Publications

The rhizosphere is the zone of soil immediately surrounding plant roots that is modified by root activity. In this critical zone, plants perceive and respond to their environment. As a consequence of normal growth and development, a large range of organic and inorganic substances are exchanged between the root and soil, which inevitably leads to changes in the biochemical and physical properties of the rhizosphere. Plants also modify their rhizosphere in response to certain environmental signals and stresses. Organic anions are commonly detected in this region, and their exudation from plant roots has now been associated with nutrient deficiencies and inorganic ion stresses. This review summarizes recent developments in the understanding of the function, mechanism, and regulation of organic anion exudation from roots. The benefits that plants derive from the presence of organic anions in the rhizosphere are described and the potential for biotechnology to increase organic anion exudation is highlighted.

The bioavailability of nitrogen (N) in soil relies on the progressive breakdown of necromass protein to peptide and amino acid components and conversion to inorganic N forms. We understand the fluxes and pathways of the N cycle downstream from amino acids, but our understanding of the factors controlling peptide and amino acid mineralization, particularly in arid soils, is lacking. We investigated the influence of temperature on the rate of dissolved organic carbon (DOC) and nitrogen (DON) cycling in three agricultural soils from Saudi Arabia. Although the physical and chemical properties of the soils differed markedly, phospholipid fatty acid (PLFA) analysis revealed they had similar topsoil and subsoil microbial communities. Soils behaved similarly in terms of the rate of substrate use, microbial C-use efficiency, and response to temperature. Substrate mineralization rate increased with temperature with more C being allocated to microbial catabolic rather than anabolic processes. Our results show that climate change is likely to lead to changes in soil organic matter turnover and shift C allocation patterns within the soil microbial community. This is expected to reduce soil quality and exacerbate nutrient losses. Management strategies are required to promote the retention of organic matter in these soils.

1. Two fungi, Coniothyrium minitans Campbell and Trichoderma viride Pers. ex Fr., were grown on autoclaved crushed sclerotia of the species Sclerotinia sclerotiorum, which they parasitize. 2. In vitro the crude culture filtrates would lyse walls isolated from hyphal cells or the inner pseudoparenchymatous cells of the sclerotia, in which a branched beta-(1-->3)-beta-(1-->6)-glucan, sclerotan, is a major constituent. 3. Chromatographic fractionation of the enzymes in each culture filtrate revealed the presence of several laminarinases, the most active being an exo-beta-(1-->3)-glucanase, known from previous studies to attack sclerotan. Acting alone this brought about a limited degradation of the glucan, but the addition of fractions containing an endo-beta-(1-->3)-glucanase led to almost complete breakdown. A similar synergism between the two enzymes was found in their lytic action on cell walls. 4. When acting alone the endo-beta-(1-->3)-glucanase had a restricted action, the products including a trisaccharide, tentatively identified as 6(2)-beta-glucosyl-laminaribiose. 5. These results are discussed in relation to the structure of the cell walls and of their glucan constituents.

This paper empirically examines the hypothesis that popularity is typified by ‘electoral cycle effects’. We suggest that if the data is filtered, on the basis of a model assuming informed voters, there is no evidence for the electoral cycle hypothesis.

Cross-sectional survey results from a COVID19 plane infection risk survey conducted between the 22^nd to 23^rd October, 2020. Participants (<em>n</em> = 2103) were aged 18 years or older, were living in the UK and had undertaken foreign air travel. The survey consisted of 18 closed-ended questions, with seventeen of the questions addressing issues associated with travelling by air and 11 questions addressing specific demographic topics. The questionnaire was designed by the research team, consisting of environmental microbiologists, public health specialists and social scientists, based on the study objectives and incorporating information from previous studies on same topic. The draft questionnaire was then tested on an expert panel, a panel of non-experts, a local ethics committee. First, perceived risks, concerns, and subjective knowledge of COVID-19 symptoms were measured using 16 options that included 14 actual symptoms and 2 which were not. Other questions about perception and risk were measured by statements with a 5-point Likert scale (e.g. strongly disagree to strongly agree).

