Uses of plants in the future

David S. Seigler Department of Plant Biology University of Illinois Urbana, Illinois USA

Uses of plants in the future - Outline Crop improvement Loss of genetic variation and gene sources Expanding agriculture Fossil fuels Plants as chemical precursors Plants as fuels o Methanol o Ethanol o Methane o Seed oils

Reading CHAPTER 19 IN THE TEXT, 458 ff.

Introduction Plants are renewable resources. Can plant resources support increasing population in the future? Will we have sufficient plant diversity to choose new crops or to improve present day ones?

Over half the world's population is inadequately fed. The average American consumes about 5 pounds of grain per day. About 80% of this is fed to animals. In many underdeveloped countries, individuals consume about 1 pound of grain daily, mostly directly. The problem is complex. There is already enough food produced to feed everyone. Our farming methods are not applicable in most of the world.

Yields can be improved greatly in many cases by selection of better cultivars. There is resistance to change in cultivars by farmers. Another problem is the loss of "land races" and hence genetic variation however. See p Changes in human population and food production. The major problem is that all this so far has just barely kept pace with human population growth. Better crops

The Green Revolution In the 1960s, wheat varieties were selected that could grow well in humid tropics. They were widely planted in India. For several years, production increased markedly and India even began exporting wheat. Then the population increase caught up. Now India is back in the importing category again.

A similar thing happened with rice. Shorter cultivars of rice that matured more rapidly permitting the farmers to grow more crops per year were developed. Most tropical crop plants are relatively unselected and probably yields could be improved dramatically. Will all this solve the problem? See p. 459.

Genetic variability People are gradually depending on fewer and fewer crops. Further, they are cultivating fewer and fewer types of these crops. Wild forms are, in many cases, even eradicated to prevent them from crossing with the cultivated forms.

Almost all hybrid corns in the U.S. come from selections made by one family in the 1840's and 1850's. Almost all hard red wheat comes from a hybrid cross made in Canada about 1900.

The same is true for many other crop plants. All of these things can lead to disastrous problems with monocultures. This happened with the southern leaf blight of corn in the early 1970's.

Gene banks have been established for many of the major crops. However, many tropical crops are still not included. The quality of preservation in these gene banks also varies widely. We are just now learning how to preserve and maintain seeds for long periods of time. The seeds must periodically be taken out and grown. Care must be given to prevent any hybridization with nearby similar plants. Gene banks

Many of these methods involve plant tissue culture. This is especially useful for plants that are reproduced vegetatively. Somatic mutations may be created. Protoplast fusion can also be used. Genetic engineering. New ways of making plant variation

Expanding agriculture Agriculture can possibly be expanded into areas that are presently too cold, too dry, or too saline. Some crop plants already have been grown in many cases and may well be adaptable. Knowledge of minor crops may be useful in this regard. Many areas used for expanded farming are not appropriate for agriculture. As tropical forests are destroyed, many species will be lost.

There are very limited potential sources of arable lands. We don’t know all the long term effects of forest destruction, but they don't look positive.

Dependence on fossil fuels Although our system of farming appears to work well, we are heavily dependent on fossil fuels (petroleum, natural gas and coal) to make fertilizer, drive tractors etc. We put six times more energy into farming than we get out.

More energy efficient methods of agriculture will almost certainly have to be developed. Some crops require much less energy input than others. This has led to reduced tillage agriculture, which has its own set of problems.

There are also problems with inappropriate use of pesticides, herbicides, and genetically modified crops. Many of these problems will have to be resolved in the future. Naturally occurring compounds from plants may provide a partial solution. Biological control will almost certainly become more important.

Uses of plants as chemical precursors Plant seed oils for diesel Fermentation of plants for ethanol Production of methanol. Biomass is the total quantity of organic material produced.

Ultimately, all fuels come from CO 2 fixation by plants or solar energy. Methane: Biomass can be fermented anaerobically to produce methane. Methane is easy to transport and use. The systems for delivery are already largely in place. Cellulose is probably the most abundant organic compound. Lignins are also very common. Fuel uses

When dried, straw or wood has only about half the energy content of oil. Sewage and animal wastes can also be fermented to produce methane.

Some of the limits are the cost and land area requirements to grow the crops. Many schemes of this type produce less energy than they consume.

Methanol Destructive distillation of wood and many other plant materials produces methanol. Methane can be converted by steam reforming into methanol. Methanol can be added to gasoline or used directly.

Ethanol This is the most common approach. In countries like Brazil, it's fairly favorable. The cost and land area to grow the crops is a major limitation. Sugar, in some cases from starch, is converted by yeast into ethanol The scheme is not new. Ethanol was first used as a fuel in Gasohol was first marketed about 1936 (8-10% ethanol). Almost all U.S. gasoline contains about 5% ethanol in any case.

Ethanol plants in the U.S.

In Brazil, in 1973, they began to make EtOH in a big way. They have abundant cassava and sugar cane. Hydrolysis of wood, bagasse, straw, paper, cotton, to sugar is a major problem. This can be done by acid hydrolysis under pressure or cellulase enzymes. Sugar cane is one of the most efficient plants. The materials are already collected, but not all are used.

Generally alcohol is two to four times more expensive than gasoline in the U.S. The Brazilians have improved sugar cane yields, improved alcohol production, and improved the yeasts. Brazil has about everything going for it: lots of land, little oil, adverse balance of payments, rural unemployment problems, and good climate.

Production of ethanol from biomass

Fuel cells based on ethanol

Switch grass, Panicum virgatum Miscanthus X giganteus

These are already similar to diesel fuels in many of their properties. They can probably be used without major work except for economics. They will work in basically unaltered diesel engines, but gums and waxes must be removed. Antioxidants must be added to prevent polymerization. Mixing about 50:50 with diesel fuel improves the properties quite a lot, but viscosity is still a problem. Seed oils for fuel

Some farmers are already using biodiesel because they can make it at home. This involves conversion of the fatty acids to methyl esters. Sunflower oil is the most popular. About % of the crop is needed to provide energy to grow the next crop. Sunflower oil costs about two times more than diesel fuel. Peanut oil is also usable. Soybean oil works, but they are grown on more valuable farm land and compete directly with corn and wheat.

Oils can also be isolated from algae and fungi in culture, but the costs of culture are usually too high to permit this to be a good alternative. As much as 70-80% of some Candida species are oil.

Sunflower, soybean, and similar crops yield about 1 barrel per acre. Crambe, peanut, safflower all yield about 2 barrels per acre. African oil palm yields about 7-10 barrels per acre.

Ricinoleic acid from castor beans is used to make nylon. Ricinoleic acid is converted to an 11-carbon precursor which is made into nylon in France. Erucic acid is made into plasticizers and lubricants as well as nylon 13/3. Jojoba oil is made into a lubricant. Other chemical precursors