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).
Hydrolase kinetics to detect temperature-related changes in the rates of soil organic matter decomposition
Abstract To evaluate the importance of the role of temperature on the decomposition of soil organic matter (SOM), we investigated the SOM decomposition rates and the kinetics of two hydrolases involved in carbon (C) and nitrogen (N) cycling, namely β-1,4-glucosidase (βG) and β-1,4-N-acetylglucosaminidase (NAG), and their sensitivity to temperature in representative temperate forests. Soils were collected from three spatially-separate replicate plots at study sites distributed at heights of 1233, 1060, and 825 m a.s.l. along an elevation gradient on the southern slopes of Laotuding Mountain, Northeast China. Soils were incubated at temperatures between 4 and 40 °C at 6 °C intervals for 7 days in our laboratory. Decomposition rates of SOM responded positively to temperature, and, at the same temperature, were highest in the soil from 1233 m a.s.l. than in the soils from the other elevations. SOM decomposition rates were positively correlated with the maximum activity (Vmax) of βG and the contents of total and particulate organic C, but were negatively correlated with the soil silt and clay contents. The Vmax and the Michaelis constant (Km) of the two hydrolases were positively correlated and were also correlated with increases in temperature, suggesting that the Km values could offset increases in Vmax with increases in temperature. These correlations also highlight the enzymatic tradeoff between the maximum catalytic rate and the substrate binding affinity for the two hydrolases. The catalytic efficiencies of the two hydrolases were highest at 1060 m a.s.l., followed by 1233 m a.s.l., and were lowest at 825 m a.s.l. The catalytic efficiencies were positively correlated with the soil water contents and macroaggregate contents (>250 μm), but negatively with the soil C/N ratios. The temperature sensitivities (Q10) of the SOM decomposition rates were similar at the different elevations (P > 0.05), but generally increased as the temperature increased (P   0.05). Our results suggest that, in spite of the negative effects of increased temperatures on enzyme substrate affinity, increases in hydrolytic activity will lead to accelerated SOM decomposition in temperate forests.
Protective effect of ginsenoside Re on acute gastric mucosal lesion induced by compound 48/80
The protective effect of ginsenoside Re, isolated from ginseng berry, against acute gastric mucosal lesions was examined in rats with a single intraperitoneal injection of compound 48/80 (C48/80). Ginsenoside Re (20 mg/kg or 100 mg/kg) was orally administered 0.5 h prior to C48/80 treatment. Ginsenoside Re dose-dependently prevented gastric mucosal lesion development 3 h after C48/80 treatment. Increases in the activities of myeloperoxidase (MPO; an index of neutrophil infiltration) and xanthine oxidase (XO) and the content of thiobarbituric acid reactive substances (TBARS; an index of lipid peroxidation) and decreases in the contents of hexosamine (a marker of gastric mucus) and adherent mucus, which occurred in gastric mucosal tissues after C48/80 treatment, were significantly attenuated by ginsenoside Re. The elevation of Bax expression and the decrease in Bcl2 expression after C48/80 treatment were also attenuated by ginsenoside Re. Ginsenoside Re significantly attenuated all these changes 3 h after C48/80 treatment. These results indicate that orally administered ginsenoside Re protects against C48/80-induced acute gastric mucosal lesions in rats, possibly through its stimulatory action on gastric mucus synthesis and secretion, its inhibitory action on neutrophil infiltration, and enhanced lipid peroxidation in the gastric mucosal tissue.