Could recent increases in atmospheric CO2 have acted as a selection factor in Avena fatua populations? A case study of cultivated and wild oat competition

Abstract

SummaryProjected increases in atmospheric carbon dioxide concentration [CO2] may lead to differential selection and competition between weeds and crops. Yet, the current level of atmospheric [CO2] already reflects a rapid rise (~25%) from mid‐20th century levels. To assess whether this increase could have already resulted in differential selection between weeds and crops, two temporally distinct populations of Avena fatua (wild oat) from the same geographic location, one from the 1960s (WOold) and one from 2014 (WOnew), were grown with and without a cultivated oat (CO) line, Clintland 64 (Avena sativa) at current and mid‐20th century [CO2] levels (ca 320 and 402 μmol mol−1 respectively). Monocultures of each WO population differed in their response to recent increases in atmospheric [CO2], with WOnew showing a significantly higher response for all vegetative parameters relative to WOold. Assessment of competitive outcomes indicated that at 315 μmol mol−1 cultivated oat was at a competitive advantage relative to either A. fatua population for leaf area and total above‐ground biomass. However, at current levels of CO2, an overall increase in WOnew competitive ability was observed relative to the cultivated oat line. Overall, these differences are consistent with, but not conclusive for, improved evolutionary fitness and increased early competitive ability of A. fatua relative to cultivated oat as a function of the recent increase in atmospheric [CO2]. While additional empirical studies are needed, these preliminary results indicate that weeds may be adapting rapidly to rising levels of atmospheric carbon dioxide.