Effects of cover crop quality and quantity on nematode-based soil food webs and nutrient cycling

Soil food webs cycle nutrients and regulate parasites and pathogens, services essential for both agricultural productivity and ecosystem health. Nematodes provide useful indicators of soil food web dynamics. This study was conducted to determine if nematode soil food web indicators and crop yield can be enhanced by combinations of cover crops in a conservation tillage system. The effects of three cover crop treatments (vetch/pea, oat/wheat and oat/wheat/pea/vetch) with low, medium and high C:N and a bare fallow control were investigated in Davis, CA. Nematode fauna, soil properties and plant productivity were measured. Soil food web indices, including the Enrichment Index (EI), Structure Index (SI), Basal Index (BI), and Channel Index (CI), based on the composition of nematode assemblages, were calculated to infer soil food web condition. Cover cropped tomato/corn rotations had twice the number of enrichment opportunist bacterial feeding nematodes, active participants in nitrogen mineralization, than fallowed tomato/corn rotations (opportunist bacterial feeders = 163 versus 98). In winter fallowed plots food webs were basal, common in disturbed, nutrient-poor conditions (BI = 37). Total number of enrichment opportunist nematodes, soil NH₄-N levels, and inferred nitrogen mineralization, were higher in cover crop treatments with low to mid C:N ratios. Omnivore and predator nematodes were scarce, averaging less than 6 nematodes 100 g^?1 in all treatments. In year one, plant productivity was highest after fallow. In contrast, in year two productivity was highest after cover crops with high nitrogen content and productivity significantly correlated with the structure of the soil fauna. Monitoring the abundance of enrichment opportunists may provide managers with a new tool to evaluate soil food web nitrogen mineralization and plant productivity.     

The source of autumn and spring downstream migrating juvenile Atlantic salmon in a small lowland river

Over 3 years, 32,444 age‐0 group Atlantic salmon (Salmo salar) parr tagged with passive integrated transponder tags throughout the River Frome catchment were assigned to one of three groups, nonmigrants, autumn migrants and spring smolts, depending on the detection and the timing of detection at downstream tag readers (situated 8.6 km above the tidal limit). We examined the effect of density at the time of tagging (n·m^?2), distance upstream from the tidal limit (km), fish length (mm), Fulton condition index, habitat type (divided into two types, main river and carrier), days after 1 September that each fish was tagged and year (replication) on the proportions of fish in each of the migration groups. Distance upstream from tidal limit was strongly negatively related to the proportion of autumn migrants and positively related to the proportion of spring smolts. Nonmigrants had a lower average body size than migrants, although there were no differences in the sizes of autumn migrants and spring smolts in September prior to migration. Fish density had no effect on migration strategy. A lower proportion of fish migrated as autumn migrants from the smaller carrier habitats than the main river channel. There is some evidence that those parr destined to become autumn migrants underwent a lower mortality rate during September before tagging than those destined to become spring migrants indicating possible physiological or behavioural differences between these two groups of fish at that time. More research into the factors responsible for initiating the autumn migration is required.     

Dislodgeable residues and persistence of diazinon,chlorpyrifos and isofenphos following their application to turfgrass

In laboratory experiments, residues of diazinon applied to turfgrass, Poa pratensis L., that could be dislodged by rubbing with cheese-cloth, declined from c. 10% of the total applied when the grass was vigorously rubbed immediately after application to 0.3% after 1 day. Sunlight did not influence the rate of decline in dislodgeable residues or residues remaining on or within the leaf blades. In field experiments where 4.5 kg ha^?1 of diazinon was applied in liquid or granular form, about 20 times more diazinon was dislodged from the liquid formulation immediately after application than from the granular. By 1 day after application the percentage of the total applied diazinon that could be dislodged was equal for both formulations. Rainfall had a significant effect on the amount dislodged from grass blades, but mowing did not. Similar rates of decline in the dislodgeable fraction of diazinon, chlorpyrifos and isofenphos were observed in field experiments. Recovery of the dislodgeable fraction declined to 0.25% or less of the total amount of any of these insecticides by 1 day after application. However, residues in the thatch remained sufficiently high for control of insects for up to 7 days after application for diazinon and 14 days for chlorpyrifos and isofenphos.     

Habitat-related prevalence of macroscopic Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula), Hohonu Range, Westland, New Zealand

AIM: To identify broadscale habitat factors influencing the prevalence of macroscopic Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula) at a site in Westland, New Zealand. METHODS: During 1973/74, 1989/90 and 1997, we undertook repeated cross-sectional surveys of M. bovis infection in a possum population on the Hohonu Range , Westland. Data were analysed to determine the influence of site-specific habitat characteristics (land form, aspect, slope, altitude), distance from forest-pasture margin and time since infection on the spatial and temporal prevalence of macroscopic M. bovis infection. RESULTS: The prevalence of M. bovis infection was highest in 1973/74 (13.4%), compared with 1989/90 (3.1%) and 1997 (9.4%). The prevalence of macroscopic M. bovis infection was significantly influenced by habitat, as indexed by altitude and slope in this study site. Every 100 m increase in elevation was associated with a 29% decrease in the odds of infection, and every 10 degrees increase in slope was associated with a 20% decrease in the odds of infection. For possums caught in the lowland podocarp forest (altitude 100-200 m, average slope=5.7 degrees ), the odds of infection were nearly 30-fold higher than those for possums caught in high-altitude hardwood forest near the tree line (altitude 900-1000 m, average slope=28 degrees ). Whilst the prevalence of disease fluctuated markedly between surveys, its broadscale spatial distribution changed little over time. Proximity to the forest-pasture margin had no significant influence on the prevalence of disease, once the effect of habitat was taken into account. CONCLUSION: The prevalence of macroscopic M. bovis infection in possums was strongly influenced by habitat type, being highest in habitats that supported the highest density of possums, and lowest in habitats where population density was low. There was no evidence of progressive spread of M. bovis infection in possums into forest away from pasture-forest margins over the 24-year period of these surveys.     

