Coping with water scarcity in developing countries: What role for agricultural biotechnologies?
The central role that water plays for this planet and its inhabitants has often been summed up by the expression 'water is life'. The water that falls from the sky represents, directly or indirectly, the basis for life on Earth. Water is a renewable but finite resource on our blue planet and one which is increasingly threatened. We are living in a time of great change and humankind's activities have put an ever-increasing strain on all of the world's resources including the most precious of all, water. Most of the freshwater supplies that are withdrawn for human use are employed in agriculture. The aim of this conference, hosted by the FAO Biotechnology Forum, is to debate the role that biotechnology tools applied for agricultural purposes may play in helping us to cope with life on a water-scarce planet.
The conference is organised in collaboration with our colleagues in FAO's water programme and is one of the many activities planned to coincide with the World Water Day, which is celebrated each year on 22 March. This year its theme is "Coping with water scarcity' and FAO is the coordinating agency within the UN system for the theme. The conference theme also complements those of two recent meetings supported by FAO, i.e. "The 2nd international conference on integrated approaches to sustain and improve plant production under drought stress" (InterDrought-II) and the workshop on "Improving water use efficiency in Mediterranean agriculture: What limits the adoption of new technologies?".
For people who are not familiar with the Forum, it was launched by FAO in March 2000 with the goal of providing access to quality balanced information and to make a neutral platform available for all interested stakeholders to openly exchange views and experiences on agricultural biotechnology in developing countries. It covers applications in the crop, forestry, livestock, fisheries and agro-industry sectors. It has hosted 13 moderated e-mail conferences so far, and in these the e-mail messages have come roughly 50:50 from participants living in developing and developed countries respectively (FAO, 2001, 2006a).
Each conference takes one particular theme that is relevant to agricultural biotechnology in developing countries and opens it up for debate for a limited amount of time. The Forum covers the broad range of tools included under the general term 'biotechnology'. Some of the technologies may be applied to all the food and agriculture sectors, such as the use of genomics, molecular DNA markers or genetic modification, while others are more sector-specific, such as vegetative reproduction (crops and forest trees) or embryo transfer and freezing (livestock). This conference is therefore not just about genetically modified organisms (GMOs) and discussions in this conference will not consider the issues of whether GMOs should or should not be used per se or the attributes, positive or negative, of GMOs themselves. Instead, the goal is to discuss the potential role that applications of biotechnology tools (including genetic modification) can play in helping developing countries cope with growing water scarcity.
In this context, the primary focus will be on the use of biotechnology tools to increase the efficiency of water use in agriculture, while a secondary focus will be on two specific water-related applications of micro-organisms, in wastewater treatment and in inoculation of crops and forest trees with mycorrhizal fungi. To allow in-depth discussion of these areas and to avoid the debate becoming too broad, topics such as the use of biotechnology to increase yields (discussed e.g. in Conferences 1 and 5 of this Forum [FAO, 2001]) or to produce crops tolerant to soil salinity (resulting from irrigation), although related to water and agriculture, will not be discussed in this conference.
This Background Document aims to provide information about the conference theme that participants will find useful for the debate. Firstly, a brief overview of the current status and future perspectives regarding water availability and use on Earth is provided (Section 2), followed by discussion of some major strategies that can be employed to deal with water scarcity (Section 3). More details on water use in agriculture are then given (Section 4). Some of the potential ways in which biotechnology could contribute to this area are then considered (Section 5). Some of the kinds of specific questions that should be addressed in the conference are listed in Section 6 and, finally, references to articles mentioned in the document and abbreviations are provided in Section 7.
As for all previous conferences hosted by the Forum, a document will be prepared after the e-mail conference is finished to provide a summary of the main issues that were discussed, based on the messages posted by the participants.
2. A Water-Scarce Planet
There is lots of water here on Earth; over 70% of the planet's surface is covered with water. However, almost all of it (97%) is found as saltwater in the oceans. The remaining 3%, nevertheless, still represents an enormous quantity of water, around 40 million cubic kilometres (km3). Most of this is held as freshwater in glaciers and icecaps (2% of all water) while 0.7% is groundwater (i.e. water found in the cracks or pores between rocks or grains of sand at varying depths below the ground surface). The remaining freshwater is found in lakes, soil, the atmosphere, in streams and rivers and within living organisms (e.g. Ritter, 2006). Note, a single km3 can be visualised as the amount of water needed to fill a hole one km deep, one km long and one km wide; and one km3 is equivalent to a thousand billion litres of water.
Each year, an estimated 510,000 km3 of water fall from the skies, mainly in the form of rain, but also in other forms such as snow and sleet. Roughly 400,000 km3 fall on the seas and 110,000 km3 fall on land, with very uneven temporal and spatial distribution patterns. The latter is obviously essential for agriculture and can be classified into two categories of freshwater. The first, green water, is the soil moisture generated by rainfall and available for root water uptake by plants. It is the main water resource for rainfed agriculture. The second, blue water, is the stored runoff of rainfall in lakes, streams, rivers, dams and aquifers (i.e. water-bearing layers of permeable rock, sand, or gravel that store and/or transmit water). It is the main water resource for irrigated agriculture. Of the 110,000 km3 that fall on the land annually, an estimated 35% result in blue water and 65% in green water (SIWI et al, 2005; Falkenmark and Rockström, 2005).
