PARENT SESSION
Oral Session #8: Plant Ecology: Nutrient Uptake, Movement, Use.
Presiding: V. Gutschick
Monday, August 5. 8:00 AM to 11:30 AM. Grand Ballroom West, Radisson.

Nitrogen transfer between Lupinus perennis and non-leguminous prairie plants under elevated CO2 and N .

SABO, AUTUMN^*,1, REICH, PETER¹, LEE, TALI¹, ¹ UNIVERSITY OF MINNESOTA, ST. PAUL, MN

ABSTRACT- Nitrogen transfer from legumes to non-legumes is heavily utilized in agricultural systems but little is known about its role in structuring natural communities. Furthermore, plant-plant interactions like nitrogen transfer may differ under elevated atmospheric CO₂ and increased nitrogen deposition. At our free-air CO₂ enrichment site in Minnesota, USA, we used ¹⁵N techniques to examine N transfer in mixed grassland species plots that received a combination of CO₂ (368 vs. 560 mol mol-1) and soil N (umamended vs. fertilization of 4 g N m^-2y^-1) treatments. In our previous work, we have seen significant increases in N fixation by Lupinus perennis under elevated CO₂ . Our hypotheses are that: 1) since elevated CO₂ increases N fixation by L. perennis, N transfer will be higher in elevated CO₂ treatments 2) N transfer will be lower in plots that receive N fertilizer since there is more readily available N for non-legume uptake 3) the CO₂ and N treatments will interact but the CO₂ will be more important in controlling the amount of N transfer to non-legumes. Preliminary results show that our 3 non-legume species (Achillea millefolium, Agropyron repens, and Andropogon gerardi) react differently to CO₂ enrichment. Only A. repens supports hypothesis 1, with significant N transfer under elevated CO₂ but not under ambient CO₂. All 3 non-legumes support hypothesis 2, as there is greater N transfer under ambient N. There appear to be no interacting effects to support hypothesis 3.

KEY WORDS: nitrogen transfer, ¹⁵N, lupinus perennis, CO₂