Identification of a Brevibacterium marker gene specific to poultry litter and development of a quantitative PCR assay

Aim: To identify a DNA sequence specific to a bacterium found in poultry litter that was indicative of faecal contamination by poultry sources. Methods and Results: Faecally contaminated poultry litter and soils were used as source material for the development of a quantitative polymerase chain reaction (qPCR) method targeting the 16S rRNA gene of a Brevibacterium sp. The identified sequence had 98% nucleotide identity to the 16S rRNA gene of Brevibacterium avium. The qPCR method was tested on 17 soiled litter samples; 40 chicken faecal samples; and 116 nontarget faecal samples from cattle, swine, ducks, geese, and human sewage collected across the United States. The 571‐bp product was detected in 76% of poultry‐associated samples, but not in 93% of faecal samples from other sources. Marker concentrations were 10⁷–10⁹ gene copies per gram in soiled litter, up to 10⁵ gene copies per gram in spread‐site soils, and 10⁷ gene copies per litre in field run‐off water. Results were corroborated by a blinded study conducted by a second laboratory. Conclusion: The poultry‐specific PCR product is a useful marker gene for assessing the impact of faecal contamination as a result of land‐applied poultry litter. Significance and Impact of the Study: This study describes the first quantitative, sensitive and specific microbial source tracking method for the detection of poultry litter contamination.     

Leaf litter identity rather than diversity shapes microbial functions and microarthropod abundance in tropical montane rainforests

In tropical forest ecosystems leaf litter from a large variety of species enters the decomposer system, however, the impact of leaf litter diversity on the abundance and activity of soil organisms during decomposition is little known. We investigated the effect of leaf litter diversity and identity on microbial functions and the abundance of microarthropods in Ecuadorian tropical montane rainforests. We used litterbags filled with leaves of six native tree species (Cecropia andina, Dictyocaryum lamarckianum, Myrcia pubescens, Cavendishia zamorensis, Graffenrieda emarginata, and Clusia spp.) and incubated monocultures and all possible two‐ and four‐species combinations in the field for 6 and 12 months. Mass loss, microbial biomass, basal respiration, metabolic quotient, and the slope of microbial growth after glucose addition, as well as the abundance of microarthropods (Acari and Collembola), were measured at both sampling dates. Leaf litter diversity significantly increased mass loss after 6 months of exposure, but reduced microbial biomass after 12 months of exposure. Leaf litter species identity significantly changed both microbial activity and microarthropod abundance with species of high quality (low C‐to‐N ratio), such as C. andina, improving resource quality as indicated by lower metabolic quotient and higher abundance of microarthropods. Nonetheless, species of low quality, such as Clusia spp., also increased the abundance of Oribatida suggesting that leaf litter chemical composition alone is insufficient to explain variation in the abundances of soil microarthropods. Overall, the results provide evidence that decomposition and microbial biomass in litter respond to leaf litter diversity as well as litter identity (chemical and physical characteristics), while microarthropods respond only to litter identity but not litter diversity.     

Anthropogenic N deposition alters soil organic matter biochemistry and microbial communities on decaying fine roots

Fine root litter is a primary source of soil organic matter (SOM), which is a globally important pool of C that is responsive to climate change. We previously established that ~20 years of experimental nitrogen (N) deposition has slowed fine root decay and increased the storage of soil carbon (C; +18%) across a widespread northern hardwood forest ecosystem. However, the microbial mechanisms that have directly slowed fine root decay are unknown. Here, we show that experimental N deposition has decreased the relative abundance of Agaricales fungi (?31%) and increased that of partially ligninolytic Actinobacteria (+24%) on decaying fine roots. Moreover, experimental N deposition has increased the relative abundance of lignin‐derived compounds residing in SOM (+53%), and this biochemical response is significantly related to shifts in both fungal and bacterial community composition. Specifically, the accumulation of lignin‐derived compounds in SOM is negatively related to the relative abundance of ligninolytic Mycena and Kuehneromyces fungi, and positively related to Microbacteriaceae. Our findings suggest that by altering the composition of microbial communities on decaying fine roots such that their capacity for lignin degradation is reduced, experimental N deposition has slowed fine root litter decay, and increased the contribution of lignin‐derived compounds from fine roots to SOM. The microbial responses we observed may explain widespread findings that anthropogenic N deposition increases soil C storage in terrestrial ecosystems. More broadly, our findings directly link composition to function in soil microbial communities, and implicate compositional shifts in mediating biogeochemical processes of global significance.     

