The effects of nitrogen and phosphorus on fine roots and mycorrhizae across different taxonomic groups, mycorrhizal types and biomes
MetadataShow full item record
Nitrogen (N) often limits productivity and can alter carbon allocation to, and the dynamics of, tree root systems. However, the effects of N on belowground processes are inconsistent, and can differ significantly among forest types. The primary goal of this project is to better understand how N and phosphorus (P) interact with different mycorrhizal types (ectomycorrhizal, or ECM and vesicular arbuscular mycorrhizal, or AM) and taxonomic groups (conifers vs. angiosperms) across different ecosystems in controlling mycorrhizal dynamics. The effect that differences in N and P availability (created by fertilizer treatment) had on hyphal length, phosphatase, percent mycorrhizal colonization, and fungal biomass measured as ergosterol, were evaluated between bulk or root-free (i.e. ingrowth cores) soil over two growing seasons. First-year field data indicated that there were no significant effects of N or P, alone or in combination, on any of the variables measured. There were, however, significant differences among sites and between bulk vs. root-free soil on hyphal length (216.8 cm g soil-1 to 161.0 cm g soil-1) and phosphatase activity. The ECM species (Picea glauca and Populus balsamifera) had much greater hyphal length in both bulk and root–free soil than the AM species (Acer saccharum and Liriodendron tulipifera), 324.4 cm g soil-1 to 49.0 cm g soil-1. Second-year field data indicated an interactive response between species and P on phosphatase, percent mycorrhizal colonization, and hyphal length between the root and mycorrhizal cores. Nitrogen fertilization increased mycorrhizal colonization in conifer species in the controlled greenhouse study. There were no significant effects of fertilization on ergosterol in either the field or greenhouse study. There seems to be considerable variation in the direction and magnitude of fungal response to fertilizer in the forests we studied.