Magnesium influence on plant uptake of phosphorus in a calcareous soil

A pot experiment was conducted to investigate the role of magnesium (Mg) in plant utilization of ³²phoshorus (P)‐labelled P in a calcareous soil (Typic Hapluquent). Results with two successive harvests of ryegrass shoots indicated that Mg had no obvious influence on plant uptake of the P applied. In a separate incubation study with the same soil, labelled P along with different levels of Mg was introduced to the soil at two time intervals and soil inorganic P was fractionated. The isotope data of P in various fractions indicated that Mg at the test levels had no obvious influence on P transformation either. It is suggested from the experiments that Mg is unlikely to be able to promote plant utilization of fertilizer P in calcareous soils.     

Carbon flux and growth in mature deciduous forest trees exposed to elevated CO2

Whether rising atmospheric carbon dioxide (CO2) concentrations will cause forests to grow faster and store more carbon is an open question. Using free air CO2 release in combination with a canopy crane, we found an immediate and sustained enhancement of carbon flux through 35-meter-tall temperate forest trees when exposed to elevated CO2. However, there was no overall stimulation in stem growth and leaf litter production after 4 years. Photosynthetic capacity was not reduced, leaf chemistry changes were minor, and tree species differed in their responses. Although growing vigorously, these trees did not accrete more biomass carbon in stems in response to elevated CO2, thus challenging projections of growth responses derived from tests with smaller trees.     

Rhabdochona longleyi sp. n. (Nematoda: Rhabdochonidae) from blind catfishes, Trogloglanis pattersoni and Satan eurystomus (Ictaluridae) from the subterranean waters of Texas

A new nematode species, Rhabdochona longleyi sp. n. is described from the intestine of two species of blind catfishes, Trogloglanis pattersoni Eigenmann (type host) and Satan eurystomus Hubbs et Bailey (both fam. Ictaluridae, Siluriformes) from the subterranean waters (artesian wells penetrating San Antonio pool of Edwards Aquifer) of Texas, USA. It is characterized largely by the presence of only six anterior teeth in the prostom, simple deirids, by the shape and length of spicules (0.42 to 0.50 mm and 0.093-0.102 mm), shape of the tail tip (rounded), and by filamented eggs. R. longleyi probably adapted to the environment of the aquifer by utilizing available troglobitic crustaceans instead of aquatic insects as an intermediate host.     

Renal T-cell lymphoma with cerebral metastasis in a dog with chronic canine ehrlichiosis

A renal T-cell lymphoma with exclusive cerebral metastasis was diagnosed in a 5-year-old Staffordshire bull terrier bitch euthanased for aggression. This is the first recorded case of primary renal lymphoma in a dog. Immune suppression, due to chronic canine monocytic ehrlichiosis, may account for the unusual primary site and metastatic pattern of the tumour.     

Influence of variety on the within-plant distribution of cassava green spider mite (Acari: Tetranychidae), and leaf anatomical characteristics and chemical components in relation to varietal resistance

The within-plant distribution of the cassava green spider mite, Mononychellus tanajoa Bondar, and the anatomical characteristics and the chemical components relating to varietal resistance of cassava, were studied using 11 cassava genotypes with varying levels of resistance for two dry seasons and one wet season. The results show that M. tanajoa aggregates on the top leaves of cassava at low levels of resistance as compared with a more even within-plant distribution at higher levels of resistance. Thus, for accurate sampling of mite populations, it might be important to consider young and old leaves, not just the young leaves, in fields containing resistant and susceptible cassava genotypes. Correlations between the anatomical characteristics and mite population density and damage scores were not consistent across months, either within or over seasons. This suggests that leaf anatomical characteristics may not be important in the varietal resistance of cassava to M. tanajoa. During the dry season, mite population density was positively correlated with leaf nitrogen, potassium and phosphorus and negatively correlated with leaf calcium and fat. Only calcium was negatively associated with mite damage at the peak of the dry season (January 1993 and 1994). Breeding cassava genotypes with high levels of leaf calcium and fat, and low levels of leaf nitrogen, potassium and phosphorus, may improve the level of resistance to M. tanajoa.