First Stages Of Decomposition Research Articles

Degradation of peat-forming plants at the first stages of decomposition in natural and post-pyrogenic peatlands of West Siberia

The aim of the study. Assessment of the phytomass stocks and decomposition rate of peat-forming plants’ residues in peat deposits of natural and post-pyrogenic peatlands at the initial stages of decomposition. Location and time of the study. The study was carried out in 2022 (May-September) at two oligotrophic bog sites: “Bakcharskoye” (field station “Vasyuganye”, IMCES SB RAS) and “Iksinskoye”, which are located in the north eastern spurs of the Great Vasyugan mire in the Bakcharsky and Shegarsky districts of the Tomsk region, Russia. Methods. The phytomass stocks were determined by the cutting method. The following fractions were separated: living phytomass (annual and perennial photosynthetic phytomass, i.e. green parts of grasses, shrubs leaves, mosses); perennial non-photosynthetic phytomass, i.e. shrubs stems, roots of grasses and shrubs; and dead phytomass (mortmass), i.e. litter, moss litter, standing dead phytomass. The decomposition rate of plant residues was determined by the method of litter bags placement in peat (Chamaedaphne calyculata, Sphagnum fuscum, Mixed sample consisting of 60% S. fuscum and 40% Ch. calyculata). In the initial and decomposed samples, the ash content was determined by the dry combustion method. The total carbon and nitrogen content, as well as the carbon and nitrogen isotopic composition, were determined using a DELTA V Advantage isotope ratio mass spectrometer. Results. This short-term study conducted during the growing season in conditions of undisturbed (Natural Ryam) and post-pyrogenic (Gar) phytocenoses showed that due to a significant amount of mortmass (2402 g/m2) Natural Ryam had organic matter stock exceeding that in the Gar by 1.7 times. On average, 59% of organic matter loss from the total losses during the growing season occurred in the first month. In both Gar and Natural Ryam conditions, minimal losses of organic matter were characteristic for Sphagnum fuscum (3.1 and 3.5% respectively). For the remaining samples the Gar conditions were more favorable for the degradation at the initial stages of decomposition. The Mixed sample occupied an intermediate position between its individual components in terms of mass losses. Carbon losses correlated well with mass losses both over 1 month of degradation (r=0.87) and over 4 months (r=0.96). In contrast to carbon, nitrogen accumulated in the Mixed sample at the initial stages of degradation, both after 1 month and 4 months. Conclusions. With smaller phytomass stocks in areas of post-pyrogenic succession, more active decay at the initial stages of organic matter decomposition occurs exactly under these conditions. The impact of post-pyrogenic succession on the rate of organic matter decomposition of Chamaedaphne calyculata plant residues and the Mixed sample was demonstrated. The most intensive decomposition of litter occured during the first month of degradation. Additionally, in the conditions of a burnt bog, a more intense release of nitrogen from all plant residues and accumulation of ash elements in Sphagnum fuscum samples were observed. The mixing of litter components influenced both the rate and dynamics of decomposition. The carbon and nitrogen isotopic composition began to change during the initial stages of decomposition, leading to enrichment with heavier isotopes 15N and 13C. This research emphasizes the importance of studying the processes of plant litter decomposition at the initial stages and considering the plant residue composition when studying the processes of organic matter transformation.

Decomposition rate of peat-forming plants at the initial stages of destruction in peat deposits of the oligotrophic bogs “Bakcharskoe” and “Timiryasevskoe”

