Introduction
The world population is projected to grow to 10 billion
before reaching a plateau in the later part of this century,
and increasing economic prosperity of the developing
world is forecast to soon place even greater demands on
agricultural production than on population growth. With
very few prospects to sustainably expand the 1.5 billion ha
of cropland currently under cultivation [1], a doubling of
productivity will be needed to meet the increasing demand
before the end of this century. Current photosynthesis
underlies the production of all of our food and fiber and
biomass-based biofuel is increasingly being viewed as a
source of renewable fuels. More solar energy reaches the
Earth’s surface every hour (4.3 1020 J) than is consumed
on the planetin a year (4.1 1020 J) (Basic Research Needs
for Solar Energy Utilization, DOE Solar Energy Workshop
rreport, http://www.sc.doe.gov/bes/reports/abstracts.html#-
SEU_rpt.pdf). Despite its quantity, solar energy is dif- Q2
fused, which places a premium in all sectors of production
and agriculture on the overall efficiency of photosynthetic
solar energy conversion. In this context it is not surprising
that ‘application of the revolutionary advances in
biology and biotechnology to the design of plants and
organisms that are more efficient energy conversion
machines’ was identified as a major solar energy research
goal for the coming decades (Basic Research Needs for
Solar Energy Utilization, DOE Solar Energy Workshop
report, http://www.sc.doe.gov/bes/reports/abstracts.html#-
SEU_rpt.pdf). A key starting point for identifying and
evaluating biotechnology targets for improving photosynthetic
solar conversion efficiency is a critical re-examination
of the maximum efficiency of photosynthetic solar
energy conversion that could theoretically be achieved in
managed ecosystems. The purpose of the analysis undertaken
here is to draw on the state-of-the art understanding
of the mechanism of plant photosynthesis to establish the
theoretical limit on photosynthetic solar energy conversion
efficiency that improved agronomy, breeding, and biotechnology
can hope to approach.