From sunlight to phytomass: on the potential efficiency of converting solar radiation to phyto-energy

摘要

ContentsSummary939I.Introduction940II.Approach940III.Solar radiation absorption942IV.Quantum requirement for CO2 assimilation943V.Respiration946VI.Photosynthate mobilization and translocation948VII.Maintenance949VIII.Substrate requirement for growth949IX.From sunlight to phyto-energy: potential overall efficiency953X.Assessment955Acknowledgements955Refe r ences955SummaryThe relationship between solar radiation capture and potential plant growth is of theoretical and practical importance. The key processes constraining the transduction of solar radiation into phyto-energy (i.e. free energy in phytomass) were reviewed to estimate potential solar-energy-use efficiency. Specifically, the out-put : input stoichiometries of photosynthesis and photorespiration in C3 and C4 systems, mobilization and translocation of photosynthate, and biosynthesis of major plant biochemical constituents were evaluated. The maintenance requirement, an area of important uncertainty, was also considered. For a hypothetical C3 grain crop with a full canopy at 30C and 350 ppm atmospheric [CO2], theoretically potential efficiencies (based on extant plant metabolic reactions and pathways) were estimated at c. 0.041 J J-1 incident total solar radiation, and c. 0.092 J J-1 absorbed photosynthetically active radiation (PAR). At 20C, the calculated potential efficiencies increased to 0.053 and 0.118 J J-1 (incident total radiation and absorbed PAR, respectively). Estimates for a hypothetical C4 cereal were c. 0.051 and c. 0.114 J J-1, respectively. These values, which cannot be considered as precise, are less than some previous estimates, and the reasons for the differences are considered. Field-based data indicate that exceptional crops may attain a significant fraction of potential efficiency.