Determinants of genotypic variations in the yield response of soybean to elevated atmospheric CO₂

The large genotypic differences in yield response within crop species to elevated CO2 concentration (e[CO2]) suggest that there is potential to ensure food security under future e[CO2], by actively selecting and breeding cultivars that maximize yield under e[CO2]. Identifying the determinants of yield response is important for breeding these cultivars. In soybean, genotypic variations in yield response to e[CO2] may be explained by increased pod number. However, the relative contributions of other yield components, such as node number, number of pods per node, number of seeds per pod, and single-seed mass, to yield increase are not fully understood. Increased node number in response to e[CO2] has also been observed and hypothesized to be a determinant of the genotypic increase in yield due to e[CO2]. This was tested using six cultivars grown in controlled-environment chambers. Surprisingly, it was the increase in pods per node, rather than increased node number per se, that was most strongly associated with yield increase. This emphasizes the importance of studying the responses to e[CO2] of the components which contribute to yield, including flower number and pod set (both of which can affect pods per node), to develop cultivars that can maximize yield under e[CO2].