Stronger effects of litter origin on the processing of conifer than broadleaf leaves: A test of home‐field advantage of stream litter breakdown

相似文献   

Resource–consumer diversity: testing the effects of leaf litter species diversity on stream macroinvertebrate communities

1. Understanding relationships between resource and consumer diversity is essential to predicting how changes in resource diversity might affect several trophic levels and overall ecosystem functioning. 2. We tested for the effects of leaf litter species diversity (i.e. litter mixing) on litter mass remaining and macroinvertebrate communities (taxon diversity, abundance and biomass) during breakdown in a detritus‐based headwater stream (North Carolina, U.S.A.). We used full‐factorial analyses of single‐ and mixed‐species litter from dominant riparian tree species with distinct leaf chemistries [red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera), chestnut oak (Quercus prinus) and rhododendron (Rhododendron maximum)] to test for additivity (single‐species litter presence/absence effects) and non‐additivity (emergent effects of litter species interactions). 3. Significant non‐additive effects of litter mixing on litter mass remaining were explained by species composition, but not richness, and litter‐mixing effects were variable throughout breakdown. Specifically, small differences in observed versus expected litter mass remaining were measured on day 14; whereas observed litter mass remaining in mixed‐species leaf packs was significantly higher on day 70 and lower on day 118 than expected from data for single‐species leaf packs. 4. Litter mixing had non‐additive effects on macroinvertebrate community structure. The number of species in litter mixtures (two to four), but not litter species composition, was a significant predictor of the dominance of particular macroinvertebrates (i.e. indicator taxa) within mixed‐species packs. 5. In addition, the presence/absence of high‐ (L. tulipifera) and low‐quality (R. maximum) litter had additive effects on macroinvertebrate taxon richness, abundance and biomass. The presence of L. tulipifera litter had both positive (synergistic) and negative (antagonistic) effects on invertebrate taxon richness, that varied during breakdown but were not related to litter chemistry. In contrast, the presence/absence of L. tulipifera had a negative relationship with total macroinvertebrate biomass (due to low leaf mass remaining when L. tulipifera was present and higher condensed and hydrolysable tannins associated with leaf packs lacking L. tulipifera). Macroinvertebrate abundance was consistently lower when R. maximum was present, which was partially explained by litter chemistry [e.g., high concentrations of lignin, condensed tannins, hydrolysable tannins and total phenolics and high carbon to nutrient (N and P) ratios]. 6. The bottom‐up effects of litter species diversity on stream macroinvertebrates and litter breakdown are different, which suggests that structural attributes of macroinvertebrate communities may only partially explain the effects of litter‐mixing on organic matter processing in streams. In addition, stream macroinvertebrates colonising decomposing litter are influenced by resource diversity as well as resource availability. Broad‐scale shifts in riparian tree species composition will alter litter inputs to streams, and our results suggest that changes in the diversity and availability of terrestrial litter may alter stream food webs and organic matter processing.     

Experience matters: prior exposure to plant toxins enhances diversity of gut microbes in herbivores

For decades, ecologists have hypothesised that exposure to plant secondary compounds (PSCs) modifies herbivore‐associated microbial community composition. This notion has not been critically evaluated in wild mammalian herbivores on evolutionary timescales. We investigated responses of the microbial communities of two woodrat species (Neotoma bryanti and N. lepida). For each species, we compared experienced populations that independently converged to feed on the same toxic plant (creosote bush, Larrea tridentata) to naïve populations with no exposure to creosote toxins. The addition of dietary PSCs significantly altered gut microbial community structure, and the response was dependent on previous experience. Microbial diversity and relative abundances of several dominant phyla increased in experienced woodrats in response to PSCs; however, opposite effects were observed in naïve woodrats. These differential responses were convergent in experienced populations of both species. We hypothesise that adaptation of the foregut microbiota to creosote PSCs in experienced woodrats drives this differential response.     

