Carbon Budget and Soil Dynamics in Response to Lignin Modified Populus tremuloides
AdvisorJohnson, Dale W.
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ABSTRACTSoil organic carbon (SOC) pools are highly susceptible to changes in climate and land cover; and are controlled by rates of plant production and decomposition. Changes in any one of these variables can have unforeseen effects in an ecosystems carbon (C) balance. In this thesis project, the effects of genetically modified (GM) aspen trees (Populus tremuloides Michaux) on soil organic carbon (SOC) pools were examined. It is possible to manipulate several genes in the aspen genome to encode for lower lignin content and an altered lignin composition. Lower lignin in wood, as well as alterations of lignin structure, reduce the time and energy required for pulping. The modifications also allow for more energy and C to be used for cellulose and biomass production, increasing the tree's C sequestration capacity. We conducted a duplicated mesocosm study to measure the effects of four different variations of GM trees and "wild-type" control trees on SOC in a controlled environment. Our study showed that one genetic alteration (low lignin, line 23) was able to compete with the wild-type aspen (control, line 271) without altering SOC. Alterations in lignin structure (S/G ratios) had negative effects on biomass production and SOC formation. Rhizospheric soils showed no difference among lines in nutrient uptake, and N soil pools remained largely unaltered. Our results showed altered lignin can have effects on SOC, but that these come as a result of reduced biomass in the plants. Management actions aimed to alter natural systems for improved C sequestration and/or energy efficiency must be weighed against possible soil C losses. Further research should be conducted in natural conditions to determine if the low lignin lines are safe for widespread use.