An estimated 7,130 km3 of water are used each year for crop production globally, corresponding roughly to 3,000 litres used to feed a single person for one day (Molden et al, 2007a). Most of this water consumed by crop evapotranspiration comes from rain (about 80%) and about 20% is from irrigation. (Evapotranspiration, an important term in water science, is the combination of two processes: evaporation [the conversion of liquid water to water vapour] from the soil and transpiration [the process by which water absorbed by the plant, usually through the roots, is lost as vapour from the plant surface, occurring mainly at the leaves] by plants growing in the soil). Irrigation is practiced in places and times where rainwater is insufficient for adequately supplying water to crops. It provides a guaranteed supply of water and protects against droughts and dry spells. Out of the world's total land area of 13 billion hectares (ha), 12% is cultivated, and an estimated 27% is used for pasture. The 1.5 billion ha of cultivated land includes 277 million ha (18%) of irrigated land. In the period between 1960 and 2000, the amount of cultivated land increased by 13% while the human population was more than doubled, leading to a sharp reduction in the amount of land needed to produce food for one person. Between 1960 and 2000 the irrigation area almost doubled. These rapid increases in productivity were obtained through intensification of agricultural production, in which irrigation played an important role. Depending on various circumstances, irrigation helps to produce 2-3 times as much per hectare as non-irrigated agriculture (FAO/IFAD, 2006).
Blue water is very important as, apart from its use for irrigation, it is the freshwater resource that sustains aquatic ecosystems in rivers and lakes; it can also be applied to drinking or domestic purposes, to industry or hydropower. Over the 20th century, the amount of blue water withdrawn for human use at the global level increased from over 500 km3 in 1900 to just under 2,000 km3 in 1960 to almost 4,000 km3 today. Most of this water (currently estimated at 70%) is used for agriculture, mainly irrigation, although the part diverted for industrial (20%) and domestic (10%) purposes is growing rapidly (Molden et al, 2007a).
The figures given so far are all based on considerations at the global level. When the different parts of the world are examined individually, it is noted that there is tremendous variation regarding the water situation at the country level (and even at the within-country level). For example, some countries withdraw much more water per person than others, which is mainly linked to the countries' irrigated area per person. The amount of blue water withdrawn annually varies, for example, from over 1,500 m3 per person in Turkmenistan, Uzbekistan, Kazakhstan, Azerbaijan, Kyrgyzstan, Tajikistan, Iraq and the United States down to less than 20 m3 per person in many African countries such as Benin, Uganda and Rwanda (AQUASTAT database).
Many countries are withdrawing water at rates that are clearly not sustainable. Molden et al (2007a) report that 1.2 billion people live in areas characterised by physical water scarcity, where available resources are insufficient to meet all demands, including minimum environmental flow requirements. Arid regions in the world are most often associated with physical water scarcity. Symptoms of physical water scarcity include severe environmental degradation including river desiccation and pollution, declining groundwater and problems of water allocation where some groups win at the expense of others. They also estimate that another 1.6 billion people live in areas that face 'economic water scarcity', i.e. where water resources available are abundant relative to water use but there is a lack of investments in water or lack of human capacity to keep up with the growing water demand (characteristic of much of sub-Saharan Africa). So, it is estimated that, in total, around 2.8 billion people, more than 40% of the world's population, live in river basins where one or the other form of water scarcity must be reckoned with.
Looking to the future, there are also a number of factors at play that are likely to exacerbate this situation. The first factor is the rise in the global population, currently at 6.5 billion people (2005) and predicted to reach 8.2 billion by 2030 and, in addition, the accompanying increase in urbanisation of the world's population (UN, 2006). Whereas Molden et al (2007a) estimate that 7,130 km3 of water are currently used each year to feed the world's population, it is estimated that, without further improvements in water productivity or major shifts in production patterns, the amount of water consumed by evapotranspiration in agriculture will increase to between 12,000 and 13,500 km3 to feed the increased population in the year 2050 (de Fraiture et al, 2007). In addition, whereas 49% of the world's population is estimated to reside in urban areas in 2005, this proportion is predicted to rise to 60% in 2030 (UN, 2006). There will therefore be far greater demands on the blue water withdrawn for human purposes for domestic use and for industry and the proportion remaining for agriculture is likely to decline. Also, as Jury and Vaux (2005) point out, the economic value of water in industrial and urban uses is typically far greater than in agriculture (or for environmental uses), so market forces will lead to a significant reallocation of water resources from the agricultural and environmental sectors to the urban sector.
The second factor is climate change, which is expected to have significant impacts on agriculture and food production patterns through three major pathways: global warming, change in rainfall patterns and the increase in carbon dioxide concentration in the atmosphere (FAO/IFAD, 2006). While hard to predict all of the consequences, FAO/IFAD (2006) suggest that, in a scenario of moderate climate change, those most vulnerable to these changes are the poor and landless in rural areas dependent on isolated rainfed agricultural systems in semi-arid and arid regions. The changes in the water cycle and rainfall patterns - more precipitation, more frequent intense rainfall events and more evaporation - will affect soil moisture and increase erosion. In drought-prone areas, the number and duration of dry spells is expected to increase.