Non‐additive effects of litter mixing are suppressed in a nutrient‐enriched stream

Investigations of how species compositional changes interact with other aspects of global change, such as nutrient mobilization, to affect ecosystem processes are currently lacking. Many studies have shown that mixed species plant litters exhibit non‐additive effects on ecosystem functions in terrestrial and aquatic systems. Using a full‐factorial design of three leaf litter species with distinct initial chemistries (carbon:nitrogen; C:N) and breakdown rates (Liriodendron tulipifera, Acer rubrum and Rhododendron maximum), we tested for additive and non‐additive effects of litter species mixing on breakdown in southeastern US streams with and without added nutrients (N and phosphorus). We found a non‐additive (antagonistic) effect of litter mixing on breakdown rates under reference conditions but not when nutrient levels were elevated. Differential responses among single‐species litters to nutrient enrichment contributed to this result. Antagonistic litter mixing effects on breakdown were consistent with trends in litter C:N, which were higher for mixtures than for single species, suggesting lower microbial colonization on mixtures. Nutrient enrichment lowered C:N and had the greatest effect on the lowest‐ (R. maximum) and the least effect on the highest‐quality litter species (L. tulipifera), resulting in lower interspecific variation in C:N. Detritivore abundance was correlated with litter C:N in the reference stream, potentially contributing to variation in breakdown rates. In the nutrient‐enriched stream, detritivore abundance was higher for all litter and was unrelated to C:N. Thus, non‐additive effects of litter mixing were suppressed by elevated streamwater nutrients, which increased nutrient content of all litter, reduced variation in C:N among litter species and increased detritivore abundance. Nutrients reduced interspecific variation among plant litters, the base of important food web pathways in aquatic ecosystems, affecting predicted mixed‐species breakdown rates. More generally, world‐wide mobilization of nutrients may similarly modify other effects of biodiversity on ecosystem processes.     

Long‐term effects of the abandonment of grazing on steppe‐like grasslands

Question: What are the consequences of grazing abandonment on the Stipa lessingiana dominated steppe‐like grasslands? What is the relative importance of management and environmental factors in causing variation in species composition and abundance in the continuously grazed and abandoned grassland stands? Location: Transylvanian Lowland, Romania. Methods: Repeated vegetation mapping of a grassland stand, where grazing was abandoned 35 years ago; re‐sampling six grassland stands surveyed 29–57 years ago. For revealing long‐term changes in species composition and rank abundance PCoA ordination was applied. The relative importance of management and environmental factors in structuring vegetation were explored by CCA ordination. Diversity, evenness and the relative number and abundance of red‐listed species were compared between managed and abandoned stands. Results: Our results pointed out that grasslands which were formerly grazed and dominated by S. lessingiana, in the long‐term absence of grazing, have been transformed into a S. pulcherrima dominated type. Management, probably by creating bare surfaces and preventing litter accumulation, had the strongest effect on the species composition and abundance in the grasslands. Abandoned grassland stands had lower diversity and evenness compared to continuously grazed stands. While at the same time, the relative number of threatened, rare species did not differ between managed and abandoned sites. Conclusion: Maintaining extensively grazed, as well as un‐managed, Stipa dominated grasslands would be important in order to create various habitat conditions for plant species, especially threatened and rare species, and promote diversity on the landscape scale.     

Invasive litter, not an invasive insectivore, determines invertebrate communities in Hawaiian forests

In Hawaii, invasive plants have the ability to alter litter-based food chains because they often have litter traits that differ from native species. Additionally, abundant invasive predators, especially those representing new trophic levels, can reduce prey. The relative importance of these two processes on the litter invertebrate community in Hawaii is important, because they could affect the large number of endemic and endangered invertebrates. We determined the relative importance of litter resources, represented by leaf litter of two trees, an invasive nitrogen-fixer, Falcataria moluccana, and a native tree, Metrosideros polymorpha, and predation of an invasive terrestrial frog, Eleutherodactylus coqui, on leaf litter invertebrate abundance and composition. Principle component analysis revealed that F. moluccana litter creates an invertebrate community that greatly differs from that found in M. polymorpha litter. We found that F. moluccana increased the abundance of non-native fragmenters (Amphipoda and Isopoda) by 400% and non-native predaceous ants (Hymenoptera: Formicidae) by 200%. E. coqui had less effect on the litter invertebrate community; it reduced microbivores by 40% in F. moluccana and non-native ants by 30% across litter types. E. coqui stomach contents were similar in abundance and composition in both litter treatments, despite dramatic differences in the invertebrate community. Additionally, our results suggest that invertebrate community differences between litter types did not cascade to influence E. coqui growth or survivorship. In conclusion, it appears that an invasive nitrogen-fixing tree species has a greater influence on litter invertebrate community abundance and composition than the invasive predator, E. coqui.     

