PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Net ecosystem productivity and atmospheric nitrogen deposition.

Bian, Aihua^*,1, Luo, Yiqi¹, Hui, Dafeng¹, Schimel, David², ¹ University of Oklahoma, Norman, OK² National Center for Atmospheric Research, Boulder, CO

ABSTRACT- Atmospheric deposition of N to terrestrial ecosystems has increased dramatically in the past few decades, contributing up to 20 times inputs via natural processes to the northeastern United States and Europe. Chronic additions of N to these predominantly N-limited ecosystems have been shown to alter forest productivity, to modify species composition and diversity, and to affect losses of N from forest soil to stream water as NO3- and to the atmosphere as N2O and NO. However, it is still controversial whether or not N deposition will stimulate C sequestration in terrestrial ecosystems. We have developed a database that directly links C sequestration with N deposition at 35 eddy-flux sites in North and South Americas, Europe, and Asia. For each site, we collected data of net ecosystem productivity (NEP), mean annual temperature and precipitation, elevation, latitude, longitude, forest types and ages, leaf area index, and atmospheric N deposition. Our results indicate that C sequestration has no statistically significant relationship with N deposition when NEP <300 g C m-2 yr-1. When NEP >300 g C m-2 yr-1, C sequestration initially increases, reaches a peak, and then decreases with N deposition. We further investigated the relationship NEP with other environmental factors via regression analysis, indicating carbon sequestration is lower in the high-latitude and low precipitation regions than in the low-latitude and high precipitation region. Overall evidence suggests that N may not be the most limiting factor in regulating terrestrial C sequestration.

KEY WORDS: Atmospheric Nitrogen Deposition, Net ecosystem productivity, Forest, eddy-covariance