The research presents quantitative estimates of the decomposition rate of plant residues at the initial stages of the decay of four plant species (Eriophorum vaginatum, Carex rostrata, Sphagnum fuscum, Sphagnum angustifolium) in peat deposits of the oligotrophic bogs in the southern taiga subzone of Western Siberia. We also studied the change in the content of total carbon, nitrogen and ash elements in plant residues and the activity of microflora at the initial stages of decomposition. The studies were conducted in the bogs characterized by various hydrothermal conditions. At the initial stage of the decay of peat-forming plants the maximum losses of mass occur in the first month of the experiment and reach 36-52% of the total loss of organic matter during the growing season. Sphagnum fuscum is the most resistant to decomposition. The most intense decomposition of Sphagnum fuscum at the initial stages of decomposition is characteristic for warmer and less humid conditions of the Timiryazevskoe bog. It was revealed that mass losses of organic matter correlate well with total carbon losses. The most intensive decreasing of the total carbon content as well as mass loss of organic matter are observed after the first month of the experiment. The maximal decline of carbon in plant residues was received for Eriophorum vaginatum. During the decomposition of plant residues, the nitrogen content was decreasing, and the most intense nitrogen losses were characteristic for Sphagnum mosses. Nitrogen loss in peat-forming plants during the first month of decomposition varies depending on the locality conditions, but it becomes equal during the later decomposition stages. At the first stages of decomposition of plant residues, both the accumulation and the loss of ash elements were observed in the samples. Both the Bakcharskoe and Timiryazevskoe bogs were characterized by the accumulation of ash elements in plant samples of Eriophorum vaginatum. Dynamics of mass loss and removal of elements are directly related to the activity of microorganisms. The maximum number of microorganisms was found in July and September. Peat and plant samples located in the peat deposit of the Timiryazevskoe bog are more saturated with microorganisms of the nitrogen cycle, and samples from the Bakcharskoe bog are richer in carbon cycle microorganisms. Microorganisms of the lignocellulosic complex were less active as compared with other groups of microorganisms. The number of microorganisms assimilating the mineral forms of nitrogen are on average 1.5 times less than the number of microorganisms assimilating the organic forms. The positive correlation between the nitrogen content and the number of fungi was found. In addition, correlation between the numbers of denitrifiers and oligotrophs was found. It is explained by trophic relationshipsbetween these groups of microorganisms.

Function of bacterial community dynamics in the formation of cadaveric semiochemicals during in situ carcass decomposition.

The decomposition of dead mammalian tissue involves a complex temporal succession of epinecrotic bacteria. Microbial activity may release different cadaveric volatile organic compounds which in turn attract other key players of carcass decomposition such as scavenger insects. To elucidate the dynamics and potential functions of epinecrotic bacteria on carcasses, we monitored bacterial communities developing on still-born piglets incubated in different forest ecosystems by combining high-throughput Illumina 16S rRNA sequencing with gas chromatography-mass spectrometry of volatiles. Our results show that the community structure of epinecrotic bacteria and the types of cadaveric volatile compounds released over the time course of decomposition are driven by deterministic rather than stochastic processes. Individual cadaveric volatile organic compounds were correlated with specific taxa during the first stages of decomposition which are dominated by bacteria. Through best-fitting multiple linear regression models, the synthesis of acetic acid, indole and phenol could be linked to the activity of Enterobacteriaceae, Tissierellaceae and Xanthomonadaceae, respectively. These conclusions are also commensurate with the metabolism described for the dominant taxa identified for these families. The predictable nature of in situ synthesis of cadaveric volatile organic compounds by epinecrotic bacteria provides a new basis for future chemical ecology and forensic studies.

Fungal succession in relation to volatile organic compounds emissions from Scots pine and Norway spruce leaf litter-decomposing fungi

Leaf litter fungi are partly responsible for decomposition of dead material, nutrient mobilization and gas fluxes in forest ecosystems. It can be assumed that microbial destruction of dead plant materials is an important source of volatile organic compounds (VOCs) emitted into the atmosphere from terrestrial ecosystems. However, little information is available on both the composition of fungal VOCs and their producers whose community can be changed at different stages of litter decomposition. The fungal community succession was investigated in a litter bag experiment with Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) needle litter. The succession process can be divided into a several stages controlled mostly by changes in litter quality. At the very first stages of decomposition the needle litter was colonized by ascomycetes which can use readily available carbohydrates. At the later stages, the predominance of Trichoderma sp., the known producers of cellulolytic enzymes, was documented. To investigate the fungi-derived VOCs, eight fungi species were isolated. As a result of gas chromatographic analyses, as many as 75C2C15 fungal volatile compounds were identified. Most components detected in emissions were very reactive substances: the principal groups of VOCs were formed by monoterpenes, carbonyl compounds and aliphatic alcohols. It was found that production of VOCs by fungi is species specific: only 10 metabolites were emitted into the gas phase by all eight species. The reported data confirm that the leave litter decomposition is important source of reactive organic compounds under the forest canopy.