Old‐field grassland successional dynamics following cessation of chronic disturbance

Question: Does increasing Festuca canopy cover reduce plant species richness and, therefore, alter plant community composition and the relationship of litter to species richness in old‐field grassland? Location: Southeastern Oklahoma, USA. Methods: Canopy cover by species, species richness, and litter mass were collected within an old‐field grassland site on 16, 40 m × 40 m plots. Our study was conducted during the first three years of a long‐term study that investigated the effects of low‐level nitrogen enrichment and small mammal herbivory manipulations. Results: Succession was altered by an increase in abundance of Festuca over the 3‐yr study period. Species richness did not decline with litter accumulation. Instead, Festuca increased most on species‐poor plots, and Festuca abundance remained low on species‐rich plots. Conclusions: Festuca may act as an invasive transformer‐species in warm‐season dominated old‐field grasslands, a phenomenon associated more with invasions of cool‐season grasses at higher latitudes in North America.     

Seasonal Variations of Indoor Microbial Exposures and Their Relation to Temperature,Relative Humidity,and Air Exchange Rate

Indoor microbial exposure has been related to adverse pulmonary health effects. Exposure assessment is not standardized, and various factors may affect the measured exposure. The aim of this study was to investigate the seasonal variation of selected microbial exposures and their associations with temperature, relative humidity, and air exchange rates in Danish homes. Airborne inhalable dust was sampled in five Danish homes throughout the four seasons of 1 year (indoors, n = 127; outdoors, n = 37). Measurements included culturable fungi and bacteria, endotoxin, N-acetyl-beta-d-glucosaminidase, total inflammatory potential, particles (0.75 to 15 μm), temperature, relative humidity, and air exchange rates. Significant seasonal variation was found for all indoor microbial exposures, excluding endotoxin. Indoor fungi peaked in summer (median, 235 CFU/m³) and were lowest in winter (median, 26 CFU/m³). Indoor bacteria peaked in spring (median, 2,165 CFU/m³) and were lowest in summer (median, 240 CFU/m³). Concentrations of fungi were predominately higher outdoors than indoors, whereas bacteria, endotoxin, and inhalable dust concentrations were highest indoors. Bacteria and endotoxin correlated with the mass of inhalable dust and number of particles. Temperature and air exchange rates were positively associated with fungi and N-acetyl-beta-d-glucosaminidase and negatively with bacteria and the total inflammatory potential. Although temperature, relative humidity, and air exchange rates were significantly associated with several indoor microbial exposures, they could not fully explain the observed seasonal variations when tested in a mixed statistical model. In conclusion, the season significantly affects indoor microbial exposures, which are influenced by temperature, relative humidity, and air exchange rates.     

