Genetic Analysis of Populus Tremuloides in the Great Lakes Region Long-Term Soil Productivity Study.

The North American Long-Term Soil Productivity Study (LTSP), started in 1989, investigates forest productivity under altered soil conditions. While the LTSP study thoroughly examined soil and forest productivity relationships, it does not include genetic variation as part of its forest productivity assessment. Genetic variation among numerous tree species has repeatedly been shown to influence aspects of tree growth directly and certain soil traits indirectly, consequently making genetic analysis important in forest-soil studies. Our research is focused on analyzing growth using diameter at breast height (DBH), environmental variations, and phenotypic clone identification traits (ex. timing of leaf fall) between Populus tremuloides LTSP clonal populations within the Ottawa National Forest, MI. Twenty-seven plots were established in 1992 to study forest responses to altered soil porosity and organic matter content. A subset of six plots was chosen for genetic analysis: three had no organic matter removal and no soil compaction, and three had forest floor removal and heavy soil compaction. Putative clones in each plot were identified phenotypically using bark color and timing of bud burst, then mapped and measured for DBH. Leaf samples were collected for morphometric measurements and DNA analysis. Samples were collected from two of the largest putative clones in each plot. Exhaustive sampling was conducted within one plot to analyze phenotypic identification accuracy and genotypic diversity. Ten highly variable nuclear microsatellite markers will be used to confirm clonal identity. Genetic analyses using five markers on 92 samples collected within a 314m2 area identified 30 genotypes, which included 19 unique stems and 11 clones with an average of six stems/clone. No correlation was found between DBH variance and the number of stems per clone, demonstrating a poor correlation between DBH and clone identity. Continued research will further analyze DBH and other phenotypic expressions between genotypes.