Mass and Nutrient Loss of Leaf Litter Collecting in Littertraps: An In Situ and Ex Situ Study

In forest ecosystems, litterfall collected in trapping devices is exposed to periods of wetting and drying, which may initiate the first stages of decomposition. This could lead to an underestimation of organic matter and nutrient input due to leaching or an overestimation due to immobilization. The objectives of this study were to quantify changes in mass and nutrient stocks of sugar maple (Acer saccharum Marsh.), basswood (Tilia americana L.), and beech (Fagus grandifolia Ehrh.) leaves under in situ conditions and to quantify changes in leaf mass and nutrient stocks and leachate concentration when exposed to different quantities of moisture (high 100 mm, medium 60 mm, and low 30 mm) under ex situ conditions. Results from this study showed that sugar maple and basswood had a significantly greater (P 0.05) mass loss than beech in the in situ and ex situ study. Nutrient stocks either decreased significantly (P 0.05) or remained the same, depending on species in the in situ study. Similar results were observed in the ex situ study, in which carbon, nitrogen, phosphorus, and potassium stocks decreased significantly (P 0.05) with increasing exposure to moisture, but calcium and magnesium stocks showed less pronounced changes. Mean concentrations of dissolved organic carbon, dissolved organic nitrogen, and ammonium were significantly different (P 0.05) between species and moisture treatments, whereas nitrite showed no such differences. Results from this study suggested that the collection of leaf litter should take place frequently during the peak leaf abscission period and during periods of high precipitation. This would provide a more accurate quantification of the quantity of nutrients entering the forest ecosystem in the within-system pathway between live vegetation and the forest floor detritus pool. In addition, more frequent litterfall collection may also minimize litter decomposition and nitrification. FOR .S CI. 59(4):484-493.

Species-Specific Effects of Epigeic Earthworms on Microbial Community Structure during First Stages of Decomposition of Organic Matter

BackgroundEpigeic earthworms are key organisms in organic matter decomposition because of the interactions they establish with microorganisms. The earthworm species and the quality and/or substrate availability are expected to be major factors influencing the outcome of these interactions. Here we tested whether and to what extent the epigeic earthworms Eisenia andrei, Eisenia fetida and Perionyx excavatus, widely used in vermicomposting, are capable of altering the microbiological properties of fresh organic matter in the short-term. We also questioned if the earthworm-induced modifications to the microbial communities are dependent on the type of substrate ingested.Methodology/Principal FindingsTo address these questions we determined the microbial community structure (phospholipid fatty acid profiles) and microbial activity (basal respiration and microbial growth rates) of three types of animal manure (cow, horse and rabbit) that differed in microbial composition, after being processed by each species of earthworm for one month. No differences were found between earthworm-worked samples with regards to microbial community structure, irrespective of type of manure, which suggests the existence of a bottleneck effect of worm digestion on microbial populations of the original material consumed. Moreover, in mesocosms containing cow manure the presence of E. andrei resulted not only in a decrease in bacterial and fungal biomass, but also in a reduced bacterial growth rate and total microbial activity, while no such reduction was found with E. fetida and P. excavatus.Conclusions/SignificanceOur results point to the species of earthworm with its associated gut microbiota as a strong determinant of the process shaping the structure of microbial communities in the short-term. This must nonetheless be weighed against the fact that further knowledge is necessary to evaluate whether the changes in the composition of microbiota in response to the earthworm species is accompanied by a change in the microbial community diversity and/or function.