不同树叶凋落物对人参土壤理化性质及微生物群落结构的影响

树种选择是林下山参护育成败的关键,研究树叶凋落物对人参土壤养分、微生物群落结构组成的影响,旨在为林下山参护育选择适宜林地及农田栽参土壤改良提供科学依据和理论指导。通过盆栽试验,研究添加5.0 g色木槭Acer mono.Maxim.var.mono(A)、赤松Pinus densiflora Sieb.et Zucc.(B)、胡桃楸Juglans mandshurica Maxim.(C)、紫椴Tilia amurensis Rupr.(D)、蒙古栎Quercus mongolica Fisch.ex Ledeb.(E)树叶凋落物到土壤中,种植人参(Panax ginseng C.A.meyer)后研究土壤理化性质以及微生物群落结构的变化。结果表明:添加不同树叶处理后人参土壤性质发生改变,土壤p H值显著高于对照土壤5.91(P0.05),土壤全氮、速效氮磷、微生物碳氮在所有树叶处理中显著增加(P0.05),而土壤容重、速效钾和C/N在添加树叶处理中降低。18个土壤样品基因组,经16S和ITS1测序分别得到6064和1900个OUTs。其中细菌涵盖了42门、117纲、170目、213科、225属,真菌涵盖了24门、98纲、196目、330科、435属。不同树叶处理人参土壤细菌和真菌地位发生改变,细菌Proteobacteria是树叶分解的关键微生物,添加树叶后其多样性显著高于对照(P0.05)。而细菌Bacteroidetes和真菌Basidiomycota可能是区别阔叶林和针叶林树种的关键微生物,针叶林中含量显著低于阔叶林(P0.05),而真菌Ascomycota是针叶林分解的关键微生物。进一步从不同分类水平上得到特定树叶凋落物的特异细菌和真菌。典型相关分析(CDA)表明细菌Bacteroidetes、Chloroflexi、Actinobacteria及真菌Basidiomycota、Zygomycota、Chytridiomycota及Ascomycota的位置及多样性的改变均与土壤因子SMBN、TN、AP、SOC、AK、C/N、p H有关。综上所述,添加不同树叶后不仅提高土壤微生物量碳氮、改善土壤理化性质,同时改变微生物群落结构组成,不同树叶处理土壤理化性质不同导致人参土壤微生物组成的差异,本结果对于林下参选地和农田栽参土壤微生物改良具有理论指导作用。     

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。     

Diverse mechanisms for CO2 effects on grassland litter decomposition

The ongoing increase in atmospheric CO₂ concentration ([CO₂]) can potentially alter litter decomposition rates by changing: (i) the litter quality of individual species, (ii) allocation patterns of individual species, (iii) the species composition of ecosystems (which could alter ecosystem‐level litter quality and allocation), (iv) patterns of soil moisture, and (v) the composition and size of microbial communities. To determine the relative importance of these mechanisms in a California annual grassland, we created four mixtures of litter that differed in species composition (the annual legume Lotus wrangelianus Fischer & C. Meyer comprised either 10% or 40% of the initial mass) and atmospheric [CO₂] during growth (ambient or double‐ambient). These mixtures decomposed for 33 weeks at three positions (above, on, and below the soil surface) in four types of grassland microcosms (fertilized and unfertilized microcosms exposed to elevated or ambient [CO₂]) and at a common field site. Initially, legume‐rich litter mixtures had higher nitrogen concentrations ([N]) than legume‐poor mixtures. In most positions and environments, the different litter mixtures decomposed at approximately the same rate. Fertilization and CO₂ enrichment of microcosms had no effect on mass loss of litter within them. However, mass loss was strongly related to litter position in both microcosms and the field. Nitrogen dynamics of litter were significantly related to the initial [N] of litter on the soil surface, but not in other positions. We conclude that changes in allocation patterns and species composition are likely to be the dominant mechanisms through which ecosystem‐level decomposition rates respond to increasing atmospheric [CO₂].     

A comparison of worker exposure to inhalable and total dust, inorganic arsenic, and borates using two types of particulate sampling assemblies in a borate mining and processing facility

This study describes a comparison of worker exposure to total and inhalable dust, inorganic As, and borates using two types of particulate sampling assemblies as part of a comprehensive industrial hygiene evaluation in a borate mining and processing facility. Employees were segmented into similar exposure groups (SEG) based on work location within the facility, job classification, and type of chemical agent. Approximately 10% of the employees from each SEG wore two personal sampling devices simultaneously for the purpose of collecting total and inhalable particulate fractions using a closed face, 37-mm mixed cellulose ester matched-weight filters (MMW), and Institute of Occupational Medicine (IOM) sampling assembly. Sample results indicated that the IOM concentrations were consistently higher than the corresponding MMW concentrations for all three agents. An analysis was performed to investigate a relationship between MMW and IOM. The data revealed correlation coefficient values of 0.72, 0.82, and 0.84 for total dust (n = 197), inorganic As (n = 137), and borates (n = 194), respectively. These positive correlation coefficients indicate that the IOM and MMW measurements are consistent with each other, and can be used for predicting exposure levels. The total dust and borate large mean ratios should be considered in developing inhalable fraction-based regulatory standards.     

