No abstract is provided for this article.
The Fibrobacteres phylum contains two described species, Fibrobacter succinogenes and Fibrobacter intestinalis, both of which are prolific degraders of cellulosic plant biomass in the herbivore gut. However, recent 16S rRNA gene sequencing studies have identified novel Fibrobacteres in landfill sites, freshwater lakes and the termite hindgut, suggesting that members of the Fibrobacteres occupy a broader ecological range than previously appreciated. In this study, the ecology and diversity of Fibrobacteres was evaluated in 64 samples from contrasting environments where cellulose degradation occurred. Fibrobacters were detected in 23 of the 64 samples using Fibrobacter genus-specific 16S rRNA gene PCR, which provided their first targeted detection in marine and estuarine sediments, cryoconite from Arctic glaciers, as well as a broader range of environmental samples. To determine the phylogenetic diversity of the Fibrobacteres phylum, Fibrobacter-specific 16S rRNA gene clone libraries derived from 17 samples were sequenced (384 clones) and compared with all available Fibrobacteres sequences in the Ribosomal Database Project repository. Phylogenetic analysis revealed 63 lineages of Fibrobacteres (95% OTUs), with many representing as yet unclassified species. Of these, 24 OTUs were exclusively comprised of fibrobacters derived from environmental (non-gut) samples, 17 were exclusive to the mammalian gut, 15 to the termite hindgut, and 7 comprised both environmental and mammalian strains, thus establishing Fibrobacter spp. as indigenous members of microbial communities beyond the gut ecosystem. The data highlighted significant taxonomic and ecological diversity within the Fibrobacteres, a phylum circumscribed by potent cellulolytic activity, suggesting considerable functional importance in the conversion of lignocellulosic biomass in the biosphere.
Modifications of Alexander and Jackson's1 technique for the preparation of thin soil sections are described. The distribution of bacterial colonies wit
Microbial decomposition of soil organic matter (SOM) is the source of most of the terrestrial carbon dioxide emission. Consequently, our ability to predict how climate warming will affect the global carbon (C) budget relies on our understanding of the temperature relationship and adaptability of microbial processes. We exposed soil microcosms to temperatures between 0 and 54 °C for 2 months. After this, bacterial growth (leucine incorporation) and functioning (14C-glucose mineralisation) were estimated at 8 temperatures in the interval 0–54 °C to determine temperature relationships and apparent minimum (T min) and optimum (T opt) temperatures for growth and mineralisation. We predicted that incubation at temperatures above the initial T opt for bacteria would select for a warm-adapted community, i.e. a positive shift in T min and T opt for bacterial growth, and that this adaptation of the bacterial community would coincide with a similar shift also for their functioning. As anticipated, we found that exposure to temperatures below T opt did not change the temperature relationship of bacterial growth or mineralisation. Interestingly, T opt for glucose mineralisation was >20 °C higher than that for growth. For bacterial growth, the temperature relationship for the bacterial community was modulated when soils were incubated at temperature above their initial T opt (≈30 °C). This was shown by an increase in T min of 0.8 °C for every 1 °C increase in soil temperature, evidencing a shift towards warm-adapted bacteria. Similarly, the Q 10 (15–25 °C) for bacterial growth increased at temperature higher than T opt. We could not detect a corresponding temperature adaptation of the decomposer functioning. We discuss possible underlying reasons for the temperature-responses of bacterial processes. We note that a temperature adaptation will be rapid when exceeding the T opt, which initially were >20 °C higher for glucose mineralisation than growth. This difference could suggest that different responses to warming exposure should be expected for these microbial processes.
example, perchloroethylene, dichlorobenzene, trichlorobenzene, etc. may be removed by in situ AC heating. It is planned to demonstrate the technology by heating approximately 400 tons of soil in the K-1070 Classified Burial Ground located at DOE`s K-25 Site located in Oak Ridge, TN. It is estimated that the heating portion of the demonstration will take approximately 3 weeks at an average power input rate of 150 to 175 kill. IITRI expects to spend considerable time in the front end reviewing site characteristics, preparing detail design, developing Health and Safety Plans and other documents needed to obtain regulatory approval for the demonstration, arranging for site sampling, infrastructure development and document preparation. It is anticipated that site activities will begin in approximately 5 to 6 months. This contract was signed on September 30, 1993. IITRI started work on it in October 1993. It is planned to complete the demonstration and submit approved final reports by September 30, 1994. This project has 12 tasks and four major milestones. The major milestones and their planned completion dates are presented.
The rhizosphere: biochemistry and organic substances at the soil–plant interface Ed. by Pinton R, Varanini Z & Nannipieri P. 1st edn. 424 pages. New York, USA: Marcel Dekker, Inc, 2001. $175.00 h/b. ISBN 08247 0427 4 This is the third book that aims to present a holistic view of rhizosphere ecology. The two previous texts (Curl & Trueglove, 1986; Lynch, 1990) were good, so the question arises as to whether this book can provide a worthwhile addition to the library. The answer is a wholehearted yes. Unlike the previous volumes, this book attempts to assign a pivotal role to root exudates driving the rhizosphere. For this reason, most of the book is dedicated to understanding the ecological significance of root exudates from various perspectives. The book is an edited collection of chapters, each of which is written by an expert in its respective area. In most cases the selection of authors appears well justified and this is borne out by the quality of texts that have emerged. However, through the multiauthored nature of the book it lacks a certain degree of the coherence that is found in single-authored texts such as ‘Mineral nutrition of higher plants’ (Marschner, 1986). For example, the basic constituents of root exudates, and some of their interactions in soil, are repeated in many of the chapters. Despite this, however, most of the chapters are very well written, can be read in isolation and contain up-to-date literature. In its entirety, the book brings together more than 1200 references on rhizosphere biology and so provides a good synthesis of published material. Typically, each page contains 5–6 citations providing ample room for the authors’ views to be expressed. The literature is critically assessed, in contrast to many books where the tendency is simply to bring information together without synthesizing it. The ‘future prospects’ at the end of each chapter are also an indication of level of thought given by authors to this exercise. The book contains sufficient illustrations to highlight the key points from each chapter. With respect to readership, the book contains many chapters that will be beyond the capability of most undergraduate students as the book, quite rightly in my view, spends little time covering introductory material dealing with soil science, plant physiology, microbiology, etc. The main market for this book therefore will be researchers for whom it provides a fundamental rhizosphere text. The book is somewhat expensive, which will prevent adoption as a general undergraduate text and will also discourage purchase by most individuals. This is a particular shame, as the true value of the book will probably be lost by its absence from most researchers’ bookshelves. In conclusion, I can thoroughly recommend this book as a worthwhile purchase for any science library and for researchers with money left in the grant at the end of the financial year.