Chemical composition of volatile and extractive compounds of pine and spruce leaf litter in the initial stages of decomposition

Abstract. A litter bag experiment was conducted to analyze changes in chemical composition in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) needle litter in the first stages of decomposition in natural conditions. The emission rates of monoterpenes and concentration of extractive secondary metabolites were determined five times over a 16-month period. It has been shown that pine and spruce needle litter in the first stages of decomposition (up to 165 days) emits monoterpene hydrocarbons into the gas phase with the rates comparable to those in emissions from live needles of these trees. This suggests that leaf litter is an important source of atmospheric terpenes. It has also been proved that the litter contains considerable amounts of non-volatile substances that can be precursors of oxidized volatile compounds formed as a result of enzymatic reactions. Non-volatile but water soluble secondary metabolites of the leaf litter may be involved in nutrient cycling and have an influence on soil community.

Evaluation of Efficiency of Schoenly Trap for Collecting Adult Sarcosaprophagous Dipterans

Communities of adult sarcosaprophagous dipterans were evaluated using both Schoenly traps (BST) baited with rabbit carcasses and the traditional forensic methodology (TradC) in the Sabana de Bogotà, Colombia. During 42 sampling days, 2,726 adult dipterans were collected (2,291 by BST and 435 by TradC) belonging to 31 morphospecies (31 by BST and 23 by TradC) and 14 families (14 by BST and 10 by TradC). Significant differences in the species abundance, richness, diversity, and dominance were found between BTC and TradC. BST collected more individuals and species than TradC. Rank correlations and matched rank-abundance plots indicated a significant nesting of the dipteran community collected by TradC with respect to BST captures. By comparing the structure and composition of the collected communities, only those collected by BST showed repeatability of the results. The above-mentioned information allows us to consider BST as a superior methodology to perform inventories of Diptera imagoes associated with carcasses. In the community collected by BST, the most abundant and rich families were Calliphoridae, Muscidae, Phoridae, and Sarcophagidae, all of them necrophagous species associated with carcasses. Calliphoridae and Muscidae were dominant in the first stages of decomposition (fresh and active decomposition), and Phoridae was the principal family during decomposition, dry remains, and bones stages.

Study of the early deactivation in pyrolysis of polymers in the presence of catalysts

In this work, the early degradation step of the pyrolysis of some polymers in the presence of certain catalysts has been studied using thermogravimetric analysis (TGA). Three commercial polymers (PE, PP and EVA) and three catalysts were studied (ZSM-5, MCM-41a, and MCM-41b), and the MCM-41a catalyst has been selected for the analysis of the earlier steps of the pyrolysis process carried out in the presence of catalysts. Several cycles of heating–cooling were performed using a thermobalance, in order to analyze the influence of the first stages of decomposition on the activity of the more accessible active sites involved. In this way, the behaviour of the polymer–catalyst mixtures (20% (w/w) of catalyst) was studied and compared with that observed in the corresponding thermal degradation as well as in the pyrolysis in the presence of catalysts, in a single heating cycle. The results obtained clearly show the existence of an early degradation step. For a polymer–catalyst system with low steric hindrances such as PE-MCM-41, this early degradation step causes a noticeable decrease of the catalyst activity for the main decomposition step (i.e., cracking of the chain). The decrease of the catalytic activity is lower for a polymer–catalyst system with higher steric restrictions, as occurs in the EVA-MCM-41 degradation process. However, in this case, the catalyst activity in the first decomposition step (i.e., the loss of the acetoxi groups) is noticeable decreased after one pyrolysis run, thus reflecting that the active sites involved are mainly the most accessible ones.

