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Physiology

More food and forests in the air

Plants insatiability for carbon dioxide paves the way to producing more food in less space, also easing global warming

Still life of pineapple and pawpaw, oil painting on canvas by Albert Eckhout

The current crop of studies into sugarcane bestows yet another task on the plant which is used to produce the sugar that is indispensable for most Brazilians and the alcohol that is grabbing the world’s attention and fueling almost half the automobiles in this country. Sugarcane now emerges as a possible candidate to halt global warming: the continuous accumulation of carbon dioxide (CO2) in the atmosphere, which tends to raise temperatures across the planet, may be a source of concern for mankind, but it is great for plants and for sugarcane. The same CO2 that we see as pollution is a type of fertilizer for plants. Therefore, sugarcane, along with other agricultural crops and many species of trees, could benefit and grow faster in more polluted air.

Biologist Amanda Pereira de Souza worked with sugarcane for five years at the Botanical Institute of the State University of Campinas (Unicamp) and at the University of São Paulo (USP). She carried out a series of experiments and was finally able to show that sugarcane, in an environment with double the current concentration of CO2, shows a 30% increase in photosynthesis and produces 30% more sugar than the plants grown under the normal concentration of CO2. The chambers that maintained this carbon-dioxide rich atmosphere also produced taller, denser plants, with 40% more biomass. Soy beans and potatoes produced roughly the same results in similar experiments. The increasingly logical conclusion is that most of the other plants, including trees, should be likely to benefit from the probable excess of carbon dioxide, one of the essential ingredients for photosynthesis to occur, although some plants benefit more than others (see table).

These results could provide added advantages for Brazil, India and China, the largest producers of sugarcane, in a scenario especially rich in carbon dioxide. However, this conclusion must be carefully examined, to avoid exaggerated proliferation of sugarcane plantations as a means of cleansing the air and producing wealth. The role of sugarcane plantations in removing carbon dioxide from the air would be a very modest one compared to that of the tropical forests, warns Marcos Buckeridge, an USP botanist and this experiment’s coordinator. His estimates indicate that all of Brazil’s sugarcane plantations together would only absorb one thousandth of the three billion tons of CO2 released into the atmosphere every year by the forest fires in the Amazon region.

According to the experiments coordinated by Carlos Martinez at the USP unit in the city of Ribeirão Preto, soybeans, which cover an area three times larger than that of sugarcane, generate even more photosynthesis and use water more efficiently, when subjected to the same concentration of CO2. According to him, plants that have sugar storage structures – such as sugarcane, potatoes, tomato plants, soybeans and corn – can grow as much as 40% more with added CO2. “However”, he stresses, “having an excess of CO2 will not per se increase the plants’ productivity. The other determinants, such as the amount of water, nutrients, sunshine and temperature, must also be favorable.” In a recent study, two plant physiology specialists, Jon Lloyd from England, and Graham Farquhar from Australia, warned that the rate of photosynthesis might drop when temperatures exceed 30° Celsius.

Up until now the experiments have been carried out in laboratories: the plants are grown in vases surrounded by cylindrical transparent chambers with open tops, with plenty of carbon dioxide, water, sunshine and nutrients. What is yet to be done is to carry out tests under real conditions in the field, where the plants experience daily variations in terms of water and temperature. However, already at this point, it makes sense that the excess CO2 in the atmosphere should change forests’ biodiversity and composition. Species of pioneering trees such as the feijão-do-mato [Rhyncosia phaseoloides] and the embaúba [trumpet-tree, i.e., Cecropia] are usually among the first to occupy former forest areas that have been cleared for pasture or modified by human activity, and tend to grow even faster than the definitive, longer-living species such as the jacaranda-da-baia [Brazilian Rosewood] and the jatobá [stinkingtoe]. Incidentally, it was in a pioneering study using the jatobá that Buckeridge showed in 2001 that a plant can grow faster and faster as concentrations of carbon gas increase.

