FACE-ing the global change: Opportunities for improvement in photosynthetic radiation use efficiency and crop yield

The earth is rapidly changing through processes such as rising [CO₂], [O₃], and increased food demand. By 2050 the projected atmospheric [CO₂] and ground level [O₃] will be 50% and 20% higher than today. To meet future agricultural demand, amplified by an increasing population and economic progress in developing countries, crop yields will have to increase by at least 50% by the middle of the century. FACE (Free Air Concentration Enrichment) experiments have been conducted for more than 20 years in various parts of world to estimate, under the most realistic agricultural conditions possible, the impact of the CO₂ levels projected for the middle of this century on crops. The stimulations of crop seed yields by the projected CO₂ levels across FACE studies are about 18% on average and up to 30% for the hybrid rice varieties and vary among crops, cultivars, nitrogen levels and soil moisture. The observed increase in crop yields under the projected CO₂ levels fall short of what would be required to meet the projected future food demand, even with the most responsive varieties. Crop biomass production and seed yield is the product of photosynthetic solar energy conversion. Improvement in photosynthetic radiation use efficiency stands as the most promising opportunity allowing for major increases in crop yield in a future that portends major changes in climate and crop growing environments. Our advanced understanding of the photosynthetic process along with rapidly advancing capabilities in functional genomics, genetic transformation and synthetic biology promises new opportunities for crop improvement by greater photosynthesis and crop yield. Traits and genes that show promise for improving photosynthesis are briefly reviewed, including enhancing leaf photosynthesis capacity and reducing photorespiration loss, manipulating plant hormones’ responses for better ideotypes, extending duration of photosynthesis, and increasing carbon partitioning to the sink to alleviate feedback inhibition of photosynthesis.     

Closing Yield Gaps: How Sustainable Can We Be?

Global food production needs to be increased by 60–110% between 2005 and 2050 to meet growing food and feed demand. Intensification and/or expansion of agriculture are the two main options available to meet the growing crop demands. Land conversion to expand cultivated land increases GHG emissions and impacts biodiversity and ecosystem services. Closing yield gaps to attain potential yields may be a viable option to increase the global crop production. Traditional methods of agricultural intensification often have negative externalities. Therefore, there is a need to explore location-specific methods of sustainable agricultural intensification. We identified regions where the achievement of potential crop calorie production on currently cultivated land will meet the present and future food demand based on scenario analyses considering population growth and changes in dietary habits. By closing yield gaps in the current irrigated and rain-fed cultivated land, about 24% and 80% more crop calories can respectively be produced compared to 2000. Most countries will reach food self-sufficiency or improve their current food self-sufficiency levels if potential crop production levels are achieved. As a novel approach, we defined specific input and agricultural management strategies required to achieve the potential production by overcoming biophysical and socioeconomic constraints causing yield gaps. The management strategies include: fertilizers, pesticides, advanced soil management, land improvement, management strategies coping with weather induced yield variability, and improving market accessibility. Finally, we estimated the required fertilizers (N, P₂O₅, and K₂O) to attain the potential yields. Globally, N-fertilizer application needs to increase by 45–73%, P₂O₅-fertilizer by 22–46%, and K₂O-fertilizer by 2–3 times compared to the year 2010 to attain potential crop production. The sustainability of such agricultural intensification largely depends on the way management strategies for closing yield gaps are chosen and implemented.     

Agricultural biotechnology for crop improvement in a variable climate: hope or hype?

Developing crops that are better adapted to abiotic stresses is important for food production in many parts of the world today. Anticipated changes in climate and its variability, particularly extreme temperatures and changes in rainfall, are expected to make crop improvement even more crucial for food production. Here, we review two key biotechnology approaches, molecular breeding and genetic engineering, and their integration with conventional breeding to develop crops that are more tolerant of abiotic stresses. In addition to a multidisciplinary approach, we also examine some constraints that need to be overcome to realize the full potential of agricultural biotechnology for sustainable crop production to meet the demands of a projected world population of nine billion in 2050.     