Litter decomposition and faunal activity in Mediterranean forest soils: effects of N content and the moss layer

Accumulation of soil carbon is mainly controlled by the balance between litter production and litter decomposition. Usually In Mediterranean forests there are contrasting conditions in the distribution of faunal activity and the moss layer that may have different effects on litter decomposition. Decomposition and faunal activity were studied by exposing litter of contrasting quality (Pinus halepensis Mill. and Quercus ilex L.) for 3.5 yr in three Mediterranean pine forests of the eastern Iberian Peninsula. The effects of mosses on decomposition and on faunal activity were studied by exposing P. halepensis litter either on moss patches or directly on the forest floor. Faecal pellet production was used as an indication of faunal activity. Water availability or soil characteristics seem to limit faunal activities in the drier sites. Faecal pellets were not found during the first stages of decomposition and in all sites they appeared when about a 30% of the initial litter had decomposed. Under wet conditions faecal pellet production was very high and a mass balance suggested that soil faunal activity may result in a net flow of organic matter from the lower organic horizons to the surface Oi horizon. Mosses slightly increased mass loss of pine litter probably as a consequence of high potentially mineralizable nitrogen in the Oa horizon of moss patches and also, perhaps, as a consequence of the higher moisture content measured in the Oi horizon needles sampled among the mosses. In contrast, moss patches reduced faunal activity. The effect of litter quality on mass loss was not always significant, suggesting an interaction between litter quality and site conditions. During the first stages of decomposition there was N immobilisation in P. halepensis litter (poorer in N) and N release from Q. ilex litter (richer in N). In conclusion, in these forests soil microclimate and/or N availability appear to be more important controlling litter decomposition than the distribution of faunal activity.

Litter decomposition and faunal activity in Mediterranean forest soils: effects of N content and the moss layer

Accumulation of soil carbon is mainly controlled by the balance between litter production and litter decomposition. Usually In Mediterranean forests there are contrasting conditions in the distribution of faunal activity and the moss layer that may have different effects on litter decomposition. Decomposition and faunal activity were studied by exposing litter of contrasting quality ( Pinus halepensis Mill. and Quercus ilex L.) for 3.5 yr in three Mediterranean pine forests of the eastern Iberian Peninsula. The effects of mosses on decomposition and on faunal activity were studied by exposing P. halepensis litter either on moss patches or directly on the forest floor. Faecal pellet production was used as an indication of faunal activity. Water availability or soil characteristics seem to limit faunal activities in the drier sites. Faecal pellets were not found during the first stages of decomposition and in all sites they appeared when about a 30% of the initial litter had decomposed. Under wet conditions faecal pellet production was very high and a mass balance suggested that soil faunal activity may result in a net flow of organic matter from the lower organic horizons to the surface Oi horizon. Mosses slightly increased mass loss of pine litter probably as a consequence of high potentially mineralizable nitrogen in the Oa horizon of moss patches and also, perhaps, as a consequence of the higher moisture content measured in the Oi horizon needles sampled among the mosses. In contrast, moss patches reduced faunal activity. The effect of litter quality on mass loss was not always significant, suggesting an interaction between litter quality and site conditions. During the first stages of decomposition there was N immobilisation in P. halepensis litter (poorer in N) and N release from Q. ilex litter (richer in N). In conclusion, in these forests soil microclimate and/or N availability appear to be more important controlling litter decomposition than the distribution of faunal activity.

Discrimination against 13C during degradation of simple and complex substrates by two white rot fungi.

