PARENT SESSION
Poster Session # 10: Soil Ecology.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Reducing carbon substrate affects nitrogen availability in relation to soil respiration in a tallgrass prairie.
Su, Bo*,1, Wan, Shiqiang1, Belay, Asfaw1, Hui, Dafeng1, Luo, Yiqi1, 1 University of Oklahoma, Norman, OK, USA
ABSTRACT- Carbon (C) substrate is the major energy source for microorganisms mediating C and nitrogen (N) cycles. However, little is known about how reducing C substrate affects N cycling and C-N interactions in tallgrass prairie. By reducing C substrate input via shading, clipping and shading+clipping, we examined C reduction effect on soil inorganic N concentrations, net N mineralization and nitrification rates in relation to soil respiration in a tallgrass priaire ecosystem from July 2001 to July 2002. Results showed that shading/clipping decreased soil respiration, but increased or tended to increase inorganic N concentrations on most sampling dates. Shading and shading+clipping tended to increase net N mineralization and nitrification during most incubation periods, but clipping tended to reduce net N mineralization and nitrification during the last four incubation periods. Consequently, shading and shading+clipping increased but clipping reduced annual net N mineralization and nitrification. The increased N availability under shading and shading+cliping treatments is primarily due to reduced plant N uptake, N immobilization and increased microbial turnover caused by the more favorable microclimates under shading. Seasonally, inorganic N concentrations and net N mineralization and nitrification rates were positively related to microbial biomass C/N ratio, but negatively related to soil respiration. Multiple regression analysis showed that without soil respiration included, soil moisture and temperature altogether explained 18% and 36% of the seasonal variations in NH4+-N and NO3--N concentrations, respectively, but could not explain any seasonal variations in N transformation rates among treatments. With soil respiration included, however, 45%, 37%, 37% and 38% of the seasonal variations in NH4+-N, NO3--N, net N mineralization and nitrification were explained, respectively. These results suggest that although microclimates more or less affected inorganic N concentrations, both inorganic N (esp., NH4+-N) concentrations and N cycling rates were mainly determined by C substrate input as reflected by soil respiration in tallgrass prairie.
Key words: carbon and nitrogen interactions, soil respiration, carbon substrate, nitrogen mineralization and nitrification