The Role of Latin America’s Land and Water Resources for Global Food Security: Environmental Trade-Offs of Future Food Production Pathways

One of humanity’s major challenges of the 21st century will be meeting future food demands on an increasingly resource constrained-planet. Global food production will have to rise by 70 percent between 2000 and 2050 to meet effective demand which poses major challenges to food production systems. Doing so without compromising environmental integrity is an even greater challenge. This study looks at the interdependencies between land and water resources, agricultural production and environmental outcomes in Latin America and the Caribbean (LAC), an area of growing importance in international agricultural markets. Special emphasis is given to the role of LAC’s agriculture for (a) global food security and (b) environmental sustainability. We use the International Model for Policy Analysis of Agricultural Commodities and Trade (IMPACT)—a global dynamic partial equilibrium model of the agricultural sector—to run different future production scenarios, and agricultural trade regimes out to 2050, and assess changes in related environmental indicators. Results indicate that further trade liberalization is crucial for improving food security globally, but that it would also lead to more environmental pressures in some regions across Latin America. Contrasting land expansion versus more intensified agriculture shows that productivity improvements are generally superior to agricultural land expansion, from an economic and environmental point of view. Finally, our analysis shows that there are trade-offs between environmental and food security goals for all agricultural development paths.     

The role of community and population ecology in applying mycorrhizal fungi for improved food security

The global human population is expected to reach ∼9 billion by 2050. Feeding this many people represents a major challenge requiring global crop yield increases of up to 100%. Microbial symbionts of plants such as arbuscular mycorrhizal fungi (AMF) represent a huge, but unrealized resource for improving yields of globally important crops, especially in the tropics. We argue that the application of AMF in agriculture is too simplistic and ignores basic ecological principals. To achieve this challenge, a community and population ecology approach can contribute greatly. First, ecologists could significantly improve our understanding of the determinants of the survival of introduced AMF, the role of adaptability and intraspecific diversity of AMF and whether inoculation has a direct or indirect effect on plant production. Second, we call for extensive metagenomics as well as population genomics studies that are crucial to assess the environmental impact that introduction of non-local AMF may have on native AMF communities and populations. Finally, we plead for an ecologically sound use of AMF in efforts to increase food security at a global scale in a sustainable manner.     

Possible changes to arable crop yields by 2050

By 2050, the world population is likely to be 9.1 billion, the CO₂ concentration 550 ppm, the ozone concentration 60 ppb and the climate warmer by ca 2°C. In these conditions, what contribution can increased crop yield make to feeding the world?CO₂ enrichment is likely to increase yields of most crops by approximately 13 per cent but leave yields of C4 crops unchanged. It will tend to reduce water consumption by all crops, but this effect will be approximately cancelled out by the effect of the increased temperature on evaporation rates. In many places increased temperature will provide opportunities to manipulate agronomy to improve crop performance. Ozone concentration increases will decrease yields by 5 per cent or more.Plant breeders will probably be able to increase yields considerably in the CO₂-enriched environment of the future, and most weeds and airborne pests and diseases should remain controllable, so long as policy changes do not remove too many types of crop-protection chemicals. However, soil-borne pathogens are likely to be an increasing problem when warmer weather will increase their multiplication rates; control is likely to need a transgenic approach to breeding for resistance. There is a large gap between achievable yields and those delivered by farmers, even in the most efficient agricultural systems. A gap is inevitable, but there are large differences between farmers, even between those who have used the same resources. If this gap is closed and accompanied by improvements in potential yields then there is a good prospect that crop production will increase by approximately 50 per cent or more by 2050 without extra land. However, the demands for land to produce bio-energy have not been factored into these calculations.     

