Crop Adaptation to Climate Change (Yadav/Crop Adaptation to Climate Change) || Energy Crops to Combat Climate Change

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BLBS082-28 BLBS082-Yadav July 12, 2011 17:18 Trim: 246mm X 189mm

Chapter 28

Energy Crops to Combat Climate ChangeAbdullah A. Jaradat

Introduction

The public interest in stabilizing the atmosphericabundance of CO2 and other greenhouse gases(GHG) and mitigating the risk of global climatechange (GCC) places new and more challeng-ing demands on agricultural productivity, landand water resources, biodiversity, environmen-tal health, and ecosystem services (IPCC 2007;Lal 2009). Biomass has the potential to becomeone of the major global primary energy sourcesduring the twenty-first century, and the futuredemand for biofuels is one component of theexpanding human demand for plant-fixed car-bon (C) (Carroll and Somerville 2009). Modernbioenergy systems will be important contributorsto future sustainable energy systems; whereas,biomass derived from dedicated energy crops(DECs) will play an important role in combat-ing GCC and will increase the share of renew-able energy sources worldwide (Muller 2009).However, using biological systems to store Cand reduce GHG emissions is a potential mit-igation approach for which equity considera-tions are complex and contentious (IPCC 2007).Nevertheless, positive impacts on ecosystem ser-vices will be more important when DECs are de-ployed on a large scale in the landscape (Oliveret al. 2009).

The amount of biofuel that can be producedglobally in an environmentally responsible wayis limited, and needs of land provide one of themajor constraints. For example, conversion offorest, grassland, and abandoned cropland to bio-fuel crops could lead to significant CO2 emis-sions and C-debt of up to several hundred years;whereas, the conversion from forest peat-landto oil palm releases about 3450 tCO2/ha over50 years and requires 420 years to pay the C-debt(IPCC 2007). Currently, only about 10% of theglobal primary energy demand is covered byrenewable resources and humans, already ap-propriate large percentages (from 20% to 90%)of potentially available biomass; therefore, thegrand challenge for biomass production is to de-velop DECs with a suite of desirable physical andchemical traits while, at least, doubling biomassproduction (IFPRI 2007).

Dedicated energy crops

The development and deployment of DECs havebeen proposed as a strategy to produce alterna-tive energy without impacting food security orthe environment (Ferre et al. 2005; Carroll andSomerville 2009). Potential DECs are mainlyperennial herbaceous and woody plants and mayinclude algae, which are typically, at least, an

Crop Adaptation to Climate Change, First Edition. Edited by Shyam S. Yadav, Robert J. Redden, Jerry L. Hatfield,Hermann Lotze-Campen and Anthony E. Hall.c© 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd.

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ENERGY CROPS TO COMBAT CLIMATE CHANGE 547

order of magnitude more productive than thefastest growing DECs. Potential DECs should beeasy to propagate and establish, capable of rapidgrowth in a wide range of environments, andhave considerable genetic diversity, especiallyfor water-use efficiency (WUE) and nitrogen-useefficiency (NUE). Moreover, DECs should havethe added benefit of providing certain ecosys-tem services, including C sequestration, biodi-versity enrichment, salinity mitigation, and en-hancement of soil and water quality. The valueof these services will depend on the particu-lar bioenergy system in question and the ref-erence land use (LU) that it displaces (Tilmanet al. 2006, 2009). However, under certain GCCscenarios (IPCC 2007), inevitably DECs willcompete with food crops for land, water, nu-trient resources, and other inputs (Searchingeret al. 2008). A significant advantage of devel-oping and using DECs is that the plants can bebred exclusively for that purpose, and they havea rich and largely untapped genetic resourcesbase to develop high-yielding cultivars (Oliveret al. 2009). This could involve development ofhigher C : N ratios, higher yields of biomass oroil, and cell wall lingo-cellulose characteristicsthat make the feedstock more amenable for pro-cessing (Boe and Beck 2008). Genetic resourcesfor the development of DECs with low re-quirements for biological, chemical, or physicalpretreatments are expected to be moreenvironment-friendly and contribute positivelyto GCC mitigation more than current energycrops (Carpita and McCann 2008).

