Friday, August 10, 2007 - 10:30 AMOOS 51-8: Connecting soil microbial N transformations to plant N processing
Mary K. Firestone1, Sarah A. Placella1, Stephanie M. Bernard2, Donald J Herman1, and Gary L. Andersen2. (1) University of California, (2) Lawrence Berkeley National Laboratory
There is much current interest in whether we can enhance our ability to understand terrestrial ecosystem function by evaluating the genomic basis of soil microbial processes and plant eco- physiology. Utilizing plant-soil mesocosms incubated under controlled temperature and precipitation conditions we have varied precipitation, temperature, plant communities, and soil type in order to assess the relationship among genomic and transcriptomic indices, enzyme activities, soil process rates, and plant physiological characteristics. Nitrogen-related parameters were emphasized in an attempt to assess connectivity between soil microbial N transformations and plant N processing. Preliminary data showed the RNA content of Avena barbata leaves to be positively correlated with nitrogen pools (ammonium and nitrate) as well as with gross nitrification rates; but the strongest correlate of leaf RNA content was nitrification potential, a measure of the activity of the nitrifying community and an indicator of recent ammonium availability. Transcript levels for nia, which encodes nitrate reductase in the leaf, were strongly correlated to the nitrate-ammonium ratio. Nitrate availability and leaf RNA of gs1 (cytosolic glutamine synthetase) were negatively correlated, suggesting that under nitrogen deficiency plants remobilize nitrogen for growth of young tissues. In addition, the dependence of nitrate availability on the precipitation regime implies that the projected increase in rainfall in California