TRFLP Analysis of the Effect of a Forest-to-Gap Ectone on Soil Microbial Diversity

Abstract

To investigate how soil microbial diversity is influenced by the formation of an experimental edge-creating gap within a southern New England oak-hickory forest, I used a molecular fingerprinting technique known as terminal restriction fragment length polymorphism (TRFLP). Sequence variability in the 16S ribosomal RNA (rRNA) gene in soil bacterial communities is detected by differences in the length and abundance of fragments produced by digesting PCR products amplified from rRNA genes. The different patterns observed are assumed to represent unique phylotypes. How does the forest-gap ecotone influence soil bacterial diversity? Based on other studies, I hypothesized that the edge would contain the most diverse bacterial community, followed by the gap, and as distance from the gap into the forest increased, bacterial diversity would decrease. Soil samples were collected along 40m transects perpendicular to the northern edge of the gap. DNA was extracted from each sample, PCR was used to amplify the 16S rRNA gene, and DNA fragments were cut by restriction enzyme digestion and separated via electrophoresis. The DNA fragments were analyzed by TRFLP. Environmental variables (soil pH, soil temperature and soil gravimetric moisture) were different in the gap compared to all other distances, but not significantly so. Phylotype richness and diversity (Simpson’s index) was greatest at the edge. Canonical Correspondence Analysis (CCA) produced a phylotype-by-distance ordination that supports my hypothesis and shows that the edge is an ecotone (transitional zone) between the gap and forest.