What is the maximum efficiency that What is the maximum efficiency that What is the maximum efficiency that What is the maximum efficiency that photosynthesis can convert solar energy into photosynthesis can convert solar energy into biomass? biomass? biomass? biomass? Light to Liquids: Improving biological energy capture Light to Liquids: Improving biological energy capture Advanced Research Projects Agency Advanced Research Projects Agency – – Energy Energy Dec 2 Dec 2- -3, 2010 3, 2010
Total solar Conversion energy energy efficiency ff W h = W h S i c S i c Harvested H d Partitioning yield efficiency (Harvest index) Interception efficienc efficiency
i is determined by speed of canopy i s determ ned by speed of canopy closure, and canopy size & architecture - top performing crops achieve i = 0.9 - little potential for further improvement
Partitioning efficiency ( ) - for some crops, yield increase has been due in large part to has been due in large part to improved - Harvest index ( ) for corn H t i d ( ) f grain in modern cultivars is ~55% of above ground biomass (i.e. = f d ( 0.55) - little room for improvement in major grain crops
Lignocellulosic Feedstock Harvest Index Feedstock F d t k C ll l Cellulose H mi Hemicellulose ll l Li Lignin i A h Ash Oth Other HI HI Hardwoods 39-50% 18-28% 15- 0.3-1 % 3–6% 0.65-0.82 28% Softwoods 41-57% 8-12% 24- 0.1- 5-9% 0.63-0.69 27% 0.4% Miscanthus 43-48% 23-27% 9-22% 1.7- ? 0.78-0.89 2.1%
is d t c is determined by combined photo- min d b mbin d ph t synthetic rate of leaves in the canopy corrected for respiratory loses.
Annual solar energy conversion efficiencies of C3 and C4 agricultural crops. d C4 i l l Crop Crop Type Type Yield Yield Efficiency Efficiency (t ha -1 y -1 ) (%) Pennisetum purpureum C4 88 0.8 Saccharum officaarum C4 66 0.6 Zea mays C4 27 0.4 Beta vulgaris C3 32 0.5 Lolium perenne C3 23 0.7 Solanium tuberosum C3 11 0.3 Triticum aestivum C3 12 0.2
Modified from Zhu et al. 2008 Current Opinion in Biotechnology. 19:153-159.
C3 Potential ε c = 0.046 Maximum observed ε c = 0.024 c Average observed ε c = 0.007 C4 Potential ε c = 0.060 Maximum observed ε c = 0.037 Average Observed ε c = 0.012 Modified from Zhu et al. 2008 Current Opinion in Biotechnology. 19:153-159.
Why is maximum observed below theortical Why is maximum observed below theortical ε c ? -1 ) J m -2 s 15 hesis ( 10 otosynth 75% of daylight hours 5 Pho 0 0 0 0 500 500 1000 1000 -2 s -1 ) Solar energy (J m
Raising the theoretical upper Raising the theoretical upper limit of photosynthetic limit of photosynthetic limit of photosynthetic limit of photosynthetic efficiency. efficiency. y
PGA PGA G CH 2 OPO 3 2- CH 2 OPO 3 2- CH OPO 2- CH 2 OPO 3 2- HO HO C C H H HO HO C C H H O 2 CO 2 C O COO - COO - H C OH H H C C OH OH COO COO - COO - COO CH 2 OPO 3 2- HO C H CH 2 OPO 3 2- CH 2 OPO 3 2- Ribulose-1,5- 2-phospho- bisphosphate PGA glycolate glycolate
Photorespiratory “by-pass”
Effects of temperature and [CO 2 ] on c of C3 vs C4 photosynthesis vs C4 photosynthesis Zhu , Long, and Ort (2008) Current Opinion in Biotechnology 19, 153-159
Redesigning photosystem absorption Redesigning photosystem absorption to better match energetic to better match energetic requirements of H 2 O oxidation and requirements of H f H f H O oxidation and d d d d carbon reduction to solar spectrum carbon reduction to solar spectrum Blankenship et al. submitted
Targets and timelines for improving photosynthetic efficiency Targets and timelines for improving photosynthetic efficiency Zhu, Long, Ort (2010) Annu Rev Plant Biol 61:235-261
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