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Soil Variability along a Nitrogen Mineralization and Nitrification Gradient in a Nitrogen-Saturated Hardwood Forest

^a Dep. of Biological Sciences, Marshall Univ., Huntington, WV 25755-2510
^b USDA-Forest Service, Timber and Watershed Research Lab., Parsons, WV 26287

View larger version (16K): [in a new window]   Fig. 1. Map of Watersheds 3 and 4 of Fernow Experimental Forest, West Virginia, showing sample sites for the present study. Values shown are monthly means from a 3-yr period (1993–1995), wherein the first value is net N mineralization and the second value is net N nitrification (g N m–2 mo–1). Data taken from Gilliam et al. (2001b).

View larger version (25K): [in a new window]   Fig. 2. Effects of incubation temperature on N dynamics of soils from four sites within the Fernow Experimental Forest, West Virginia. (A) Net N mineralization, (B) net nitrification.

View larger version (23K): [in a new window]   Fig. 3. Relationship between extractable Ca and extractable NO3 in soils from the Fernow Experimental Forest, West Virginia. Points shown are means of three replicates for each of five incubations periods (30°C only)—0 (preincubation), 7, 14, 21, and 28 d. Error bars (±1 SE of the mean) are shown for mean extractable Ca and NO3 for all significant relationships with extractable NO3: control–high N, y = –85.1 + 112.9ln(X), r2 = 0.90, P < 0.01; N-treated–high N, y = 74.9 + 15.6ln(x), r2 = 0.84, P < 0.01; N-treated–low N, y = 32.9 + 5.3ln(x), r2 = 0.92, P < 0.01.

View larger version (17K): [in a new window]   Fig. 4. Net Ca mineralization vs. net nitrification at 30°C across all four study sites. Equation for curve is y = 0.21 – 0.20x + 0.20x2, r2 = 0.998, P < 0.01. Points shown are means of three replicates; error bars shown are ±1 SE of the mean.

View larger version (28K): [in a new window]   Fig. 5. Effects on net N mineralization and nitrification of additions of sucrose to soils with high N processing, Fernow Experimental Forest, West Virginia. Error bars (n = 4) shown are ±1 SE of the mean. Means with the same superscript are not significantly different at P < 0.05.

View larger version (16K): [in a new window]   Fig. 6. Effects on net N mineralization and nitrification of additions of glycine to soils with low N processing, Fernow Experimental Forest, West Virginia. Error bars (n = 4) shown are ±1 SE of the mean. Note: lack of error bars for net nitrification due to lack of net nitrification. Means with the same superscript are not significantly different at P < 0.05.

View larger version (18K): [in a new window]   Fig. 7. Net nitrification at 30°C vs. preincubation extractable Al across all four study sites. Equation for curve is y = 36.37 – 5.66ln(x), r2 = 0.96, P < 0.01. Points shown are means of three replicates; error bars shown are ±1 SE of the mean. Note that there are error bars occurring on the line of the x axis that are associated with mean extractable Al for the site that exhibited no net nitrification.