Monday, November 13, 2006
94-2
Effect of Grazing and Cultivation on Activities of Enzymes Involved in Carbon and Nitrogen Cycles.
Eirini Katsalirou, Shiping Deng, and David L. Nofziger. Oklahoma State Univ, Dept of Plant and Soil Sciences, Stillwater, OK 74078-6028
As the key factors regulating C and N cycling in soil ecosystems, activities of 11 enzymes involved in C and N transformation, and microbial biomass C and N were evaluated to assess impacts of grazing and cultivation on prairie soils. Activities of β-glucosaminidase, α- and β-glucosidases, α- and β-galactosidases, cellulase, invertase, protease, L-asparaginase, L-glutaminase, and urease were determined. Treatments included cultivated, abandoned (cultivated but returned to grassland >30 yr ago), undisturbed native prairie, or grazed at high and moderate intensities. Higher organic C and total N in grazed and undisturbed soils supported higher microbial biomass C and N. These systems also had the highest activities for α- and β-glucosidases, α- and β-galactosidases, cellulase, and urease. The cultivated soils had the lowest enzyme activities, except for invertase and protease. Enzyme activities were significantly correlated with microbial biomass C and N, except for invertase and protease, indicating possible predominant plant origin of the latter two enzymes. Enzyme activities in the abandoned system were generally significantly higher than those in the cultivated one, but lower than the grazed and native systems. These results suggested partial restoration of the soil ecosystem from impact of cultivation. However, changes induced by cultivation in the abandoned soils were detectable, suggesting that more than 30 years of conservation was not long enough to erase human impact on ecosystem function. When compared with the native prairie, grazing maintained or even enhanced enzyme activities. Moderately grazed system had the highest microbial biomass and activities of several C- and N-transforming enzymes. Thus it was the most sustainable management alternative. Of the enzymes evaluated, principal component analysis indicated that the activities of β-glucosidase, α- and β-galactosidase, invertase, L-glutaminase, and β-glucosaminidase were most sensitive in discriminating the effect of management practices.