Pacific Northwest Laboratory compared intact soil-core microcosms and the field for ecosystem structural and functional properties after the introduction of a model genetically engineered microorganism (GEM). The project used two distinct microbial types as model GEMs, Gram-negative Pseudomonas sp RC1, which was an aggressive root colonizer, and Gram-positive Streptomyces lividans TK24. The model GEMs were added to surface soil in separate studies throughout a ten month period. Also, RC1 was used in studies conducted during two consecutive field seasons to determine how year-to-year field variability influenced the calibration of microcosms with the field. The main conclusions of the research were that intact soil-core microcosms can be useful to simulate the field for studies of microbial fate and effects on ecosystem structural and functional properties.