Quantum yield variation across the three pathways of photosynthesis: not yet out of the dark

Abstract

The convergent quantum yield hypothesis (CQY) assumes that thermodynamics and natural selection jointly limit variation in the maximum energetic efficiency of photosynthesis in low light under otherwise specified conditions (e.g. temperature and CO(2) concentration). A literature survey of photosynthetic quantum yield (phi) studies in terrestrial plants from C(3), C(4), and CAM photosynthetic types was conducted to test the CQY hypothesis. Broad variation in phi values from C(3) plants could partially be explained by accounting for whether the measuring conditions were permissive or restrictive for photorespiration. Assimilatory quotients (AQ), calculated from the CO(2) phi:O(2) phi ratios, indicated that 49% and 29% of absorbed light energy was allocated to carbon fixation and photorespiration in C(3) plants, respectively. The unexplained remainder (22%) may represent diversion to various other energy-demanding processes (e.g. starch synthesis, nitrogen assimilation). Individual and cumulative effects of these other processes on photosynthetic efficiency are poorly quantified. In C(4) plants, little variation in phi values was observed, consistent with the fact that C(4) plants exhibit little photorespiration. As before, AQ values indicate that 22% of absorbed light energy cannot be accounted for by carbon fixation in C(4) plants. Among all three photosynthetic types, the phi of photosynthesis in CAM plants is the least studied, appears to be highly variable, and may present the greatest challenge to the CQY hypothesis. The high amount of energy diverted to processes other than carbon fixation in C(3) and C(4) plants and the poor characterization of photosynthetic efficiency in CAM plants are significant deficiencies in our otherwise robust understanding of the energetics of terrestrial photoautotrophy.

Improved representation of plant functional types and physiology in the Joint UK Land Environment Simulator (JULES v4.2) using plant trait information

“…Quantum efficiency was set at 0.10 for NDT. These values are still within the range reported in Skillman (2008). An example of the changes is shown in the Supplement, Fig.…”

Non-linear mixed-effects modeling for photosynthetic response of Rosa hybrida L. under elevated CO₂in greenhouses - Short communication

“…Th e parameter estimates regarding α were similar to those reported by Peek et al (2002). It was shown that the quantum effi ciency is an intrinsic characteristic, and its upper ceiling in C 3 plants is set fi rmly by physiochemical limitations (Skillman 2008). Under steady-state and non-stressed conditions, quantum yield is generally regarded as constant (Ehleringer, Bjorkman 1977;Oberhuber et al 1993).…”

Photosynthetic Productivity: Can Plants do Better?

“…This suggests there is strong selection for plants to produce leaves that are as efficient as possible in capturing solar energy in carbohydrates. Interestingly, the maximum realized QY, measured under ambient CO 2 and O 2 concentrations, always falls well below the maximum potential QY determined in the lab under optimal, albeit artificial, controlled CO 2 and O 2 concentrations (Skillman, 2008). This 'real world' inefficiency is largely due to energy losses associated with photorespiration (discussed below).…”