Measuring Changes in Soil Microbial Communities After 10 Years of Organic Matter Manipulations in An Old-Growth Douglas-Fir Soil Using High-Throughput Sequencing.

In 1997, a long-term organic matter manipulation experiment (DIRT—detritus inputs and removal treatments) was established in an old-growth Douglas-fir forest located in the western Cascades of Oregon at the H.J. Andrews Experimental forest. The experiment consists of six, replicated treatments designed to alter the amounts of above- and below-ground organic matter inputs: control, doubled inputs of leaf litter or woody debris, exclusion of leaf litter, exclusion of roots, and exclusion of litter and roots. Soils from this experiment were sampled 10 years after treatments were established. Our objective was to measure changes in soil microbial communities as a result of the organic matter manipulations. DNA was extracted from soil, amplified by PCR with primers specific to prokaryotes or fungi, and the resulting amplicons were analyzed by high-throughput sequencing. In total, ~10,000 bacterial and fungal sequences were obtained.  Most of the prokaryotic sequences were from Bacteria (99%); the remainder was from Archeae (mainly Crenarchaeota). Dominant bacterial phyla or classes included: Acidobacteria, Alphaproteobacteria, Betaproteobacteria, and Sphingobacteria. Bacterial communities in the double wood and root exclusion plots were significantly different from the control. More detailed analysis will be used to compare the diversity and composition of bacterial and fungal communities.