The effect of microbial challenge on the intestinal proteome of broiler chickens

Background

In poultry production intestinal health and function is paramount to achieving efficient feed utilisation and growth. Uncovering the localised molecular mechanisms that occur during the early and important periods of growth that allow birds to grow optimally is important for this species. The exposure of young chicks to used litter from older flocks, containing mixed microbial populations, is a widely utilised model in poultry research. It rarely causes mortality but effects an immunogenic stimulation sufficient enough to cause reduced and uneven growth that is reflective of a challenging growing environment.

Methods

A mixed microbial challenge was delivered as used litter containing Campylobacter jejuni and coccidial oocysts to 120 male Ross 308 broiler chicks, randomly divided into two groups: control and challenged. On day 12, 15, 18 and 22 (pre- and 3, 6 and 10 days post-addition of the used litter) the proximal jejunum was recovered from 6 replicates per group and differentially abundant proteins identified between groups and over time using 2D DiGE.

Results

The abundance of cytoskeletal proteins of the chicken small intestinal proteome, particularly actin and actin associated proteins, increased over time in both challenged and control birds. Villin-1, an actin associated anti-apoptotic protein, was reduced in abundance in the challenged birds indicating that many of the changes in cytoskeletal protein abundance in the challenged birds were as a result of an increased rate of apoptosis. A number of heat shock proteins decreased in abundance over time in the intestine and this was more pronounced in the challenged birds.

Conclusions

The small intestinal proteome sampled from 12 to 22 days of age showed considerable developmental change, comparable to other species indicating that many of the changes in protein abundance in the small intestine are conserved among vertebrates. Identifying and distinguishing the changes in proteins abundance and molecular pathways that occur as a result of normal growth from those that occur as a result of a challenging microbial environment is important in this major food producing animal.

     

Litter Breakdown and Microbial Succession on Two Submerged Leaf Species in a Small Forested Stream

Microbial succession during leaf breakdown was investigated in a small forested stream in west-central Georgia, USA, using multiple culture-independent techniques. Red maple (Acer rubrum) and water oak (Quercus nigra) leaf litter were incubated in situ for 128 days, and litter breakdown was quantified by ash-free dry mass (AFDM) method and microbial assemblage composition using phospholipid fatty acid analysis (PLFA), ribosomal intergenic spacer analysis (RISA), denaturing gradient gel electrophoresis (DGGE), and bar-coded next-generation sequencing of 16S rRNA gene amplicons. Leaf breakdown was faster for red maple than water oak. PLFA revealed a significant time effect on microbial lipid profiles for both leaf species. Microbial assemblages on maple contained a higher relative abundance of bacterial lipids than oak, and oak microbial assemblages contained higher relative abundance of fungal lipids than maple. RISA showed that incubation time was more important in structuring bacterial assemblages than leaf physicochemistry. DGGE profiles revealed high variability in bacterial assemblages over time, and sequencing of DGGE-resolved amplicons indicated several taxa present on degrading litter. Next-generation sequencing revealed temporal shifts in dominant taxa within the phylum Proteobacteria, whereas γ-Proteobacteria dominated pre-immersion and α- and β-Proteobacteria dominated after 1 month of instream incubation; the latter groups contain taxa that are predicted to be capable of using organic material to fuel further breakdown. Our results suggest that incubation time is more important than leaf species physicochemistry in influencing leaf litter microbial assemblage composition, and indicate the need for investigation into seasonal and temporal dynamics of leaf litter microbial assemblage succession.     