An Integrated Approach to Crop Genetic Improvement

The balance between the supply and demand of the major food crops is fragile,fueling concerns for long-term global food security.The rising population,increasing wealth and a proliferation of nonfood uses(e.g.bioenergy) has led to growing demands on agriculture,while increased production is limited by greater urbanization,and the degradation of land.Furthermore,global climate change with increasing temperatures and lower,more erratic rainfall is projected to decrease agricultural yields.There is a predicted need to increase food production by at least 70% by 2050 and therefore an urgent need to develop novel and integrated approaches,incorporating high-throughput phenotyping that will both increaseproduction per unit area and simultaneously improve the resource use efficiency of crops.Yield potential,yield stability,nutrient and water use are all complex multigenic traits and while there is genetic variability,their complexity makes such traits difficult to breed for directly.Nevertheless molecular plant breeding has the potential to deliver substantial improvements,once the component traits and the genes underlying these traits have been identified.In addition,interactions between the individual traits must also be taken into account,a demand that is difficult to fulfill with traditional screening approaches.Identified traits will be incorporated into new cultivars using conventional or biotechnological tools.In order to better understand the relationship between genotype,component traits,and environment over time,a multidisciplinary approach must be adopted to both understand the underlying processes and identify candidate genes,QTLs and traits that can be used to develop improved crops.     

Increasing global agricultural production by reducing ozone damages via methane emission controls and ozone‐resistant cultivar selection

Meeting the projected 50% increase in global grain demand by 2030 without further environmental degradation poses a major challenge for agricultural production. Because surface ozone (O₃) has a significant negative impact on crop yields, one way to increase future production is to reduce O₃‐induced agricultural losses. We present two strategies whereby O₃ damage to crops may be reduced. We first examine the potential benefits of an O₃ mitigation strategy motivated by climate change goals: gradual emission reductions of methane (CH₄), an important greenhouse gas and tropospheric O₃ precursor that has not yet been targeted for O₃ pollution abatement. Our second strategy focuses on adapting crops to O₃ exposure by selecting cultivars with demonstrated O₃ resistance. We find that the CH₄ reductions considered would increase global production of soybean, maize, and wheat by 23–102 Mt in 2030 – the equivalent of a ~2–8% increase in year 2000 production worth $3.5–15 billion worldwide (USD₂₀₀₀), increasing the cost effectiveness of this CH₄ mitigation policy. Choosing crop varieties with O₃ resistance (relative to median‐sensitivity cultivars) could improve global agricultural production in 2030 by over 140 Mt, the equivalent of a 12% increase in 2000 production worth ~$22 billion. Benefits are dominated by improvements for wheat in South Asia, where O₃‐induced crop losses would otherwise be severe. Combining the two strategies generates benefits that are less than fully additive, given the nature of O₃ effects on crops. Our results demonstrate the significant potential to sustainably improve global agricultural production by decreasing O₃‐induced reductions in crop yields.     

Traversing the mountaintop: world fossil fuel production to 2050

During the past century, fossil fuels—petroleum liquids, natural gas and coal—were the dominant source of world energy production. From 1950 to 2005, fossil fuels provided 85–93% of all energy production. All fossil fuels grew substantially during this period, their combined growth exceeding the increase in world population. This growth, however, was irregular, providing for rapidly growing per capita production from 1950 to 1980, stable per capita production from 1980 to 2000 and rising per capita production again after 2000. During the past half century, growth in fossil fuel production was essentially limited by energy demand. During the next half century, fossil fuel production will be limited primarily by the amount and characteristics of remaining fossil fuel resources. Three possible scenarios—low, medium and high—are developed for the production of each of the fossil fuels to 2050. These scenarios differ primarily by the amount of ultimate resources estimated for each fossil fuel. Total fossil fuel production will continue to grow, but only slowly for the next 15–30 years. The subsequent peak plateau will last for 10–15 years. These production peaks are robust; none of the fossil fuels, even with highly optimistic resource estimates, is projected to keep growing beyond 2050. World fossil fuel production per capita will thus begin an irreversible decline between 2020 and 2030.     

Do We Produce Enough Fruits and Vegetables to Meet Global Health Need?

Background

Low fruit and vegetable (FV) intake is a leading risk factor for chronic disease globally, but much of the world’s population does not consume the recommended servings of FV daily. It remains unknown whether global supply of FV is sufficient to meet current and growing population needs. We sought to determine whether supply of FV is sufficient to meet current and growing population needs, globally and in individual countries.

