Document: HEA-3-59-23

Simulated effects of elevated nitrogen deposition on Colorado Englemann spruce forests.

RUETH, H.M.* ¹ and W.J.PARTON ¹

Colorado State University, Fort Collins, CO 80523 ¹
USGS ²

Abstract:
Field survey results of twelve similar old-growth Englemann spruce stands suggest that current levels of N deposition are altering forest biogeochemistry on the east side of the Colorado Front Range. It is difficult in surveys to control potentially confounding factors. CENTURY, a biogeochemical cycling model, was used to address whether elevated N deposition can explain observed differences in N pools and cycling rates between high and low N deposition sites. Increased N inputs should decrease soil organic matter (SOM) C:N and foliar C:N, and increase net primary production, mineralization rates and inorganic N loss. The active and slow SOM C:N decreased following N additions and the passive SOM pool was unresponsive. Simulated results captured the observed differences in foliar C:N. Nitrogen additions increased fine root and leaf production and N, which accounted for a majority of the increase in total production and total live biomass N. N mineralization rates and inorganic N loss increased with elevated N inputs. The rapid response of this simulated forest system to N additions indicates it was N limited. This simulation supports our conclusions from field results, that the observed differences between high and low N deposition sites can be attributed to differences in N inputs.

Keywords: Nitrogen deposition, nitrogen cycling, CENTURY

This abstract is being presented at: 2:00 PM in session:
Oral Session #28: Effects of N Deposition in Ecosystems.