PARENT SESSION
Oral Session #98: Carbon and Nitrogen Cycling: N-addition, N-flux.
Presiding: C. Hoover
Friday, August 9. 9:00 AM to 12:00 PM. Greenlee Meeting Room, TCC.
Elevated CO2, N deposition, and plant diversity effects on soil microbial activity in a grassland field experiment.
Dijkstra, Feike*,1, Hobbie, Sarah1, Reich, Peter1, 1 University of Minnesota, St. Paul
ABSTRACT- Human induced changes in atmospheric CO2, N deposition and plant diversity have potentially large effects on ecosystem functioning. Predicting the responses to these factors requires an understanding of their interactive effects on C and N cycling. We manipulated atmospheric CO2 (ambient, 560 ppm), N fertilization (0, 4 g m-2 yr-1), species identity (monocultures of 16 species), species number (1 or 4 species), and functional group composition (1 or 4 groups) in a grassland field experiment in Minnesota. During the fourth season of treatments, we incubated soils from monoculture and four species plots for two months in the lab and determined C respiration, net N mineralization, microbial C and N and total C and N. We estimated labile C pools as the initial amount of C respired. Elevated CO2 and increased species number increased the labile C pool by 35% and 42%, and reduced initial net N mineralization by 25% and 50% respectively. Nitrogen fertilization more than compensated for the effects of elevated CO2 and increased species number by decreasing labile C and increasing net N mineralization. Among functional groups, forbs had the highest labile C and lowest net N mineralization while legumes had the lowest labile C and highest net N mineralization. However, these differences were largely due to the effect of individual species (Achillea millefolium in the forbs, and Lupinus perennis in the legumes). Our results show that species number and species and functional group identity had more significant and sometimes larger effects on the labile C pool and net N mineralization than did atmospheric CO2 and N fertilization.
KEY WORDS: biodiversity, C and N soil interactions, climate change, soil microbial processes