There is already a greater variety of highlyproductive DECs that can be grown in trop-ical countries compared to those that can begrown in temperate countries. The private sec-tor is prospectively defining criteria to chooseplants with potential to serve as DECs (Carrolland Somerville 2009). The criteria include cellwall composition, growth rate, suitability ofgrowth in different eco-geographical regions,and resource-use efficiency. Some crops favoredfor investigation as DECs include: (1) cellu-losic crops, including short rotation trees and

shrubs, such as eucalyptus (Eucalyptus spp.),poplar (Populus spp.), willow (Salix spp.), andbirch (Betula spp.), (2) perennial grasses suchas giant reed (Arundo donax), reed canary grass(Phalaris arundinacea), switchgrass (Panicumvirgatum), elephant grass (Miscanthus × gigan-tus), Johnson grass (Sorghum halepense) andsweet sorghum (Sorghum bicolor), (3) nonedi-ble oil crops such as castor bean (Racinus com-munis), physic nut (Jatropha curcas), oil radish(Raphanus sativus), and pongamia (Pongamiaspp.), and (4) trees and shrubs such as souari nut(Caryocar brasilensis), buruti palm (Mauritiaflexuosa), grugri palm (Acronomia aculeate),and neem (Azadirchta indica). Short RotationCoppice (SRC) plantations are among the mostpromising DECs for bioenergy production andGCC mitigation. The SRC plantations may re-sult in more biomass and have larger potentialfor GCC mitigation than herbaceous perennialDECs; however, they can be more disturbingfor biodiversity (Carere et al. 2008; Kalita 2008;Rockwood et al. 2008).

Breeding dedicated energy crops

Breeding of DECs implies breeding for adapta-tion to long-term GCC and the replacement ofcrops having high interannual yield variabilitywith new ones having more stable yields (Bush2007), and may involve innovative plant designvia accelerated domestication (Rae et al. 2009). Itis unrealistic to assume that plantations of DECscan be started with little or no domestication;large deployment of wild species in the land-scape as energy crops is bound to lead to unfore-seeable biological and environmental problems(Howarth et al. 2009). Biomass and bioenergyyields of lignocellulosic crops could increasesignificantly over time since breeding research,including genetic modification of energy crops,is at an early phase compared with food crops(Rockwood et al. 2008).

A basic breeding program for DECs entailscollection and evaluation of genetic resources,genetic analyses, and development of criteria



548 CROP ADAPTATION TO CLIMATE CHANGE

for selection, development of novel tools forselection, and testing novel varietal concepts,and genetic improvement for biomass yield andenergy-related properties (Basha and Sujatha2007). Breeding objectives of DECs includethe improvement of biomass yield, quality, andconversion efficiency, either through selectionamong progeny obtained by crossing parentswith desirable traits, or as a way to enhancethe agronomic performance of promising mu-tants and transgenic plants (Bouton 2007). Forexample, breeders of SRC trees must reduce thenumber of years required to complete a gen-eration of testing and its deployment, improveunderstanding of the genetic control of desir-able timber traits, and produce fast-growing SRCcultivars (Sticklen 2006). Traditional breedinghas increased yield performance of perennialgrasses (e.g., switchgrass by 20–30% from exist-ing parental types) (Casler et al. 2007; Vogel andMitchell 2008), and several SRC species (Jessup2009). Breeding DECs for improved NUE, es-pecially under low N conditions, will help lowerN2O emissions (Rowe et al. 2009). Nevertheless,breeding challenges of DECs are numerous andinclude: (1) long-yield cycles (e.g., 4 years tofirst harvest of willow, then 3-year cycle for sub-sequent harvests), (2) complex genetics (dioecyin willow, polyploidy, and self incompatibilityin many grass species), (3) multiplication (rhi-zomes, tissue culture of perennial grasses such asMiscanthus), and (4) implementation of expen-sive long-term experiments involving perennialspecies and their interaction with the environ-ment (Bouton 2007; Bush 2007).

Further improvements both in genetics andagronomics, when achieved, will improvebiomass yield, conversion efficiency, and netenergy yield of DECs (Sticklen 2006; Carereet al. 2008). Self-incompatibility in some peren-nial grasses (e.g., switchgrass) may allow forthe development of high-yielding single crosshybrids, and the use of F1 hybrids would havethe potential of dramatically increasing biomassyield (Casler et al. 2007; Vogel and Mitchell2008). Transformation methods (e.g., Agrobac-terium-mediated transformation of switchgrass)

can be used to incorporate value-added genes thatcannot be transferred through crossing and se-lection. A transgene (e.g., for reduced lignincontent) should not cause environmental harm;however, an energy crop with reduced lignin con-tent may be less environmentally fit because of itsincreased pest problems and the need for chem-ical control (Bush 2007).

