Comment on "Unexpected reversal of C3 versus C4 grass response to elevated CO2 during a 20-year field experiment".

Reich et al (Reports, 20 April 2018, p. 317) assert that the responses of C3 and C4 grass biomass to elevated CO2 "challenge the current C3-C4 [elevated CO2] paradigm," but these responses can be explained by the natural history of the experimental plants and soils without challenging this paradigm.