Effects of experimental harvesting of an invasive hybrid cattail on wetland structure and function

Invasive plants, such as the hybrid cattail Typha × glauca, can reduce biodiversity and alter the ability of wetlands to provide critical ecosystem services, including nutrient cycling and carbon storage. Several approaches have been used to reduce Typha dominance and restore invaded wetlands, but long‐term studies assessing benefits of these restoration efforts are limited. A previous study demonstrated that aboveground harvesting of Typha × glauca stems and litter reduced Typha dominance 2 years post‐treatment in a Great Lakes coastal wetland. In the current study, we extended monitoring of experimental aboveground Typha harvest to 4 years post‐treatment and added assessments of treatment effects on soil nutrients, carbon emissions, and microbial community composition. Aboveground harvest treatment resulted in a dramatic reduction in Typha litter cover that persisted for 4 years, increased soil temperature, and increased abundance of the native plant genus Carex. However, aboveground harvest treatment did not significantly reduce Typha abundance, nor did it have significant effects on soil nutrient concentrations, carbon fluxes, or the taxonomic composition of soil microbial communities. We did observe differences in bacterial community composition between plots based on time since Typha invasion, which may indicate some legacy effects of Typha invasion. At the scale of this experiment (4 × 4 m plots), our results indicate that a single aboveground removal of Typha × glauca is not sufficient to restore a heavily invaded freshwater wetland ecosystem, and that periodic harvesting of Typha stems and litter may be required to maintain native plant abundance.     

生长猪结肠乳酸菌菌群的昼夜节律性变化

【目的】本文旨在研究生长猪在24 h内结肠乳酸菌的多样性变化、丰富度变化与节律性变化。【方法】选取6头装有结肠瘘管的“杜×长×大”三元杂交生长猪,于清晨6:00开始,每隔3 h连续采集一天内生长猪的结肠食糜,提取DNA,用乳酸菌特异性引物进行高通量测序,在属和种水平上分析结肠乳酸菌菌群丰度与节律性变化。【结果】生长猪结肠乳酸菌在24 h内Chao1和Simpson指数发生显著性变化(P<0.05);属水平上Lactobacillus相对丰度最高,一天内在6:00时相对丰度最低,为94.15%,18:00时相对丰度最高,为97.46%;种水平上Lactobacillus johnsonii相对丰度最高,一天内在3:00时相对丰度最低,为47.66%,18:00时相对丰度最高,为71.59%,Lactobacillus reuteri丰度次之。生长猪结肠乳酸菌中46个核心OTU具有节律性,均为Lactobacillus;而在种水平上Lactobacillus gasseri、Lactobacillus johnsonii、Lactobacillus sp. KC45a和Lactobacillus reuteri显现出节律性(P<0.05)。【结论】生长猪结肠乳酸菌在24 h内多样性发生显著性变化,在种水平上显现出节律性,丰富了我们对猪肠道微生物昼夜节律的了解。     

Litter effects of two co-occurring alpine species on plant growth, microbial activity and immobilization of nitrogen

We measured the litter chemistry of two co‐dominant alpine species, Acomastylis rossii, a forb characterized by a low growth rate and N uptake capacity, and Deschampsia caespitosa, a grass characterized by a high growth rate and N uptake capacity, and examined the effect litter of these two species had on the growth of Deschampsia phytometers in a greenhouse. We also examined the influence of litter from the two species on microbial respiration and immobilization of N, in two separate laboratory microcosm experiments and in the field. We hypothesized that Acomastylis litter would reduce plant growth more than Deschampsia litter, corresponding with either 1) suppression of microbial activity and thus a decrease in N mineralization, or 2) by stimulation of microbial biomass and increasing microbial immobilization of N. Relative to Deschampsia litter, Acomastylis litter had higher total water soluble organic carbon (DOC), and higher total phenolic concentration. Deschampsia litter had 30 times higher carbohydrate (primarily glucose and fructose) concentrations than Acomastylis litter. Soil respiration, microbial biomass N, and consumption of DOC and N were higher with the Acomastylis litter treatment than the Deschampsia litter treatment in experimental microcosms, and both respiration and microbial biomass N were higher in field soils under canopies dominated by Acomastylis relative to those dominated by Deschampsia. These results indicate that phenolics in Acomastylis are a C source for soil microorganisms, rather than an inhibitor of microbial activity. Deschampsia phytometers grew significantly less, had higher root: shoot biomass ratios, and acquired less nitrogen in the Acomastylis litter treatment relative to the control and Deschampsia litter treatments. The results of these experiments indicate that Acomastylis litter influences soil N cycling by increasing microbial activity and N immobilization, which may influence N supply to neighboring plants. This mechanism has the potential to influence competitive interactions between Acomastylis and its neighbors.