SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Decomposition

50

Human decomposition is a mosaic system with an intimate association between biotic and abiotic factors. Despite the integral role of bacteria in the decomposition process, few studies have catalogued bacterial biodiversity for terrestrial scenarios. To explore the microbiome of decomposition, two cadavers were placed at the Southeast Texas Applied Forensic Science facility and allowed to decompose under natural conditions. The bloat stage of decomposition, a stage easily identified in taphonomy and readily attributed to microbial physiology, was targeted. Each cadaver was sampled at two time points, at the onset and end of the bloat stage, from various body sites including internal locations. Bacterial samples were analyzed by pyrosequencing of the 16S rRNA gene. Our data show a shift from aerobic bacteria to anaerobic bacteria in all body sites sampled and demonstrate variation in community structure between bodies, between sample sites within a body, and between initial and end points of the bloat stage within a sample site. These data are best not viewed as points of comparison but rather additive data sets. While some species recovered are the same as those observed in culture-based studies, many are novel. Our results are preliminary and add to a larger emerging data set; a more comprehensive study is needed to further dissect the role of bacteria in human decomposition.

Concepts: Oxygen, Archaea, Death, Microbiology, Ribosomal RNA, 16S ribosomal RNA, Decomposition, Body

34

Peatlands contain one-third of soil carbon ©, mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have focused on surface warming. We show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH4 emissions. However, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20-30 cm of peat from experimental plots have higher CH4 production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH4 and CO2 are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. There are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. These results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.

Concepts: Carbon dioxide, Soil, Carbon, Methane, Fossil fuel, Coal, Peat, Decomposition

28

Peatlands are carbon-rich ecosystems that cover just three per cent of Earth’s land surface, but store one-third of soil carbon. Peat soils are formed by the build-up of partially decomposed organic matter under waterlogged anoxic conditions. Most peat is found in cool climatic regions where unimpeded decomposition is slower, but deposits are also found under some tropical swamp forests. Here we present field measurements from one of the world’s most extensive regions of swamp forest, the Cuvette Centrale depression in the central Congo Basin. We find extensive peat deposits beneath the swamp forest vegetation (peat defined as material with an organic matter content of at least 65 per cent to a depth of at least 0.3 metres). Radiocarbon dates indicate that peat began accumulating from about 10,600 years ago, coincident with the onset of more humid conditions in central Africa at the beginning of the Holocene. The peatlands occupy large interfluvial basins, and seem to be largely rain-fed and ombrotrophic-like (of low nutrient status) systems. Although the peat layer is relatively shallow (with a maximum depth of 5.9 metres and a median depth of 2.0 metres), by combining in situ and remotely sensed data, we estimate the area of peat to be approximately 145,500 square kilometres (95 per cent confidence interval of 131,900-156,400 square kilometres), making the Cuvette Centrale the most extensive peatland complex in the tropics. This area is more than five times the maximum possible area reported for the Congo Basin in a recent synthesis of pantropical peat extent. We estimate that the peatlands store approximately 30.6 petagrams (30.6 × 10(15) grams) of carbon belowground (95 per cent confidence interval of 6.3-46.8 petagrams of carbon)-a quantity that is similar to the above-ground carbon stocks of the tropical forests of the entire Congo Basin. Our result for the Cuvette Centrale increases the best estimate of global tropical peatland carbon stocks by 36 per cent, to 104.7 petagrams of carbon (minimum estimate of 69.6 petagrams of carbon; maximum estimate of 129.8 petagrams of carbon). This stored carbon is vulnerable to land-use change and any future reduction in precipitation.

Concepts: Tropics, Soil, Fossil fuel, Coal, Peat, Decomposition, Central Africa, Peat swamp forest

27

Despite their importance in urban drainage systems, gully pot internal processes have received little scientific study. Therefore, gully pot contents were examined to gain a basic understanding of these processes and to establish the decomposition characteristics of the contents ex situ. Moisture content, organic matter content, enzyme activity and pH were measured to investigate seasonal and geographical effects, in addition to a 5-week composting trial to determine the rate and characteristics of decomposition. Little difference was observed in the content processes, especially between seasons, and the composting trial illustrated organic content decreased at an average rate of 0.1 g of organic matter per 13 g of organic matter per day. The results from this study indicate an as yet unknown initial decomposition rate. Activity monitored between gully pots also suggests they are relatively similar systems across space and time; enabling gully contents to be evaluated universally in future research.

Concepts: Time, Scientific method, Enzyme, PH, Space, Humus, Decomposition, Sustainable urban drainage systems

27

Data on the ecology and bionomics of necrophagous beetles are scarce in tropical countries despite their relevance in forensic investigations. We performed a survey on the diversity and temporal pattern of colonization of beetles on pig carcasses in a fragment of dry forest in northeastern Brazil. We collected 1550 adults of diverse feeding habits from 12 families, of which 96% had necrophagous and/or copro-necrophagous habits and belonged to four families: Dermestidae, Scarabaeidae, Cleridae and Trogidae. Three species, Dermestes maculatus, Necrobia rufipes and Omorgus suberosus are reported for the first time with an expanded geographical distribution that includes the semi-arid region in Brazil. Adult beetles were collected as early as 24h after death. One endemic species, Deltochilum verruciferum, stood out in terms of numerical dominance and temporal occurrence during different stages of decomposition. Its intimate association with carrion emphasizes their potential role in forensic entomology in the region.