Heritability of biomass yield in perennialgrasses is high enough to allow plant breedersto predict and demonstrate adequate gain fromselection; however, yield gains per cycle variedfrom zero to a maximum of 6% and were notlinear across cycles (Lewandowski et al. 2000;Boe and Beck 2008). Significant breeding ad-vances have been documented in several peren-nial grass species for dry biomass yield (DBY),and the potential for increasing their DBY issignificant because of the large genetic varia-tion available within the species. For example,genotypes of Bermuda grass (Cynodon dactylonL. Pers.) bred for high DBY produced twice asmuch as the unimproved, and recent yield tri-als indicated that switchgrass yields were 50%greater than those achieved in early 2000 (Vogeland Mitchell 2008). Ligno-cellulosic yield ofperennial grasses and SRC trees parallels theirDBY, which is total yield of all harvested com-ponents with only the water removed; therefore,improvements in DBY should be part of all futurebreeding efforts (Carroll and Somerville 2009).Finally, the development of an index for instantdetermination of “energy value” can be a valu-able tool for plant breeders and growers to tailorhybrid selection and crop management to givethe highest DBY possible (Ortiz 2008). HybridDECs are feasible in the mid- to long term andwill undoubtedly enhance biomass and GCC mit-igation potential. Criteria for the developmentof novel hybrid DECs include (1) large-seededcrops with vigorous establishment to simplifybiofuel production systems, (2) delayed flower-ing through photoperiodism to enhance greaterbiomass accumulation and potentially preventseed-borne weed risks, and (3) sterility, based oncytoplasmic-, genetic-, or wide-hybridization, toenable larger bioenergy production and reduced




invasiveness potential (Grattapaglia et al. 2009).Improvement of these traits can be achievedthrough classical breeding and selection basedon existing genetic variation; whereas, trans-genic and genetic modification technologies canbe used to introduce new genes and modify ex-isting genes, or to interfere with gene expression(Gressel 2008; Grattapaglia et al. 2009).

Genomics and genetic modificationof energy crops

The next generation of DECs is being developed(Gressel 2008) by using marker-assisted breed-ing and the creation of hybrids and transgenicswith a broad portfolio of proven traits, such asDBY, plant architecture, tolerance to biotic andabiotic stresses, and NUE and WUE. Transgenicalfalfa lines, for example, yielded nearly twiceas much sugar from cell walls as wild plants.Although classical breeding and selection tech-niques have much to offer in developing new en-ergy crops; however, genetic modifications willovertake these practices to develop new crops, in-crease their productivity, and minimize their en-vironmental impact (Gressel 2008; Grattapagliaet al. 2009). Genomic information gathered fromacross the biosphere, including potential energycrops and microorganisms able to breakdownbiomass, will be vital for improving the prospectsof significant cellulosic biofuel production fromcurrent and future DECs with reduced conver-sion costs and favorable GHG profiles (Patil et al.2008; Grattapaglia et al. 2009).

Until recently, minimal effort has been di-rected toward optimizing potential DECs for theproduction of biofuels. However, genomic infor-mation and resources are being developed thatwill be essential for accelerating their domes-tication (Bouton 2007). Many of the traits tar-geted in the genomes of energy-relevant plantsfor optimization in potential cellulosic energycrops are those that would improve growth onpoor soils and minimize competition with foodcrops over LU, and affect growth rate, responseto competition for light, branching habit, stemthickness, and cell wall chemistry (Rubin 2008).

Genetic engineering could produce crop plantswith reduced biomass conversion costs by de-veloping crop cultivars with less lignin, cropsthat self-produce cellulase enzymes for cellu-lose degradation and liginase enzymes for lignindegradation, or plants that have increased cellu-lose content (i.e., polysaccharides) or an over-all larger dry biological yield using genes fordelayed flowering (Kalita 2008; Carroll andSomerville 2009).

Genetic modification could be a useful toolin developing fast-growing DECs to gain largeryields from lower inputs, and to reduce GHGemissions through lower inputs and reduced orno tillage of perennial energy crops. Geneticallymodified energy crops offer great potential forGCC adaptation and mitigation through multi-ple resistances or tolerance to biotic and abi-otic stresses, herbicides, salinity, and environ-mental toxicity (Gressel 2008). Preprocessing inplanta via expression of cellulases and cellulo-somes could potentially reduce the cost of enzy-matic saccharification of lignocellulosic biomass(Lee 1999). Alterations of the ratios and struc-tures of the various macromolecules forming thecell wall are a major target in energy crop do-mestication and development. This allows foreasy postharvest de-construction of these macro-molecules at the cost of a less rigid plant. Thegenetic engineering industry is actively seekingways of using genetic modification to simplifyand streamline processes to breakdown cellu-lose, hemicellulose, and lignin, so as to produceinexpensive and environment-friendly biofuelsmore easily and efficiently from plant biomass(Gressel 2008; Grattapaglia et al. 2009).

