HR: 1330h
AN: B32B-0383    [PDF]
TI: Influence of Plant and Microbial Interactions on Nitrogen Retention and Loss in Puerto Rican Forest Soils
AU: * Templer, P H
EM: ptempler@nature.berkeley.edu
AF: Pamela H. Templer, 151 Hilgard Hall Department of Environmental Science, Policy and Management, Ecosystem Science Division, University of California Berkeley, Berkeley, CA 94720-3110 United States
AB: Understanding nitrogen (N) retention mechanisms in tropical forests is important because these systems currently have high potential for N losses. They have the greatest nitrous oxide flux compared to other ecosystems and often exhibit large nitrate losses to groundwater. A significant amount of research on N biogeochemistry has been conducted in north temperate ecosystems where N limitation to net primary productivity (NPP) is common, and where anthropogenic N deposition is altering N cycling. Much less research has been conducted in the tropics, which are generally characterized by rapid rates of N cycling and the lack of strong N limitation to NPP. We conducted a field experiment using $^{15}$N tracers and root ingrowth cores to compare and contrast the relative importance of N loss pathways (denitrification, nitrous oxide production via nitrification, and N leaching) versus N retention mechanisms (dissimilatory reduction of nitrate to ammonium (DNRA) and assimilatory N uptake by plants and soil microbes) in a subtropical forest in Puerto Rico. DNRA rates were detectable and within a range comparable to gross mineralization and gross nitrification. Plant roots at all sites took up significantly greater amounts of N as ammonium than nitrate and were a relatively strong sink for N as indicated by the relatively large amount of $^{15}$N that they took up. This supports our hypothesis that DNRA is a N conserving mechanism within tropical forests because the ammonium that is produced from this process is likely to be taken up by plants rather than re-nitrified and potentially leached or lost as nitrous oxide gas from the ecosystem.
DE: 0400 Biogeosciences
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting