Scion-rootstock relationships with respect to height growth and foliar concentrations of nitrogen and phosphorus in reciprocal grafts of Pinus caribaea var. hondurensis

Both scion and rootstock clones significantly influenced scion elongation and concentrations of nitrogen and phosphorus in the scion foliage. Scion clone was the more important determinant. Scion clone × rootstock clone interactions were not significant. The ability of a clone to elongate as a scion was not correlated with its capacity to promote or retard scion elongation when used as a rootstock. Genetic differences in foliar nutrient concentrations appeared to reflect levels of nutrient demand, rather than the ability of roots to absorb nutrients. Nutrient demand of the rootstock can also explain negative correlations between nitrogen levels in rootstock clones and levels of both nitrogen and phosphorus in the scions. There was no significant relationship between scion elongation and foliar nitrogen concentrations of either rootstock or scion. The weak relationship between scion elongation and concentration of phosphorus in the rootstock apparently resulted from tissue dilution.     

Modelling and Mapping Ozone Deposition in Europe

A new dry deposition module has been developed for European-scale mapping and modelling of ozone deposition fluxes (Emberson et al., 2000a,b). The module is being implemented in the photochemical long-range transport model of EMEP that is currently used to estimate exceedance of the existing critical levels for ozone within the UN ECE LRTAP programme. The deposition model evaluates the atmospheric, boundary layer and surface resistances to ozone transfer with the calculation of the dry deposition velocity performed according to a standard resistance formulation. The approach differs from other existing methods through the use of a detailed stomatal uptake model that describes stomatal conductance as a function of plant species, phenology and four environmental variables (air temperature, solar radiation, water vapour pressure deficit and soil moisture deficit). Comparison of preliminary model outputs for selected land-cover types indicate that the model is capable of predicting the seasonal and diurnal range in deposition velocities that have been reported previously in the literature. The application of this deposition scheme enables calculations of ambient ozone concentrations to be made using a biologically based method that can distinguish stomatal and non-stomatal components of total ozone deposition. The ability to estimate stomatal ozone fluxes (according to vegetation type, phenology and spatial location) that are consistent with evaluations of atmospheric ozone concentrations will be helpful in future assessments of ozone impacts to vegetation.     

Reconstructing the paleotopography beneath the loess cover with the aid of an electromagnetic induction sensor

During the last glacial period (Weichselian), wind-blown loess was deposited over the undulating landscape of central Belgium, which had been formed in surfacing Tertiary marine sediments. Since valleys were filled up with a thicker loess layer than hill tops, the present topography is much smoother. This smoothing was enhanced by subsequent erosion processes. Reconstructing the paleolandscape at a detailed scale is almost impossible by conventional procedures based on soil augerings. Therefore, the use of the electromagnetic induction sensor, EM38DD, was evaluated as an alternative for mapping the depth to the Tertiary clay substrate. On our 2.7 ha study site, located in the loess belt of central Belgium, a strong non-linear relationship (R² = 0.86) was found between the apparent electrical conductivity (ECa), measured by the vertical dipole orientation of the EM38DD and the depth to a Tertiary clay substrate. These predictions were validated by independent observations of the depth to the Tertiary clay and a correlation coefficient of 0.83, with an average error of 0.22 m, was found. So, our dense ECa measurements (2 by 2 m resolution) allowed us to build a three-dimensionall surface of the depth to the Tertiary substrate, reconstructing the paleotopography beneath the loess cover. This paleotopography revealed distinct erosion patterns on the surface of the Tertiary clay. The continuity of these was confirmed by an analysis of surface flow patterns conducted on the reconstructed paleotopography. The non-invasive, time- and cost-effective electromagnetic induction sensor was found to offer new perspectives to reconstruct and analyse in detail the Quaternary paleotopography beneath the loess cover.     

Key soil and topographic properties to delineate potential management classes for precision agriculture in the European loess area

Recent advances in on-the-go soil sensing, terrain modelling and yield mapping have made available large quantities of information about the within-field variability of soil and crop properties. But the selection of the key variables for an identification of management zones, required for precision agriculture, is not straightforward. To investigate a procedure for this selection, an 8 ha agricultural field in the Loess belt of Belgium was considered for this study. The available information consisted of: (i) top- and subsoil samples taken at 110 locations, on which soil properties: textural fractions, organic carbon (OC), CaCO₃ and pH were analysed, (ii) soil apparent electrical conductivity (EC_a) obtained through an electromagnetic induction based sensor, and (iii) wetness index, stream power index and steepest slope angle derived from a detailed digital elevation model (DEM). A principal component analysis, involving 12 soil and topographic properties and two EC_a variables, identified three components explaining 67.4% of the total variability. These three components were best represented by pH, EC_a that strongly associated with texture and OC. However, OC was closely related to some more readily obtainable topographic properties, and therefore elevation was preferred. A fuzzy k-means classification of these three variables produced four potential management classes. Three-year average standardized yield maps of grain and straw showed productivity differences across these classes, but mainly linked to their landscape position. In the loess area with complex soil-landscape interactions pH, EC_a and elevation can be considered as key properties to delineate potential management classes.     

Purification and identification of linoleic acid hydroperoxides generated by soybean seed lipoxygenases 2 and 3

It has been known that lipoxygenase (LOX) isozymes exhibit differences in product formation, but most product information to date is for LOX 1 among soybean (Glycine max) LOX isozymes. In this study, LOXs 2 and 3 were purified and used to generate hydroperoxide (HPOD) products in an in vitro system using linoleic acid as a substrate in the presence of either air or O2. The products were analyzed to determine their stereoisomeric characteristics. The control (no enzyme) showed only low levels of hydroperoxide production and no stereoisomeric specificity. LOX 2 shows high specificity in product formation, producing roughly 4 times more 13-HPOD than 9-HPOD, nearly all of which was 13-S(Z,E)-HPOD. LOX 3 produced more 9-HPOD than 13-HPOD at approximately a 2:1 ratio. No single stereoisomer was predominant among LOX 3 products. These results demonstrate that different isozymes of LOX have characteristic product profiles in in vitro reactions.     

Chemical stratification in the Seneca/Oswego rivers (NY)

The occurrence and characteristics of chemically-based density stratification in portions of the Seneca and Oswego Rivers, downstream of ion-polluted Onondaga Lake, are described for seven different days in the summer and fall of 1978 and 1981, which covered a wide range of river flows. The results indicate that chemically-based density stratification occurs routinely in the Seneca River downstream of the lake inflow, in response to a continuous chemically-based density difference between the two systems of 0.0015 to 0.0030 g cm^?3. The persistence of the phenomenon, and therefore the longitudinal range over which the river stratification occurred, was dependent on the velocity of river flow and the magnitude of the density gradient that bordered the upper river water and the lower released lake water. During the low flows common to summer the stratification extended approximately 14 km downstream to a dam, and 3 km upstream, of the lake outlet — river junction. Vertical mixing between the stratified layers increased as the flow in the Seneca River increased, and as the vertical density gradient decreased. A dimensionless group, $$\frac{D}{{V\left( {\frac{\rho }{{\Delta _\rho /\Delta _z }}} \right)}}$$ where: D = apparent vertical diffusion (m² hr^?1), V = average velocity of the overlying river flow (m hr^?1 ), p = density at the interface between the stratified layers (g cm^?3), and Ap/Az = density gradient between the stratified layers (g cm^?3 m^?1), was found to be constant for summer low flow conditions for a 6.5 km length of the Seneca River, thus quantifying the interaction between vertical mixing and the included influences for that portion of the river. The occurrence of chemical stratification in the river had dramatic implications on the corresponding distribution of dissolved oxygen (DO). The isolation of the organically enriched lake water in the lower layer enhanced the depletion of DO there, which resulted in the development of substantial (> 4.0 mg 1^?1 ) DO stratification downstream of the discharge from the lake during summer low flow periods.     

Crossing the thresholds: human ecology and historical patterns of landscape degradation

In discussions of landscape sensitivity, human activities have generally been regarded as external forces contributing to landscape change, with a focus on the impacts of cultivation methods, fertiliser practices, grazing pressures and atmospheric pollution. However, there has been comparatively little study undertaken that integrates physical and social systems in a historic context to explain the basis of human activity in sensitive landscapes. Where such attempts have been made, the manner of common land management has figured prominently, with ‘tragedy of the commons’ concepts used to explain land degradation and to provide a foundation for policy response. This has also been the case in Southern Iceland and in this paper we assess the extent to which common land domestic grazing pressures were the primary external force causing soil erosion and land degradation during the period of occupation from ca. 874 AD. We first provide field observation of soil erosion, temporally defined by tephrochronology, to highlight the extent of land degradation during this period. The ‘tragedy of the commons’ explanation of degradation is then assessed by evaluating historic documentary sources, and by environmental reconstruction and modeling of historic grazing pressures. These analyses indicate that regulatory mechanisms were in place to prevent overgrazing from at least the 1200s AD and suggest that there was sufficient biomass to support the numbers of domestic livestock indicated from historic sources. We suggest that failure to remove domestic livestock before the end of the growing season and an absence of shepherding were more likely to contribute to land degradation than absolute numbers. Lack of appropriate regulation of domestic livestock on common grazing areas can be attributed to limited cultural knowledge of changing and rapidly fluctuating environmental conditions.     

Grain yield increases in wheat and barley to nitrogen applied after transient waterlogging in the high rainfall cropping zone of western Australia

Nitrogen (N) is a major factor limiting grain production in the high rainfall zone (HRZ, 450–700 mm annual average rainfall of southwestern Australia (SWA). Transient waterlogging and leaching of applied N fertilizer are hazards faced in most years by crop producers. The major crops are wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), canola (Brassica napus L.) and lupin (Lupinus angustifiolius L.) grown in rotation. Two series of experiments involving, levels and timing of N fertilizer application and levels of plant population were done. The first series, in 2003–2004, consisted of 3 experiments in 3 growing seasons (early May to late-October) to measure the grain yield (GY) increase (response) of wheat and barley to various methods of N fertilizer application (methods of split N application were compared to N applied at sowing). The aim of the experiments was to determine the optimal N fertilizer application strategy for maximum GY and quality in situations where transient waterlogging was a frequent occurrence. The second series of four experiments, from 2007–2009, measured the GY of wheat sown at three levels of plant population to 4 levels of N applied after transient waterlogging (taken to be rainfall events in which >25 mm of rain was recorded in 24 to 48 hours).

Applying the N fertilizer after high rainfall and transient waterlogging (tactical N application) increased GY and protein percentage of grain compared to applying all of the N fertilizer at sowing. Where transient waterlogging was not frequent, applying the N after waterlogging was not always better than applying part of the N according to growth stage of the crop or according to fixed times after sowing. When the crop was water-logged three or more times, N uptake by the crop at anthesis and apparent fertilizer N recovery in the crop was substantially increased by applying the N after waterlogging compared to applying the entire N at sowing. This study found that a tactical N management strategy for the HRZ of SWA is to apply some N at sowing with subsequent applications made after heavy rainfall that leads to transient waterlogging. Split N fertilizer applied either according to time after sowing or to growth stage of the crop was equally effective for increasing GY in situations where waterlogging was less frequent.

The observation from these experiments, that grain yield increases due to splitting the N dose were associated with increases in ear numbers, lead to a further set of experiments where plant population was increased in conjunction with N applied after waterlogging events. The combined strategy of increased plant population with strategic N application decreased the amount of N required for maximum GY where more than 3 heavy rainfall events occurred in a growing season.

One practical outcome of this research is to indicate that farmers can withhold applications of N fertilizer after sowing in seasons when transient waterlogging does not occur.     

Successful treatment of suspected essential thrombo-cythaemia in the dog

Essential thrombocythaemia in an eight-year-old Irish setter is described. The condition is characterised by an autonomous overproduction of thrombocytes in the absence of overt leukaemia. This is believed to be the first recorded case of this condition in the dog. The paper describes the diagnosis and treatment by combination chemotherapy using vincristine, cytosine arabinoside, cyclophosphamide and prednisolone.