Publications

Grassland field margin strips, including hedge bottoms, may support a high diversity of wild flower and grass species. This diversity is threatened by applications of fertilizer nitrogen. Organic fertilizer, in the form of farm-yard manure and rain-diluted liquid slurry which only slowly release nitrogen for plant uptake, might prove less damaging. A 5-year experiment on two contrasting sheep grazed, species-rich grassland field margin sites adjoining a mature hedgerow in mid-Wales compared three levels of fertilizer N (0, 100 and 300 kg N ha−1 year−1) with farm yard manure (FYM) and rain-diluted slurry containing an average annual equivalent of 30–42 kg N ha−1 and 27–72 kg N ha−1 respectively. The aim was to assess the impact of treatments on the plant communities of the hedge bottom and field margin strip ecosystems, and to establish whether the species diversity contained within the strips could be encouraged without significantly undermining the quantity and quality of the herbage. By the end of the experiment, the forb component of both ecosystems had been drastically reduced by the high N treatment, to less than half of their original level. The organic treatments on the other hand, particularly FYM showed signs of developing species-rich communities, while at the same time providing a relatively high yielding and nutrient-rich field margin sward of high mineral content. The implications of FYM deposition, particularly in terms of nature conservation considerations are highlighted.

Starch gel electrophoresis was employed to estimate the levels of genetic variation among seven species of the Macrozamia plurinervia complex (Zamiaceae) from eastern Australia. A total of 295 specimens were assayed for 11 enzyme systems coded by 17 loci. The mean number of alleles per locus (A) and proportion of polymorphic loci (P) averaged over seven species were 1.5 and 36.58%. The average observed and expected heterozygosity (H o, H e) were 0.08 and 0.11, respectively, which falls within the range of other Macrozamia species. In the case of Macrozamia cranei and M. machinii, they displayed strong genetic similarity, but were markedly different to the other five species. Among the seven species, M. conferta was the most and M. fearnsidei was the least variable. A fixed allele difference was found only in M. fearnsidei where locus Menadione reductase (MR2) was absent. Along with this, numbers of rare alleles were found in various species, which would facilitate distinguishing one species from another. Based on genetic identity/distance, the Macrozamia species were clustered into two groups. Although the taxa are undoubtedly closely related, the results reinforce current taxonomic concepts based on morphological characters.

Dissolved organic matter (DOM) in freshwaters is recognised as a significant and active component of the global carbon budget. DOM exported from terrestria

Summary Here, we evaluated the impact of bacterial growth stage on the effect of chitosan‐arginine (Ch‐arg) on Escherichia coli O157:H7 cell numbers and metabolic activity within contaminated beef juice held at room temperature. Using a lux‐marked metabolic reporter strain of E. coli O157:H7, the results showed that Ch‐arg was most bioactive against cells in the lag phase and exponential phase. In comparison, there was a reduced, although still significant, inhibitory effect of Ch‐arg on the viability and metabolic activity of E. coli O157 held in stationary phase. Ch‐arg reduced, but did not eliminate E. coli O157 growth in the meat juice over 48 h. Based on the evidence presented here and elsewhere, we conclude that Ch‐arg can limit the growth and activity of food spoilage bacteria; however, it cannot completely eliminate bacterial contaminants originally present. Ch‐arg should therefore be viewed as a potentially protective measure rather than a biocidal agent that completely eliminates the risk of pathogen transfer in the food chain.

Growing demand for agricultural produce, coupled with ambitious targets for greenhouse gas emissions reduction present the scientific, policy and agricultural sectors with a substantial mitigation challenge. Identification and implementation of suitable mitigation measures is driven by both the measures’ effectiveness and cost of implementation. Marginal abatement cost curves (MACCs) provide a simple graphical representation of the abatement potential and cost-effectiveness of mitigation measures to aid policy decision-making. Accounting for heterogeneity in farm conditions and subsequent abatement potentials in mitigation policy is problematic, and may be aided by the development of tailored MACCs. Robust MACC development is currently lacking for mitigation measures appropriate to sheep systems. This study constructed farm-specific MACCs for a lowland, upland and hill sheep farm in the UK. The stand-alone mitigation potential of six measures was modelled, against real farm baselines, according to assumed impacts on emissions and productivity. The MACCs revealed the potential for negative cost emissions’ abatement in the sheep industry. Improving ewe nutrition to increase lamb survival offered considerable abatement potential at a negative cost to the farmers across all farms while, lambing as yearlings offered negative cost abatement potential on lowland and upland farms. The results broadly advocate maximising lamb output from existing inputs on all farm categories, and highlight the importance of productivity and efficiency as influential drivers of emissions abatement in the sector. The abatement potentials and marginal costs of other measures (e.g. reducing mineral fertiliser use and selecting pasture plants bred to minimise dietary nitrogen losses) varied between farms, and this heterogeneity was more frequently attributable to differences in individual farm management than land classification. This has important implications for the high level policy sector as no two farms are likely to benefit from a generic one size fits all approach to mitigation. The construction of further case-study farm MACCs under varying farm conditions is required to define the biophysical and management conditions that each measure is most suited to, generating a more tailored set of sector-specific mitigation parameters.

No abstract is provided for this article.

