BACKGROUND AND AIMS: Climate change poses significant challenges to the enhancement of crop productivity in pace with the increasing world population. Intraspecific variability in ryegrass responses to elevated CO2 can be exploited to screen for high-producing genotypes under future atmospheres and has been used to identify targets for breeding high CO2-ready cultivars. The present study expands on this approach by investigating the responses of multiple perennial and annual ryegrass genotypes to projected future atmospheric/climatic conditions. METHODS: Ten ryegrass genotypes of diverse origin were grown under ambient and elevated CO2 and higher temperature conditions (HTC), consistent with an intermediate IPCC scenario (RCP6.0). Morphometric measurements, gas analysis and CN analysis were used to assess the responses of their biomass production and allocation, photosynthetic physiology and carbon/nitrogen elemental composition to simulated future conditions. Genotypic variability in these responses was subsequently used to identify traits and trait responses that correlate strongly with increased productivity under elevated CO2 and higher temperature. RESULTS: Biomass responses to future conditions varied significantly across genotypes, spanning a 32% reduction to a 62% enhancement, but were unrelated to corresponding changes in leaf photosynthetic rates. Although plant productivity showed a significant positive relationship with estimates of the whole-plant carbon assimilation rate, there were clear signs of sink limitation under ambient and HTC, since this correlated strongly with the leaf C:N ratio and the biomass allocation to sink tissues, especially stems. Stem biomass allocation under future conditions increased significantly and scaled positively with the corresponding plant productivity responses. No similar trend was observed for root biomass allocation, which showed no significant differences between treatments. CONCLUSIONS: Increased biomass allocation to the stem carbon sink is a key characteristic to exploit under future climate change conditions, and this would also maximize any benefits associated with an increase in leaf area on whole-plant carbon gain.
Yiotis et al. (Fri,) studied this question.