Phosphorus supply influences heathland responses to atmospheric nitrogen deposition.

On an upland moor dominated by pioneer Calluna vulgaris and with an understorey of mosses and lichens, experimental plots were treated with factorial combinations of nitrogen (N) at +0 and +20kg Nha(-1)yr(-1), and phosphorus (P) at +0 and +5kg Pha(-1)yr(-1). Over the 4-year duration of the experiment, the cover of the Calluna canopy increased in density over time as part of normal phenological development. Moss cover increased initially in response to N addition but then remained static; increases in cover in response to P addition became stronger over time, eventually causing reductions in the cover of the dominant Calluna canopy. Lichen cover virtually disappeared within 4 years in plots receiving +20kg Nha(-1)yr(-1) and also in separate plots receiving +10kg Nha(-1)yr(-1), but this effect was reversed by the addition of P.

Modelling nitrogen saturation and carbon accumulation in heathland soils under elevated nitrogen deposition.

A simple model of nitrogen (N) saturation, based on an extension of the biogeochemical model MAGIC, has been tested at two long-running heathland N manipulation experiments. The model simulates N immobilisation as a function of organic soil C/N ratio, but permits a proportion of immobilised N to be accompanied by accumulation of soil carbon (C), slowing the rate of C/N ratio change and subsequent N saturation. The model successfully reproduced observed treatment effects on soil C and N, and inorganic N leaching, for both sites. At the C-rich upland site, N addition led to relatively small reductions in soil C/N, low inorganic N leaching, and a substantial increase in organic soil C. At the C-poor lowland site, soil C/N ratio decreases and N leaching increases were much more dramatic, and soil C accumulation predicted to be smaller. The study suggests that (i) a simple model can effectively simulate observed changes in soil and leachate N; (ii) previous model predictions based on a constant soil C pool may overpredict future N leaching; (iii) N saturation may develop most rapidly in dry, organic-poor, high-decomposition systems; and (iv) N deposition may lead to significantly enhanced soil C sequestration, particularly in wet, nutrient-poor, organic-rich systems.

Effects of increased deposition of atmospheric nitrogen on an upland moor: leaching of N species and soil solution chemistry.

This study was designed to investigate the leaching response of an upland moorland to long-term (10 yr) ammonium nitrate additions of 40, 80 and 120 kg N ha(-1) yr(-1) and to relate this response to other indications of potential system damage, such as acidification and cation displacement. Results showed increases in nitrate leaching only in response to high rates of N input, in excess of 96 and 136 kg total N input ha(-1) yr(-1) for the organic Oh horizon and mineral Eag horizon, respectively. Individual N additions did not alter ammonium leaching from either horizon and ammonium was completely retained by the mineral horizon. Leaching of dissolved organic nitrogen (DON) from the Oh horizon was increased by the addition of 40 kg N ha(-1) yr(-1), but in spite of increases, retention of total dissolved nitrogen reached a maximum of 92% and 95% of 80 kg added N ha(-1) yr(-1) in the Oh and Eag horizons, respectively. Calcium concentrations and calcium/aluminium ratios were decreased in the Eag horizon solution with significant acidification mainly in the Oh horizon leachate. Nitrate leaching is currently regarded as an early indication of N saturation in forest systems. Litter C:N ratios were significantly lowered but values remained above a threshold predicted to increase leaching of N in forests.

Effects of increased deposition of atmospheric nitrogen on an upland Calluna moor: N and P transformations.

This study determined the effects of increased N deposition on rates of N and P transformations in an upland moor. The litter layer and the surface of the organic Oh horizon were taken from plots that had received long-term additions of ammonium nitrate at rates of 40, 80 and 120 kg N ha(-1) yr(-1). Net mineralisation processes were measured in both field and laboratory incubations. Soil phosphomonoesterase (PME) activity and rates of N(2)O release were measured in laboratory incubations and root-surface PME activity measured in laboratory microcosms using Calluna vulgaris bioassay seedlings. Net mineralisation rates were relatively slow, with net ammonification consistently stimulated by N addition. Net nitrification was marginally stimulated by N addition in the laboratory incubation. N additions also increased soil and root-surface (PME) activity and rates of N(2)O release. Linear correlations were found between litter C:N ratio and all the above processes except net nitrification in field incubations. When compared with data from a survey of European forest sites, values of litter C:N ratio were greater than a threshold below which substantial, N input-related increases in net nitrification rates occurred. The maintenance of high C:N ratios with negligible rates of net nitrification was associated with the common presence of ericaceous litter and a mor humus layer in both this moorland as well as the forest sites.

Effects of increased deposition of atmospheric nitrogen on an upland moor: nitrogen budgets and nutrient accumulation.

This study was designed to investigate the effect of long-term (11 years) ammonium nitrate additions on standing mass, nutrient content (% and kg ha(-1)), and the proportion of the added N retained within the different compartments of the system. The results showed that more than 90% of all N in the system was found in the soil, particularly in the organic (Oh) horizon. Added N increased the standing mass of vegetation and litter and the N content (kg N ha(-1)) of almost all measured plant, litter and soil compartments. Green tissue P and K content (kg ha(-1)) were increased, and N:P ratios were increased to levels indicative of P limitation. At the lowest treatment, most of the additional N was found in plant/litter compartments, but at higher treatments, there were steep increases in the amount of additional N in the underlying organic and mineral (Eag) horizons. The budget revealed that the proportion of added N found in the system as a whole increased from 60%, 80% and up to 90% in response to the 40, 80 and 120 kg N ha(-1) year(-1) treatments, respectively.

Gene transfer between streptomycetes in soil.