Methods and Findings

We used global data on agricultural production and population size to compare supply of FV in 2009 with population need, globally and in individual countries. We found that the global supply of FV falls, on average, 22% short of population need according to nutrition recommendations (supply:need ratio: 0.78 [Range: 0.05–2.01]). This ratio varies widely by country income level, with a median supply:need ratio of 0.42 and 1.02 in low-income and high-income countries, respectively. A sensitivity analysis accounting for need-side food wastage showed similar insufficiency, to a slightly greater extent (global supply:need ratio: 0.66, varying from 0.37 [low-income countries] to 0.77 [high-income countries]). Using agricultural production and population projections, we also estimated supply and need for FV for 2025 and 2050. Assuming medium fertility and projected growth in agricultural production, the global supply:need ratio for FV increases slightly to 0.81 by 2025 and to 0.88 by 2050, with similar patterns seen across country income levels. In a sensitivity analysis assuming no change from current levels of FV production, the global supply:need ratio for FV decreases to 0.66 by 2025 and to 0.57 by 2050.

Conclusion

The global nutrition and agricultural communities need to find innovative ways to increase FV production and consumption to meet population health needs, particularly in low-income countries.     

The dichotomy of yield and drought resistance: Translation challenges from basic research to crop adaptation to climate change

Global climate change and the increasing human population require crop varieties with higher yield and draught resistance. But meeting both goals is not an easy task for breeders and plant science.

The human population is increasing and so does the demand on food production. The Food and Agriculture Organization of the United Nations (FAO) predicts that in order to meet the global food demands by 2050, the production of staple cereal crops must be doubled at least (FAO, 2017), which means that the current rate of yield improvement needs to increase by at least 40%. Crop breeders are expected to cope with this challenge and come up with novel high‐yield varieties, but the prospects of even maintaining the current rate of yield improvement in light of climate change are unclear. To meet the growing demand for food and increase the yield of staple crops, we need a better understanding of how plants adapt to environmental factors that limit their productivity in terms of turning sunlight and CO₂ into tissues and seeds.

To meet the growing demand for food and increase the yield of staple crops, we need a better understanding of how plants adapt to environmental factors that limit their productivity…

Although nature provides many examples of how plants adapt to harsh environments, these are rarely suitable for use in an agronomic environment, mainly owing to the economics: Any stress‐tolerance variety must also be profitable for the farmer. If a stress response mechanism enables the plant to survive but reduces yield, it will not be economical and, therefore, not be used by farmers. Thus, understanding the key parameters limiting crop yield—plant‒environment interactions, in particular—will help us to cope with the food security challenges presented by changing environmental conditions. In particular, this knowledge helps to inform breeding programmes to more efficiently create and screen for crop varieties to meet the challenges of population growth and climate change. This is not an easy task.Plants are autotrophic; sessile organisms and their productivity completely depends on the temperature, light levels, and the availability of inorganic substances in the soil. Terrestrial plants are further, and primarily, limited by the availability of water, as the absorption of CO₂ from the air requires water: A few hundred water molecules are lost for each CO₂ molecule absorbed. Therefore, understanding the mechanisms that maintain water balance is critical for optimizing crop growth and fruit production in any given environment.     

Genome Elimination: Translating Basic Research into a Future Tool for Plant Breeding

During the course of our history, humankind has been through different periods of agricultural improvement aimed at enhancing our food supply and the performance of food crops. In recent years, it has become apparent that future crop improvement efforts will require new approaches to address the local challenges of farmers while empowering discovery across industry and academia. New plant breeding approaches are needed to meet this challenge to help feed a growing world population. Here I discuss how a basic research discovery is being translated into a potential future tool for plant breeding, and share the story of researcher Simon Chan, who recognized the potential application of this new approach—genome elimination—for the breeding of staple food crops in Africa and South America.

This article is part of the PLOS Biology Collection “The Promise of Plant Translational Research.”