Concepts: Biodiversity, Death, Biology, Forensic science, Calliphoridae, Decomposition, Dermestidae, Cleridae

26

Most forensic research that is used to better understand how to estimate the postmortem interval (PMI) entails the study of the physiochemical characteristics of decomposition and the effects that environmental factors have on the decomposition process. Forensic entomology exploits the life cycles of arthropods like Diptera (blow flies or flesh flies) and Coleoptera (beetles) deposited on the decaying carcass to determine PMI. Forensic taphonomy, from the Greek word taphos meaning burial, studies the creation of the fossils of decomposed cadavers to ascertain information as to the nature and time of death. Compared to other areas of taphonomy, there have been relatively few forensic science studies that have investigated the impact of human decomposition on the microbial changes occurring on or in a corpse or in the soil communities underneath a body. Such research may facilitate the critical determination of PMI. Therefore, the scope of this review is to provide a concise summary of the current progress in the newly emerging field of microbial diversity and the next-generation metagenomic sequencing approaches for assessing these communities in humans and in the soil beneath decomposing human.

Concepts: Death, Insect, Forensic science, Embalming, Decomposition, Death metal, Taphonomy, Histeridae

26

Cellulose decomposing microorganisms (CDMs) are important for efficient bioconversion of plant biomasses. To this end, we isolated seven fungal isolates (Aspergillus wentii, Fusarium solani, Mucor sp., Penicillum sp., Trichoderma harzaianum, Trichoderma sp.1 and Trichoderma sp.2) and three bacterial isolates (bacterial isolate I, II and III) from partially decomposed farm yard manure, rice straw and vermicompost, and evaluated them for decomposition of rice straw (Oryza sativa), Ipomoea camea and Eichhornia crassipes biomass. CDMs inoculation, in general, reduced the composting period by 14-28 days in rice straw, 14-34 days in Eichhornia and 10-28 days in Ipomoea biomass over control. Of the 10 CDMs tested, Mucor sp. was found to be the most effective as Mucor-inoculated biomass required minimum time, i.e. 84, 68 and 80 days respectively for composting of rice straw, Eichhornia and Ipomoea biomass as against 112, 102 and 108 days required under their respective control. CDMs inoculation also narrowed down the C:N ratio of the composts which ranged from 19.1-22.7, 12.9-14.7 and 10.5-13.1 in rice straw, Eichhornia and Ipomoea biomass respectively as against 24.1, 17.1 and 16.2 in the corresponding control treatments. Aspergillus wentii, Fusarium solani, Mucor sp., and Penicillum sp. were found most effective (statistically at par) in reducing C:N ratio and causing maximum loss of carbon and dry matter in composted materials. These benefits of CDMs inoculation were also accompanied by significant increase in NPK contents in the composted materials.

Concepts: Photosynthesis, Bacteria, Fungus, Compost, Chemical decomposition, Decomposition, Composting, Eichhornia crassipes

24

Pitfall trapping is a sampling technique frequently used by entomologists around the world. However, there exist sampling biases linked to particular trapping designs, which require investigation. In this study, we compared the effects of the type of preservative fluid (propylene glycol or formaldehyde) and the presence of fish bait in pitfall traps on the number of specimens (individuals) collected, the species richness, and the species composition of carabid (Coleoptera: Carabidae) and silphid (Coleoptera: Silphidae) beetle assemblages. Traps containing propylene glycol collected a substantially higher number of individuals of both taxa and a higher number of silphid species compared with traps containing formaldehyde. The use of fish bait in the traps increased the number of individuals collected and the number of species collected for silphid beetles but had no effect on the collection parameters for carabids. The species composition of the carabid assemblages was minimally affected by the presence of fish bait or the type of preservative fluid, whereas the fish bait had a substantial effect on the species composition of silphids. The silphid species that feed directly on vertebrate carcasses were almost completely absent in the nonbaited traps. The results suggest that pitfall traps baited with fish and containing propylene glycol as a preservative fluid are optimal for the simultaneous sampling of carabid and silphid beetles, which both provide important ecosystem services (e.g., predation of pests and decomposition of vertebrate carcasses) and are therefore interesting for ecological research.

Concepts: Beetle, Propylene glycol, Adephaga, Beetles, Ground beetle, Decomposition, Bombardier beetle, Silphidae

21

Ungulate gnawing on bone has been reported in the taphonomic and zooarchaeological literature, but there are no known reports of ungulates altering human remains. Herein, we report on the first known photographic evidence of deer gnawing human remains. As described in nonhuman scavenging literature, forking of the bone characterizes the taphonomic effect of deer gnawing in this case, which is distinct from the effect caused by other scavengers. This type of osteophagia during the winter season is consistent with previously documented behavior of deer gnawing on nonhuman bone, possibly to obtain minerals absent in their diet. In this study, we briefly discuss the distinguishing features of ungulate gnawing, the reasons for this behavior, and possible confusion with other common types of scavenging and modification. This report contributes to taphonomic literature covering the range of animal interactions with human skeletal remains.

Concepts: Deer, Report, White-tailed deer, Elk, Moose, Decomposition, Carnivore, Ungulate

18

Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon-nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.

Concepts: Climate, Nutrient, Soil, Nitrogen, Climate change, Carbon cycle, Global warming, Decomposition