Cereal-legume mixtures increase net CO2 uptake in a forage crop system in the Eastern Pyrenees

Abstract

• Cereal-legume mixtures increased net CO 2 uptake and productivity compared to cereal monocultures. • Cereal-legume mixtures increased gross uptake, while respiration did not change. • Management associated to cereal-legume mixtures enhanced net CO 2 uptake. • Cereal-legume mixtures provide enormous opportunities to mitigate climate change. Forage systems are the major land use and provide essential resources for animal feeding. Assessing the influence of annual forage crop species on net ecosystem CO 2 exchange (NEE) is key to develop management strategies that can help to mitigate climate change, while optimizing productivity of these systems. However, little is known about the effect of annual forage crop species on CO 2 exchange fluxes, considering separately net CO 2 balances during the growth and fallow periods, and species ecophysiological responses. Our study assesses the influence of cereal monocultures vs. cereal‑legume mixtures on (1) ecosystem‑scale CO 2 fluxes, for the whole crop season and separately for the two periods of growth and fallow; and (2) potential sensitivities of CO 2 exchange related to short-term variations in light, temperature, and soil water content. This is the first mid‑term (seven years) ecosystem‑scale CO 2 fluxes assessment of an intensively managed forage system in the Pyrenees region. Our results provide strong evidence that cereal‑legume mixtures lead to higher net CO 2 uptake than cereal monocultures, as a result of higher gross CO 2 uptake, while respiratory fluxes did not significantly increase. Also, cereal-legume mixtures favoured a higher voluntary regrowth during the fallow period, which was decisive for the cumulative net CO 2 uptake of the entire crop season. Overall, cereal‑legume mixtures enhanced net CO 2 sink capacity of the forage crop, while ensuring productivity and forage quality.