3. Some Major Strategies for Coping with Water Scarcity
The preceding Section has shown that scarcity of water is one of the major global problems facing humankind at the moment and that it is likely to be an ever increasing problem in the future. One clear message emerging from that Section is that there will be increased competition for the water resources available for agriculture in the future, despite the fact that there will be an ever-increasing demand for water in agriculture to meet the needs of the increasing world population. A range of major strategies have been proposed to cope with global water scarcity and a small number of them will be considered here:
a) Desalination of saline waters
Desalination is an option to increase the availability of freshwater both in coastal areas with limited freshwater resources and in areas where brackish water (i.e. a mixture of salt and fresh water), such as saline groundwater and drainage water, are available. It can be carried out by distillation of saline water or using membrane technologies, such as electro-dialysis and reverse osmosis. Desalination processes require large amounts of energy and the energy required as well as the high cost of desalinating brackish waters and seawater have been the major constraints to large-scale production of freshwater from saline waters. It is, nevertheless, a well-established technology primarily for drinking-water supply in water scarce regions, such as the Near East. It is the main source of potable (drinking) water in the Persian Gulf countries and in many islands around the world and it is also being used in certain countries to irrigate high-value crops (FAO, 2006b). Desalinated water is becoming more competitive for urban uses because desalinating costs are declining and the costs of surface water and groundwater are increasing. In spite of this development, the costs of desalinated water are still too high for the full use of this resource in irrigated agriculture, with the exception of intensive horticulture for high-value cash crops, such as vegetables and flowers (mainly in greenhouses), grown in coastal areas (where safe waste disposal is easier than in inland areas). At the global level, the volume of desalinated water produced annually, estimated at 7.5 km3, is currently quite low, representing about 0.2% of the water withdrawn for human use (FAO, 2006b).
b) Use of wastewater
As mentioned in Section 2, although the majority of blue water withdrawn for human consumption is used for agriculture (70%), a substantial proportion is also used for industrial (20%) and domestic (10%) purposes and this proportion is growing. With increased use of this water by urban communities and industries, larger volumes of wastewater are also generated. Millions of small-scale farmers in urban and peri-urban areas of developing countries use this wastewater for irrigating crops or forest trees or for aquaculture, thus reducing the pressure on other freshwater resources. Surveys across 50 cities in Asia, Africa and Latin America show that wastewater irrigation is currently a common reality in three-fourths of the cities (IWMI, 2006). Additional benefits of applying wastewater to land are that it also removes a number of contaminants from that water, making irrigation a low-cost method for the sanitary disposal of municipal wastewater, and that it can significantly contribute to urban food security and nutrition (IWMI, 2003).
The wastewater may or may not be treated before use. When untreated, its use brings with it potential health risks to the farmer and to the consumer of any food produced using the irrigated water, as well as potential environmental risks. For example, the presence of heavy metals, such as arsenic, in irrigation water is a problem in several developing countries, including Bangladesh (FAO, 2006c). Guidelines on the safe use of wastewater in irrigated agriculture have been developed to adequately address health protection and risk reduction measures (WHO, 2006).
Most of the domestic wastewater generated in developing countries is discharged into the environment without treatment. Wastewater treatment and use is an issue primarily in urban areas with sewerage systems. Wastewater treatment is a great challenge for developing countries because of its high costs and the technical skills required for operation and maintenance. Experience shows that wastewater treatment and use is more likely to be funded in national budgets if integrated with national integrated water resources management plans or with environmental policies. Some countries, such as Mexico, Brazil, Chile and Costa Rica, are moving in this direction (UNCSD, 2005). Israel currently uses 84% of its treated sewage effluent in agricultural irrigation and in a few cities, such as Windhoek in Namibia, the water is treated to a very high standard so that it can even be used as drinking water (UNIDO, 2006). Despite the obstacles for developing countries, the long-term goal of integrated wastewater management will always be to move from the unregulated use of untreated wastewater to the regulated use of treated wastewater (IWMI, 2006). The use of biotechnology in wastewater treatment is discussed in Section 5.
Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and, sometimes, nutrients from wastewater. Different sequential stages of wastewater treatment can be generally distinguished (see e.g. the FAO wastewater glossary, FAO (1992) or WHO (2006) for more details):
i) Preliminary treatment, whose objective is the removal of coarse solids and other large materials (such as sticks and stones) often found in raw wastewater.
ii) Primary treatment, whose objective is the removal of settleable organic (i.e. containing carbon) and inorganic (not containing carbon) solids by sedimentation, and the removal of materials that will float (scum) by skimming. The preliminary and primary treatments are usually physical processes.
iii) Secondary treatment, involving further treatment of the effluent from primary treatment to remove the residual organic material and suspended solids. This stage typically uses biological treatment processes where micro-organisms convert non-settleable solids to settleable solids. Several aerobic (involving the presence of oxygen) biological processes are used for secondary treatment, differing primarily in the manner in which oxygen is supplied to the micro-organisms (mainly bacteria) and in the rate at which the micro-organisms metabolise the organic matter. For example, in the activated sludge process, the contents of aeration tanks, containing wastewater and micro-organisms, are mixed vigorously by aeration devices that also supply oxygen; the micro-organisms feed on organic matter and aggregate into flocs (clumps) that remove organic material and that settle out in settling tanks (clarifiers). Part of the settled biological material (sludge) is then recycled from the settling tanks to the aeration tanks in order to speed up the process.
iv) Tertiary and/or advanced treatment is employed to remove specific wastewater constituents which cannot be removed by secondary treatment e.g. nitrogen, phosphorus or heavy metals. Heavy metals, such as lead, cadmium, arsenic and mercury, have potential negative impacts on human health and the environment and can find their way into the wastewater in a number of ways e.g. through industrial or domestic activities. High levels of nitrogen and phosphorus are undesirable because they can lead to the process of eutrophication where algal growth is stimulated resulting in reduced oxygen levels in the water and release of toxins that can harm aquatic organisms and even humans.