One of the immediate objectives of tree ge-nomic research is to identify genes for increasedC partitioning to above-ground woody matter,increased cellulose availability for enzymatic di-gestion, manipulating genes for N metabolism,delaying senescence and dormancy, increasedphotosynthesis, and adaptation to drought andsalinity. Mapping of genomes of ∼40 feedstockmodel crops, and eight energy-producer microor-ganismsis in draft form, in progress or alreadycompleted (Carroll and Somerville 2009; Jessup




2009). Genomic information and resources arebeing developed that will be essential for accel-erating their domestication. Populus trichocarpawas the first tree and potential energy crop tohave its genome sequenced (Rae et al. 2009); thealready identified quantitative trait loci (QTL)hotspots will serve as useful targets for directedbreeding for improved biomass productivity thatmay also be relevant across additional poplarhybrids.

Ediotypes of energy crops

Most traits that have been suggested to developDECs ideotypes are similar to those that used todevelop cereal ideotypes of the Green Revolutionera. However, additional traits that may provide avariety of ecosystem services, such as C seques-tration, pollination, and biodiversity conserva-tion, should be considered for the development ofDECs ideotypes (Bouton 2007; Carpita and Mc-Cann 2008). Corn and sorghum are suggested asgenetic models for the improvement of perennialC4 energy grasses. Both crops have close evolu-tionary relationship with future energy peren-nial grasses, C4 photosynthetic pathway, histor-ical depth of genetic knowledge and a rapidlygrowing resource of genetic tools. Rice (Oryzasativa) and brachypodium (Brachypodium dis-tachyon), a grass with a small genome, are alsosuggested as comparative models for grass cellbiology (Carpita and McCann 2008).

SRC is considered to be amenable to ideotypebreeding, and poplars are recognized as modelsystems for woody species with a broad geneticbase for breeding, an extensive understanding ofgenetics, biology, and physiology, the availabil-ity of sequenced genome, and a well-establishedset of molecular tools that can be used for im-provement of energy SRC and other tree species(Rockwood et al. 2008; Rae et al. 2009).

Balancing food and biofuelproduction

The growing threat of food insecurity, whichwas confounded by the emphasis on biofuels

in large parts of the world, necessitates a crit-ical appraisal of agronomic strategies needed toenhance and sustain productivity while mitigat-ing GCC, improving biodiversity, restoring wa-ter and soil quality, and improving the environ-ment (Lal 2009). Bioenergy is expected to createadditional demand for crop production; there-fore, biofuels may increase farm income and en-hance rural development. Nevertheless, the ac-tual or perceived negative impact of biofuel pro-duction on food prices may have tempered theenthusiasm about their potential to reduce GHGemissions and address energy security concerns(Rosegrant 2008). Substantial opportunities areprojected for developing countries to produceDECs (e.g., sugarcane) and transition away fromsubsistence farming largely due to lower op-portunity costs of marginal lands (Alston et al.2009); bioenergy crops would not be displacingfood or feed crops in these countries. In order tominimize adverse effects on food and feed pro-duction, it is suggested that a substantial propor-tion of bioenergy can be produced on marginallands in South America and sub-Saharan Africawhere agricultural land base can be quadrupledto accommodate DECs (Searchinger et al. 2008).

Based on current biofuel production technolo-gies, it is highly unlikely that most countrieswill be able to displace any significant share oftheir fossil fuel consumption. The United States,Canada, and Europe, for example, could displacea small portion (10%) of their gasoline consump-tion with biofuel, if they recruit 30–70% of theirrespective croplands (Rajagopal and Zilberman2007). Searchinger et al. (2008), for example,estimated that 10.8 million hectares (Mha) haveto be brought under cultivation to expand the UScorn ethanol production and produce 56 billionliters; the diversion of such land area is unlikelyand would entail significant increases in foodprices. Therefore, unless and until DEC-basedsustainable production systems on marginallands and more efficient conversion technolo-gies are developed, more productive land will bediverted for bioenergy production, especially ifeconomic incentives became available (Khanna