Changes in isotopic 13C signatures of CO2-C evolved during decomposition of a sugar (glucose), a fatty acid (palmitic acid), a protein (albumin), a structural biopolymer (lignin) and bulk plant tissue (aerial shoots from Lolium perenne) were monitored over a period of 76 days. All materials were sterilized and inoculated with either of two different species of white rot fungi, Phanerochaete chrysosporium or Coriolus versicolor, and incubated in sealed bottles at 28 degrees C. The CO2 concentration in the jars was periodically determined using an infrared gas analyzer and its isotopic (13C) signature was assessed using a trace gas (ANCA TGII) module coupled to an isotope ratio mass spectrometer (IRMS, Europa 20-20). L. perenne material inoculated with C. versicolor showed the highest C mineralization activity with approximately 70% of total C evolved as CO2 after 76 days of incubation, followed by glucose. Substrates inoculated with C. versicolor generally decomposed faster than when degraded by P. chrysosporium, except for lignin, where no significant differences between the two fungi types were found and CO2-C released was less than 2% of the initial C. Considerable 13C isotopic fractionation during the degradation of plant tissue and of pure biochemical compounds was revealed as well as progressive shifts in cumulative CO2-13C isotopic signatures over time. During the first stages of decomposition, the CO2-C released was usually depleted in 13C as compared with the initial solid substrate, but with ongoing decomposition the CO2-C evolved became progressively more enriched in 13C. P. chrysosporium usually showed a slightly higher 13C fractionation than C. versicolor during the first decomposition phase. At posterior decomposition stages isotopic discrimination was often stronger by C. versicolor. These findings on isotopic 13C discrimination during microbial degradation both of simple biochemical compounds and of complex vegetal tissue confirmed not only the existence of significant 13C isotopic fractionation during plant residue decomposition, but also the existence of non-random isotopic distribution within substrates. They also demonstrated the ability of microorganisms to selectively discriminate against 13C even when degrading an isolated simple substrate.

Synthesis, Spectra, Thermal Analysis and Crystal Structure of Trans-Bis(2-Pyridinepropanol)Bis (Saccharinato)Cobalt(II)

The title complex, [Co(pypr)2(sac)2] (pypr = 2-pyridinepropanol and sac = saccharinate), has been prepared and characterized by elemental analysis, electronic and FTIR spectra, magnetic susceptibility measurements, thermal analysis and X-ray diffractometry. The complex crystallizes in triclinic space group PI with a = 8.1836(2), b = 10.0062(2), c = 10.4989(3) Å, α = 90.474(1), β = 107.989(1) and γ = 110.923(1)°. The cobalt(II) ion sits on a center of symmetry and is octahedrally coordinated by two pypr and two sac ligands. Both pypr and sac ligands occupy the trans positions of the coordination octahedron. The two pypr ligands are neutral and act as bidentate N- and O-donor ligands forming two symmetry-related seven-membered chelate rings around the cobalt(II) ion, while both sac ligands are O-coordinated through the carbonyl oxygen atoms. On heating the endothermic removal of two pypr ligands occurs in the first stages of decomposition and at higher temperatures the Co/sac intermediate decomposes to Co3O4 and finally to CoO.

Saccharin complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with ethanolamine and diethanolamine: synthesis, spectroscopic and thermal characteristics. Crystal structures of [Zn(ea) 2(sac) 2] and [Cu 2(μ-dea) 2(sac) 2

New mixed ligand Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes of saccharin (sac) with ethanolamine (ea) and diethanolamine (dea) were synthesized and characterized by elemental analyses, magnetic moments, UV–Vis and IR spectra. The Co(II)–ea, Co(II)–dea and Cu(II)–dea complexes are dimeric, while all the other complexes of ea and dea are mononuclear. The crystal structures of [Zn(ea) 2(sac) 2] and [Cu 2(μ-dea) 2(sac) 2] complexes were determined by single crystal X-ray diffraction. In the Zn(II) complex, the Zn(II) ion sits on a center of symmetry and is octahedrally coordinated by two bidentate ea (N, O) and two monodentate sac (N) ligands. The centrosymmetric binuclear Cu(II) complex contains two strongly distorted square-planarly coordinated Cu(II) ions bridged by two alkoxo groups of the deprotonated dea. The dea ligand also coordinates to the Cu(II) ions through its nitrogen, while the other ethanolic group does not involve in coordination. The saccharinate anion coordinates to the Cu(II) ion with its nitrogen. Thermal behavior of the complexes was studied using DTA and TG in nitrogen atmosphere. Endothermic degradation of the ea and dea ligands occurs in the first stages of decomposition and the sac anions decompose at higher temperatures to give corresponding metal oxides or metals.