The level of water treatment varies between countries. For example, in the European Union, where the wastewater of about 85% of the population is collected and treated, a small number of countries have mainly primary treatment; most countries give at least secondary treatment to the water and four countries apply tertiary treatment for 80% or more of their population (EU, 2006). Data for developing countries are much less complete, although the FAO wastewater database provides an overview of the types of treatment applied in individual FAO member states.
c) Virtual water and food trade
Whereas the use of water for agriculture might require large proportions of already-scarce water in some countries (e.g. in the Middle East), it would not have the same potential negative impacts on the environment, industry and drinking water supplies in other water-rich countries (e.g. in Western and Eastern Europe or Latin America). It has therefore been argued that import of food from water-rich countries allows water-poor countries to save the water they would have used to grow the food themselves, thus being equivalent to the import of 'virtual water', and that their scarce water reserves can instead be used for more valuable domestic, environmental and industrial purposes. The amount of virtual water (defined as the amount of water used in the production and processing of a given product) saved depends not only on the amount of food imported but also on the kind of food imported (e.g. beef vs. maize) and the production system and management practices they would have used if they had produced it themselves. Depending on these factors, it can e.g. take between 400 and 2,000 litres of water to produce a kilo of wheat and between 3,000 to 15,000 litres per kilo of meat (Molden et al, 2007b). Countries with limited water resources might also change their production patterns to prioritise production of agricultural commodities requiring relatively little water and to import those requiring more water (FAO/IFAD, 2006). While the strategy of importing virtual water is appealing from a water perspective, it can also have substantial long-term political and economic implications for the importing countries.
d) Increasing agricultural yields
There is currently a major gap between potential and actual yields for most crop and livestock species. As most of the blue water withdrawn for human use is devoted to agriculture and as there will be increased demand for agricultural products in the future because of the rising world population, any agronomic improvements which will help to close this gap should help to reduce the demand for water for agricultural purposes. This could be done in a variety of ways e.g. by improving the efficiency of fertiliser use; preventing crop losses due to biotic stresses such as insects, diseases and weeds; or reducing post-harvest losses due to insects and to fungal and bacterial rots (e.g. FAO, 2005).
e) Improving the efficiency of water use in agriculture
Another approach to reducing the pressure on scarce water resources is to increase the efficiency of water use in agriculture so that the food and agricultural products are produced using less water. How can this be done? In order to answer this question, we will consider the use of water in agriculture in more detail in Section 4. The use of biotechnology to increase the efficiency of this water used, a major focus of this conference, will then be considered in Section 5.
4. Water Use in Agriculture: A Closer Look
To consider how its efficiency could be improved, it is important first to recognise that the use of water for agriculture involves a series of sequential steps, covering both physical and biological processes, which begins with the hypothetical water drop(s) and ends with the plant (or animal) biomass produced for human use. Any systematic attempt to improve the efficiency of water use has to consider therefore the whole pathway and not just its individual steps. This Section is based on Hsiao et al (2007). In their paper, they propose a comprehensive conceptual framework that can be used to examine the current levels of efficiency along any single pathway of agricultural water use; to assess the potential improvements that may be achieved in various parts of the pathway and their impact on the overall efficiency; and to aid in the optimal allocation of resources for the improvements. They illustrate the framework with three examples (irrigated crop production, dryland crop production and animal production on rangeland) and conclude that to improve the overall efficiency, it will be more effective to make modest improvements in several steps than to concentrate efforts on improving efficiency of just one or two steps.
For the first example, they show that the production of crop biomass using irrigation water can be analysed as a pathway with a series of eight consecutive steps. Each step has an output that is then used as the input for the next step. Most of these steps are also shared with the other two examples they consider. The eight steps are:
i) Moving water from a reservoir (i.e. a place where water is stored temporarily, such as a lake or river) to the farm gate. The efficiency of this step can be calculated as the ratio of the quantity of water that arrives at the farm gate to the quantity of water taken out of the reservoir. Efficiency could be increased by e.g. covering water channels or repairing any holes in the pipes.
ii) Moving water from the farm gate to the field. The efficiency of this step can be calculated as the ratio of the quantity of water at the field edge to the quantity of water at the farm gate. It could be increased by e.g. lining on-farm water reservoirs with plastic sheeting to reduce water leakage.
iii) Moving water from the field edge to the root zone of the crop. Efficiency of this step (known as application efficiency in irrigation engineering) can be calculated as the ratio of the quantity of water retained at the root zone to the quantity of water at the field edge. Efficiency could be increased by improving management of the existing irrigation system or changing to a better irrigation system. For example, there is growing interest in deficit irrigation, an irrigation practice whereby water supply is reduced below maximum levels and mild stress is allowed with minimal effects on crop yield (FAO, 2002). As most or all of the water applied remains in the root zone, deficit irrigation should increase efficiency of this step.
iv) Removal of water in the root zone by evapotranspiration (see Section 2 for definition). Efficiency of this step (known as consumptive efficiency) can be calculated as the ratio of the quantity of water evapotranspired to the quantity of water retained at the root zone. The loss of efficiency in this step is due to water left in the soil at harvest time.
v) Use of the water removed by evapotranspiration for crop transpiration. The water that is evapotranspired can have been either taken up by the crop and transpired (which is generally regarded as a beneficial use of the water) or simply evaporated from the soil (not beneficial). Efficiency of this step can be calculated as the ratio of the quantity of water transpired to the quantity of water that is evapotranspired. Efficiency could be increased by e.g. promoting plant canopy growth to cover the soil (thus reducing water evaporation).
