Ancient and modern wheat varieties: A trade-off between soil CO2 emissions and grain yield?

Introduction: Humanity is facing two great challenges: producing enough food for a growing population and mitigating greenhouse gas emissions. In this study, we investigated the choice of specific wheat varieties to improve carbon storage in soil while producing enough grain to assure food security. We hypothesize that ancient wheat varieties could store more carbon than modern ones, due to a likely bigger and deeper root system or to more recalcitrant root organic matter. Materials and Methods: We conducted a field experiment with four modern and four ancient wheat varieties, on four different sites with contrasted soil properties. Root morphology was assessed by image analysis and potential CO2 emissions by incubation for 60 days. Since in situ carbon storage differences between ancient and modern varieties were expected to be weak and not cumulated due to rotation, we estimated expected CO2 emissions from root biomass and potential CO2 emissions. The grain yield was also measured. Results: The breeding type (ancient vs. modern varieties) affected root length in two of our four sites, with longer roots for ancient varieties, but it did not affect other root traits such as biomass. The breeding type also affected CO2 emissions, with higher measured CO2 emissions for modern than ancient varieties in Arenic Cambisol conditions (Morvan), and higher estimated (considering root biomass variations) CO2 emissions for modern varieties in Rendzic Leptosol conditions (Saint Romain). Root traits and estimated CO2 emissions were also dependent on the soil properties of the different sites. We did not find any significant differences in grain yield between ancient and modern varieties. Conclusion: A possible trade-off between carbon storage and grain production was expected, but our results suggest that some types of soil can support both high grain yield and C storage, especially those with an important depth, a neutral pH and a fine texture.