Di- and triethanolamine complexes of Co(II), Ni(II), Cu(II) and Zn(II) with thiocyanate: synthesis, spectral and thermal studies. Crystal structure of dimeric Cu(II) complex with deprotonated diethanolamine, [Cu 2(μ-dea) 2(NCS) 2

New mixed ligand Co(II), Ni(II), Cu(II) and Zn(II) complexes of di- (dea) and triethanolamine (tea) with thiocyanate were synthesized and characterized by elemental analyses, magnetic moments, UV–Vis and IR spectra. All the metal complexes of tea, and the Ni(II) and Zn(II) complexes of dea are mononuclear, while the Co(II) and Cu(II) complexes of dea are dimeric. The crystal structure of the bis(μ-diethanolaminato) bis(isothiocyanato)dicopper(II) complex were determined by single crystal X-ray diffraction. The centrosymmetric binuclear complex contains two strongly distorted square-pyramidally coordinated copper ions bound together by two alkoxo bridges. The bridging oxygen is a deprotonated oxygen of the ethanolic group of dea. The dea ligand also coordinates to the Cu(II) ions through its nitrogen, while the other ethanolic group does not involve in coordination. The thiocyanate anion coordinates to the Cu(II) ion with its nitrogen. Thermal reactivity of the complexes was studied using DTA and TG. Degradation of the amine ligands in the complexes occurs in the first stages of decomposition and the thiocyanate anions decompose at higher temperatures to give corresponding metal oxides.

Hardness of Cu–Mn–Al alloys as a function of the annealing temperature in the β phase

Samples of Cu–10.0at.%Mn–18.8at.%Al and Cu–11.0at.%Mn–18.1at.%Al alloys were prepared in the metastable austenitic β phase, by quenching from 1123 K into water at room temperature. The as quenched samples were found to be L2 1 ordered. Aging of these alloys at different temperatures induced an evolution of the microhardness. These microhardness changes are interpreted using the information from X-ray diffraction (XRD), martensitic transformation temperature measurements, transmission electron microscopy (TEM) and microanalysis using scanning electron microscopy (SEM). Changes in microhardness at low temperatures are correlated with the martensitic transformation temperature M s provided that M s is close to room temperature. Microhardness changes at higher temperatures are caused by the decomposition of the β phase. The kinetics of β phase decomposition was followed measuring its 200 XRD peak intensity. The experiments suggest that the last vestiges of β phase are L2 1 long range ordered and that an α fcc phase is formed during the first stages of decomposition.

Nutrient cycling in forests.