vi) Assimilation of carbon dioxide by photosynthesis. Transpiration of water from the crop occurs mainly at the leaves, through specialised openings (called stomata) that allow the passage of carbon dioxide into the leaf (and of oxygen out of the leaf) for photosynthesis. Efficiency of this step (known as transpiration efficiency) can be calculated as the ratio of the mass of carbon dioxide assimilated (i.e. taken up) by photosynthesis to the quantity of water taken up by the crop and transpired. Efficiency is influenced by factors such as the species being cultivated (as different species carry out photosynthesis in different ways) or the location of the crop (e.g. the temperature/humidity where it is cultivated).
vii) Conversion of the assimilated carbon dioxide to crop biomass (i.e. the leaves, stems, roots, grains etc.). Efficiency of this step (known as biomass efficiency) can be calculated as the ratio of the crop biomass produced to the mass of carbon dioxide assimilated by photosynthesis. It could be increased by e.g. growing the crop at lower temperatures (e.g. in a cooler location or part of the year) so that loss of the assimilated carbon dioxide by respiration could be reduced (respiration, the reverse process of photosynthesis, involves the reaction of carbohydrates with oxygen to produce energy, water and carbon dioxide).
viii) Partitioning the crop biomass. Only a part (e.g. the grains) of the plant biomass produced may be of value for food and agriculture purposes. Efficiency of this step (termed yield efficiency, equivalent to the well-known agronomic term harvest index) can be calculated as the ratio of the crop biomass that ends up in the harvested yield to the crop biomass produced. The efficiency will vary according to the species involved e.g. it is almost 1 for fodder crops and about 0.5 for grain crops. It has increased over the last century as a consequence of genetic improvement.
The pathway above began with blue water stored in a reservoir and ended with harvested crop biomass for human use. Hsiao et al (2007) also use the same approach to consider rainfed crops and animal production on rangelands, two pathways involving non-irrigated water resources that begin with water inputs in the form of precipitation and end with production of crop and animal biomass respectively.
For rainfed crops, a total of seven consecutive steps can be described. The first step is the movement of water from the atmosphere into the soil. Its efficiency can be measured as the ratio of the amount of water that infiltrates the soil to the amount of water that falls as precipitation. Its efficiency can be increased by e.g. improving soil management practices (e.g. use of conservation tillage) or increasing plant canopy cover (so the momentum of rain is dissipated by the leaves before hitting the soil). The second step is the movement of water in the soil to the root zone of the crop. Its efficiency can be measured as the ratio of the amount of water retained at the root zone to the quantity of water that infiltrates the soil. The efficiency of the water use process thereafter is the same as for irrigated crop production, continuing from steps iv) to viii).
To consider the pathway of water usage for animal production on rangelands, a total of eight steps can be considered. The first six steps are the same as for rainfed cropping (i.e. beginning with the movement of water from the atmosphere into the soil and ending with the conversion of carbon dioxide assimilated by photosynthesis to plant biomass (step vii)). The next step is the consumption of the plant biomass by the animal through grazing. Efficiency of this step, calculated as the ratio of the plant biomass grazed to the plant biomass available, is influenced by factors such as the palatability of the plant material and the grazing density. The final step is the conversion of plant to animal biomass within the animals. Its efficiency can be roughly calculated as the ratio of live mass of the grazing animal to the plant biomass consumed and is influenced by factors such as the digestibility and nutritional content of the consumed plant biomass and the energy requirement of the animal for maintenance, grazing and other activities.
Similar pathways exist to describe water use in other kinds of livestock production systems and in aquaculture and forestry. For livestock production, the main use of water is for the feed and plants they consume as only a small fraction is devoted to their drinking water requirements. For aquaculture, the main uses of water are for production of feed they consume and for freshwater required in operation of aquaculture farms (Molden et al, 2007b). For forestry, most of the resources worldwide are found in natural, largely unmanaged forests and only about 5% of the forest cover is in forest plantations (defined as forest stands established by planting or/and seeding in the process of afforestation or reforestation). There is a growing use of wastewater for irrigation in forestry, in particular for hybrid poplars and eucalyptus which are effective in removal of nutrients and offer biomass from short-rotation forestry (Christersson and Verma, 2006).
5. What Role Can Biotechnologies Play?
As described in Section 1, the term biotechnology includes a broad suite of tools. They present varying degrees of technical sophistication, requiring differing levels of human capacity, infrastructure and capital inputs. They encompass techniques such as the relatively simple application of micro-organisms for pest control or as fertilisers in agriculture; the use of molecular DNA markers located close to genes affecting traits of interest (i.e. marker-assisted selection [MAS], where the traits might be genetically simple [e.g. many disease resistance traits in plants that are controlled by just one or a few genes] or complex [includes most economically important agronomic traits, which are typically influenced by many genes, so-called quantitative trait loci (QTLs), and environmental effects]); and the transfer of genes from one species into the genetic material of another species, producing transgenic or genetically modified organisms. All of these will be mentioned in this Section.
The main application of biotechnology that will be considered in this conference is in improving the efficiency of water use in agriculture and this will be discussed first. Then, two specific applications of micro-organisms in agriculture (as biofertilisers and for wastewater treatment) will be briefly discussed.
a) Improving the efficiency of water use in agriculture
As described in Section 4, to improve the efficiency of water use in agriculture, all the sequential steps in the water use pathways need to be considered in an integrated approach as it is more effective to make modest improvements in several of these steps than major improvements in just one or two steps. For some of them (e.g. involving the movement of irrigation water from the reservoir to the farm), improvements can be made by non-biological means only while others are influenced by both biological (e.g. physical characteristics of the crop) and non-biological (e.g. air temperature) factors. Several of the steps are shared in different water use pathways in agriculture. Thus steps iv) to vii) in Section 4, beginning with the availability of water retained at the root zone of the plant and ending with production of plant biomass, are common to the pathways for production of crop biomass (using either irrigation or rainfed water resources) and to animal production (through grazing and/or consumption of feed) as well as to aquaculture (when plant material is used in aquafeeds). For the steps influenced by biological processes, efforts can be made to increase their efficiency through application of conventional plant breeding and/or biotechnology tools.
