Influence of clear-cutting on ectomycorrhizal fungi associated with lodgepole pine (Pinus contorta)

Abstract

Several aspects of ectomycorrhizal ecology were studied in a southwestern Alberta lodgepole pine (Pinus contorta Loud.) chronosequence. Soil cores from 6, 10, 19 and 90 year-old stands were removed, and the ectomycorrhizal fungi colonizing lodgepole pine roots were identified and counted . Twenty different ectomycorrhizal taxa were identified on roots throughout the chronosequence. Of these 20 ectomycorrhizal taxa, none were restricted to any specific age class, therefore succession of ectomycorrhizal fungi throughout the chronosequence was not detected. This conclusion was supported by three years of ectomycorrhizal fruit body surveys in the sites where soil cores were removed. Furthermore, colonization of lodgepole pine seedlings in three 2 year-old clear-cuts, was monitored for three successive growing seasons. Ectomycorrhizal fungi colonizing regenerating seedlings were from the same taxa as those fungi observed in other age classes from the lodgepole pine chronosequence. Species richness, of ectomycorrhizas and fruit bodies, increased with stand age, but diversity, as determined by the inverse of Simpson's index, was highest in the 19 year-old stands. Evenness of the ectomycorrhizal data followed the same trend. Due to the large amount of overlap in ectomycorrhiza and fruit body species composition, similarity among stands was high. Thus, changes in community indices were due to differences in relative abundance and not species composition. Correspondence analysis of ectomycorrhiza and fruit body data, revealed that there was as much variation in community composition in the clear-cut stands as there was in mature lodgepole pine stands. Typically, this trend was the same for ectomycorrhizas found in whole soil cores, organic soil and mineral soil. Canonical correspondence analysis revealed that organic soil factors (percent organic matter and organic layer depth) and lodgepole pine density were important environmental variables structuring the ectomycorrhizal and fruit body communities. Molecular analysis, using random amplified polymorphic DNA (RAPD) markers, of Cenococcum geophilum L. in 12, 21 and 92 year-old stands, revealed a high level of genetic variation among sites. The number and sizes of C. geophilum clones did not change in the different aged stands, therefore, C. geophilum inoculum persisted in situ from clear-cutting disturbance to stand regeneration, and throughout stand development.