Studies of nutrient cycling in forests span more than 100 yr. In earlier years, most attention was given to the measurement of the pools of nutrients in plants and soil and of the return of nutrients from plant to soil in litterfall. The past 20 yr or so have seen a major concentration on the processes of nutrient cycling, with particular emphasis on those processes by which the supply of nutrients to the growing forest is sustained. In the more highly productive forests, up to 10 tonnes of litter of low nutritional quality is deposited annually on the forest floor. The decomposition of this litter, the mineralization of the nutrients it holds, and the uptake of nutrients by tree roots in the carbon-rich environment which results are the themes of this review. Studies of decomposition of litter in forests have been dominated by the role of nitrogen as a limiting factor, a domination which reflects the preponderance of studies of temperate forests in the Northern Hemisphere. For many forests of the world growing on soils of considerable age, it seems more probable that growth and nutrient cycling are limited by phosphorus (or some other element). There is increasing evidence for a number of forests that phosphorus is immobilized in the first stages of decomposition to a significantly greater extent than is nitrogen. Advances in research will depend, as with studies of soil organic matter, in denning and developing analytical techniques for studying biologically active forms of potentially limiting nutrients, rather than total elemental concentrations. The availability of phosphorus in forests is sustained by phosphorus cycling. More than 50% of the total phosphorus in the surface soils is in organic forms and much of the more labile phosphorus is in the form of diesters. Phosphorus availability is determined by competition between biological and geochemical sinks, and it is clear that the sinks in the rhizosphere (plant roots, microorganisms, soil mineral and organic components) are extensively modified by active processes (e.g. production of exudates, nutrient storage in a variety of organic or polymeric forms and nutrient transport away from sites of uptake). There is abundant evidence that roots of many species exude compounds which have the ability to solubilize sources of phosphorus of otherwise low availability. The significance of root exudates (for example, phosphatases, organic acids) in the functioning of perennial ecosystems has yet to be quantified and there are conflicting reports as to the effects of simple organic acids on phosphorus availability. The distribution of phosphorus sinks and their relative competitiveness and their modification are topics of fundamental importance for future research. In contrast to the mineralization of phosphorus, our knowledge of transformations and availability of nitrogen in forest soils is well-developed. Net nitrogen mineralization rates approximate rates of nitrogen return in litterfall but the contribution of nitrification is variable. Nitrification is not inhibited by the low pH of many forest soils and there is increasing evidence of nitrate immobilization by microorganisms and of increased diversity and better competitiveness for NH4 + of nitrifying microorganisms than has previously been accepted. Variability in rates of nitrification is often interpreted as being due to allelopathy. Hypotheses invoking allelopathy are more or less untestable, and it seems likely that new techniques using 15 N in situ will lead to a more fundamental understanding of nitrogen transformations in forest soils. Recent studies in coniferous forest soils have highlighted the short (< 1 d) turnover time of NH4 + . Finally, it seems that forest soils are resistant to major changes in patterns of nitrogen mineralization (and certainly, because of the large number of sinks, in patterns of phosphorus mineralization) following disturbance by natural events such as wind-throw and fire, and by man-made events such as logging and fertilizing. The long-term disturbance by acid rain is a more complex matter since forest ecosystems are not adequate buffers for nitrate. Contents Summary 561 I. Introduction 562 II. Linking nutrient cycling to nutrient availability - Setting the themes 563 III. The nature of soil organic matter 566 IV. Tree roots and the availability of nutrients 566 V. The decomposition of forest litter 569 VI. Mineralization of organically-bound nutrients 571 Acknowledgements 576 References 576.

Thermogravimetric study of polyacrylamide with evolved gas analysis

AbstractDried samples of polyacrylamide in an He atmosphere have been subjected to thermogravimetric analysis in the 30–600°C range, and the evolved gases were monitored by FTIR. Water, ammonia, and small quantities of carbon dioxide are released in the first stages of decomposition (220–340°C), where the polymer chains remain intact and the reaction occurs on the pendant amide groups. In the second stage of decomposition (340–440°C), the majority of the weight loss occurs, and main chain breakdown occurs, releasing carbon dioxide, water, nitrile compounds, and imides. Trapping of the gases in this stage and analysis by GC–FTIR and GC–MS reveals the presence of more than 20 decomposition products, and confirms that a large proportion of these can be assigned to glutarimide and its substituted analogs. Imidization and dehydration reactions on the amide groups, as well as free radical breakdown of the main chains, with inter‐ and intramolecular hydrogen transfer, can account for many of the products of the decomposition. © 1993 John Wiley &amp; Sons, Inc.

A comparison of the thermal behaviour of α-AIF3 and aluminium fluoride hydrates

The thermal decompositions ofβ-AlF3 · 3H2O, AlF3 · 3.5H2O, AlF3 · 1.5H2O,β-AlF3 and hydroxyfluorides of aluminium were investigated. The literature data were complemented with X-ray results. The first stages of decomposition are described. The AlF3 hydrates and hydroxyfluorides were used as model systems in order to interpret the thermal behaviour of α-AlF3 in more detail.

ChemInform Abstract: STUDY OF HETEROPOLYANIONS BY SOLID‐STATE NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

AbstractDie Anwendbarkeit der Festkörper‐"P‐ und 29Si‐NMR‐Spektroskopie zur Charakterisierung von festen Heteropolyanionen wird demonstriert.