Water scarcity and drought is a problem for many economically developed countries (e.g. Australia, United States) as well as many developing countries, so both public research organisations as well as private breeding companies in developed countries have invested considerable resources into investigating the genetic mechanisms controlling crop water use, albeit in a relatively limited number of crop species. While impossible to describe in detail here, a brief illustration of these advances can be provided by considering step vi) described in Section 4 i.e. involving transpiration efficiency, which describes the ratio of carbon dioxide fixation during photosynthesis relative to water loss through transpiration. Transpiration efficiency has been shown through extensive research to display significant genetic variation both within and between plant species. Using molecular markers, several potential QTLs for the trait have been detected over the last 15 years and the first one has been isolated recently, in the extensively-studied model plant species Arabidopsis thaliana (Masle et al, 2005). This erecta gene, previously known for its effects on flowering, influences transpiration efficiency in a number of ways (through e.g. an effect on the density of stomata on the leaves) and, using its DNA sequence, similar genes in species like rice, sorghum and wheat have been found. Masle et al (2005) conclude that finding the gene will "assist in designing strategies for improved transpiration efficiency under dry conditions on the one hand, and removal of stomatal limitations and increase of yield potential in well-watered conditions on the other". Several kinds of tools and approaches exist for the introgression of such genes and genomic regions into elite crop varieties that are sensitive to water scarcity (e.g. Varshney et al, 2005).
Transpiration efficiency is also influenced by the basic photosynthetic pathways used by plants i.e. whether they are C3 plants (where carbon dioxide is taken up by the plant to form molecules with 3 carbon atoms; includes most plant species e.g. rice), C4 plants (where carbon dioxide is taken up to form molecules with 4 carbon atoms; represents over 8,000 species of flowering plants e.g. corn, sugarcane, sorghum) or crassulacean acid metabolism (CAM) plants (where the C4 and C3 pathways are used at different parts of the day, e.g. cacti, pineapple). Transpiration efficiency is highest for CAM plants, which open their stomata at night when water evaporation rates are low, and are higher for C4 than C3 plants (Hsiao et al, 2007). Indeed, the International Rice Research Institute (IRRI) is interested in developing rice plants that are C4 rather than C3 (Normile, 2006).
Similarly, biotechnology can play a role in increasing the understanding and efficiency of other steps in the water use pathways. For example, for the 2nd step in the pathway described in Section 4 for rainfed crops, involving water that has infiltrated the soil moving to the root zone of the crop, the plant's roots system is clearly important and much work has been done to identify genes and biochemical pathways controlling the mechanisms of root growth (see e.g. rootgenomics.rnet.missouri.edu/prgc/index.html). Several studies have investigated QTLs for root traits (such as total root number, maximum root length) in rice and their associated effects on other drought-related traits. A small number of these studies have used MAS to introgress the desirable QTL alleles into different genetic backgrounds and these results indicate that the effect of the QTL alleles can be influenced by the genetic background (Tuberosa and Salvi, 2006).
Throughout this document, the focus so far has been on the improvement of water use efficiency, defined as output of harvestable biomass per input of water and little mention has been made so far of the many drought-related terms used in the scientific literature. Following Blum (2005), when one plant variety or species yields better than another one under a severe strain of drought, it is relatively more drought resistant. Plants can resist drought in two ways: by dehydration avoidance or dehydration tolerance. Dehydration avoidance is the plant's capacity to sustain high plant water status or cellular hydration under the effect of drought. The plant avoids being stressed through mechanisms such as enhanced capture of soil moisture (e.g. reaching deep soil moisture with a long root) or reduced water loss (e.g. having reduced plant size and/or leaf area). Reduced growth duration (with early flowering) is also an important mechanism as the plant generally uses less water and can also avoid the end of season (terminal) stress. Note, as the amount of rainfall generally varies throughout the year, the farmer can also sow in the season when water will be more plentiful for the growing crops, thus giving them the possibility of avoiding water stress. However, in some cases, there are barriers to choosing the planting season to optimise water use, and conventional breeding and biotechnology can assist here. For example, in the Central and West Asia and North Africa region, chickpea is traditionally planted in spring and drought is a major problem. Research has shown that if planted in winter, it can produce higher yields because there is more rainfall and it can escape terminal drought as it matures about a month earlier. However, for winter planting the cultivars must possess resistance to Ascochyta blight (a fungal disease that is especially damaging when the crop is sown in winter) and tolerance to cold. Cultivars for winter planting can, however, be developed using conventional breeding, MAS or genetic modification (ICARDA, 2006).
Dehydration tolerance is the plant's capacity to sustain or conserve plant function in a dehydrated state. This strategy is relatively rare, with the notable exception of a group of flowering plants called 'resurrection plants', which can withstand severe water loss and stay in the dehydrated state until water becomes available, allowing them to rehydrate and resume full physiological activities (e.g. Bartels, 2005). In general, natural and artificial selection have given a preference to dehydration avoidance over dehydration tolerance as the major strategy for plants to cope with drought stress (Blum, 2005).
