Kirschbaum, M.U.F., Lambie, S.M. (2015). Re-analysis of plant CO₂ responses during the exponential growth phase: interactions with light, temperature, nutrients and water availability. Functional Plant Biology 42: 989-1000.

Abstract. Many short-term experiments have been conducted under increasing CO₂ but results have been varied and have not yet led to a conclusive quantitative understanding of the CO₂ response of plant growth. This may have been partly due to a lack of explicit consideration of the positive feedback inherent in plant growth during periods of exponential growth. This feedback can increase an initial physiological enhancement of relative growth rate (RGR) into a much larger biomass enhancement. To overcome this problem, we re-analysed existing experimental data from 78 publications. We calculated the RGRs of C₃ plants and their relative enhancement under elevated CO₂ and derived response indices that were independent of the duration of experiments and the RGR at normal atmospheric CO₂. The RGR of unstressed plants increased by 14 +/- 2% under doubled CO₂, with observed RGR enhancement linearly correlated with calculated photosynthetic enhancements (based on the Farquhar-von Caemmerer-Berry photosynthesis model), but at only half their numeric values. Calculated RGR enhancements did not change significantly for temperatures from 12 to 40 ^oC, but were reduced under nutrient limitation, and were increased under water stress or low irradiance. We concluded that short-term experiments can offer simple and cost-effective insights into plant CO₂ responses, provided they are analysed by calculating relative changes in RGR during the strictly exponential initial growth phase.

Keywords: nutrient limitation, photosynthesis, PAR, photosynthetically active radiation, relative growth rate, RGR, water limitation.

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