A number of studies have attempted to address the question of source–sink relations under e[CO2] directly by manipulating leaves and/or reproductive organs with somewhat inconclusive results: Shimono et al. (2010) removed the panicle of rice plants grown under e[CO2] in field chambers to impose strong sink limitation.
Plants with their panicles removed had a greater allocation of nitrogen (N) to their leaves, and tended to have greater Rubisco concentrations, but this had no alleviating effect on photosynthetic downward acclimation to e[CO2]. In a comparable study, Uddling et al. (2008) removed the spike (sink) or the flag leaf (source) of e[CO2] grown wheat plants to manipulate source:sink ratio. This study reported somewhat unusual results in that photosynthetic acclimation in non-manipulated shoots was so strong that e[CO2] had no stimulating effect on yield and even decreased aboveground
biomass, and individual grain weights. Lower source:sink ratios may have alleviated these negative effects of e[CO2] leading the authors to conclude that sink limitation constrains responsiveness to CO2.