The relationship between the different water-related traits is sometimes not straightforward, which has important implications for deciding what the selection goal should be. For example, although water use efficiency is often equated with drought resistance, this is not always the case. Some studies have found that differences in drought resistance among populations may not be related to differences in water use efficiency. Furthermore, Blum (2005) concludes from a review of the scientific evidence that plants achieve high water use efficiency (which is a ratio) by reducing water use (e.g. by reduced plant size, leaf area or growth duration), the denominator, rather than by increasing plant production, the numerator, and that if low water use is the breeder's target, it is highly probable that selection for the trait can be achieved by directly selecting for characteristics such as small plant size, small leaf area or reduced growth duration rather than attempting to measure water use efficiency and select for this trait.
Whether low water use, or high water use efficiency, is the breeder's target can be influenced by socio-economic factors, such as whether the cost of water is low (e.g. due to government subsidies) or whether the farmers are motivated to conserve water to be used by other people (Hsiao et al, 2007). In addition, there are differences between irrigated agriculture, where the farmer is generally interested in saving water to lower input costs or increase production, and rainfed agriculture where the farmer is generally interested in maximising use of the water that falls as precipitation in an effective and efficient way (e.g. through reducing evaporation and capturing deep soil water).
Finally, as further 'food for thought' for the debate during the upcoming e-mail conference, some of the conclusions from an important recent conference on sustaining and improving plant production under drought stress and water-limited agriculture are reproduced below (InterDrought-II, 2005):
- "As a result of the spectacular development and attraction of molecular plant biology, emphasis in research and education in plant and agriculture sciences has shifted to an appreciable extent from plant breeding, agronomy and physiology towards biotechnology and molecular biology. This has resulted in a general reduction in the expert workforce and the research/teaching infrastructure of these disciplines. Education in agronomy, soil science, plant breeding, and plant physiology is hindered in terms of available teaching capacity and studentships".
- "While basic research in plant biotechnology research towards the genetic improvement of crop productivity in water-limited conditions has expanded in recent years, the collaboration with plant breeding has been insufficient (with the exception perhaps of the private sector). This lack of collaboration hinders the delivery of biotechnology-based solutions to the end-user in the field, i.e. the farmer. There is an exponential growth of information in genomics with a proportionally minute rate of application of this information to effective problem-solving in farming under water-limited conditions".
- "At the same time, conventional plant breeding has been making well-recorded achievements in releasing improved varieties that perform relatively well under water-limited conditions, almost everywhere around the world".
- "Although substantial progress has been achieved during the past decade in our capacity to identify and clone genes and QTLs, the contribution of MAS towards improved crop production under water-limited conditions has not met the original expectations".
- "Transgenic technology is coming of age in the sense that certain genes conferring drought resistance that were identified in model organisms are now being tested in the field in transgenic crop plants, with encouraging results. Successful case histories should be duly reported and further confirmed by multidisciplinary scientific teams operating under field conditions".
b) Two specific applications of micro-organisms
Micro-organisms (or microbes) are living organisms which are microscopic in size, and include bacteria, fungi and viruses. Here, two specific applications of micro-organisms of relevance to water use in agriculture are discussed; the first regarding inoculation of crops and forest trees with mycorrhizal fungi, which can improve plant productivity in water-limited conditions, and the second regarding use of micro-organisms to improve the treatment of wastewater that can then be used e.g. in agriculture.
i) Mycorrhizal fungi
Mycorrhizae are symbiotic associations that form between the roots of plant species and fungi (see e.g. Sylvia et al, 2005). The hyphae (thread-like structures that are part of the body of the fungi) spread through the soil, taking up nutrients such as phosphorus and absorbing water, and transporting them to the plant root, and in return the fungi receive sugars from the plant. Almost all plant species form mycorrhizae. A number of different types of associations exist, of which arbuscular mycorrhizae (AM, also called vesicular-arbuscular mycorrhizae [VAM]) and ectomycorrhizae (EM) are the most widespread and economically important. In AM, the hyphae penetrate and grow within the plant root cells. The fungi that form AM are part of the Glomeromycota fungi, involving less than 200 described species, and most crops and forest trees form AM with these fungi which tend to have a broad host plant range. In EM, the hyphae of the fungi do not penetrate the plant root cells and the external surface of the roots is covered by a characteristic sheath of hyphae. Compared to AM, the fungi that form EM are more diverse, involving over 4,000 fungal species (including e.g. truffles), although the range of plant species that form EM is more limited, involving trees from just a few families, including the fir, oak and pine.
The extensive amount of research literature available on the subject (mostly on AM) indicates that mycorrhizae often have a substantive impact on water movement into, through and out of host plants, with consequent effects on plant tissue hydration and leaf physiology. They usually increase host growth rates during drought, by affecting nutrient acquisition and possibly hydration, and typically increase water use efficiency, with the effects influenced by the kind of fungi involved (Augé, 2001).
