recalcitrance. This was reflected in reduced activities of enzymes associated with the hydrolysis of cellulose and the oxidation of lignin, leading to reduced rates of soil CO2 and CH4 production. The effects of long-term saltwater additions contrasted with the effects of short-term exposure to brackish water during three-day laboratory incubations, which increased rates of CO2 production but lowered rates of CH4 production. Collectively, our data suggest that the long-term effect of saltwater intrusion on soil CO2 production is indirect, mediated through the effects of elevated salinity on the quantity and quality of autochthonous organic matter inputs to the soil. In contrast, salinity, organic matter content, and enzyme activities directly influence CH4 production. Our analyses demonstrate that saltwater intrusion into tidal freshwater marshes affects the entire process of carbon mineralization, from the availability of organic carbon through its terminal metabolism to CO2 and/or CH4, and illustrate that long-term shifts in biogeochemical functioning are not necessarily consistent with short-term disturbance-type responses.

English

Oil sludge is a thick viscous mixture of sediments, water, oil and hydrocarbons, encountered during crude oil refining, cleaning of oil storage vessels and waste treatment. Polycyclic aromatic hydrocarbons (PAHs), which are components of crude oil sludge, constitute serious environmental concerns, as many of them are cytotoxic, mutagenic and potentially carcinogenic. Improper management and disposal of oil sludge causes environmental pollution. The adverse effects of oil sludge on soil ecology and fertility have been of growing interest among environmental scientist and an important consideration in the development of efficient technologies for remediation of contaminated land, with a view to making such land available for further use. Oil sludge can be treated by several methods such as physical, chemical and biological processes. The biological processes are mostly cost effective and environmentally friendly, as they are easy to design and implement, as such they are more acceptable to the public. Compost, the product of biological breakdown of organic matter is a rich source of hydrocarbon-degrading microorganisms such as bacteria and fungi. These microorganisms can degrade the oil sludge to less toxic compounds such as carbon dioxide, water and salts. Compost bioremediation, the application of composting in remediation of contaminated environment, is beginning to gain popularity among remediation scientists. The success or failure of compost bioremediation depends on a number of factors such as nutrients, pH, moisture, aeration and temperature within the compost pile. The bioavailability and biodegradability of the substrate to the degrading microorganisms also contributes to the success of the bioremediation process. This is a review on the biological remediation technologies employed in the treatment oil sludge. It further assesses the feasibility of using compost technology for the treatment of oil sludge, as a better, faster and more cost effective option. Key words: Biodegradation, bioremediation, composting, oil sludge, polycyclic aromatic hydrocarbons (PAHs).

Screening of Earthworm (Eudrilus eugeniae) Gut as a Transient Microbial Habitat

Earthworms are soil invertebrates which play a major role in recycling organic matter in soils. The unique microenvironment of the earthworm gut impacts on the catabolic activities of ingested soil microorganisms. The ingested microbial populations play an important role in earthworm nutrition by helping in the breakdown of organic matter. A study was carried out to find out the distribution of microorganisms in the gut of earthworm, Eudrilus eugeniae. The vermibeds were prepared with cow dung and pre-decomposed banyan leaf litter. The population of bacteria, fungi and actinomycetes were determined in the gut regions (foregut, midgut and hindgut) of earthworm E. eugeniae. The predominant microorganisms found in the foregut, midgut and hindgut were bacteria, actinomycetes and fungi respectively. It was observed that there are variations in the population of microorganisms in the foregut, midgut and hindgut. This report shows the distribution of various microorganisms in the gut regions and how it favors the animal to have a healthy life in the environment.

COMPOSTING OF ACACIA LONGIFOLIA AND ACACIA MELANOXYLON INVASIVE SPECIES

Acacias are invasive Fabaceae species that are highly competitive and a serious threat to local biodiversity and natural habitats. Taking into account their high availability and low cost, a valorization approach for acacia shrubs may be composting to produce horticultural organic amendments and substrate components. With this aim, two big piles (100 m3) were set up with grinded and screened Acacia longifolia and Acacia melanoxylon shrubs, and managed with different turning frequency, to analyze the physicochemical characteristics during composting and to model the breakdown of acacia organic matter (OM). Time-temperature conditions in both piles exceeded the more stringent criteria for complete pathogen inactivation as temperatures were between 65°C and 75°C for several months, indicating high amount of biodegradable OM in this material, as found here by the high amount of mineralizable OM (640-690 g kg-1 of initial OM). High temperature and high pH conditions promoted significant N losses (455-465 g kg-1 of initial N). Nevertheless, these were smaller compared to C losses and so the C/N ratio decreased from 50 to 29-32 after 231 days of composting. This study indicates that composting acacia can produce organic amendments with high OM content, and low electrical conductivity ( 231 days) is required to achieve full compost maturation.

