SGER: Effects on Record Precipitation Inputs on Soil-Plant Nitrogen Relationships in Tallgrass Prairie

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9321592 Blair Our conceptual understanding of the structure and function of tallgrass ecosystems is based on the central role that an extremely variable climate, particularly precipitation, plays in this system. Previous research has documented the importance of seasonal water deficits, and longer-term droughts, on nutrient cycling processes and plant responses. However, much less is known about the impacts of excessive precipitation inputs on plant communities and ecosystem-level responses in tallgrass prairie. At the Konza Prairie LTER site we are currently experiencing the wettest consecutive one-year period since local weather data collections began in 1890. This "100-500 year event" has presented us with an unique opportunity to examine the effects of excess precipitation on soil and plant processes in tallgrass prairie, a system adapted to moisture deficits. We expect excess precipitation inputs to alter soil-plant N relationships and to increase N losses and N limitations, with greatest subsequent impacts occurring on the upland sites of annually burned watersheds. We request funding which will allow us to (1) quantify the immediate effects of record precipitation inputs on annual production of forbs and grasses on upland and lowland sites of annually burned and long-term unburned watersheds that are not currently measured with core LTER funds, (2) evaluate changes in soil nutrient pools, with emphasis on patterns on patterns of N availability and plant responses in the short term (end of this growing season and the year following excess precipitation), and (3) provide a basis for evaluating longer-term interactions of elevated annual precipitation and fire frequency on N-limitations and plant responses. SGER funding will provide for more detailed measurement of responses over two growing seasons(1993 and 1994), and provide a baseline for longer-term monitoring by the Konza LTER program. We will establish a series of paired experimental plots in both upland and lowland areas of annually burned and long-term unburned watersheds, consisting of control and N fertilized plots. Response variables to be measured will include above-and below-ground plant biomass, N losses to fire next spring, rates of N mineralization and patterns of N availability in the next growing season, annual above-ground NPP, and plant community composition.