Factors influencing spatial variability in soil nitrogen (N) dynamics in N-treated and untreated watersheds of the Fernow Experimental Forest, West Virginia
Date of Award
College of Science
Type of Degree
Frank S. Gilliam
Charles C. Somerville
Leonard J. Deutsch
The central Appalachian region of the United States receives some of the highest inputs of nitrogen (N) due to acidic deposition in the nation. It is believed that these high could levels contribute to a decline in forest soils within the next 50 to 70 yrs. This study examines factors that influence spatial variability in N-treated and untreated watersheds of the Fernow Experimental Forest, Parsons, West Virginia. Within each of the two watersheds [WS4 untreated control, > 100 yr.; WS3 N-treated, acidified, clear cut, ~ 31 yr.], two 0.04 ha plots, one high N and one low N, were selected for study. Three subplots were chosen from within each of the two sample plots, for a total of 12 subplots. Soil samples were collected with a hand trowel. Nitrogen extractions were performed using 10 g of soil and 100 ml of 1 N KCl. Litter samples were ground using a Wiley Mill and analyzed for foliar lignin concentration, C:N, and %N. Nitrogen extracts were analyzed with a Bran + Luebbe TrAAcs 2000 automatic analysis system. Bacterial DNA was analyzed using primer sets. The primer sets (1-6) were designed for the specific detection of ammonia oxidizing bacteria in forest soils by PCR. DNA was purified and amplified by PCR.
All plots detected AMO gene groups during pre-incubation, but by day 7 only WS4/low N had detectable gene groups present. On day 14 all plots, with the exception of WS4/high N, had detectable groups present. At days 21 and 28 only one plot for each day had detected AMO genes. On day 21 WS4/low N had group 2 present and on day 28 WS3/high N had group 2 present. Overall, it is clear that the nitrifying bacterial community is very dynamic. AMO genes were readily detected at pre-incubation, but were nearly absent after seven days of incubation. By fourteen days of incubation the communities had shifted. Only AMO genes of the group 2 were detected after three and four weeks of incubation. The data suggest either that incubation conditions were not suitable for nitrifying bacteria, or that previously uncharacterized AMO genes were dominant after prolonged incubation.
The first hypothesis posed was that soil incubation temperature and net mineralization and nitrification were correlated. This hypothesis was supported. The lowest rates for both net mineralization and nitrification were seen at the 10 C incubation temperature. The 30 C incubation temperature allowed the highest rates. This was true of all the study plots within WS3 and WS4.
The second hypothesis, that the lack of net nitrification on WS4/low N was caused by a lack of nitrifying bacteria at that site, was rejected. The opposite was found to be true. The high N plot of WS4 did have bacterial communities present. The lack of nitrification be attributed to the inactivity of the bacterial communities due to an unknown environmental limitation.
Fernow Experimental Forest (W. Va.).
Soils – Nitrogen content – West Virginia.
Watersheds – West Virginia.
Lyttle, Nikki Lenore, "Factors influencing spatial variability in soil nitrogen (N) dynamics in N-treated and untreated watersheds of the Fernow Experimental Forest, West Virginia" (2001). Theses, Dissertations and Capstones. 1697.
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