AVIS, PETER.1,2
1University of North Carolina, Department of Biology, Chapel Hill, NC, USA. 21000 East Augusta Drive, Augusta, MI 49012, USA.
The response of arbuscular mycorrhizae (AM) to increased atmospheric deposition of nitrogen (N) was studied by assessing the mycorrhizal inoculum potentials (MIPs) of long term nutrient addition experiment plots in an oak-maple forest. Two contrasting hypotheses were examined. MIP would decrease if N addition resulted only in above-ground growth allocation by the forest plants. However, MIP would remain constant or increase if N addition stimulated not only above-ground growth but also phosphorus (P) demand. Increased P demand would result in increased below-ground allocation to roots and mycorrhizae. The field experiment included 32 10 * 10 m plots in the forest each receiving one of four treatments: addition of N only, addition of N and P together, addition P only and control receiving no fertilization. MIPs of the treatment groups were determined using sorghum-sudan grass hybrid plants grown on soil samples in greenhouse conditions. Results show that MIPs of control and +N treatments are similar while those of +P and N+P treatments are significantly lower. This suggests AM-mediated P remains important for plants in this oak-maple forest under increased N deposition conditions.