These and other studies carried out in Brazil and other countries recognize the value of sugarcane as a source of ethanol, a green and renewable fuel, unlike fossil fuels such as petroleum. To date, corn, the raw material used to make ethanol in the United States, has not been shown to have the same appetite for CO2 as sugarcane. In addition, knowing that sugarcane grows more with more carbon dioxide would make it possible to generate the same income from half the plantation area, using the other half to plant beans, rice or corn, for instance. “We can produce more and do so sustainably”, Buckeridge believes. He argues in favor of the idea of a sugarcane plantation combined with a forest: the area no longer used for growing sugarcane could be used to create forests for sustainable use, which would help to generate revenue, retain CO2 and mitigate the environmental impact of sugarcane. “Why not also think about how to use the carbon dioxide produced by sugarcane fermentation vats at the sugar mills to irrigate sugarcane plantations and increase their productivity and sugar content?”

The USP biologists, along with their colleagues at Unicamp, at the Botanical Institute and the Centro de Cultura Canaviera sugarcane crop center (a private-sector institution), found that sugarcane not only uses more CO2, but also more light, another essential ingredient for photosynthesis. Shortly thereafter, they identified four genes linked to greater light absorption and two that cause growth of the cell wall, which retains almost half the carbon obtained as a result of CO2 absorption.

Finding genes such as these is no easy task: in genetic terms, sugarcane is very complex. The varieties of sugarcane that are currently used the most to produce sugar, alcohol, sugarcane spirit, sugarcane juice and raw brown sugar have chromosomes ranging from 100 to 130 in number. Each cell retains at least part of the genetic inheritance of the original species, Sacharum spontaneum, which has 36 to 128 chromosomes, and Sacharum officinarum, which has 70 to 140 chromosomes. And each chromosome has between six and ten copies – which are not always the same.

There is no longer any reason to get lost in this maze. Between 1999 and 2003, almost 250 researchers at institutions in the states of São Paulo, Pernambuco and the Rio de Janeiro coastal region worked on the so-called Cane Genome or Sucest project and succeeded in identifying 90% of sugarcane’s estimated 80 thousand genes, represented by 43 thousand active gene sequences. “We were able to keep up, step by step, with the international development in molecular plant genetics”, notes Marie-Anne Van Sluys, an USP researcher involved in the Sucest project.

Useful genes
So much information on the genetics of sugarcane has helped validate and guide the improvement of classical genetics, which got underway at the start of the century at institutions such as the Agronomical Institute of Campinas (IAC) and which is also taking place today at universities across Brazil. In a recent article, the Sucest team presents the genes that may help to improve desirable agronomic characteristics, such as sugar content or resistance to pests and diseases, or potential molecular identifiers of the most sought-after sugarcane characteristics. Another paper describes the genes and the biochemical mechanisms whereby one of the current varieties of sugarcane accumulates sucrose. “For the first time”, says Marie-Anne, “we are witnessing the combined efforts of geneticists, biochemists and agronomists to identify genes that may speed up the identification of new varieties and facilitate the selection of the most promising plants.”

eduardo cesar Jatobá: one of the plants benefiting from excess carbon dioxide in the atmosphereeduardo cesar

This two-way road between geneticists and those working on improvements also give us the transgenic or genetically modified varieties of sugarcane that contain more sugar or are more resistant to drought, which could increase productivity and check expansion into Brazil’s tropical savannah region, whose natural vegetation is among those most replaced by farming. Some of these experimental varieties have already undergone the first trials, carried out in university greenhouses or domestic biotech companies. In one of the experiments only two out of the 40 plants that could supply more sucrose than the currently used varieties passed the test. These new plants now move on to the real trial: field testing, with fluctuating sunshine, rain and humidity, as well as the pests to which plants are normally subject. Even the most optimistic scientists are not sure that these field tests will be successful: to date, most of the genetically modified plants have proven to be a disappointment when subjected to real plantation conditions. A series of articles and reports on plant genomes, published in the April 25 edition of the journal Science (www.sciencemag.org/plantgenomes/), indicates that optimism is not always rewarded. Rice genetically modified to avoid blindness and death in millions of children due to a lack of vitamin A remains just a promise, almost eight years after having been featured on the cover of Time magazine.

Still, agricultural engineer and Unicamp professor Luís Augusto Cortez does not lose heart easily. For 15 years he has been working on the idea of extracting a great deal more from sugarcane than just sugar and alcohol. He has not given up and, with his team, has built an experimental plant that turns 200 kilos of sugarcane bagasse into 80 kilos of oil that, along with other applications, could replace diesel in turbines and boilers, and 50 kilos of coal that could be used as fuel or soil additives. Both the raw material and the end products are versatile; chemical engineer Juan Pérez guarantees that other agricultural waste, such as orange pulp and sawdust, could be used in lieu of sugarcane with the same results.

