Tissue distribution, elimination, and metabolism of dietary sodium [36Cl]chlorate in beef cattle

Two steers (approximately 195 kg) were each dosed with 62.5 or 130.6 mg/kg body weight sodium [36Cl]chlorate for three consecutive days. All excreta were collected during the dosing and 8 h withdrawal periods. The apparent radiochlorine absorption was 62-68% of the total dose with the major excretory route being urine. Parent chlorate was 65-100% of the urinary radiochlorine; chloride was the only other radiochlorine species present. Similarly, residues in edible tissues were composed of chloride and chlorate with chloride being the major radiolabeled species present. Chlorate represented 28-57% of the total radioactive residues in skeletal muscle; in liver, kidney, and adipose tissues, chlorate ion represented a smaller percentage of the total residues. Chlorate residues in the low dose steer were 26 ppm in kidney, 14 ppm in skeletal muscle, 2.0 ppm in adipose tissue, and 0.7 ppm in liver. These data indicate that sodium chlorate may be a viable preharvest food safety tool for use by the cattle industry.     

Effects of elevated CO2 concentration on rhizodeposition from Lolium perenne grown on soil exposed to 9 years of CO2 enrichment

The effects of enriched CO₂ atmosphere on partitioning of recently assimilated carbon were investigated in a plant-soil-microorganism system in which Lolium perenne seedlings were planted into cores inserted into the resident soil within a sward that had been treated with elevated CO₂ for 9 consecutive years, under two N fertilisation levels (Swiss FACE experiment). The planted cores were excavated from the ambient (35 Pa pCO₂) and enriched (60 Pa pCO₂) rings at two dates, in spring and autumn, during the growing season. The cores were brought back to the laboratory for ¹⁴C labelling of shoots in order to trace the transfer of recently assimilated C both within the plant and to the soil and microbial biomass. At the spring sampling, high N supply stimulated shoot and total dry matter production. Consistently, high N enhanced the allocation of recently fixed C to shoots, and reduced it to belowground compartments. Elevated CO₂ had no consequences for DM or the pattern of C allocation. At the autumn sampling, at high N plot, yield of L. perenne was stimulated by elevated CO₂. Consistently, ¹⁴C was preferentially allocated aboveground and, consequently belowground recent C allocation was depressed and rhizodeposition reduced. At both experimental periods, total soil C content was similar in all treatments, providing no evidence for soil carbon sequestration in the Swiss Free Air CO₂ Enrichment experiment (FACE) after 9 years of enrichment. Recently assimilated C and soil C were mineralised faster in soils from enriched rings, suggesting a CO₂-induced shift in the microbial biomass characteristics (structure, diversity, activity) and/or in the quality of the root-released organic compounds.     

Short and long-term effects of elevated CO2 on Lolium perenne rhizodeposition and its consequences on soil organic matter turnover and plant N yield

It is still unclear whether elevated CO₂ increases plant root exudation and consequently affects the soil microbial biomass. The effects of elevated CO₂ on the fate of the C and nitrogen (N) contained in old soil organic matter pools is also unclear. In this study the short and long-term effects of elevated CO₂ on C and N pools and fluxes were assessed by growing isolated plants of ryegrass (Lolium perenne) in glasshouses at elevated and ambient atmospheric CO₂ and using soil from the New Zealand FACE site that had >4 years exposure to CO₂ enrichment. Using ¹⁴CO₂ pulse labelling, the effects of elevated CO₂ on C allocation within the plant-soil system were studied. Under elevated CO₂ more root derived C was found in the soil and in the microbial biomass 48 h after labelling. The increased availability of substrate significantly stimulated soil microbial growth and acted as priming effect, enhancing native soil organic matter decomposition regardless of the mineral N supply. Despite indications of faster N cycling in soil under elevated CO₂, N availability to plants stayed unchanged. Soil previously exposed to elevated CO₂ exhibited a higher N cycling rate but again there was no effect on plant N uptake. With respect to the difficulties of extrapolating glasshouse experiment results to the field, we concluded that the accumulation of coarse organic matter observed in the field under elevated CO₂ was probably not created by an imbalance between C and N but was likely to be due to more complex phenomena involving soil mesofauna and/or other nutrients limitations.     

Geographic origin of Pinus sylvestris populations influences the effects of air pollution on flowering and growth

Flowering and height growth of 20 Scots pine (Pinus sylvestris L.) populations from 10 countries were analyzed at two replicated provenance sites established in 1984 in western Poland. One site was 2 km from a phosphate fertilizer factory that emits SO₂ and fluorides, and the other 12 km to the southeast in an area free of acute air pollution levels was treated as a control. Slow-growing populations from the southern (40 to 45°N) and northern (58 to 61°N) part of the species range exhibited relatively smaller air pollutioninduced growth reductions than those from the central part of the range (45 to 58°N). Trees growing in the control area started flowering 4 yrs earlier than those at the polluted site. The percent of trees flowering at the control site differed significantly among provenances in both 1988 and 1990. The mean percent of trees with flowers was three times lower at the polluted site. The least sensitive southern and northern provenances in terms of pollutioninduced reductions in growth exhibited the largest pollution-induced decreases in flowering. These findings indicate that the sensitivity of vegetative organs to air pollution stress is not always paralleled by the sensitivity of reproductive organs.     

