Biological control of pedological and hydro-geomorphological processes in a deciduous forest ecosystem

This study describes the effect of soil fauna and vegetation on the development of landscapes and how these actually control soil formation, geomorphological development and hydrological response. The study area is located in a semi-natural deciduous forest on marl in Luxembourg, with a strong texture contrast in the soil at 15–25 cm depth (luvic planosols). The methodology applied is both based on hydrological and geomorphological field measurements on runoff, sediment yield, perched water table dynamics, geomorphological survey, pedological survey and measurements related to in situ ectorganic horizon dynamics and litter decay, soil animal activity, as well as measurements of dynamic soil properties such as soil moisture and swelling and shrinkage. The results show that there is a positive feedback between tree type, soil fauna activity and the development of pipes, partial areas, soils and geomorphology. The landscape can be divided into two main types: Areas where Stellario-Carpinetum vegetation and partial areas are common and areas with Milio-Fagetum vegetation on dry slopes, which are differentiating more and more over time as a result of ongoing geo-ecosystem processes, and which also reflected in their sediment yield. The hydrological response is highly different for both landscape compartments as they are dominated by matrix (Beech) and pipe flow (Hornbeam) respectively. Soil fauna and tree type drive both soil and geomorphological evolution and they both can be considered as important ecosystem engineers.     

Potentiality of the cox1 gene in the taxonomic resolution of soil fungi

We explored the potential of the cox1 gene in the species resolution of soil fungi and compared it with the nuclear internal transcribed spacer (ITS) and small subunit (SSU)-rDNA. Conserved primers allowing the amplification of the fungal cox1 gene were designed, and a total of 47 isolates of Zygomycota and Ascomycota were investigated. The analysis revealed a lack of introns in >90% of the isolates. Comparison of the species of each of the six studied genera showed high interspecific sequence polymorphisms. Indeed, the average of nucleotide variations (4.2–11%) according to the genus, due mainly to the nucleotide substitutions, led to the taxonomic resolution of all the species studied regarding both ITS and SSU-rDNA, in which <88% were discriminated. The phylogenetic analysis performed after alignment of the cox1 gene across distant fungal species was in accordance with the well-known taxonomic position of the species studied and no overlap was observed between intra- and interspecific variations. These results clearly demonstrated that the cox1 sequences could provide good molecular markers for the determination of the species composition of environmental samples and constitute an important advance to study soil fungal biodiversity.     

Host-parasite Interactions of Pratylenchus scribneri on Selected Crop Plants

Greenhouse tests were conducted to determine the effects of soil temperature and texture on development of Pratylenchus scribneri and the pathogenicity and reproductive rates of this nematode on selected crop plants. In a sandy loam soil, greatest numbers of P. scribneri were found at 30 and 35 C on sudangrass and sugarbeet, respectively. In a silty clay loam, the nematode reproduced best at 35 C on sugarbeet. Higher populations of P. scribneri were found in the sandy loam than silty clay loam soil at corresponding temperatures. In a pathogenicity test, top and root growth of sudangrass and barley were suppressed by the nematode, whereas no significant growth inhibition was found on wheat and alfalfa. Tests with other vegetable and field crops indicated wide variance in nematode reproduction.     

An Inhibitor of the UDP-N-Acetylgalactosamine:GM3, N-Acetylgalactosaminyltransferase: Purification and Properties, and Preparation of an Antibody to This Inhibitor

An inhibitor of the UDP-N-acetylgalactosamine:GM3, N-acetylgalactosaminyltransferase (EC 2.4.1.92) has been purified close to 100-fold from chicken blood serum. The method of purification includes heating, dialysis, passage through a column of DEAE-Sephadex, filtration through Amicon XM 100, and passage through Sepharose 6B. The molecular weight determined by Sepharose 6B was 200,000, but on sodium dodecyl sulfate-polyacrylamide gel electrophoresis it appears as if the compound dissociated into components of 68,000. The inhibitor was not active on other glycosyl transferases and lost its inhibitory activity following treatment with pronase and trypsin. alpha-Chymotrypsin did not affect the inhibitor. An antibody to this inhibitor was prepared which decreased its inhibitory capability and precipitated with it in a radial double immunodiffusion experiment.     