Erosion and pollution

Sugarcane also produces controversy. Whereas some researchers emphasize the benefits of sugarcane, others highlight the negative side: the environmental and social consequences of production methods that have hardly changed in almost five centuries, when this plant first began to be grown in Brazil. The world’s interest in sugarcane ethanol is fueling this debate – without questioning the fact that this fuel is, at present, a better alternative than petroleum – and may speed up the implementation of existing proposals and laws, which would reduce the impact of sugar and alcohol production.

“The way in which it is currently produced, ethanol isn’t green, but grey”, notes the agronomist Luiz Antonio Martinelli, a professor at USP’s Center for Nuclear Energy in Agriculture (Scene) and author of a review study on the environmental and social consequences of sugarcane cultivation in Brazil. “We can no longer build sugar mills by chopping down forests”, says José Goldemberg, the USP physicist who coordinated another review study, so called because it evaluated the trends pointed out in dozens of preceding studies. Goldemberg stresses that the first sugar mills ever set up in sugarcane producing centers, such as Ribeirão Preto, were not subject to environmental restrictions. “The current owners continue to complain, alleging that their grandparents didn’t have to put up with all these restrictions.”

Martinelli and Goldemberg show that the negative effects of the current method of sugar and alcohol production are not limited to the harvesting season, when the smoke from the fires that precede cane cutting aggravates respiratory conditions such as asthma, particularly among children and the elderly. Other side effects are subtler and last the entire year: soil erosion and compaction, pollution of the rivers with fertilizers and residues from sugar and alcohol production, and the elimination of native forests, which help to stabilize temperatures and the water supply in cities.

Aware of the possibilities of change, Gláucia de Souza, a biochemist at USP, says that FAPESP’s Bioenergy Program (Bioen), which she coordinates and which will probably be publicly announced, is likely to sponsor research into new ways of reducing the consequences of sugarcane cultivation and industrial processing. According to her, the biomass research projects will try to increase sugarcane’s productivity per planted hectare and thus raise production without taking over more land.

miguel boyayan Sugarcane cutter in inner-state São Paulo: 10 tons a daymiguel boyayan

“We have to change from the production model that brought us this far to an environmentally sustainable model, which should use less water and less fertilizer, more brains and less muscle”, states Cortez, who is coordinating a public policy project in conjunction with the state of São Paulo’s Agribusiness Technology Agency (Apta) and which has the collaboration of universities, of companies, and of both private-sector and public research institutes. The summaries of discussions and studies of these and other teams can be found at www.apta.sp.gov.br/cana). “Our aim is to show what needs be studied and what must be done.”

While the debate as to what to do continues, foreign businessmen are moving in on the sugarcane plantations: in April, after the Americans and the French, it was the turn of the English to announce the purchase of ethanol production plants in Brazil. These are not isolated incidents; Brazilian sugar and alcohol production is indeed undergoing a growing denationalization: between 2006 and 2007 the percentage of Brazil’s sugar and alcohol production in foreign hands rose from 5.7% to 12% and only last year the Central Bank recorded investments of US$ 6.5 billion in this sector, according to a dossier on the sugar-alcohol agribusiness signed by the sociologist Maria Aparecida de Moraes Silva, a professor at the Federal University of São Carlos (UFScar) and at Paulista State University (Unesp).

There is also increasing pressure for changes. In May, representatives of the European Community announced that they intend to make the purchase of Brazilian ethanol conditional upon compliance with acceptable environmental and social criteria. Fábio Feldmann, one of the coordinators of the São Paulo Forum of Climate Change, believes that the international market, especially the European one, should encourage producers to fight for environmental and social certification, which is currently voluntary.

It would be unnecessary to do much more to put some order into the sugarcane sector, because there are already proposals, laws and solutions at hand. “We have to do what Mato Grosso do Sul has done, which is zoning (restricting which areas can be cultivated)”, says Goldemberg. Cortez agrees, although he notes that there is resistance: “The same public entities that should be watching out for the environment are the very ones that authorize new factories.” Defining where one can and cannot plant cane may help curb the expansion of plantations into other areas. According to a study by CENA (the Center for Nuclear Energy in Agriculture) and the Forestry Institute, sugarcane plantations and pastures take up 75% of the area bordering the rivers of the seven largest hydrographic basins in the state of São Paulo. According to the law, areas bordering water courses should maintain their natural vegetation.

