-
Gust,
D., "Why
Study Photosynthesis?", Center
for the Study of Early Events in Photosynthesis, Arizona State University
(1996). { based on the amount of carbon fixed by a field of corn during
a typical growing season, only about 1 - 2% of the solar energy falling
on the field is recovered as new photosynthetic products. The efficiency
of uncultivated plant life is only about 0.2%. In sugar
cane, which is one of the most efficient plants, about 8% of the
light absorbed by the plant is preserved as chemical energy. }
-
John Whitmarsh, Govindjee,
"The Photosynthetic
Process", in: Concepts in Photobiology: Photosynthesis and Photomorphogenesis,
Edited by G. S. Singhal, G. Renger, S. K. Sopory, K-D Irrgang and Govindjee,
Narosa Publishers/New Delhi; and Kluwer Academic/Dordrecht, pp. 11-51.
{ The energy conversion efficiency of the Calvin cycle is approximately
90%; The energy conversion efficiency of the Calvin cycle is approximately
90% (see Emerson, 1958). These quantum yield
measurements show that the quantum yields of photosystem II and
photosystem I reaction centers under optimal conditions are near 100%.
These values can be used to calculate the theoretical energy conversion
efficiency of photosynthesis (free energy stored as carbohydrate/light
energy absorbed). If 8 red quanta are absorbed (8 mol of red photons are
equivalent to 1,400 kJ) for each CO2 molecule reduced (480 kJ/mol), the
theoretical maximum energy efficiency for carbon reduction is 34%. Under
optimal conditions, plants can achieve energy conversion efficiencies within
90% of the theoretical maximum. However, under normal growing conditions
the actual performance of the plant is far below these theoretical values.
The factors that conspire to lower the quantum yield of photosynthesis
include limitations imposed by biochemical reactions in the plant and environmental
conditions that limit photosynthetic performance. One of the most efficient
crop plants is sugar cane, which has been
shown to store up to 1% of the incident visible radiation over a period
of one year. However, most crops are less productive. The annual conversion
efficiency of corn, wheat, rice, potatoes, and soybeans typically ranges
from 0.1% to 0.4% (Odum, 1971). }
-
Emerson, R., "The quantum yield of photosynthesis", Annu. Rev. Plant
Physiol. 9:1-24. (1958)
-
Odum, E.P. Fundamentals of Ecology, W.B. Saunders Co. Philadelphia
(1971).
-
Teruo Higa, James F. Parr, "Beneficial
and Effective Microorganisms for a Sustainable Agriculture and Environment"
International Nature Farming Research Center, Atami, Japan (1994). { Although
the potential utilization rate of solar energy by plants has been estimated
theoretically at between 10 and 20%, the actual utilization rate is less
than 1%. Even the utilization rate of C4 plants, such as sugar
cane whose photosynthetic efficiency is very high, barely exceeds
6 or 7% during the maximum growth period. The utilization rate is normally
less than 3% even for optimum crop yields. }
-
Miyamoto, K. (ed.), "Renewable
Biological Systems for Alternative Sustainable Energy Production" (Section
1.2.1. Photosynthetic efficiency), FAO Agricultural Services Bulletin
#128
{ Approximately 114 kilocalories of free energy are stored in plant
biomass for every mole of CO2 fixed during photosynthesis.
Solar radiation striking the earth on an annual basis is equivalent to
178,000 terawatts, i.e. 15,000 times that of current global energy consumption.
Although photosynthetic energy capture is estimated to be ten times that
of global annual energy consumption, only a small part of this solar radiation
is used for photosynthesis. Approximately two thirds of the net global
photosynthetic productivity worldwide is of terrestrial origin, while the
remainder is produced mainly by phytoplankton (microalgae) in the oceans
which cover approximately 70% of the total surface area of the earth. Since
biomass originates from plant and algal photosynthesis, both terrestrial
plants and microalgae are appropriate targets for scientific studies relevant
to biomass energy production.
Any analysis of biomass energy production must consider the potential
efficiency of the processes involved. Although photosynthesis is fundamental
to the conversion of solar radiation into stored biomass energy, its theoretically
achievable efficiency is limited both by the limited wavelength range applicable
to photosynthesis, and the quantum requirements of the photosynthetic process.
Only light within the wavelength range of 400 to 700 nm (photosynthetically
active radiation, PAR) can be utilized by plants, effectively allowing
only 45% of total solar energy to be utilized for photosynthesis. Furthermore,
fixation of one CO2 molecule during photosynthesis, necessitates
a quantum requirement of ten (or more), which results in a maximum utilization
of only 25% of the PAR absorbed by the photosynthetic system. On the basis
of these limitations, the theoretical maximum efficiency of solar energy
conversion is approximately 11%. In practice, however, the magnitude of
photosynthetic efficiency observed in the field, is further decreased by
factors such as poor absorption of sunlight due to its reflection, respiration
requirements of photosynthesis and the need for optimal solar radiation
levels. The net result being an overall photosynthetic efficiency of between
3 and 6% of total solar radiation. }
-
Photosynthesis:
"C3,
C4 and CAM. Regulation of The Activity of Photosynthesis",
Botony
Online
-
Patzek, T. W., "Photosynthesis",
E11 Lecture (3 Nov 1997). { Agricultural efficiency 0.4% for potatos
in the U.K.; theoretical efficieicnes are 4.5% }.
-
Kimball, J., "Photosynthesis:
The Role of Light"
-
Sadek, R., Ecology
Lectures: Photosynthesis,
American
University of Beruit
-
MIT Biology
Hypertextbook: Photosynthesis
Directory
-
J.
Ehleringer, Plant Ecology
(Biology 5460): "C4
Plant Biology in a Nutshell", Dept. of Biology, Univ. of Utah
-
"Questions
and Ideas for Discussion", 1999
Princeton-Rutgers Environmental Science Institute: Global Change and Its
Effects (1999).