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 captureLight to Liquids: Improving biological energy captureAdvanced Research Projects Agency Advanced Research Projects Agency –– EnergyEnergy

Dec 2Dec 2--3, 20103, 2010

Total solar energy

Conversion ffenergy efficiency

Wh = S i cWh

H d

S i c

Harvested yield

Partitioning efficiency

Interception efficienc

(Harvest index)

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

H t i d ( ) f - Harvest index () for corn grain in modern cultivars is ~55% f d ( of above ground biomass (i.e. =

0.55)- little room for improvement in

major grain crops

Lignocellulosic Feedstock Harvest Index

F d t k C ll l H mi ll l Li i A h Oth HIFeedstock Cellulose Hemicellulose Lignin Ash Other HI

Hardwoods 39-50% 18-28% 15-28%

0.3-1 % 3–6% 0.65-0.82

Softwoods 41-57% 8-12% 24-27%

0.1-0.4%

5-9% 0.63-0.69

Miscanthus 43-48% 23-27% 9-22% 1.7-2.1%

? 0.78-0.89

is d t min d b mbin d ph tc is determined by combined photo-synthetic rate of leaves in the canopy corrected for respiratory loses.

Annual solar energy conversion efficiencies of C3 d C4 i l l and C4 agricultural crops.

Crop Type Yield EfficiencyCrop Type Yield Efficiency(t ha-1y-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 εc = 0.046Maximum observed εc = 0.024cAverage observed εc = 0.007

C4 Potential εc = 0.060Maximum observed εc = 0.037Average Observed εc = 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 εεcc??

-1)

J m-2

s

15

hesi

s ( 10

otos

ynth

0

5 75% of daylight hours

0 500 1000

Pho 0

Solar energy (J m-2 s-1 )0 500 1000

Raising the theoretical upper Raising the theoretical upper limit of photosynthetic limit of photosynthetic limit of photosynthetic limit of photosynthetic

efficiency.efficiency.yy

PGAPGACH2OPO3

2-

C HHO

CH2OPO32-

C HHO

G

CH OPO 2-

CO2

C

COO-

HHOC

COO-

HHOO2

CH2OPO32-

C O

COO-COO-

C

C

OH

H OH

H

C HHO

COO

CH2OPO32-

COO C

CH2OPO32-

H OH

CH2OPO32-

PGA2-phospho-glycolate

Ribulose-1,5-bisphosphate

glycolate

Photorespiratory “by-pass”

Effects of temperature and [CO2] 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

f H f H d d d d requirements of Hrequirements of H22O oxidation and O oxidation and carbon reduction to solar spectrumcarbon 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