Mycorrhizal fungi can therefore be applied as a biofertiliser with the aim of increasing growth potential and reducing water and fertiliser use, and they are used in crop production, horticulture, habitat restoration, bioremediation and forestry. The mycorrhizal fungal inoculum can be applied in a number of ways e.g. by simply applying soils known to contain the desirable mycorrhizal fungi to areas lacking the fungi or using one of the many commercially available products available worldwide (Schwartz et al, 2006). Benefits, however, are not guaranteed and a number of factors have to be considered when assessing their potential application, such as competition with other soil micro-organisms as well as the dependence of the plant species on mycorrhizae, the nutrient status of the soil and the inoculum potential of the mycorrhizal fungi already present in the soil (Sylvia et al, 2005).
ii) Micro-organisms in wastewater treatment
As described in Section 3b, use of wastewater for crops, forestry and aquaculture is a reality in developing countries and treatment of the wastewater before use, although a major challenge, is important for human health and environmental considerations. In the secondary and tertiary stages of wastewater treatment, micro-organisms play an important role. According to Daims et al (2006), "biological wastewater treatment is among the most important biotechnological applications". A wide range of biotechnologies are applied here. A common one is selection of microbial cultures so they are highly efficient at carrying out a specialised task, such as degrading specific toxins in water. For example, Heesche-Wagner et al (2001) selected genetically improved bacteria by inducing genetic variation using ultraviolet radiation and then selecting for superior mutants in an environment with ever increasing concentrations of organic toxins.
Daims et al (2006) describe how molecular techniques have greatly improved the knowledge available about key micro-organisms involved in wastewater treatment processes. These techniques include fluorescence in situ hybridisation (FISH), where fluorescently labelled DNA sequences are added to bacterial cells, making it possible to identify, quantify and localise different bacterial species in complex microbial communities (e.g. in activated sludge) without having to actually cultivate the microbes. A further development of this technique, called FISH-MAR, which combines FISH with microautoradiography (MAR), also makes it possible to simultaneously analyse the physiology (e.g. what organic material they take up) and identity of uncultured micro-organisms. Daims et al (2006) describe the application of biotechnology to three specific aspects of wastewater treatment where e.g. one relates to the excessive growth of filamentous bacteria which can prevent settling of flocs during activated sludge processes (see Section 3b for more details), leading to potential operational difficulties as well as public health problems. Molecular techniques have been successfully applied to identify the filamentous micro-organisms involved and study how they function (what organic substrates they use etc.), in order to come up with solutions to the problem.
Sequencing of the genetic material (genome) is also underway or already completed for a number of specific micro-organisms involved in different aspects of wastewater treatment, such as ammonia oxidation, denitrification or nitrite oxidation (all involved in nitrogen removal) or floc/biofilm formation or bulking, both important in the activated sludge process (Daims et al, 2006). As a recent example (October 2006), the genome sequence of a key bacteria involved in the removal of phosphorus from wastewater was reported by Martín et al (2006). Availability of these sequences will improve understanding of the diverse processes involved in wastewater treatment and how they can be improved.
6. Some Issues and Questions Relevant to the Debate
As with each conference hosted by this FAO Biotechnology Forum, the focus is on application of agricultural biotechnology in developing countries. In this debate on the role of biotechnology for helping developing countries to cope with water scarcity, some of the specific questions that participants might wish to address in the e-mail conference are given below:
- A number of major strategies have been briefly described for coping with water scarcity (Section 3). Compared to them, how important is improving the efficiency of water use in crops through biotechnology in developing countries?
- Which biotechnology tools have greatest potential for improving the efficiency of water use in crops in developing countries?
- How important are biotechnology tools compared to conventional breeding for improving the efficiency of water use in crops in developing countries
- Research on water use in crops has focused on a few species of major economic importance while so-called orphan crops, of local or regional importance for nutrition and income in poor regions, have been neglected, despite their importance for food security. How can this situation be changed?
- Water use efficiency has different implications in irrigated and non-irrigated (dryland) agriculture. What can biotechnology offer developing countries in each of the two domains in terms of increasing productivity under water scarcity and improving the efficiency of use of the applied irrigation water?
- For the livestock sector, what role should biotechnology tools play in increasing the efficiency of water use in developing countries?
- For the forestry sector, what role should biotechnology tools play in increasing the efficiency of water use in developing countries?
- For aquaculture, what role should biotechnology tools play in increasing the efficiency of water use in developing countries?
- What role and relevance do biotechnologies currently have in wastewater treatment in developing countries? And in the future?
- Is the rapidly-accumulating molecular information on micro-organisms involved in wastewater treatment processes likely to result in the better design and operation of wastewater plants in developing countries?
- What role do biotechnologies have for the removal of heavy metals, such as arsenic, from irrigation water in developing countries?
- How important is application of mycorrhizal fungi as a biofertiliser in helping developing countries to cope with water scarcity?
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NB: When submitting messages (which should not exceed 600 words), participants are requested to ensure that their messages address the kinds of issues mentioned in Section 6. Before sending a message, members of the Forum are requested to have a look at the Rules of the Forum and the Guidelines for Participation in the E-mail Conferences. These were provided when joining the Forum, and they can also be found at www.fao.org/biotech/forum.asp. One important rule is that participants are assumed to be speaking in their personal capacity, unless they explicitly state that their contribution represents the views of their organisation.
ABBREVIATIONS: AM = Arbuscular mycorrhizae; CAM = Crassulacean acid metabolism; EM = Ectomycorrhizae; FAO = Food and Agriculture Organization of the United Nations; FISH = Fluorescence in situ hybridisation; GMOs = Genetically modified organisms; MAS = Marker-assisted selection; QTLs = Quantitative trait loci.
ACKNOWLEDGEMENTS: The FAO Working Group on Biotechnology expresses its grateful appreciation to the following people for their comments on the document: To Karen Frenken, Sasha Koo-Oshima and Pasquale Steduto, all from FAO's water programme, and to Abraham Blum (Plantstress.com, Israel), Robert Seviour (La Trobe University, Australia) and Rajeev Varshney (International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), India).
FAO, 2 February 2007