What determines the way in which roots provide carbon to and interact with other components of the soil? Roots lose metabolites and signal molecules to the soil at rates of significance to soil organisms, and we need to know if the mechanisms of passive diffusion identified in hydroponics apply in soil, and whether other, active mechanisms complement them. New insights from biosensors into the heterogeneity and localization of exudation are transforming our understanding of root–microorganism relations. We need to know more about compounds that are exuded at subnutritional rates in soil and may act as signal molecules modifying the biology of soil organisms. Insights into one suite of such compounds is coming from studies of border cells. These cells are lost from the root cap at a rate regulated by the root and secrete compounds that alter the environment of and gene expression in soil microorganisms and fauna. The amount of root places an upper limit on the effect roots can have; carbon flow to the rhizosphere is a function of root growth. Top-down metabolic control analysis shows that the control over the rate at which roots grow is shared between root and shoot, with most control being in the shoot. Corresponding Editor: D. A. Phillips. For reprints of this Special Feature, see footnote 1, p. 815

No abstract is provided for this article.

Ultra-thin sections of the conidium and hyphae of Acremoniella velata Onions & Jones have been examined in the electron microscope. The conidium was found to possess a relatively thick fibrous wall which was enveloped by an outer membrane. The latter was firmly attached at certain points to the conidium and loosely attached at other points by strands of fibrous tissue. The fine structure of the hyphae did not differ markedly from that observed in other fungi.

: A problem confirmation study was performed at Castle AFB and included 21 potential contaninant source sites identified in the Phase I Report as requiring field investigation. The potential source sites were grouped into 16 investigation sites including the area of a confirmed plume of TCE contamination in ground water. The field investigations, conducted from October 1984 to April 1985 included installation of 27 new monitor wells and 11 shallow lysimeters, collection of sediment samples for surface soil, shallow borings, and drainage ditches, geophysical surveys of three sites, two rounds of surface and groundwater sampling and water level measurements, and pilot test operations on a Base production well. Analytes include votaile organic compounds, TOC, TOX, oil and grease, as well as phenols, nitrate, metals, pesticide and herbicides at selected sites. Of the sixtreen sites investigated, twelve were recommended for further groundwater study, either through continued monitoring of existing wells, or through expansion of the monitoring network. The TCE plume in the shallow aquifer was delineated and recommended for immediate feasibility study; additional investigation to locate the source of the plume and to define its extend in off-Base areas and in an underlying aquifer have also been recommended. Contents of this vol,: Results and Conclusions; Alternatives; Recommendations; References.

Slurry acidification has been shown to be effective in reducing environmentally damaging gases. However, this involved the use of concentrated acids on farms. Therefore, due to the health and safety concerns, there is an interest in self-acidification of slurry technique. This study was designed to determine the microbial dynamics leading to self-acidification of slurry. A fresh cattle slurry was amended 10% brewing sugar and stored over 30 days. This fermentable carbon source promoted self-acidification of the slurry from pH 7.0 to 4.7 within four days, and was associated with the accumulation of lactic acid and a reduction in methane and relative ammonia emissions. A metagenomics approach through next generation sequencing (NGS) using an Illumina MiSeq platform was used to determine the microbial diversity and dynamics (bacteria and archaea) in the stored amended slurry. 16S ribosomal ribonucleic acid (rRNA) sequence data revealed the presence of the Order of <i>Lactobacillales</i> was associated with the lactic acid production. The operational taxonomic units (OTUs) abundance indicates that the methanogenic community was dominated by hydrogenotrophic methanogens from the member Order of <i>Methanobacteriales</i>, <i>Methanomicrobiales</i>, and <i>Methanosarcinales</i>. The decrease in tolerance by the methanogens in the self-acidified slurry was probably the main reason for the reduced methane emission. These results confirm, at the microbial level, the mechanism of inhibiting methane production via self-acidification during storage period.

Amino sugars represent a major constituent of microbial cell walls (e.g. chitin, peptidoglycan) and they are present in large quantities in soil organic matter (SOM). The factors regulating their turnover in soil, however, are poorly understood. Here we investigated the turnover of glucosamine (GlcN) in comparison to glucose (Glc) and N-acetylglucosamine (GlcNAc) in two agricultural grassland soils. Over the range 0–1 mM, GlcN uptake occurred via a saturable high affinity transport systems reflecting its low solution concentrations and low rates of supply. In contrast, Glc uptake was characterised by a non-saturable much lower affinity transport system. Of the GlcN-derived carbon (C) taken into the biomass, ca. 90% was used for the production of new cell biomass rather than in respiration. Whilst temperature affected the uptake (Q 10 = 1.95) and mineralization (Q 10 = 2.32) of GlcN, it did not affect its C use efficiency within the microbial community. We calculated that the average annual flux of GlcN through the soil was 0.01–0.08 g C kg−1 y−1 which equated to 0.1–1.6% of total heterotrophic soil respiration. Microbial use of GlcN was significantly repressed in the presence of sugars (e.g. Glc, sucrose) and N-acetylglucosamine (GlcNAc). We ascribe this to competition at the transport level and due to internal catabolic repression of metabolic pathways involving GlcN within the microbial biomass. Maize (Zea mays L.) roots showed no capacity to take up exogenously applied GlcN at low external concentrations (10 μM) whilst GlcN was rhizotoxic at higher concentrations (EC50 = 49 μM). This suggests that GlcN does not represent a significant source of dissolved organic nitrogen (DON) for plants. The presence of plants did indirectly, however, suppress the use of GlcN by the rhizosphere microbial community. Our work highlights the importance of GlcN in soil C and N cycling, however, we also raise concerns over its importance relative to that of GlcNAc which our evidence suggests plays a more prominent role in soil C and N cycling.