The growth and activity of Streptomyces violaceolatus and Streptomyces lividans was studied in soil under controlled conditions. The life cycle was followed under differing nutrient regimes and the fate of plasmid- and phage-borne genes determined by direct and indirect techniques. Methods were developed for the direct monitoring of plasmid DNA extracted from soil which allowed differentiation of the cellular location of plasmid DNA between mycelium and spores. In a dynamic, nutrient-fed soil microcosm, inoculants survived poorly, but a specific stage was defined by direct and indirect methods when the inoculants were most active and this correlated with the detection of gene transfer events. Plasmid transfer, phage infection and lysogeny only occurred to a significant extent within this stage at days 15-17 during a 60-day incubation. Estimates based on plasmid DNA recovery indicated that viable counts underestimated spore and mycelial propagules by a factor of greater than 100.

Oil bio-degradation in permeable pavements by microbial communities.

This paper reports on continuing research at Coventry University into the improvement of highway water quality following flow through a permeable pavement. Such pavements have been shown elsewhere to be efficient in-situ bio-reactors, capable of degrading large quantities of clean motor oil. Further laboratory research, reported here, demonstrates that a commercially obtained oil degrading, microbial mixture was not significantly better at degrading clean motor oil than the indigenous microbial biomass established within the pavement over a 4-year period, when provided with an adequate nutrient supply. Scanning electron microscopy has been used to monitor biofilm development, which has also identified that the pavement has developed a complex community structure with high bio-diversity.

The effects of prosthesis mass on metabolic cost of ambulation in non-vascular trans-tibial amputees.

The effect of prosthesis mass on the metabolic cost of steady-state walking was studied in ten male non-vascular trans-tibial amputees (TTAs) and ten non-amputee controls. The subjects underwent four trials of treadmill ambulation, with each trial performed for nine minutes at level grade and 76 m/min. Twenty minutes of seated rest followed each trial. During trials numbers one and two, TTAs ambulated without mass added to their prosthesis. During the third and fourth trials, either 454 or 907 grammes mass (1 or 2lbs mass respectively) were randomly assigned and added to either the prosthesis or the leg of the non-amputee control. Subjects were blinded to the amount of mass added to their limb. Within-group comparisons across the four trials showed significant differences in oxygen consumption (VO2) and heart rate (HR) between the two non "mass added" trials, but no effect for addition of mass. The VO2 of TTAs was only 0.6 ml/kg/min (4.7 percent) greater during walking following the addition of 907 grammes to the prosthesis than without mass addition at all, while HR averaged only 1.4 beats/min. higher under the same testing condition. Pearson-product moment correlations echoed these findings, as moderate, but in all cases, negative correlations were observed for associations among the factors of subject age, stump length, and prosthesis-shoe weight, and both VO2 and HR. It was concluded that adding up to 907 grammes mass to a non-vascular TTA's prosthesis will not significantly increase the energy expenditure or HR at a normal walking speed, and that elevated energy cost of ambulation in repeated measures testing without mass added may reflect task familiarization and not an added burden of prosthesis mass.

Growth and survival of streptomycete inoculants and extent of plasmid transfer in sterile and nonsterile soil.

The growth and survival of strains of Streptomyces lividans and S. violaceolatus in sterile and nonsterile soil was investigated by using inoculated soil microcosms run as batch systems. It was evident that, after an initial short mycelial growth phase of 2 to 3 days, sporulation occurred and inoculants survived as spores. The transfer of a high-copy-number, self-transmissible plasmid, pIJ673, was detected by using intra- and interspecific crosses. The initial detection of transconjugants correlated with the development of the mycelial state of the inoculants (as confirmed by scanning electron microscopy) after 2 days of incubation. Subsequent spread of the plasmid was attributed to spread within existing mycelium followed by sporulation. In natural soil, inoculant numbers remained constant or declined, but plasmid transfer was readily detected.

Mathematical Model of Plasmid Transfer between Strains of Streptomycetes in Soil Microcosms.

A mathematical model was developed and used to simulate the long-term dynamics of growth and plasmid transfer in nutrient-limited soil microcosms of Streptomyces lividans TK24 carrying chromosomal resistance to streptomycin, S. lividans 1326; and S. violaceolatus ISP5438. Donor, recipient, and transconjugant survival was modelled by an extension to the Verhulst logistic equation which takes account of nutrient limitation, and plasmid transfer was modelled by a mass action model. Rate parameters were derived from experimental data on the early stages of the development of sterile systems. The model predicted donor, recipient, and transconjugant populations in 2.4-h (0.1-day) steps and was tested against the long-term behavior of the experimental sterile systems and independent experimental data on nonsterile systems. Bacteria were periodically enumerated onto selective media over a 20-day period. The effects of long-term nutrient-moisture depletion were correctly predicted.

Molecular detection of streptomycin-producing streptomycetes in Brazilian soils.

Actinomycetes were isolated from soybean rhizosphere soil collected as two field sites in Brazil. All the isolates were identified as Streptomyces species and were screened for streptomycin production and the presence of two genes, strA and strB1, known to be involved in streptomycin biosynthesis in Streptomyces griseus. Antibiotic resistance profiles were determined for 53 isolates from cultivated and uncultivated sites, and approximately half the strains were streptomycin resistance. Clustering by the unweighted pair group method with averages indicated the presence of two major clusters, with the majority of resistant strains from cultivated sites being placed in cluster 1. Only representatives from this cluster contained strA. Streptomycetes containing strA and strB1 were phenotypically diverse, and only half could be assigned to known species. Sequence comparison of 16S rRNA and trpBA (tryptophan synthetase) genes revealed that streptomycin- producing streptomycetes were phylogenetically diverse. It appeared that a population of streptomycetes had colonized the rhizosphere and that a proportion of these were capable of streptomycin production.