The utilization of glucose and citrate either with or without being mixed with one of four commonly-occurring soil mineral phases was assessed using both bacterial cultures and soil incubations. Citrate and glucose, both 14C-labelled, were added separately to bacterial cultures. In each case they were rapidly degraded with >60% recovered as CO2. In the presence of soil the respired proportion declined especially for glucose. The presence of mineral phases (illite–mica, kaolinite, mixed soil clay or ferric hydroxide) had little observable affect on the utilization of glucose in either bacterial cultures or soil. However, ferric hydroxide did induce an alteration in the way 14C was partitioned within the microbial cells. In contrast, citrate degradation was greatly reduced over short periods (6–22h) in the presence of the three clay materials and almost completely inhibited by the presence of ferric hydroxide. The importance of substrate sorption in the context of carbon utilization in the rhizosphere is discussed.
Neonicotinoid pesticides are widely used within agroecosystems. Due to their systemic nature and high solubility, neonicotinoids are frequently recorded in soil, water, untreated plant matter and non-target organisms. Studies have demonstrated their capacity to induce invertebrate mortality, however, very little research has been conducted beyond pollinator exposure, particularly under field conditions. Typically, many neonicotinoids are applied via seed-dressings, reducing their direct contact with pollinators, but offering an unintended soil-exposure pathway. Soil biology underpins many vital functions, from regulating water and gas flow, to maintaining physical soil structure. In this study we investigated the effect of a commercial neonicotinoid pesticide (Insyst®) on the abundance, richness, and composition of both the mesofaunal and microbial communities and associated metabolome during oilseed rape (Brassica napus L.) production. Our results showed that over a single growing season, foliar application of Insyst® (250 g ha−1, 50 g ha−1 of the active ingredient, acetamiprid) had no significant effect (P > 0.05) on the measured soil biological indexes. Seasonal variation was a significantly greater driver in regulating biological communities within the soil than Insyst® application. In addition, we showed that the active ingredient (acetamiprid) was rapidly degraded by the soil microbial community (theoretical half-life = 119 days) during the summer cropping season. These results help highlight the need for realistic field studies, as agricultural pesticides are never pure, often containing surfactants, adjuvants, or emulsifiers which alter their behaviour and ecotoxicity. Understanding the biological interactions of vital soil fauna with necessary pesticide usage will enable proper risk alleviation measures to maintain soil biological and ecological health.
The bulk density, total porosity, air porosity and water-holding capacity of mixtures of equal parts of either sand or scoria with peat moss, pinebark, poppy straw and sawdust can be predicted from the respective properties of the ingredients. Total porosity of the media was inversely correlated to bulk density, but there is no clear correlation between air porosity and bulk density. Air porosity increased with pot size.
Macrozamia johnsonii
Ruminant urine nitrogen (N) concentration and volume are important parameters influencing the size and N loading rate of urine patches deposited to soil. Such parameters can influence N cycling and emissions of the greenhouse gas, nitrous oxide (N2O) from grazed grassland, yet, there is limited information on the effect of these parameters within typical ranges reported for sheep. We used an automated, high-frequency gas monitoring system to investigate N2O emissions from varying urine N application rates and patch sizes under field conditions. Using artificial sheep urine, we manipulated urine N concentration to provide two urine N application rates (4 and 16 g N/L; equivalent to 200 and 800 kg N/ha). We investigated the effect of urine patch size with equal N application rates (4 × 125 cm2 vs 500 cm2, at 200 and 800 kg N/ha) and the effect of patch size with unequal N application rates, but the same total amount of N applied (62.5 mL over 125 cm2 at 800 kg N/ha and 250 mL over 500 cm2 at 200 kg N/ha). Cumulative emissions of N2O generally increased with N loading rate, whether applied as one large urine patch or four smaller ones. Cumulative N2O emissions increased when the N was applied in four smaller urine patches compared with one large patch; this difference was significant at 800 kg N/ha, but not at 200 kg N/ha. When the total amount of N applied was held constant (1 g of N), the amount of N2O released was similar when urine was applied as a high N concentration small patch (800 kg N/ha) compared with a low N concentration large patch (200 kg N/ha). Urine N2O emission factors in this study were, on average, 10 times lower than the IPCC default of 1% for sheep excreta. This research clearly demonstrates that the chemical and physical nature of the urine patch influences N2O emissions, yet further research is required to gather more data on typical sheep urine volumes (individual and daily), urination frequency, urine N concentrations and the typical volumes of soil influenced by urine deposition, to provide more accurate estimates of emissions from sheep grazed pastures.
