Short-term patterns of carbon and nitrogen mineralisation in a fallow field amended with green manures from agroforestry trees

The mineralisation of green manure from agroforestry trees was monitored with the objective to compare the temporal dynamics of mineralisation of litter from different species. Green manures from five agroforestry tree species were used on a fallow field during the long rainy season of 1997 (March-August) and from two species in the following short rainy season (September-January) in western Kenya. Different methods, i.e. measurements of isotopic ratios of C in respired CO₂ and of soil organic matter (SOM) fractions, soil inorganic N and mass loss from litterbags, were used in the field to study decomposition and C and N mineralisation. Soil respiration, with the separation of added C from old soil C by using the isotopic ratio of ¹³C/¹²C in the respired CO₂, correlated well with extractable NH₄⁺ in the soil. Mineralisation was high and very rapid from residues of Sesbania sesban of high quality [e.g. low ratio of (polyphenol+lignin)/N] and low and slow from low quality residues of Grevillea robusta. Ten days after application, 37% and 8% of the added C had been respired from Sesbania and Grevillea, respectively. Apparently, as much as 70-90% of the added C was respired in 40 days from high quality green manure. Weight losses of around 80%, from high quality residues in litterbags, also indicate substantial C losses and that a build-up of SOM is unlikely. For immediate effects on soil fertility, application of high quality green manure may, however, be a viable management option. To achieve synchrony with crop demand, caution is needed in management as large amounts of N are mineralised within a few days after application.     

Enzymatic solubilization of arabinoxylans from isolated rye pentosans and rye flour by different endo-xylanases and other hydrolyzing enzymes. Effect of a fungal caccase on the flour extracts oxidative gelation

Water-extractable (WEP) and water-unextractable (WUP) pentosans were isolated from a rye flour. The effect of a commercial enzyme preparation, Grindamyl S 100 (GS100), containing pentosanase activities, was investigated on WEP, WUP, a mix of WEP and WUP, and the rye flour, with the aim to monitor the solubilization and depolymerization of high molecular weight arabinoxylans and the effect on the viscosity of the reaction medium. The effects of other hydrolyzing enzymes were also tested. Three xylanases were used: xylanase 1 (Xyl-1) from Aspergillus niger, the main activity present in GS100; xylanase 2 (Xyl-2) from Talaromyces emersonii; and xylanase 3 (Xyl-3) from Bacillus subtilis. Xyl-3 was used in combination with Xyl-1, (1,4)-beta-D-arabinoxylan arabinofuranohydrolase, endo-beta-D-glucanase, or ferulate esterase from A. niger, but no synergism was observed. GS100 and xylanases increased the arabinoxylan solubilization, Xyl-3 and Xyl-1 being those that presented the best yields of extraction without extensive depolymerization of water-extractable arabinoxylans. Both xylanases were affected by an inhibitor in rye flour. Flour treated with hot ethanol was used to study the oxidative gelation of flour extracts treated with xylanases, in the presence of laccase from Pycnoporus cinnabarinus. Two doses of xylanases were tested (0.5 and 2.5 units). Only the flour extracts treated with 0.5 unit of Xyl-1 thickened.     

Influence of soil pH on the toxicity of aluminium for Eisenia andrei (Oligochaeta: Lumbricidae) in an artificial soil substrate

