|Scott, Russell - Russ|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2009
Publication Date: 1/20/2010
Citation: Gilmanov, T.G., Aires, L.M., Barcza, Z., Baron, V., Belelli, L., Beringer, J., Billesbach, D., Bonal, D., Bradford, J., Ceschia, E., Cook, D., Corradi, C., Frank, A.T., Gianelle, D., Gimeno, C., Grunwald, T., Gao, H., Hanan, N., Haszpra, L., Heilman, J., Jacobs, A., Jones, M., Johnson, D., Kiely, G., Li, S., Magliulo, V., Moors, E., Nagy, Z., Nasyrov, M., Owensby, C., Pinter, K., Pio, C., Reichstein, M., Sanz, M., Scott, R.L., Soussana, J., Stoy, P.C., Svejcar, A.J., Tuba, Z., Zhou, G. 2010. Productivity, respiration, and light-response parameters of world grassland and agroecosystems derived from flux-tower measurements. Rangeland Ecology and Management. 63:16-39. Interpretive Summary: Grasslands and cultivated lands occupy one-third of the earth’s land surface area, but their contribution to the global carbon cycle remains uncertain. We used a large dataset of carbon dioxide exchange measurements to quantify plant productivity, respiration, and growth parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We found that the growth of these types of ecosystems exceeded those of most forest ecosystems, indicating the potential of non-forest ecosystems for uptake of atmospheric carbon dioxide. Maximum values of plant productivity, respiration, and net carbon dioxide exchange were observed for intensively managed grasslands and high-yield crops, and were comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of these sites were apparent sinks for atmospheric carbon dioxide. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. .
Technical Abstract: Grasslands and agroecosystems occupy one-third of the terrestrial area, but their contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of CO2 exchange measurements to quantify gross primary productivity, respiration, and light-response parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We analyzed data from 72 global flux-tower sites partitioned into gross photosynthesis and ecosystem respiration with the use of the light response method (Gilmanov, T. G., D. A. Johnson, and N. Z. Saliendra. 2003. Growing season CO2 fluxes in a sagebrush-steppe ecosystem in Idaho: Bowen ratio/energy balance measurements and modeling. Basic and Applied Ecology 4:167–183) from the RANGEFLUX and WORLDGRASSAGRIFLUX data sets supplemented by 46 sites from the FLUXNET La Thuile data set partitioned with the use of the temperature-response method (Reichstein, M., E. Falge, D. Baldocchi, D. Papale, R. Valentini, M. Aubinet, P. Berbigier, C. Bernhofer, N. Buchmann, M. Falk, T. Gilmanov, A. Granier, T. Gru¨ nwald, K. Havra´nkova´, D. Janous, A. Knohl, T. Laurela, A. Lohila, D. Loustau, G. Matteucci, T. Meyers, F. Miglietta, J. M. Ourcival, D. Perrin, J. Pumpanen, S. Rambal, E. Rotenberg, M. Sanz, J. Tenhunen, G. Seufert, F. Vaccari, T. Vesala, and D. Yakir. 2005. On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biology 11:1424–1439). Maximum values of the quantum yield (a = 75 mmol mol-1), photosynthetic capacity (Amax= 3.4 mg CO2 m-2 s-1), gross photosynthesis (Pg,max=116 g CO2 m-2 d-1), and ecological light-use efficiency (eecol=59 mmol mol-1) of managed grasslands and high-production croplands exceeded those of most forest ecosystems, indicating the potential of nonforest ecosystems for uptake of atmospheric CO2. Maximum values of gross primary production (8600 g CO2 m-2 yr-1), total ecosystem respiration (7900 g CO2 m-2 yr-1), and net CO2 exchange (2400 g CO2 m-2 yr-1) were observed for intensively managed grasslands and high-yield crops, and are comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of the nonforest sites were apparent sinks for atmospheric CO2, with mean net uptake of 700 g CO2 m-2 yr-1for intensive grasslands and 933 g CO2 m-2 yr-1for croplands. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. Therefore, although agricultural fields may be predominantly sinks for atmospheric CO2, this does not imply that they are necessarily increasing their carbon stock.