SOIL β-GLUCOSIDASE ACTIVITY UNDER WINTER WHEAT CULTIVATED IN CROP ROTATION SYSTEMS DEPLETING AND ENRICHING THE SOIL IN ORGANIC MATTER
β-glucosidase (E.C. 3.2.1.21), an enzyme involved in cellulose degradation, plays an important role in the soil organic carbon cycle. Cellulose is the most abundant organic compound in the biosphere so a product of its enzymatic hydrolysis is important as an energy source for soil microorganisms. Since β-glucosidase is very sensitive to different factors, determination of its activity might be helpful in soil quality monitoring. The objective of the study was to assess the effect of various doses of farmyard manure (FYM) and mineral nitrogen on β-glucosidase activity in soil samples taken under winter wheat cultivated in crop rotation systems depleting soil from organic matter (A) and enriching soil in organic matter (B). Soil samples were taken in 2002 from a two-factor fertilization experiment carried out as randomized sub-blocks cropped with winter wheat cultivated on lessive soil. The experiment was located at the Experimental Station of the Institute of Tillage and Soil Science in Grabowo on the Vistula River. All fertilization combinations included FYM (0, 20, 40, 60 and 80 t.ha–1) and nitrogen fertilization (0, 40, 80 and 120 kg ha–1). The activity of β-glucosidase was determined according to Eivazi, Tabatabai (1988). The enzyme activity ranged 3.604-7.041 mM pNP g–1 h–1 in soil samples taken from crop rotation A and between 4.931-7.445 mM pNP g –1 h –1 in those collected from the crop rotation enriching the soil in organic matter. These data were closely related to the applied FYM and nitrogen fertilization doses. Moreover, β-glucosidase activity depended significantly on sampling dates. Enzyme activity was closely connected with soil organic carbon and total nitrogen content, which was confirmed by highly significant correlation coefficients between these parameters (r=0.611-0.770 for C org, and r=0.844-0.912 for N og ; p<0.01 and p<0.001).
Factors affecting glucosidase and galactosidase activities in soils
Abstract This study was carried out to assess the effects of soil treatments, the addition of 12 inorganic salts and of 20 trace elements on α- and β-glucosidase and α- and β-galactosidase activities in soils. Results showed that air-drying of field-moist soils resulted in marked increases in the activity of these enzymes and that steam sterilization of soils completely destroyed the activities. In general, the inorganic salts were stronger inhibitors of α-glucosidase and α-galactosidase activities (range 0 to 70%) than the activities of their β counterparts (range 0 to 44%). The effect of trace elements on the activities of these enzymes varied considerably among the elements, enzymes and soils. The percentage inhibition of α-glucosidase activity in Webster soil ranged from 4% with Mo(VI) to 66% with Ag(I) and in Luton soil ranged from 9% with V(IV) to 66% with Cd(II). In general, the inhibition values of β-glucosidase activity by trace elements were much lower than those obtained for α-glucosidase activity. The inhibition values of α-galactosidase activity in Webster soil ranged from 10% with Hg(II) to 13% with Sn(II). The inhibition values for this enzyme in Luton soil ranged from 12% with Hg(II) to 73% with Mo(VI). Studies on the distribution of the activities of these enzymes showed that they are concentrated in surface soils and decrease with depth. The activities of these enzymes were significantly correlated with organic C in soil profiles and surface soils and were, in most cases, significantly but negatively correlated with pH.
Optimal Combination and Concentration of Antibiotics in Media for Isolation of Pathogenic Fungi and Nocardia asteroides
Strains of Blastomyces dermatitidis, Sporothrix schenckii, Histoplasma capsulatum, Cryptococcus neoformans, Nocardia asteroides, and Coccidioides immitis were tested for in vitro susceptibility to polymyxin, gentamicin, kanamycin, chloramphenicol, and neomycin at concentrations of 1, 2, 4, 8, and 16 μg/ml. Polymyxin was the most inhibitory and gentamicin was the least inhibitory of the five antibiotics. Two Histoplasma mycelial strains were partially inhibited by 2 and 8 μg of gentamicin per ml and showed at least a 2+ growth at the higher antibiotic concentration. Kanamycin and neomycin produced significant inhibition of N. asteroides but otherwise were noninhibitory. A combination of chloramphenicol and kanamycin, each at 16 μg/ml, and gentamicin, at 4 μg/ml, was noninhibitory to the strains tested except for N. asteroides. Chloramphenicol at 16 μg/ml was not inhibitory for N. asteroides. The results suggest that the optimal antibiotic combination to use in the isolation of fungi and higher bacteria is chloramphenicol, 16 μg/ml, and gentamicin, 4 μg/ml. Addition of sheep blood (5%) had no effect on antibiotic susceptibility of the organisms studied.