Toxicity of aluminium for the earthworm Eisenia andrei was studied in artificial soil at different pH levels. In a range-finding test, effects of three different aluminium salts on earthworm survival were determined. AlCl₃ appeared to be most toxic, with LC₅₀ values of 316, 359 and >1000 mg Al/kg dry soil at pH_KCl of 3.5, 4.4 and 6.7, respectively in the control soils. Effects of this salt interfered with a strong decrease of soil pH with increasing aluminium concentration. Al₂(SO₄)₃ was less toxic with LC₅₀ values of 457, >4000 and >4000 mg Al/kg dry soil at pH 3.24, 4.86 and 7.22, respectively. Al₂O₃ did not affect earthworm survival at concentrations of 5000 mg Al/kg and pH levels between 2.4 and 7.1.In the main test, earthworms were exposed for 6 weeks to soils treated with Al₂(SO₄)₃. As in the range-finding test, aluminium sulfate was most toxic at a pH of 3.4 with an LC₅₀ of 589 mg Al/kg dry soil. At this pH, growth and cocoon production of earthworms were significantly reduced at 320 mg Al/kg dry soil, while at 1000 mg Al/kg dry soil all earthworms died. Survival was not affected by 1000 mg Al/kg dry soil at pH 4.3 and 7.3. At pH 4.3, growth was significantly reduced at 1000 mg Al/kg dry soil and cocoon production at 320 and 1000 mg Al/kg dry soil. At pH 7.3, aluminium only affected cocoon production at the two highest exposure levels. At the highest two exposure levels at pH 7.3, growth was significantly increased, suggesting a trade-off between growth and reproduction. These effects of aluminium at the highest soil pH could not be explained from the concentration of extractable, monomeric (labile) aluminium in soil, which decreased with increasing soil pH.     

Tree thinning as an option to increase herbaceous yield of an encroached semi-arid savanna in South Africa

Background  

The investigation was conducted in a savanna area covered by what was considered an undesirably dense stand of Colophospermum mopane trees, mainly because such a dense stand of trees often results in the suppression of herbaceous plants. The objectives of this study were to determine the influence of intensity of tree thinning on the dry matter yield of herbaceous plants (notably grasses) and to investigate differences in herbaceous species composition between defined subhabitats (under tree canopies, between tree canopies and where trees have been removed). Seven plots (65 × 180 m) were subjected to different intensities of tree thinning, ranging from a totally cleared plot (0 %) to plots thinned to the equivalent of 10 %, 20%, 35 %, 50% and 75 % of the leaf biomass of a control plot (100 %) with a tree density of 2711 plants ha^-1. The establishment of herbaceous plants (grasses and forbs) in response to reduced competition from the woody plants was measured during three full growing seasons following the thinning treatments.     

A surgical technique for implantation of the vibrant soundbridge middle ear implant in dogs

Objective: To report a surgical implantation of the Vibrant Soundbridge (VSB) middle ear implant in dogs. Study Design: Pilot study. Animals: Dogs (n=3). Methods: A lateral approach to the tympanic bulla was used to insert the floating mass transducer of the VSB into the tympanic bulla. Using microscopic guidance the transducer was moved to and inserted into the round window niche by manipulation through the acoustic bony meatus, after reflection of the tympanic membrane. VSB position was confirmed by computed tomography (CT) imaging. Results: No intraoperative complications occurred and CT images confirmed correct placement of the VSB. Conclusions: A VSB can be safely implanted in the middle of dogs.     

Factors controlling sediment yield at the catchment scale in NW Mediterranean geoecosystems

Purpose  

This study aimed to (1) increase understanding of the relation between sediment yield and environmental variables at the catchment scale; (2) test and validate existing and newly developed regression equations for prediction of sediment yield; and (3) identify how better predictions may be obtained.     

Sponge paleogenomics reveals an ancient role for carbonic anhydrase in skeletogenesis

Sponges (phylum Porifera) were prolific reef-building organisms during the Paleozoic and Mesozoic approximately 542 to 65 million years ago. These ancient animals inherited components of the first multicellular skeletogenic toolkit from the last common ancestor of the Metazoa. Using a paleogenomics approach, including gene- and protein-expression techniques and phylogenetic reconstruction, we show that a molecular component of this toolkit was the precursor to the alpha-carbonic anhydrases (alpha-CAs), a gene family used by extant animals in a variety of fundamental physiological processes. We used the coralline demosponge Astrosclera willeyana, a "living fossil" that has survived from the Mesozoic, to provide insight into the evolution of the ability to biocalcify, and show that the alpha-CA family expanded from a single ancestral gene through several independent gene-duplication events in sponges and eumetazoans.