Dr. Frank S Gilliam

Nitrogen (N) saturation is an environmental concern for forests in the eastern U.S. Although several watersheds of the Fernow Experimental Forest (FEF), West Virginia exhibit symptoms of Nsaturation, many watersheds display a high degree of spatial variability in soil N processing. This study examined the effects of temperature on net N mineralization and nitrification in N-saturatedsoils from FEF, and how these effects varied between high N-processing vs. low N-processingsoils collected from two watersheds, WS3 (fertilized with [NH4]2SO4) and WS4 (untreated control). Samples of forest floor material (O2 horizon) and mineral soil (to a 5-cm depth) were taken from three subplots within each of four plots that represented the extremes of highest and lowest ratesof net N mineralization and nitrification (hereafter, high N and low N, respectively) of untreated WS4 and N-treated WS3: control/low N, control/high N, N-treated/low N, N-treated/high N. Forest floor material was analyzed for carbon (C), lignin,and N. Subsamples of mineral soil were extractedimmediately with 1 N KCl and analyzed for NH4+and NO3– to determine preincubation levels. Extracts were also analyzed for Mg, Ca, Al, and pH. To test the hypothesis that the lack of net nitrification observed in field incubations on the untreated/low N plot was the result of absence ofnitrifier populations, we characterized the bacterial community involved in N cycling by amplification of amoA genes. Remaining soil was incubated for 28 d at three temperatures (10, 20, and30°C), followed by 1 N KCl extraction and analysis for NH4+ and NO3–. Net nitrification was essentially 100% of net N mineralization for all samples combined. Nitrification rates from lab incubation sat all temperatures supported earlier observations based on field incubations. At 30°C, rates from N- t reated/high N were three times those of N-treated/low N. Highest rates were found for untreated/high N (two times greater than those of N-treated/high N), whereas untreated/low N exhibited no net nitrification. However, soils exhibitingno net nitrification tested positive for presence of nitrifying bacteria, causing us to reject our initial hypothesis. We hypothesize that nitrifier populations in such soil are being inhibited by a combination of low Ca:Al ratios in mineral soil and allelopathic interactions with mycorrhizae of ericaceous species in the herbaceous layer.

The Konza Prairie Research Natural Area (KPRNA) in Kansas is the largest representative tract of tallgrass prairie. Less than 2 percent of the Konza Prairie has ever been plowed, and the KPRNA is managed to provide a range of conditions encompassing those of tallgrass prairie prior to settlement. The 1,060 ha Kings Creek watershed is located entirely within the Konza boundaries. The watershed has been a U.S. Geological Survey bench-mark watershed since 1979. It represents the landscape type that gave rise to much of the agricultural midwestern United States. Hydrologic, chemical, and biological measurements have been made by ecologists performing long-term ecological research (LTER) in tallgrass prairie. Streamwater chemistry varies seasonally with the amount and movement of ground water and soil water, with changes in prairie vegetation, and in response to changes in surface water discharge. Concentrations of nutrients increase during storm flows. The particulate fractions in transport and in storage in the stream bed and on the flood plain vary seasonally with recent hydrologic history and changes in vegetation.

Prescribed fire is an important practice in the multiresource management of forests, and controlled burning is now applied annually to about 1 million hectares (2.4 million acres) of forest in the southeastern United States. Prescribed fires had few detectable effects on forest soils, nutrient cycling, and hydrologic systems of a pine-flatwoods watershed at the Santee Experimental Forest in the Francis Marion National Forest in South Carolina, a site of long-term watershed research by the US Forest Service and Duke University. Experiments were designed so that treatment effects would simulate responses of an operational southern pine forest, and it was concluded that nutrient fluxes from burned pine litter to ground and stream waters are not likely to have appreciable effects on the quality of waters that drain southern pine watersheds, especially those with fine-textured soils.