     

Decreasing,not increasing,leaf area will raise crop yields under global atmospheric change

Without new innovations, present rates of increase in yields of food crops globally are inadequate to meet the projected rising food demand for 2050 and beyond. A prevailing response of crops to rising [CO₂] is an increase in leaf area. This is especially marked in soybean, the world's fourth largest food crop in terms of seed production, and the most important vegetable protein source. Is this increase in leaf area beneficial, with respect to increasing yield, or is it detrimental? It is shown from theory and experiment using open‐air whole‐season elevation of atmospheric [CO₂] that it is detrimental not only under future conditions of elevated [CO₂] but also under today's [CO₂]. A mechanistic biophysical and biochemical model of canopy carbon exchange and microclimate (MLCan) was parameterized for a modern US Midwest soybean cultivar. Model simulations showed that soybean crops grown under current and elevated (550 [ppm]) [CO₂] overinvest in leaves, and this is predicted to decrease productivity and seed yield 8% and 10%, respectively. This prediction was tested in replicated field trials in which a proportion of emerging leaves was removed prior to expansion, so lowering investment in leaves. The experiment was conducted under open‐air conditions for current and future elevated [CO₂] within the Soybean Free Air Concentration Enrichment facility (SoyFACE) in central Illinois. This treatment resulted in a statistically significant 8% yield increase. This is the first direct proof that a modern crop cultivar produces more leaf than is optimal for yield under today's and future [CO₂] and that reducing leaf area would give higher yields. Breeding or bioengineering for lower leaf area could, therefore, contribute very significantly to meeting future demand for staple food crops given that an 8% yield increase across the USA alone would amount to 6.5 million metric tons annually.     

Origins of food crops connect countries worldwide

Research into the origins of food plants has led to the recognition that specific geographical regions around the world have been of particular importance to the development of agricultural crops. Yet the relative contributions of these different regions in the context of current food systems have not been quantified. Here we determine the origins (‘primary regions of diversity’) of the crops comprising the food supplies and agricultural production of countries worldwide. We estimate the degree to which countries use crops from regions of diversity other than their own (‘foreign crops’), and quantify changes in this usage over the past 50 years. Countries are highly interconnected with regard to primary regions of diversity of the crops they cultivate and/or consume. Foreign crops are extensively used in food supplies (68.7% of national food supplies as a global mean are derived from foreign crops) and production systems (69.3% of crops grown are foreign). Foreign crop usage has increased significantly over the past 50 years, including in countries with high indigenous crop diversity. The results provide a novel perspective on the ongoing globalization of food systems worldwide, and bolster evidence for the importance of international collaboration on genetic resource conservation and exchange.     

Sparing land for nature: exploring the potential impact of changes in agricultural yield on the area needed for crop production

How can rapidly growing food demands be met with least adverse impact on nature? Two very different sorts of suggestions predominate in the literature: wildlife‐friendly farming, whereby on‐farm practices are made as benign to wildlife as possible (at the potential cost of decreasing yields); and land‐sparing, in which farm yields are increased and pressure to convert land for agriculture thereby reduced (at the potential cost of decreasing wildlife populations on farmland). This paper is about one important aspect of the land‐sparing idea – the sensitivity of future requirements for cropland to plausible variation in yield increases, relative to other variables. Focusing on the 23 most energetically important food crops, we use data from the Food and Agriculture Organisation (FAO) and the United Nations Population Division (UNPD) to project plausible values for 2050 for population size, diet, yield, and trade, and then look at their effect on the area needed to meet demand for the 23 crops, for the developing and developed worlds in turn. Our calculations suggest that across developing countries, the area under those crops will need to increase very considerably by 2050 (by 23% under intermediate projections), and that plausible variation in average yield has as much bearing on the extent of that expansion as does variation in population size or per capita consumption; future cropland area varies far less under foreseeable variation in the net import of food from the rest of the world. By contrast, cropland area in developed countries is likely to decrease slightly by 2050 (by 4% under intermediate projections for those 23 crops), and will be less sensitive to variation in population growth, diet, yield, or trade. Other contentious aspects of the land‐sparing idea require further scrutiny, but these results confirm its potential significance and suggest that conservationists should be as concerned about future agricultural yields as they are about population growth and rising per capita consumption.     

