Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Response of belowground carbon cycling to water and nitrogen in tallgrass prairie.

Clark, James*,1, Johnson, Loretta1, Suelter, Tyler1, Koelliker, James2, Knapp, Alan1, 1 Division of Biology, Manhattan, KS, USA2 Department of Biological and Agricultural Engineering, Manhattan, KS, USA

ABSTRACT- Atmospheric N deposition and water availability may have profound effects on whether prairie ecosystems sequester or release C. Objectives are to determine separate and interactive effects of water and N on belowground carbon (C) cycling (soil respiration and root decomposition) and root biomass at Konza Prairie. We hypothesized that water will increase C cycling, while N will be neutral or negative. Plots (2x2m) were treated with 3 levels of water (250, 150 and 0 mm in excess of natural precipitation) combined with 4 levels of N (0, 2.5, 5, and 10gN/m2/season). Plots were replicated 6 times in upland and lowlands (144 plots total). Root decomposition was determined by burying 2g of Andropogon roots in mesh bags. Soil CO2 efflux was measured on 14 dates spanning two treatment seasons. After 7 months, water increased root decomposition in uplands and lowlands (p=<.0001), but high N and high water depressed decomposition in uplands (p=.01). However, one year later, N had no significant effect on mass loss in upland or lowland. Soil respiration was enhanced in uplands and lowlands with water (p=<.0001) but was significantly depressed in high N treatments. Root biomass increased in uplands and lowlands in response to water (p<.0001) but not to N. Removal of water limitation increases belowground C cycling in tallgrass prairie. In contrast, N addition may depress soil C cycling and lead to greater belowground C sequestration.

Key words: belowground C cycling, litter decomposition, water and nitrogen availability, soil respiration