Location: Soil and Water Management ResearchTitle: Productivity and carbon dioxide exchange of the leguminous crops: Estimates from flux tower measurements Author
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2013
Publication Date: 3/6/2014
Publication URL: http://handle.nal.usda.gov/10113/59545
Citation: Gilmanov, T., Baker, J.M., Bernacchi, C.J., Billesbach, D.P., Burba, G.G., Castro, S., Eugster, W., Fischer, M.L., Gamon, J.A., Gebremedhin, M.T., Glenn, A.J., Griffis, T.J., Hatfield, J.L., Heuer, M.W., Howard, D.M., Leclerc, M.Y., Loescher, H.L., Matloie, O., Matamala, R., Meyers, T.P., Olioso, A., Phillips, R.L., Prueger, J.H., Skinner, R.H., Suyker, A.E., Tenuta, M., Wylie, B.K. 2014. Productivity and carbon dioxide exchange of the leguminous crops: Estimates from flux tower measurements. Agronomy Journal. 106(2):545-559. Interpretive Summary: The widespread deployment of systems for measuring CO2 exchange in recent years has provided a rich data set for analyzing the carbon balance of agricultural systems, but the primary emphasis has been on conventionally fertilized grain crops like maize and wheat, with less attention paid to legumes. In this project, 29 site-years of data were collated and analyzed, from 17 locations in North America and 3 in Europe. Most of thesewere comprised of annual legumes like soybean, but several were perennial legumes (alfalfa). Annual totals of gross photosynthesis, respiration, and net ecosystem production were calculated for all sites, as well as daily and weekly totals, which were compared against the normalized difference vegetation index (NDVI) derived from satellite images. Comparison of photosynthetic parameters against grain crops showed that they were intermediate -lower than those for maize, but higher than wheat. This was somewhat surprising, considering the metabolic cost of nitrogen fixation. On an annual basis, there was a broad range of net ecosstem production from strong net sinks to strong sources, with the perennial alfalfa sites showing the storngest carbon sink activity. There was good correspondence between integrated carbon balance and integrated NDVI, providing an opportunity in the future to map legume productivity with satellite imagery, which will be useful for forecasting crop yields and carbon balance.
Technical Abstract: Net CO2 exchange data on legume crops at 17 flux tower sites in North America and 3 sites in Europe representing 29 site-years of measurements were partitioned into gross photosynthesis and ecosystem respiration using a light-response function method, resulting in new estimates of ecosystem-scale ecophysiological parameters (apparent quantum yield, photosynthetic capacity, daytime ecosystem respiration, gross photosynthetic light use efficiency) of legume crops determined at the diurnal and weekly time steps. Dynamics and annual totals of gross photosynthesis, ecosystem respiration, and net ecosystem production were calculated by gap-filling using multivariate non-linear regresion. Relationships of these CO2 exchange characteristics to weekly and seasonally integrated normalized difference vegetation index (eMODIS NDVI) were established. Comparison with the data from grain crops obtained with the same method demonstrated that CO2 exchange rates and ecophysiological parameters of legumes were lower than for maize, but higher than for wheat crops. Year-round annual legume crops demonstrated a broad range of net ecosystem production (NEP) from sinks of +760 g CO2 m-2 yr-1 to sources of -2100 g CO2 m-2 yr-1, with an average of -330 g m-2 yr-1, indicating overall moderate CO2- source activity related to shorter period of photosynthetic uptake and metabolic costs of nitrogen fixation. Perennial legumes (alfalfa) were strong sinks for atospheric CO2 with average NEP of +980 (range 550 to 1200 g m-2 yr-1. Integrals of gross photosynthesis and ecosystem respiration of legume crops over their growing period closely correlated with corresponding integrals of eMODIS NDVI, providing opportunities to use remote sensing for mapping CO2 exhcnage of legume crops over regions with high gradients of productivity and greenness.