The effects of organic amendments on the interactions between a nematophagous fungus Arthrobotrys oligospora and the root-knot nematode Meloidogyne mayaguensis parasitizing tomato plants

The aim of this study was to examine the effects of amendments with leaf biomass on the development of tomato plants in a soil where root-knot nematodes (Meloidogyne mayaguensis) and/or a nematophagous fungus (Arthrobotrys oligospora, strain ORS 18697) had been inoculated. Six origins of leaf biomass were chosen: Acacia mangium, Acacia holosericea, Eucalyptus camaldulensis, Casuarina equisetifolia, Azadirachta indica and Sorghum vulgare. These leaf biomass types inhibited the development of the aerial parts of the tomato plants. This negative effect was not observed when the fungus was inoculated. On the contrary, plant growth was stimulated. Moreover, the antagonistic activity of Arthrobotrys oligospora was strengthened in the presence of ground leaf powder, especially that from Acacia holosericea. The effects of phenolic compounds on fungal growth and predatory activity and on plant growth are discussed.     

Distribution of the Mallorcan midwife toad (Alytes muletensis) in relation to landscape topography and introduced predators

The endemic midwife toad of Mallorca (Alytes muletensis) is restricted to a small number of breeding populations in the mountainous northwest of the island. The decline of the species has been attributed to the impacts of introduced species such as the viperine snake (Natrix maura) and green frog (Rana perezi), and toads may be surviving only in areas that are suboptimal for these predators. The influence of landscape features (elevation, aspect and maximum slope) on the distribution of toads and associated predators was therefore investigated using GIS. The presence of toads was positively associated with steep slopes. At sites where they occurred with toads, the distribution of predators was negatively associated with elevation. Reproductive success within toad populations was strongly associated with the number of pools at each site, while reproductive success within individual pools was positively associated with elevation. These findings may be used to optimise the design and location of future reintroduction sites.     

Nematofauna associated with exotic and native leguminous plant species in West Africa: effect of<Emphasis Type="Italic"> Glomus intraradices</Emphasis> arbuscular mycorrhizal symbiosis

Ten leguminous trees, four exotic species (Australian Acacia) and six indigenous species (three Sahelian Acacia spp. and three Sesbania spp.), were grown for 4 months in a natural Sahelian soil inoculated with or without the endomycorrhizal fungus, Glomus intraradices. In control trials, the determinant factor structuring the soil nematode fauna was the plant species, related plants having a similar influence on the nematode community in the soil. Soil nematode abundance increased from exotic acacias (3.3 g^-1 dry soil) to native acacias (11.5 g^-1 dry soil) and Sesbania species (17.6 g^-1 dry soil). Plant feeding nematodes (mainly Scutellonema and Tylenchorhynchus) were significantly less abundant under exotic acacias (1.4 g^-1 dry soil) than under native acacias (7.2 g^-1 dry soil) or Sesbania species (7.3 g^-1 dry soil). Bacterial feeding nematode density increased from exotic acacias (1.2 g^-1 dry soil) to native acacias (3.0 g^-1 dry soil) and Sesbania species (7.7 g^-1 dry soil) as total densities. However, the differences in the structure of the nematode communities between plant groups were suppressed in the presence of the mycorrhizal fungus. In fact, no difference in nematode densities remained between plant groups when G. intraradices developed in several dominant taxa belonging to different trophic groups, particularly: Tylenchorhynchus, Apelenchina, Cephalobus and Dorylaimoidea. This study clearly indicated that inoculation with the arbuscular mycorrhizal fungus G. intraradices diminished the plant-specific effect on the structure of the soil nematode community.     

Bromine residues in potato and wheat crops grown in soil fumigated with methyl bromide

The bromine content of potato tubers grown in soil fumigated with methyl bromide at 487 and 975 kg/ha (1 lb and 2 lb/100 ft2) averaged 170 and 280 mg/kg of dry weight. Most of the bromine was in the outer layers of the tubers; peeled tubers has less than 100 mg/kg, which remained after boiling. Potato haulm contained 4000 or 6700 mg/kg bromine respectively for the two rates of application. The bromine content of wheat grain grown after potatoes depended on the rate of application of methyl bromide and the time interval between treatment and wheat crop. Wheat grain harvested 31/2 21/2 and 11/2 years after fumigation with methyl bromide at 975 kg/ha had mean bromine contents of 4.5, 15 and 44 mg/kg. but the amounts in grain from plots having the same treatments varied more than two-fold; wheat grain harvested 11/2 years after fumigation at 487 kg/ha contained 23 mg bromine/kg. Wheat yields were unaffected by fumigation.