Isolation of chicken anaemia virus from broiler chickens in New Zealand

Chicken anaemia virus was isolated for the first time in New Zealand from the New Zealand domestic chicken population. The virus was recovered from diseased birds in five separate flocks of broiler chickens aged between 14 and 33 days of age. Six isolates were obtained from bone marrow and lymphoid tissues using the MDCC-MSB1 cell line derived from Marek's disease lymphoma. All isolates were resistant to chloroform and survived exposure to 70 degrees C for 5 minutes. The main clinical features consistently associated with the disease outbreaks were increased mortality, yolk sac infections, sub-cutaneous haemorrhages and atrophy of the thymus. Fungal pneumonia occurred in two flocks, and gangrenous dermatitis as a result of bacterial infection in another flock. Microscopic examination showed atrophy of the thymus, reduced medullary haematopoiesis and inflammation resulting from secondary infections.     

Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency

Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (I_gross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from I_gross irrigation application losses for a reduced, or net, interception (I_net) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 mm, estimated average I_gross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced I_gross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced I_gross loss an additional 1.2%. Further 4–6% reductions in I_gross losses were predicted when aerodynamic and canopy resistances were considered. Irrigation water applied only at the soil surface by LEPA irrigation had little effect on the microclimate within the canopy and consequently on Tr or ET, or irrigation application efficiency.     

Predicting use of habitat patches by spawning horseshoe crabs (Limulus polyphemus) along a complex coastline with field surveys and geospatial analyses

相似文献   

Evaluating eddy covariance cotton ET measurements in an advective environment with large weighing lysimeters

Eddy covariance (EC) systems are being used to assess the accuracy of remote sensing methods in mapping surface sensible and latent heat fluxes and evapotranspiration (ET) from local to regional scales, and in crop coefficient development. Therefore, the objective was to evaluate the accuracy of EC systems in measuring sensible heat (H) and latent heat (LE) fluxes. For this purpose, two EC systems were installed near large monolithic weighing lysimeters, on irrigated cotton fields in the Texas High Plains, during the months of June and July 2008. Sensible and latent heat fluxes were underestimated with an average error of about 30%. Most of the errors were from nocturnal measurements. Energy balance (EB) closure was 73.2–78.0% for daytime fluxes. Thus, daylight fluxes were adjusted for lack of EB closure using the Bowen ratio/preservation of energy principle, which improved the resulting EC heat flux agreement with lysimetric values. Further adjustments to EC-based ET included nighttime ET (composite) incorporation, and the use of ‘heat flux source area’ (footprint) functions to compensate ET when the footprint expanded beyond the crop field boundary. As a result, ET values remarkably matched lysimetric ET values, with a ‘mean bias error ± root mean square error’ of −0.03 ± 0.5 mm day⁻¹ (or −0.6 ± 10.2%).     

Effects of Supplemental Calcium on Ion Accumulation,Transport and Plant Growth of Salt Sensitive Brassica Rapa Landrace

ABSTRACT

Effects of three supplemental calcium (Ca⁺⁺; 2.5, 5.0, and 10 mole m^?3) concentrations on ion accumulation, transport, selectivity, and plant growth of salt-sensitive species, Brassica rapa ‘Sani’ in saline medium were investigated. Supplemental Ca⁺⁺ in the presence of 125 mol m^?3 sodium chloride (NaCl) did not improve the dry weight and leaf area indicating no role played by Ca⁺⁺ in the alleviation of salinity induced growth inhibition. However, calcium chloride (CaCl₂) did significantly affect sodium (Na⁺), potassium (K⁺), and Ca⁺⁺ contents of roots and shoots. The ion contents of shoots were significantly greater than those of roots per g dry weight, indicating ion transportation to shoots is greater than ion accumulation in roots. Use of CaCl₂ in 125 mol m^?3 NaCl reduced the Na⁺ content but increased K⁺ and Ca⁺⁺ contents in shoots. Sodium contents in shoots differed among the supplemental Ca⁺⁺ treatments indicating the role of CaCl₂ in Na⁺ ions transportation. Calcium content in shoots declined significantly in the control treatment (0 CaCl₂) but increased significantly in 10 mol m^?3 CaCl₂. The root also showed the effects of Ca⁺⁺ on the reduction of Na⁺ content and the increase of K⁺ and Ca⁺⁺ content. Unexpectedly, 5 mol m^?3 CaCl₂ induced the highest Na⁺ content in roots at 16 days after treatment. Supplemental CaCl₂ application influenced the K⁺ or Ca⁺⁺ selectivity over Na⁺ in two ways, ion accumulation at roots and transport to shoots. However, high CaCl₂ treatments allowed greater Ca⁺⁺ selectivity over Na⁺ than low CaCl₂. Likewise, high supplemental CaCl₂ showed higher K⁺ selectivity over Na⁺ than low CaCl₂. A marked increase in K⁺ versus Na⁺ selectivity for the transport process occurred at 10 mol m^?3 CaCl₂ treatments. The roots and shoots exhibited higher K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios in high CaCl₂ treatment than in low. The results are discussed in context to supplemental Ca⁺⁺ concentrations, ions accumulation, transportation and selectivity of salt sensitive Brassica rapa cultivar.     

Starving the soil of plant inputs for 50 years reduces abundance but not diversity of soil bacterial communities

If soil communities rely on plant-derived carbon, is biodiversity lost when this primary source is removed? Soil microbial and mesofaunal communities at the Rothamsted Highfield site were compared under a mixed grass sward, arable rotation and a section maintained as a bare-fallow for the past 50 years by regular tillage. Organic matter reserves have been degraded and microbial and mesofaunal numbers and mite diversity have declined in this unique bare-fallow site, where fresh carbon inputs have been drastically reduced. However, it supports a species-rich metabolically active bacterial community of similar diversity to that in soil maintained as grass sward. Thus in contrast to soil mesofauna, bacterial diversity (but not abundance) is apparently independent of plant inputs.