Commercial Seed Lots Exhibit Reduced Seed Dormancy in Comparison to Wild Seed Lots of Echinacea purpurea

Seed germination patterns were studied in E. purpurea (L.) Moench grouped by seed source, one group of seven lots from commercially cultivated populations and a second group of nine lots regenerated from ex situ conserved wild populations. Germination tests were conducted in a growth chamber in light (40 μmol·m(-2)·s(-1)) or darkness at 25 °C for 20 days after soaking the seeds in water for 10 minutes. Except for two seed lots from wild populations, better germination was observed for commercially cultivated populations in light (90% mean among seed lots, ranging from 82% to 95%) and in darkness (88% mean among seed lots, ranging from 82% to 97%) than for wild populations in light (56% mean among seed lots, ranging from 9% to 92%) or in darkness (37% mean among seed lots, ranging from 4% to 78%). No germination difference was measured between treatments in light and darkness in the commercially cultivated populations, but significant differences were noted for treatments among wild populations. These results suggest that repeated cycles of sowing seeds during cultivation without treatments for dormancy release resulted in reduced seed dormancy in E. purpurea.     

Clostridium septicum myositis in a western lowland gorilla (Gorilla gorilla gorilla).

A 10-yr-old male gorilla (Gorilla gorilla gorilla) with a history of conspecific bite wounds was evaluated for acute onset of depression, anorexia, and right hemiparesis. The animal was immobilized for diagnostic examination and treatment for suspected toxic shock from a necrotizing, emphysematous wound infection, but was euthanized due to complications during recovery. Gross and histopathologic examination revealed acute necrotizing myositis, fasciitis, cellulitis, and emphysema in the affected wound area, with large numbers of large Gram-positive rods among necrotic muscle fibers. Severe pulmonary edema with airways containing fibrin, acute hemorrhage in multiple body sites, thrombosis in blood vessels in the skeletal muscle, liver, and lung, and lymph node hyperplasia with lymphoid necrosis and hemorrhage. Immunohistochemical fluorescent antibody staining of muscle from the wound site was positive for     

Quantifying patch distribution at multiple spatial scales: Applications to wildlife-habitat models

Multiscale analyses are widely employed for wildlife-habitat studies. In most cases, however, each scale is considered discrete and little emphasis is placed on incorporating or measuring the responses of wildlife to resources across multiple scales. We modeled the responses of three Arctic wildlife species to vegetative resources distributed at two spatial scales: patches and collections of patches aggregated across a regional area. We defined a patch as a single or homogeneous collection of pixels representing 1 of 10 unique vegetation types. We employed a spatial pattern technique, three-term local quadrat variance, to quantify the distribution of patches at a larger regional scale. We used the distance at which the variance for each of 10 vegetation types peaked to define a moving window for calculating the density of patches. When measures of vegetation patch and density were applied to resource selection functions, the most parsimonious models for wolves and grizzly bears included covariates recorded at both scales. Seasonal resource selection by caribou was best described using a model consisting of only regional scale covariates. Our results suggest that for some species and environments simple patch-scale models may not capture the full range of spatial variation in resources to which wildlife may respond. For mobile animals that range across heterogeneous areas we recommend selection models that integrate resources occurring at a number of spatial scales. Patch density is a simple technique for representing such higher-order spatial patterns.     

Heinz Body Formation Associated With Ketoacidosis in Diabetic Cats

Oxidative damage plays an important role in the pathophysiology of diabetes and diabetic complications. Feline hemoglobin is uniquely susceptible to oxidative denaturation; therefore, Heinz body formation is a highly sensitive indicator of in vivo oxidative stress in this species. Heinz bodies also contribute to anemia. We investigated hematological and clinical biochemical changes in 30 cats with spontaneous diabetes mellitus (as compared to 15 healthy control cats) and evaluated the relationship of these changes to erythrocyte oxidative damage. Cats were categorized as ketoacidotic or nonketoacidotic based on their clinical presentation and the presence of urine ketones. Ketoacidotic cats had significantly ( P = .0009) more Heinz bodies (28.3% ± 9.1 %) than nonketotic diabetic cats (6.5% ± 1.60%) and healthy control cats (0.6% ± 0.2%). Percent Heinz bodies in diabetic cats directly correlated with plasma β-hydroxy-butyrate concentration ( r = .622; P = .0002), as well as with serum chloride concentration ( r = -0.576; P = 0.0009) and the number of monocytes ( r = .536; P = .0023). Percent Heinz bodies were negatively correlated with erythrocyte glutathione concentrations. Erythrocyte membrane lipid peroxidation was slightly but not significantly increased in diabetic cats. There were no significant associations between percent Heinz bodies and degree of anemia, hyperglycemia, or glycohemoglobin. These data indicate that ketones are associated with oxidative hemoglobin damage in cats, and suggest that ketone metabolism, ie by cytochrome P450 2E1, may be a potential source of in vivo oxygen radical generation in animals with ketosis.