Modelling macronutrients in shelf sea sediments: fitting model output to experimental data using a genetic algorithm

PurposeDiagenetic modelling, the mathematical simulation of the breakdown of sedimentary organic matter and subsequent fate of associated nutrients, has progressed to a point where complex, non-steady state environments can be accurately modelled. A genetic algorithm has never been used in conjunction with an early diagenetic model, and so we aim to discover whether this method is viable to determining a set of realistic model parameters, which itself is often a difficult task.Materials and methodsA range of sensitivity analyses were conducted to establish the parameters for which the model was most sensitive before a micro-genetic algorithm (μGA) was used to fit an output from a previously published diagenetic model (OMEXDIA) to observational data, taken at the North Dogger site from a series of cruises in the North Sea. Profiles of carbon, oxygen, nitrate and ammonia were considered. The method allows a set of parameters to be determined in a manner analogous to natural selection. Each iteration of the genetic algorithm within each experiment decreases the variance between the observed profiles and those calculated by OMEXDIA.Results and discussionDespite some of the observed profiles, particularly for carbon, showing unusual patterns, the genetic algorithm was able to generate a set of parameters which was able to fit the observations. The genetic algorithm can therefore help to determine the values of other parameters used in the model, for which observational values are difficult to measure (e.g. the flux of organic matter to the sediment from the overlying water column and the rates of degradation of organic matter). We also show that the values of the parameters determined by the μGA technique are able to be used in a potentially temporally predictive manner.ConclusionsThe μGA used is a viable method to fit carbon and nutrient sedimentary profiles observed in complex, dynamic shelf sea systems, despite OMEXDIA originally being designed for a different sedimentary environment. The results therefore show that this novel use of a genetic algorithm is a suitable method for both model calibration and validation and that the technique may help in explaining processes which are poorly understood.

Host Plant Specific Control of 2,4-Diacetylphloroglucinol Production in the Rhizosphere

To shed light on phytobeneficial bacterial gene expression in situ, we investigated the expression of phlD gene involved in 2,4-diacetylphloroglucinol production. For that purpose, stable isotope probing (SIP) of DNA and mRNA approaches were used. Arabidopsis thaliana seedlings were grown under 13 CO2 for 27 days, and the presence and expression of phlD gene was determined in the rhizosphere soil and on the roots of A. thaliana. Results showed that phlD was present and expressed by bacteria inhabiting rhizosphere soil and deriving nutrients from the breakdown of organic matter and from root exudates, whereas phlD gene expression seemed to be repressed on roots. These data were validated in vitro by inoculating four plant species by the phytobeneficial bacterium Pseudomonas brassicacearum. phlD gene expression was highly activated by root exudates of wheat and that of Medicago truncatula and to a lesser extent by that of Brassica napus while it was completely suppressed by root exudates of A. thaliana. Overall, these results lead us to the conclusion that the signals to down regulate phl gene expression may derive from A. thaliana root exudates.

Methodologies for Extracellular Enzyme Assays from Wetland Soils

Measurement of extracellular enzymic activity in wetland soils can give an indication of the ecosystems biogeochemical processes, and rates of nutrient and carbon cycling. Analysis of these have allowed researchers to gain an understanding of the ecosystems’ microbial ecology and how it can be affected by environmental factors. Here we give a detailed description of the assays necessary to determine the activity of a suite of key hydrolase enzymes and phenol oxidases. These enzymes control the rates of decomposition and consequently the production of biogenic greenhouse gases. Knowing the processes responsible for the breakdown of organic matter is therefore essential if it becomes necessary to curb these emissions. Our protocols allow for cost effective analysis of a large number of samples and provide sufficient accuracy to determine differences between soil types. When coupled with contemporary microbial techniques these enzyme assays permit entire biochemical pathways to be determined, giving unparalleled knowledge on the processes involved in wetland ecosystems.

Irrigation agriculture affects organic matter decomposition in semi-arid terrestrial and aquatic ecosystems

Many dryland areas are being converted into intensively managed irrigation crops, what can disrupt the hydrological regime, degrade soil and water quality, enhance siltation, erosion and bank instability, and affect biological communities. Still, the impacts of irrigation schemes on the functioning of terrestrial and aquatic ecosystems are poorly understood. Here we assess the effects of irrigation agriculture on breakdown of coarse organic matter in soil and water. We measured breakdown rates of alder and holm oak leaves, and of poplar sticks in terrestrial and aquatic sites following a gradient of increasing irrigation agriculture in a semi-arid Mediterranean basin transformed into irrigation agriculture in 50% of its surface. Spatial patterns of stick breakdown paralleled those of leaf breakdown. In soil, stick breakdown rates were extremely low in non-irrigated sites (0.0001–0.0003day−1), and increased with the intensity of agriculture (0.0018–0.0044day−1). In water, stick breakdown rates ranged from 0.0005 to 0.001day−1, and increased with the area of the basin subject to irrigation agriculture. Results showed that irrigation agriculture affects functioning of both terrestrial and aquatic ecosystems, accelerating decomposition of organic matter, especially in soil. These changes can have important consequences for global carbon budgets.