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Title: Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables

Author
item YUAN, W. - UNIVERSITY OF OKLAHOMA
item LUO, Y. - UNIVERSITY OF OKLAHOMA
item RICHARDSON, A. - UNIV. OF NEW HAMPSHIRE
item OREN, R. - DUKE UNIVERSITY
item LUYSSAERT, S. - UNIVERSITY OF ANTWERPEN
item JANSSENS, I. - UNIVERSITY OF ANTWERPEN
item CEULEMANS, R. - UNIVERSITY OF ANTWERPEN
item AUBINET, M. - UNITE DE PHYSIQUE
item BERNHOFER, C. - INST. OF HYDR AND METEOR
item BALDOCCHI, D. - UNIV. CALIFORNIA BERKELEY
item CEHN, J. - UNIVERSITY OF TOLEDO
item DUNN, A. - WORCESTER STATE COLLEGE
item DEFOREST, J. - UNIVERSITY OF TOLEDO
item GOLDSTEIN, A. - UNIV. CALIFORNIA BERKELEY
item MOORS, E. - ALTERRA
item MUNGER, J. - HARVARD
item MONSON, R. - UNIVERSITY OF COLORADO
item SUYKER, A. - UNIVERSITY OF NEBRASKA
item STARR, G. - UNIVERSITY OF ALABAMA
item Scott, Russell - Russ
item TENHUNEN, J. - UNIVERSITY OF BAYREUTH
item VERMA, S. - UNIVERSITY OF NEBRASKA
item VESALA, T. - UNIVERSITY OF HELSINKI
item WOFSY, S. - HARVARD

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2008
Publication Date: 1/15/2009
Citation: Yuan, W., Luo, Y., Richardson, A., Oren, R., Luyssaert, S., Janssens, I.A., Ceulemans, R., Aubinet, M., Bernhofer, C., Baldocchi, D.D., Cehn, J., Dunn, A.L., Deforest, J.D., Goldstein, A.H., Moors, E., Munger, J.W., Monson, R.K., Suyker, A.E., Starr, G., Scott, R.L., Tenhunen, J., Verma, S.B., Vesala, T.V., Wofsy, S.C. 2009. Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables. Global Change Biology. 15:2905-2920. doi:10.1111/j.1365-486.2009.01870.x.

Interpretive Summary: In the face of climate change, in part caused by increases in atmospheric carbon dioxide due to human activities, it is important to properly account for amount of carbon dioxide that is released or taken in by Earth’s biosphere. This study used measurements of carbon dioxide exchange between the atmosphere and the land surface from a large diversity of ecosystems in the northern hemisphere to determine the year-to-year magnitude and variation in components of this exchange. Results were compared across a range of latitudes. It was found that the yearly amount of photosynthesis in evergreen forests largely determined the net carbon dioxide exchange whereas the amount of respiration largely controlled the variability of the net change for deciduous forests. For grasslands, the net exchange was found to increase with latitude and precipitation was found to be the dominant factor that controlled the net exchange as well as the variability of the component fluxes. This study takes a broad look across a large range of latitudes to help better understand what environmental factors help to dictate the amount and variability of carbon dioxide exchange of ecosystems around the world.

Technical Abstract: Over the last two and half decades, strong evidence has emerged indicating that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However, the spatial and temporal (particularly with regard to year-to-year variation) patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of magnitude and interannual variability in net ecosystem exchange of CO2 (NEE) based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ~29oN to ~64oN. We computed the standard deviation (SD) of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation (CV) as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the variation of NEE across evergreen needleleaf forests, whereas ecosystem respiration (Re) explained a significant proportion of the spatial variation of NEE across deciduous broadleaf forests. In addition, absolute interannual variability in GPP and Re increased significantly with increasing latitude in deciduous broadleaf forests, but absolute interannual variability in GPP showed significant decreased latitudinal gradient in evergreen needleleaf forests. Furthermore, relative interannual variability in NEE, GPP and Re appeared to increase significantly with increasing latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined relative interannual variability of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain relative interannual variability of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of NEE as well as interannual variability in GPP and Re in grasslands.