Monday, August 6, 2007
Exhibit Halls 1 and 2, San Jose McEnery Convention Center
The ability of trees to sequester carbon (C) is likely to be limited by the availability of soil nutrients, particularly nitrogen (N). One mechanism by which trees may increase nutrient availability in forest soils is through the release of soluble organic compounds from roots. Root exudates are low molecular weight compounds released by roots that have the potential to alter nutrient availability due to their chelating properties and their role in stimulating microbial activity. The goals of this experiment were to examine the effects of several organic acids commonly found in root exudates on nutrient transformations and microbial activity in forest soils. Low and high concentrations of acids (singly, and in cocktail) were delivered to re-packed soil columns via artificial roots. After several weeks the soil solution was collected via lysimeters and analyzed for inorganic N and P. At low concentrations, none of the acids significantly affected nutrient transformations or microbial activity, with the exception of oxalic acid which increased P and decreased N. At high concentrations, oxalic acid increased microbial activity by 25% as compared to a DI control. A subsequent experiment comparing the effects of functional groups of exudates (amino acids, organic acids, simple sugars) led to more dramatic differences in microbial activity and inorganic N availability. These results suggest that changes in root exudation have the potential to affect nutrient availability in forest soils, but the magnitude of such effects will likely depend on which compounds are released.