Development of a low input system for growing wheat (Triticum vulgare) in a permanent understorey of white clover (Trifolium repens)

In three field experiments carried out during 1989-91, a permanent sward of pure white clover (Trifolium repens) was established to provide a source of N for winter or spring wheat crops (Triticum vulgare) directly drilled into the legume. Spring-sown wheat failed to compete with the clover, but wheat sown in the autumn established successfully. N fertiliser was applied to all three experiments at rates of 0, 50 and 100 kg N ha“¹ measurements of grain and whole-crop silage yields were made. Yields were low for all treatments, probably because of the dry conditions prevailing and the low soil N status of the site used. Yield responses to fertiliser were significant, despite the contribution to plant nutrition that the clover was intended to make. A key feature of the work was that the clover survived successive cereal crops and could be grazed and used as an understorey for later crops. Further, response to fertiliser N diminished with a successive crop implying a build-up of available soil N, which measurements confirmed had occurred. Use of the system obviated the need to use pesticides, although reasons for the lack of pest damage were not clear.     

Role of isovaleroyl lipids in channeling of sound in the porpoise melon

Physical properties (e.g. specific gravity, adiabatic compressibility and sound velocity) of lipids isolated from tissues from contiguous areas of the fatty melon of an echo-locating porpoise (Delphinus delphis) were determined to elucidate relations between lipid composition and structure, and sound transmission in the head. Lipid content varied greatly within the melon (13.6–77.6% of the tissue weight) and triacylglycerols (80–100%) were the major lipid components. This lipid class was composed of diisovaleroylglycerides (triacylglycerols containing two isovaleroyl moieties and a long-chain acyl moiety), monoisovaleroyldiacylglycerols and triacylglycerols consisting of long-chain acids. The lipid-rich (>45%) areas in the melon contained a high proportion (>45% of total triacylglycerols) of diisovaleroylglycerides. There were gradations of sound velocities within the melon; the lowest sound velocities were associated with high concentrations of diisovaleroylglycerides (<1400 m/s) and the highest with high concentrations of long-chain triacylglycerols. Assuming an average sound frequency of 75 kHz, and considering dimensions of melon (path length and width of 12–14 cm and 5 cm, respectively), a forward radiating lobe of 15–25 degrees is produced. Thus, the deposition of lipids of different acoustic properties in a three-dimensional matrix within the porpoise melon results in a lens for the projection of sound into the marine environment.     

The effects of soluble-Al on root growth and radicle elongation

Summary In order to determine the effects of concentration on plant growth, aluminium (Al) was extracted (10^–3 M CaCl₂) from 4 acid brown hill soils which had been treated with superphosphate at rates equivalent to 0 to 300 kg P ha^–1. The soils ranged in pH (CaCl₂) from 3.5 to 4.9, and Al concentration from 0 to 0.6 mM. The effects of Al on ryegrass growth in the 4 soils in a glasshouse was compared with its effect on radicle elongation of seeds germinated in contact with CaCl₂ extracts from the same soils.Ryegrass root growth in the glasshouse, and radicle elongation in the bioassay test were both unaffected by Al concentrations below 0.1 mM. Root growth was substantially reduced when Al concentration exceeded 0.1 mM and above 0.2 mM growth was almost completely inhibited. Radicle elongation rate was also reduced when the concentration of Al was greater than 0.2 mM agreeing well with the observation from the pot experiment.It is concluded that because of its speed and convenience the bioassay method offers a useful method of establishing critical levels of Al for crop plants.     

Resistance of Anhydrobiotic Aphelenchus avenae to Methyl Bromide Fumigation

The effect of methyl bromide (MB) was tested on active and anhydrobiotic Aphelenchus avenae. A. avenae was induced into anhydrobiosis by three different techniques. Both active and anhydrobiotic nematodes were subjected to 3,000 μ1 MB/liter air for 14 periods from 0 to 82 h. Anhydrobiotic nematodes were more resistant to fumigation than active nematodes, regardless of the technique used to induce anhydrobiosis. The percent survival decreased with increasing MB exposures (μ1 MB × h). For an LD₉₅ of 45,000-54,000 μ1/1 × h were required for active nematodes and >279,000 μ1/1 × h for anhydrobiotic nematodes.