“Production can be adapted to meet environmental demands by means of simple measures and compliance with current laws” says Martinelli. There are a number of approaches available to anyone who wants to comply with the law by restoring the original vegetation, some of which have already proven to be effective (see FAPESP Survey no. 144, from February 2008). Moreover, it would be inexpensive, in relation to the income generated by the land. A team from USP’s Luiz de Queiroz School of Agriculture (Esalq) developed one of these methods and estimated that it would cost R$ 3,500 per hectare to restore the original vegetation to the land. This equals less than 10% of the revenue earned from agriculture and industry in the regions that are drained by the basins of the Piracicaba and Mogí rivers, which are two extreme cases in terms of agricultural occupation and which currently have less than 20% of their original forest area.

In March, the federal government announced its intention to invest R$ 9 billion in expanding ethanol production from its current level of 17.7 billion liters to 23.3 billion liters by 2010. “If we maintain the current production model, the environmental and social damage will become even greater”, warns Martinelli. He stresses that for each liter of ethanol, the mills produce 10 to 12 liters of slop, a strong smelling brown residue that is corrosive and rich in organic matter. Therefore, anyone who fills their tank with 50 liters of alcohol consumes the result of 40 minutes work of a sugarcane harvester and the production of at least 500 liters of a residue whose final destination is uncertain. “Few sugar mills can use all the slop that they produce as fertilizer on their own sugarcane plantations “, he says. “When the storage tanks burst and the slop reaches the rivers, the level of oxygen drops to zero and the fish die. It has the same effect as sewage.”

During the sugarcane burning season (November to April), in-patient levels at hospitals in cities near sugarcane plantations triple, on account of respiratory problems, according to Eduardo Cançado, from the University of São Paulo (USP) Medical School. The particles, driven by the wind and the rain, can carry pesticides. One of the types of pesticides in question consists of organochlorates, prohibited in 1985, but found in 1997 in fish from the Piracicaba basin, according to Martinelli and Fernando Lanças, from the USP unit in São Carlos. Organochlorates made a further appearance in 2003 in streams near sugarcane plantations in the central part of the state.

The results of Martinelli’s and Goldemberg’s studies are not always in agreement: Martinelli concluded that sugarcane uses 80 to 100 kilos of nitrogen as fertilizer per hectare a year, whereas Goldemberg argues that the right figure is 50 kilos. However, both of them recognize that it would be wise to seize this historic moment, in which one has an already mature industry that shows increasing productivity, to adjust the production methods. From 1960 to 2007 productivity per hectare rose from 45 tons of sugarcane to 75 tons, thanks to better farming techniques and genetic improvement of the varieties planted. The sugarcane harvesters have also become more productive: in 1950 they cut an average of three tons of sugarcane a day. This figure had risen to six tons a day by 1980 and, today, the sugarcane cutter’s machete fells an average of 10 tons a day. “We must find better alternatives that pay more and that don’t harm health”, Cortez proposes.

He suggests that we should take a broader approach to sugar and alcohol, seeing them as the results of a production chain, and therefore deserving more than only studies on isolated aspects of planting or production. Maria Moraes proposes an even broader approach. “If we don’t understand the country’s situation, we will always end up with a very compartmentalized grasp of the situation.” In April last year she spent many hours listening to the residents of the outskirts of Timbiras and Codó, two towns in the state of Maranhão that are surrounded by forests of babassu palm trees. Her aim was to find out why hundreds of men left their families and traveled for three days and nights to cut and drag sugarcane in inner-state São Paulo.

She found that the men migrated to São Paulo because they had been expelled from the land on which they had grown crops in even more remote towns. Representatives of companies that breed cattle had burned their crops of rice, beans and corn, along with the babassu palm tree forests, the livestock and homes of the families that used to live there. Then they threatened people with death if they did not leave the land they did not own. The 85 lawsuits that she examined describe what happened, raise doubts about the legitimacy of the property deeds that back these behaviors and tell of the efforts of families to return to the lands that they used to farm.

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