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THE ROLE OF THE PHYTOMICROBIOME IN MAINTAINING BIOFUEL CROP PRODUCTION IN A CHANGING CLIMATE
Gayathri Ilangumaran, John R. Lamont and Donald L. Smith
Plant Science Department, McGill University/Macdonald Campus, Sainte Anne de Bellevue, QC, Canada
1.1 GENERAL BACKGROUND ON CLIMATE CHANGE
The marked increase in persistent anthropogenic changes to the biogeochemical cycles on Earth, beginning with the industrial revolution at the end of the 18th century and developing even faster with the āGreat Accelerationā of the midā20th century, has prompted a proposal for a new geological epoch termed the Anthropocene (Waters et al., 2016; Lewis and Maslin, 2015; Ogden et al., 2015; Zalasiewicz et al., 2011). The combined effects of rapid population growth, industrialization and globalization in the Anthropocene have allowed the greatest gains in standard of living ever, while also creating the most dramatic anthropogenic changes to the environment. In the relatively short duration of the Anthropocene thus far, human activity has altered numerous natural processes, including nutrient cycles, water dynamics, erosion, species extinction and global climate patterns. Of all the rapid changes associated with the Anthropocene, global climate change, as a result of fossil fuel combustion, is likely to have the most dramatic and widespread effects on the environment and human society. Anthropogenic climate change is caused, in large part by the introduction of greenhouse gases into the atmosphere through the combustion of fossil fuels. Without human intervention, the carbon contained in fossil fuels would remain sequestered in the Earth rather than being released as greenhouse gases into the atmosphere, disrupting the global carbon equilibrium established over millions of years. Greenhouse gas levels are now at about 400 ppm, the highest in human history (IPCC, 2014). Greenhouse gases cause more solar radiation to be trapped in the earthās atmosphere, as heat, raising global temperatures and adding more energy to climate systems. The effects of climate change and other Anthropocene changes pose great challenges to current and future global food and energy security (Gornall et al., 2010).
1.2 MORE EXTREME WEATHER MORE OFTEN ā MORE CROP STRESS
The effects of climate change pose a significant threat to global food security not only by increasing global surface temperatures by a predicted 1.5 to 2 Ā°C over the 20th and 21st centuries, but also by increasing the severity and frequency of extreme weather events (IPCC, 2014). Increasing heatwaves, droughts, flooding, and pest pressure impose direct stresses on crops resulting in decreased yields (Gornall et al., 2010). Likewise, climate change is projected to increase desertification (Salinas and Mendieta, 2013), soil salinization (Dasgupta et al., 2015), soil erosion (Burt et al., 2015) and sea level rise (Church et al., 2013), leading to an overall decrease in arable land. All regions will be affected by changes in extreme weather patterns, however, the type of extreme weather will vary between regions. There will be increased rainfall in the tropics and at high latitudes, drying in the subtropics and midālatitudes and increases in extreme precipitation events in the tropics and midālatitudes (IPCC, 2014).
Competition for remaining arable land, increased food demand from a growing population, and growing needs for biofuels will likely push more production to marginal lands, leading to still more stresses on crops (ColemanāDerr and Tringe, 2014; Kang et al., 2014). Competition for other vital resources such as water (Falkenmark, 2013; Famiglietti, 2014; Lal, 2015) and phosphorus (Cordell and White, 2011; Scholz, 2013) are likely to impose further limitations on agricultural production (Odegard and Van der Voet, 2014) and still more stress on crops. To meet the food, fiber and biofuel needs of a growing population, technologies and practices to maximize production under these stressful conditions must be developed. Moreover, the International Panel on Climate Change (IPCC, 2014) recommends mitigation leading to GHG atmospheric levels of only about 450 ppm by 2100 (a 40 to 70% reduction in GHG emissions by 2050 relative to 2010) to keep global warming below 2 Ā°C above preāindustrial temperatures. The International Energy Agency released data from 2014 and 2015 that showed a leveling off of global energyārelated CO2 emissions, suggesting policies enacted to reduce the use of coal and increase the use of renewable energy sources are beginning to yield tangible results (International Energy Agency, 2015). Agricultural activity is a significant source of GHG emissions and measures can be taken to reduce its contribution to climate change (Beach et al., 2016; Bennetzen et al., 2016), such as using low input technologies that can ensure adequate yields without contributing further to GHG emissions. Such actions will be critical in mitigating future climate change (IPCC, 2014).
1.3 BIOFUEL CROPS ā ALTERNATIVE TO FOSSIL FUELS
The growing demand for energy (transportation, household and industry) and negative impacts of most widely used fossil fuels (greenhouse gas emissions and organic pollutants) has led to the development and usage of renewable energy sources including biofuels. Biomass production for biofuel is also driven by political and environmental goals around the globe, amid growing concern over renewable energy and climate change. The United States renewable fuels standard program (RFS2) mandated that by 2022 at least 36 billion gallons of biofuel must be blended to automobile fuel including 16 billion gallons per year from cellulosic biofuels (U.S. EPA, 2010). Likewise, the European Union has set a 10% target of overall petrol consumption in transportation fuels to be replaced by biofuels by 2020 (Commission of the European Committees, 2007). Ethanol is the most common biofuel produced from fermentation of grains containing sugarārich compounds. However, ethanol production is not sufficient to meet demands for energy and its production from materials such as sugar and starch has raised food security issues. Development of second generation biofuels, which use cellulosic feedstock obtained from biomass of dedicated energy crops, or crop residues and other biomass, is now an area of active research. Advanced biofuels support agriculture and forestry activities through cultivation of energy crops, and lead to reduced greenhouse gas emissions, as compared to petroleum, by 86% (Wang et al., 2007). They are expected to offer better environmental performance in terms of reduced emissions from the biofuel production supply chains. Only demonstration biorefineries producing advanced biofuels are currently operational and production economics must be optimized. Bioconversion of lignocellulose is complex, involving enzymatic hydrolysis of both glucose from cellulose and pentose sugars (xylose, arabinose) from hemiācellulose, followed by fermentation. These advanced biofuels are not commercially widely available yet; however bioenergy production goals have to be met with consideration of land use, environmental risks, ecosystem functions, mitigating climate change and sustainability. Manipulation of plantāmicrobe interactions will provide opportunities to optimize production from bioāenergy crops.
1.4 AVOIDING COMPETITION WITH FOOD PRODUCTION
Food and forage crops, notably sugarcane, corn and sorghum are grown on agricultural lands for bioethanol production, which could have been otherwise used for human consumption, and this is a major concern for food security; if food production levels are to be maintained, new land resources have to be brought under cultivation in order to grow biofuel crops. Plants that provide simple sugars, which can be easily converted to ethanol are widely cultivated as biofuel crops. Since the majority of them (maize, sugar cane and sugar beet) are grown on agriculture lands, they require extensive inputs and compete with food production. Production of these crops are being studied to evaluate their tolerance to varied climatic conditions and avoid competition with food production during the growing season. In one such study, sugar beet was grown as a winter crop in the Southeast USA, planted in autumn and harvested in spring, with variable yields, but potentially equivalent to that of summer production in Midwest USA (Webster et al., 2016).
Utilization of marginally productive crop lands is becoming an attractive alternative for growing bioenergy crops (Albanito et al., 2016). Ma...
