ICOM1 Abstract

CULLINGS, K.W., AND V.T. PARKER San Francisco State University,Department of Biology, 1600 Holloway Ave., San Francisco, CA. 94132. - Changes in distribution and relative frequency of Pinus contorta mycorrhizae through succession. The Greater Yellowstone Ecosystem is fire driven, and forest succession proceeds from pure seedling Pinus contorta, to adult P. contorta, to mixed P. contorta, Picea engelmanii, and Abies lasiocarpa. In this study, we determined the location and relative frequency of active mycorrhizae of each tree species in the system through succession. In each forest type, mycorrhizae were sampled by soil core (9 cm- diameter) and separated into three, 6 cm. deep sections. Three cores were taken from 2 locations in 3 different stands ( total of 18 cores) cores were sifted, and mycorrhizae were divided by morphotype. In pure P. contorta stands, mycorrhizae in each core were counted. In mixed stands, tree species forming ectomycorrhizae were identified using PCR; DNA from 5- 10 mycorrhizae of each morphotype was amplified using the plant specific primer combination 28KJ/28C, and tree species forming individual mycorrhizae identified by comparing RFLP patterns of DNA amplified from root tips to reference DNA amplified from needles. Results indicate that mycorrhizae of P. contorta occupy the upper layers in pure stands, but once P. engelmanii and A. concolor are established, mycorrhizae of P. contorta become restricted to the bottom 6 cm of the soil column, while the upper layers are dominated by mycorrhizae of the late successional species. Furthermore, P. contorta is usually does not dominatet even in the lower soil layer, even though individuals of this species are always larger and more numerous in the mixed species stands. This result suggests that mycorrhizae of late successional species are out-competing mycorrhizae of P. contorta for space, and that P. contorta may therefore be at increasing nutritional disadvantage as stands develop.