Disciplinary Research Relevant
for Plant Productivity
 Research in the biological and physical sciences of
particular relevance for agriculture will include im-
proved photosynthesis, the effects of rising levels of at-
mospheric carbon dioxide, atmospheric pollutants and
trace elements, biological nitrogen fixation, mycor-
rhizal-root interactions, root-colonizing bacteria, nitri-
fication and denitrification, cell fusion and tissue
culture, plant growth regulants, greater resistance to
competing biological systems and more resistance to
environmental stress, and forestry.
 Photosynthesis Photosynthesis is the most impor-
tant biochemical process on earth. It is primarily
through photosynthesis that green plants harvest the
renewable flow of solar energy. Each day plants store
17 times as much energy as is consumed worldwide.
Photosynthesis also provided the original plant
materials that formed our oil, natural gas and coal
resources. Improvements in the photosynthetic process
are the key to adequate future food supplies.
 All practices that increase the productivity of crops
must ultimately be related to an increased appropria-
tion of solar energy by plants. Yet, our support of basic
research on photosynthetic processes is extremely
meager, in spite of the high priority assigned to it by
every major study of research priorities for agriculture
and forestry. The capture of solar energy by food crop
plants through photosynthesis averages less than 0.1
percent of all solar energy falling on them during the
entire year. For most crops, the proportion of solar
energy utilized during the growing season does not ex-
ceed 1 percent. Under the best of conditions, it can be
2 to 3 percent for such crops as sugarcane, maize,
hybrid napiergrass and water hyacinths. Many
environmental variables affect photosynthesis and
yields. There is a great diversity among plants.
 Little progress has been made during the past decade
in support of DISC research on photosynthesis. In cur-
rent dollars, funding levels in the United States are
about 50 percent above those of seven to eight years
ago. This means that there has been no increase in real
dollar funding. As one projects output from present
support levels into the 21st century, it appears that we
will have a better understanding of photosynthesis but
not be able to regulate it in the year 2030. By the 21st
century, however, it may be possible to make bene-
ficial genetic modifications in photosynthetic cycles.
Though mutations with improved photosynthetic proc-
esses do occur, it is difficult to improve and speed up
this natural process.
 The most photosynthetically productive crops on
earth in an appropriate environment (high tempera-
tures and adequate sunlight, water and mineral


nutrients) are C4 plants (the first product of photosyn-
thesis is a 4-carbon molecule). These include sugar-
cane, maize (corn), sorghum, millet, some tropical
grasses and many noxious weeds. Most food crops are
C3 plants, of which the first product is a 3-carbon
molecule. These include the small grains, legumes, root
and tuber crops, and most fruits, vegetables and forest
crops. Little is known about the photosynthetic proc-
esses of forest trees.
 Research opportunities exist to enhance photosyn-
thesis and reduce photorespiration, which destroys
carbohydrates containing energy that were fixed
through photosynthesis. These opportunities include
identification and possible control of the mechanisms
that regulate the wasteful processes of both direct and
light-induced (photo) respiration. Photorespiration
(light-induced destruction of carbohydrates) occurs in
C3 plants. Its control would represent a major con-
tribution to increased crop productivity.
 Other research imperatives to improve photosyn-
thesis include identification of the growth regulators
involved in the process, heritable components that con-
trol flowering and leaf senescence; improvements in
plant architecture, anatomy, cropping systems, plant-
ing designs and cultural practices for better light recep-
tion; and carbon dioxide enrichment of crop atmos-
pheres. Faster initial growth for quick ground cover
and higher leaf area would also help.
 One of the most immediate improvements in photo-
synthesis for a large number of crop species is genetic
alteration of plant architecture. An example of a recent
technological achievement is the vertical positioning of
the flag leaves of the rice plant above the panicles of
grain, rather than letting them droop horizontally
below. The resultant improvement in light reception
increases yields.
 Approximately $10 million is currently spent in
DISC research on photosynthesis to improve our
understanding of it. Much of this can be made more
relevant by redirecting it to economically important
crops grown under field or forest conditions, as well as
in the laboratory. As one moves in research from the
microscopic laboratory level to field experiments, the
advantages of the highly productive C4 photosynthetic
mechanism over the C3 are progressively diminished.
The more efficient C3 plant grows better at higher
temperatures than the C3 crop plants because photo-
respiration in the C3 plant rapidly increases at high
temperatures. Differences between SM agronomicc)
and DISC (plant physiology) research disappear as
informed scientists from each area seek the common
objective of improving photosynthesis.
 Rising Levels of Atmospheric Carbon Dioxide-
Great concern is being expressed about the rising level