Soil microbial community responses to altered lignin biosynthesis in Populus tremuloides vary among three distinct soils

The development and use of transgenic plants has steadily increased, but there are still little data about the responses of soil microorganisms to these genetic modifications. We utilized a greenhouse trial approach to evaluate the effects of altered stem lignin in trembling aspen (Populus tremuloides) on soil microbial communities in three soils which differed in their chemical and physical properties; they included a sandy loam (CO-Colorado), a silt loam (KS-Kansas), and a clay loam (TX-Texas). Three transgenic aspen lines were developed from a natural clone common to the Great Lakes region of North America. The concentrations of stem lignin concentrations were reduced by 35% (Line 23), 40% (Line 141) and 50% (Line 72). Line 72 and Line 141 also had a 40 and 20% increase in syringyl-type stem lignin, respectively. Indirectly, these modifications resulted in increased (5–13%) and decreased (−5 to −57%) levels of root production across the lines and soil types. Responses of the soil microbial communities were investigated using: phospholipid fatty acids (PLFA), neutral lipid fatty acids (NLFA), and 3) extracellular enzyme assays. PLFA analyses indicated that there were large differences in microbial community composition between the three soils. Similarly, there were large differences in total NLFA between soils, with the KS soils having the highest amount and CO the lowest. Enzyme activities did not differ between soils, except for cellubiohydrolase, which was highest in CO soil. Across all three soils, responses to the four genetic lines were not consistent. Interactions between soil type and genetic line make it difficult to assess the potential ecological impacts of transgenic aspen on soil microbial communities and their associated functions. Given these interactions, field trials with transgenic aspen should encompass the wide range of soils targeted for commercial planting in order to determine their effect(s) on the resident soil microbial community. Responsible Editor: Barbara Wick