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GROSS N TRANSFORMATION RATES AND MICROBIAL POPULATION DYNAMICS UNDER FIELD AND LABORATORY CONDITIONS FROM TWO DIFFERENT ECOSYSTEMS
Citation:
Silva, R. G., E E. Jorgensen*, AND M E. Gonsoulin*. GROSS N TRANSFORMATION RATES AND MICROBIAL POPULATION DYNAMICS UNDER FIELD AND LABORATORY CONDITIONS FROM TWO DIFFERENT ECOSYSTEMS. Presented at American Society of Agronomy; Crop Science Socity of America; Soil Science Socity of America, Denver, CO, 11/2-6/2003.
Description:
Change of soil and environmental conditions can influence microbial activities and subsequent soil nitrogen (N) transformation processes. The objective of this study was to compare gross N transformation rates between field and laboratory incubation conditions using an old-field and forest soil. Soil samples (Vertic Argiustolls, USDA) were analyzed at 2, 4, 6, 8 and 12 weeks to determine gross N transformation rates and some microbial community changes. Gross mineralization rates were similar between field and laboratory conditions in both forest soil (2.4 and 2.0 mg kg-1 d-1 respectively) and in old-field soil (1.0 and 1.1 mg kg-1 d-1 respectively). The similar gross mineralization rates from the two different techniques used in this study could be due to the overwhelming impact of other factors besides soil mixing. The average rate of gross N mineralization was significantly greater (p < 0.001) in forest soil than old-field soil under both conditions. In contrast, gross nitrification rates did not differ between ecosystems in either techniques, but were significantly (p < 0.001) lower under field conditions than laboratory conditions in both ecosystems. This could be attributed to lower available NH4+ for microbes under field conditions due to root NH4+ uptake. Total aerobic microbial and actinomycete populations were significantly greater in forest soil than old-field soil, but both populations were significantly (p < 0.01) diminished in disturbed soils. Fungi and denitrifier populations were each similar between sites. It was found that either technique can be used for the measurement of gross mineralization, but undisturbed soil cores were more useful for gross nitrification measurements