Measuring Changes in Soil Microbial Communities during 30 Years of Winter Wheat Management using High-Throughput Sequencing.

In 1931, a long-term crop residue management experiment was established in a winter wheat-summer fallow cropping system located at Pendleton, Oregon. The experiment consists of ten management treatments designed to alter the amount of crop residue inputs. Soils from this experiment have been sampled periodically to monitor changes in soil physical and chemical properties, such as soil organic matter. Our objective was to measure changes in soil microbial communities as a result of the treatments that currently have the lowest (fall burning) and highest (manured) soil organic matter contents. We used archived soil samples collected at decadal intervals since 1976 along with freshly sampled soil collected in fall 2007 to assess these changes in bacterial and fungal communities. 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 (95%); the remainder were from Archeae (mainly Crenarchaeota). Known bacterial phyla or classes that represented more than 5% of the bacterial sequences included: Acidobacteria, Bacilli, Sphingobacteria, Alphaproteobacteria, Betaproteobacteria, and Actinobacteria. More detailed analysis will be used to compare the diversity and composition of bacterial and fungal communities.