Plastid biotechnology for crop production: present status and future perspectives

The world population is expected to reach an estimated 9.2 billion by 2050. Therefore, food production globally has to increase by 70% in order to feed the world, while total arable land, which has reached its maximal utilization, may even decrease. Moreover, climate change adds yet another challenge to global food security. In order to feed the world in 2050, biotechnological advances in modern agriculture are essential. Plant genetic engineering, which has created a new wave of global crop production after the first green revolution, will continue to play an important role in modern agriculture to meet these challenges. Plastid genetic engineering, with several unique advantages including transgene containment, has made significant progress in the last two decades in various biotechnology applications including development of crops with high levels of resistance to insects, bacterial, fungal and viral diseases, different types of herbicides, drought, salt and cold tolerance, cytoplasmic male sterility, metabolic engineering, phytoremediation of toxic metals and production of many vaccine antigens, biopharmaceuticals and biofuels. However, useful traits should be engineered via chloroplast genomes of several major crops. This review provides insight into the current state of the art of plastid engineering in relation to agricultural production, especially for engineering agronomic traits. Understanding the bottleneck of this technology and challenges for improvement of major crops in a changing climate are discussed.     

Carbon assimilation in crops at high temperatures

Global temperatures are rising, and higher rates of temperature increase are projected over land areas that encompass the globe's major agricultural regions. In addition to increased growing season temperatures, heat waves are predicted to become more common and severe. High temperatures can inhibit photosynthetic carbon gain of crop plants and thus threaten productivity, the effects of which may interact with other aspects of climate change. Here, we review the current literature assessing temperature effects on photosynthesis in key crops with special attention to field studies using crop canopy heating technology and in combination with other climate variables. We also discuss the biochemical reactions related to carbon fixation that may limit crop photosynthesis under warming temperatures and the current strategies for adaptation. Important progress has been made on several adaptation strategies demonstrating proof‐of‐concept for translating improved photosynthesis into higher yields. These are now poised to test in important food crops.     

Potential and attainable food production and food security in different regions

Growing prosperity in the South is accompanied by human diets that will claim more natural resources per capita. This reality, combined with growing populations, may raise the global demand for food crops two- to four-fold within two generations. Considering the large volume of natural resources and potential crop yields, it seems that this demand can be met smoothly. However, this is a fallacy for the following reasons. (i) Geographic regions differ widely in their potential food security: policy choices for agricultural use of natural resources are limited in Asia. For example, to ensure national self-sufficiency and food security, most of the suitable land (China) and nearly all of the surface water (India) are needed. Degradation restricts options further. (ii) The attainable level of agricultural production depends also on socio-economic conditions. Extensive poverty keeps the attainable food production too low to achieve food security, even when the yield gap is wide, as in Africa. (iii) Bio-energy, non-food crops and nature compete with food crops for natural resources. Global and regional food security are attainable, but only with major efforts. Strategies to achieve alternative aims will be discussed. <br>     

Smaller than predicted increase in aboveground net primary production and yield of field-grown soybean under fully open-air [CO2] elevation

The Intergovernmental Panel on Climate Change projects that atmospheric [CO₂] will reach 550 ppm by 2050. Numerous assessments of plant response to elevated [CO₂] have been conducted in chambers and enclosures, with only a few studies reporting responses in fully open‐air, field conditions. Reported yields for the world's two major grain crops, wheat and rice, are substantially lower in free‐air CO₂ enrichment (FACE) than predicted from similar elevated [CO₂] experiments within chambers. This discrepancy has major implications for forecasting future global food supply. Globally, the leguminous‐crop soybean (Glycine max (L.) Merr.) is planted on more land than any other dicotyledonous crop. Previous studies have shown that total dry mass production increased on average 37% in response to increasing [CO₂] to approximately 700 ppm, but harvestable yield will increase only 24%. Is this representative of soybean responses under open‐air field conditions? The effects of elevation of [CO₂] to 550 ppm on total production, partitioning and yield of soybean over 3 years are reported. This is the first FACE study of soybean ( http://www.soyface.uiuc.edu ) and the first on crops in the Midwest of North America, one of the major food production regions of the globe. Although increases in both aboveground net primary production (17–18%) and yield (15%) were consistent across three growing seasons and two cultivars, the relative stimulation was less than projected from previous chamber experiments. As in previous studies, partitioning to seed dry mass decreased; however, net production during vegetative growth did not increase and crop maturation was delayed, not accelerated as previously reported. These results suggest that chamber studies may have over‐estimated the stimulatory effect of rising [CO₂], with important implications on global food supply forecasts.