Impact of pea growth and arbuscular mycorrhizal fungi on the decomposition of 15N-labeled maize residues

A pot experiment was carried out (1) to compare C and N yield of different plant parts, nutrient concentrations, and root colonization between the non-mycorrhizal mutant P2 (myc ^?) and the symbiotic isoline Frisson (myc ⁺), (2) to investigate the effects of arbuscular mycorrhizal fungi and growing pea plants on microbial decomposition of ¹⁵N-labeled maize residues, and (3) to follow the distribution of the added substrate over different soil fractions, such as particulate organic matter, soil microbial biomass, and microbial residues. Yields of C in straw, grain, and roots of myc ⁺ peas were significantly higher by 27%, 11%, and 92%, respectively, compared with those of myc ^? peas. The δ¹³ C values in the different plant parts were significantly higher in myc ⁺ than in myc ^? tissue with and without maize. Application of labeled maize residues generally resulted in ¹⁵N enrichment of pea plants. At the end of the experiment, the ergosterol concentration in roots of mature peas did not differ between the two isolines, indicating similar colonization by saprotrophic fungi. The decomposition of added maize residues was significantly reduced by the myc ^? peas, but especially by myc ⁺ peas. The formation of microbial residue C was increased and that of microbial residue N was reduced in the presence of plants. The insufficient N supply to soil microorganisms reduced decomposition of maize residues in the presence of peas, especially myc ⁺ peas.     

The role of trypsin in plaque formation by simian rotavirus SA-11.

The role of trypsin in plaque production by simian rotavirus SA-11 monolayers of MA-104 cells are investigated. Initial trypsin treatment of the virus alone or its presence only during the early phases of virus-cell interaction was found to be insufficient for plaque production by the virus. Presence of trypsin (5 microgram/mL) in the agar overlay throughout the five day incubation period was essential for the optimal development of the virus plaques. Production of plaques by the incorporation of trypsin in the overlay was not due to the enzymatic degradation of any plaque-inhibitors in the agar used. Experiments using high (4 PFU/cell) and low (35 PFU/10(6) cells) multiplicities of infection suggest that trypsin added to fluid maintenance medium facilitates the cell-to-cell spread of progeny virus particles. Therefore, the enzyme incorporated in the agar overlay appears to play a similar role thereby assisting in the formation of SA-11 plaques.     

Coffee mucilage impact on young coffee seedlings and soil microorganisms

A greenhouse pot experiment was carried out to assess the effects of fermented coffee mucilage applied as mulch together with maize leaves on the growth of young coffee plants of two different varieties and on soil microbial biomass indices. The coffee variety Catuai required 32% more water per g plant biomass than the variety Yellow Caturra, but had a 49% lower leaf area, 34% less shoot and 46% less root biomass. Maize and mucilage amendments did not affect leaf area, shoot and root yield, or the N concentration in shoot and root dry matter. The amendments always reduced the water use efficiency values, but this reduction was only significant in the maize+mucilage‐14 (= 14 g mucilage pot^?1) treatment. Soil pH significantly increased from 4.30 in the control to 4.63 in the maize+mucilage‐14 treatment. Microbial biomass C increased by 18.5 µg g^?1 soil, microbial biomass N by 3.1 µg g^?1 soil, and ergosterol by 0.21 µg g^?1 soil per g mucilage added pot^?1. The presence of mucilage significantly reduced the microbial biomass‐C/N ratio from a mean of 13.4 in the control and maize treatments to 9.3, without addition rate and coffee variety effects. The application of non‐composted mucilage is recommended in areas where drought leads to economic losses and in coffee plantations on low fertility soils like Oxisols, where Al toxicity is a major constraint.     

Proteolytic enzymes and rotavirus SA-11 plaque formation.

In addition to trypsin, eight other proteolytic enzyme preparations were tested for their ability to assist simian rotavirus SA-11 plaque formation in MA-104 cells. When incorporated in the overlay (minimal essential medium and 0.7% Ionagar No. 2) in the concentrations per mL indicated, alpha-chymotrypsin (10 micrograms), elastase (0.5 micrograms), subtilisin (0.5 micrograms), pronase (2.5 micrograms) and pancreatin (25 micrograms) were as efficient as trypsin (5 micrograms) in helping SA-11 produce 3-4 mm diameter plaques after five days of incubation at 37 degrees C. No plaques were produced when pepsin (25 micrograms), papain (10 micrograms) or thermolysin (10 micrograms) was added to the overlay. Addition of soybean trypsin inhibitor to alpha-chymotrypsin-, pronase- or pancreatin-containing overlays completely inhibited virus plaque production. A similar effect was not seen with elastase or subtilisin.