Nitrogen and mycorrhiza formation in Pinus ponderosa and Pinus contorta germinants the first growing season after wildfire or clearcutting. Fungi

1. Even though ectomycorrhizal associations have been studied in great detail in mature forests, lab settings, and greenhouses, the early stages of the symbiosis have rarely been studied on seedlings germinating in the field. With a changing climate, fire regimes, and timber harvesting negatively affecting forest regeneration, it is imperative we understand how ectomycorrhizae establish under natural conditions.2. By collecting lodgepole and ponderosa pine seedlings during their first growing season in areas that had been disturbed by clearcut timber harvesting or severe wildfire the year before, we were able to identify when colonization of pine roots first began, the rate at which ectomycorrhizal fungi colonized new germinants, and how this related to N nutrition and growth.3. Pine seedlings started to show signs of colonization in July, a month after germination was first observed. By the end of the season, all collected seedlings had ectomycorrhizae present on their roots.4. Ascomycetes, with a Pustularia sp. and Wilcoxina spp. most abundant, formed 80 % of the ectomycorrhizae. Lodgepole pine seedlings colonized by Wilcoxina spp. in clearcut sites had higher shoot %N than those colonized by Cenococcum spp., with other ascomycete mycobionts intermediate. Over the summer, ectomycorrhizal lodgepole pine seedlings generally had higher N contents and biomass compared to uncolonized seedlings collected at the same time.