1. Commercial pressed baker's yeast, and cell walls prepared from it, were extracted in various ways and the products examined by a number of techniques, including infrared spectroscopy and electron microscopy. 2. The glucan components of the walls cannot be extracted from intact yeast cells by 3% (w/v) sodium hydroxide at 75 degrees , but at least one-third of the glucan of cell wall preparations is dissolved under these conditions, and more will dissolve after ultrasonic treatment. 3. If intact cells are given a preliminary treatment with acid the wall glucans dissolve in dilute aqueous alkali. 4. Acid conditions as mild as sodium acetate buffer, pH5.0, for 3hr. at 75 degrees are sufficient for this preliminary treatment; the glucan then dissolves in 3% sodium hydroxide at 75 degrees leaving a very small residue, which contains chitin and about 1% of the initial glucan of the wall. Dissolution is hindered by exclusion of air, or by a preliminary reduction with sodium borohydride, suggesting that some degradation of the glucan by alkali is taking place. 5. After treatment with 0.5m-acetic acid for 24hr. at 90 degrees the glucan dissolves slowly at room temperature in 3% sodium hydroxide, or in dimethyl sulphoxide. The extraction with acetic acid removes glycogen and a predominantly beta-(1-->6)-linked glucan (not hitherto recognized as a component of baker's yeast), but none of the beta-(1-->3)-glucan, which remains water-insoluble. 6. Without treatment with acid, the glucan is not significantly soluble in dimethyl sulphoxide, but can be induced to dissolve by ultrasonic treatment. 7. These results are interpreted by postulating the presence of an enclosing membrane, composed of chitin and glucan, that when intact acts as a semipermeable membrane preventing the escape of the alkali- and dimethyl sulphoxide-soluble fraction of the glucan. Mild acid treatments damage this membrane, and ultrasonic and ballistic disintegration disrupt it. 8. Some support for this hypothesis is given by the effects of certain enzyme preparations, which have been found to render a substantial part of the glucan extractable by dimethyl sulphoxide.

The combined impacts of simulated increased nitrogen (N) deposition (75kgNha−1 yr−1) and increasing background ozone (O3) were studied using two mesotrophic grassland species (Dactylis glomerata and Ranunculus acris) in solardomes, by means of eight O3 treatments ranging from 15.5ppb to 92.7ppb (24h average mean). A–C i curves were constructed for each species to gauge effects on photosynthetic efficiency and capacity, and effects on biomass partitioning were determined after 14 weeks. Increasing the background concentration of O3 reduced the healthy above ground and root biomass of both species, and increased senesced biomass. N fertilisation increased biomass production in D. glomerata, and a significantly greater than additive effect of O3 and N on root biomass was evident. In contrast, R. acris biomass was not affected by high N. The study shows the combined effects of these pollutants have differential implications for carbon allocation patterns in common grassland species.

Nitrogen (N2) fixation in feather moss-cyanobacteria associations is a major source of N for boreal ecosystems. However, mosses experience significant shif

The biological fixation of atmospheric nitrogen (N) is a major pathway for available N entering ecosystems. In N-limited boreal forests, a significant amount of N2 is fixed by cyanobacteria living in association with mosses, contributing up to 50 % to the total N input. In this review, we synthesize reports on the drivers of N2 fixation in feather moss-cyanobacteria associations to gain a deeper understanding of their role for ecosystem-N-cycling. Nitrogen fixation in moss-cyanobacteria associations is inhibited by N inputs and therefore, significant fixation occurs only in low N-deposition areas. While it has been shown that artificial N additions in the laboratory as well as in the field inhibit N2 fixation in moss-cyanobacteria associations, the type, as well as the amounts of N that enters the system, affect N2 fixation differently. Another major driver of N2 fixation is the moisture status of the cyanobacteria-hosting moss, wherein moist conditions promote N2 fixation. Mosses experience large fluctuations in their hydrological status, undergoing significant natural drying and rewetting cycles over the course of only a few hours, especially in summer, which likely compromises the N input to the system via N2 fixation. Perhaps the most central question, however, that remains unanswered is the fate of the fixed N2 in mosses. The cyanobacteria are likely to leak N, but whether this N is transferred to the soil and if so, at which rates and timescales, is unknown. Despite our increasing understanding of the drivers of N2 fixation, the role moss-cyanobacteria associations play in ecosystem-N-cycling remains unresolved. Further, the relationship mosses and cyanobacteria share is unknown to date and warrants further investigation.

In this article the performance of a grid-connected PV system supplying a farmstead was evaluated using a commercially available energy balance simulation model, Hybrid2. By performing annual hourly simulations, theinfluence of system size, actual radiation data, and estimated radiation data on economic and energy production were assessed. The estimated radiation data were developed from kriging actual radiation data from 16 weather stations in western Nebraska. The results indicated that the capital costs associated with a PV system dictate the economicperformance of the overall system. The energy costs associated with the grid-connected PV system were six times the retail price of electricity. The use of actual or estimated data had little effect on the simulated performance of the system.

Journal Article Effects of Dazomet on Phenolase Activity in Sclerotia of Sclerotinia sclerotiorum Get access D. VAUGHAN, D. VAUGHAN Departments of Soil Organic Chemistry and Microbiology, The Macaulay Institute for Soil ResearchCraigiebuckler, Aberdeen AB9 2QJ, Scotland Search for other works by this author on: Oxford Academic PubMed Google Scholar D. JONES D. JONES Departments of Soil Organic Chemistry and Microbiology, The Macaulay Institute for Soil ResearchCraigiebuckler, Aberdeen AB9 2QJ, Scotland Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Experimental Botany, Volume 30, Issue 4, August 1979, Pages 751–758, https://doi.org/10.1093/jxb/30.4.751 Published: 01 August 1979 Article history Received: 09 January 1979 Published: 01 August 1979