PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Quantitative assessment of climatic effects on seasonal and interannual variabilities in net ecosystem exchange.
Hui, Dafeng*,1, Xu, Tao1, Luo, Yiqi1, Wofsy, Steven 2, 1 University of Oklahoma, Norman, OK2 Harvard University, Cambridge, MA
ABSTRACT- Seasonal and interannual variabilities in net ecosystem exchange (NEE) of CO2 are observed at many FluxNet sites. These variabilities have been linked to direct effect of climatic variations and climate-induced functional changes (e.g., changes in growing season length and the timing of leaf emergence). However, we still lack the quantitative understanding of climatic effects on NEE variations. In order to study the climatic and functional effects on NEE, we applied a recently developed homogeneity-of-slopes (HOS) model (Hui et al. 2003, Tree Physiology, in press) and wavelet analysis to a long-term dataset with eight years′ measurements of NEE and climatic variables in Harvard Forest. HOS model showed that photosynthetically active radiation, soil temperature, relative humidity and vertical velocity (ustar) had significant influences on daytime NEE. Functional change contributed 2.7% of variation in NEE. The direct interannual climatic variations contributed 4.8% and seasonal climatic changes contributed 77.5% of NEE variation. Soil temperature and ustar were two important factors influencing nighttime ecosystem respiration (RE). About 10.0% variation in RE was contributed by the functional change. The direct interannual climatic variations contributed 4.4% while the seasonal climatic changes explained 60.2% of variation in RE. When NEE and climatic variables were decomposed to the fourth level using wavelet analysis, 95.4% of the variation in approximation of NEE was explained by those of climatic variables and 86.4% of the variation in detail of NEE was explained by those of climatic variables. The fact that less than 30% of the variations in detail of NEE at lower levels were explained by climatic variables confirmed that functional change and other factors might have significant effects on NEE.
Key words: interannual variability, eddy covariance, net ecosystem exchange, climatic effect