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Title: Endogenous circadian regulation of carbon dioxide exchange in terrestrial ecosystems

item RESCO, V. - Castilla Institute
item GOULDEN, M. - University Of California
item OGLE, K. - University Of Wyoming
item RICHARDSON, A. - Harvard University
item HOLLINGER, D. - Us Forest Service (FS)
item DAVIDSON, E. - Woods Hole Oceanographic Institute (WHOI)
item ALDAY, J. - University Of Virginia
item BARRON-GAFFORD, G. - University Of Arizona
item CARRARA, A. - Fundacion Aquila
item KOWALSKI, A. - University De Granada
item OECHEL, W. - San Diego State University
item REVERTER, B. - University De Granada
item Scott, Russell - Russ
item VARNER, R. - University Of New Hampshire
item DIAZ-SIERRA, R. - University Of Spain
item MORENO, J. - Castilla Institute

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2012
Publication Date: 6/1/2012
Citation: Resco, V., Goulden, M., Ogle, K., Richardson, A.D., Hollinger, D.Y., Davidson, E.A., Alday, J.G., Barron-Gafford, G.A., Carrara, A., Kowalski, A.S., Oechel, W.C., Reverter, B.R., Scott, R.L., Varner, R.K., Diaz-Sierra, R., Moreno, J.M. 2012. Endogenous circadian regulation of carbon dioxide exchange in terrestrial ecosystems. Global Change Biology. 18:1956-1970.

Interpretive Summary: We tested one of the major assumptions underlying studies on the exchange of carbon dioxide between terrestrial ecosystems and the atmosphere: that daily fluctuations in the net exchange of carbon dioxide are driven almost exclusively by the immediate physiological responses to changes in environmental factors like light, humidity and temperature. However, it is increasingly recognized that photosynthesis may also vary over time in the absence of variation in external forcing because of internal plant controls from the circadian clock. We analyzed observations of carbon dioxide exchange recorded at sites around the world. We found large daily fluctuations in ecosystem carbon exchange even after removing variation in the physical environment across a wide-variety of ecosystems. This analysis poses a new paradigm for understanding controls on carbon dioxide exchange of terrestrial ecosystems.

Technical Abstract: It is often assumed that daytime patterns of ecosystem carbon assimilation are mostly driven by direct physiological responses to exogenous environmental cues. Under limited environmental variability, little variation in carbon assimilation should thus be expected unless endogenous plant controls on carbon assimilation, which regulate photosynthesis in time, are active. We evaluated this assumption with eddy flux data, and we selected periods when net ecosystem exchange (NEE) was decoupled from environmental variability in seven sites from highly contrasting biomes across a 74° latitudinal gradient over a total of 36 site-years. Under relatively constant conditions of light, temperature, and other environmental factors, significant diurnal NEE oscillations were observed at six sites, where daily NEE variation was between 20% and 90% of that under variable environmental conditions. These results are consistent with fluctuations driven by the circadian clock and other endogenous processes. Our results open a promising avenue of research for a more complete understanding of ecosystem fluxes that integrates from cellular to ecosystem processes.