et al. 2009). In addition, the use of crop residues,and biomass from double or mixed cropping sys-tems, in which food and energy crops are grownon the same land, are LU options with poten-tial to produce biofuels without decreasing foodproduction or clearing natural habitats (Tilmanet al. 2009). However, these options may lead toextractive farming practices and would result inagrarian stagnation and perpetual food deficits,as was the case in sub-Saharan Africa (IFPRI2007). Retention of crop residues is essential to alarge number of ecosystem services such as C se-questration, soil and water conservation, and sus-taining soil fertility and productivity. The futureof biofuels will depend on their ability to miti-gate negative impacts on food availability and se-curity. Scientific breakthroughs and agriculturalproductivity gains similar to those realized dur-ing the last 50 years could free enough farmlandfor DEC production and, at the same time, feed apopulation of 9 billion people in 2050 (Lal 2009;Young 2009); therefore, future investments in re-search on food crops and DECs should be viewedas a policy to enhance food security.

Climate change and biofuels

The potential of bioenergy to reduce GHG emis-sions largely depends on the source of thebiomass and its LU effects (IPCC 2007). Recentstudies suggested that current bioenergy policydirectives may have negative and indirect effects,not only on food security but on local, regional,and global climate systems as well (Georgescuet al. 2009). Therefore, it is imperative to iden-tify the potential magnitude of regional temper-ature and precipitation effects due to land-usechange (LUC), and to diagnose the relativeclimate importance of the different phenolog-ical and eco-physiological variables of DECs.This information would help design schemes forspatio-temporal deployment of DECs and theirspecies and varietal composition.

The impact on local and regional climate,especially at higher latitudes, can be attributedto changes in the energy and moisture balance

of land surface following LUC, and upon con-version to large-scale DEC plantations suchas switchgrass, Miscanthus, and SRC poplars.Changes attributed to albedo variability, mini-mum canopy resistance, and rooting depth ofDECs are expected to drive local and regionalchanges in temperature and summertime rainfall(Georgescu et al. 2009). However, phenologi-cal and eco-physiological differences betweenDECs and annual bioenergy crops may revealadditional climate impacts. Therefore, not allDECs, annual bioenergy crops, or regions mayhave the same or significant impact on climate.Identifying biophysical variables and regionaldifferences will be critical to informing bio-fuel policy design that considers impact of GHGemissions as well as LUC on the climate. Recentstudies (Wise et al. 2009 and references therein)estimated that a global CO2 target of 450 ppm(IPCC 2007) would cause DECs to expand to dis-place virtually all the world’s natural forests andsavannahs by 2065, releasing up to 37 Gt of CO2

per year, if all bioenergy crops are considered Cneutral. However, based on economic consider-ations only, bioenergy could displace 59% of theworld’s natural forests and release an additional9 Gt of CO2 per year to achieve a 50% reductionin GHG emissions by 2050.

Environmental impact of biofuels

Biofuels have the potential to reduce net GHGemissions to the atmosphere through enhancedC management and may contribute to the devel-opment of a sustainable bioenergy system withpositive environmental, economic, and social im-pacts (Rowe et al. 2009). However, the impactsof biofuels on GCC, LUC, water resources, de-forestation, and energy and food security varyby feedstock, and method and location of pro-duction. These impacts can be predicted throughcomplex models based on numerous assump-tions, many of which are open to critical review(Fan et al. 2007; Tilman et al. 2009).

Biofuel production from DECs has a vari-ety of positive and negative effects on local and




regional environments, and may help relax someof the biophysical constraints on food and feedproduction. Therefore (Howarth et al. 2009), as-sessing the environmental performances of en-ergy crops and their biofuels implies covering awide range of different DECs as sources of di-verse feedstocks, conversion technologies, LUoptions, and issues related to LUC and wa-ter availability. The success of DECs is depen-dent on the proper functioning and integrity ofecosystems and particularly on ecosystem ser-vices related to soil, air, water, and biodiver-sity; therefore, DECs will have environmentaleffects beyond their impacts on GHG emissionssuch as water use and quality (Fan et al. 2007;Lal 2009). Water is needed to grow bioenergycrops and for the conversion process, which iswater intensive. One liter of ethanol producedfrom corn and sugar beets requires 3500–5800liters of water; in comparison, average daily dietin the United States and sub-Saharan Africa re-quires 5000 and 1900 liters, respectively. Thesevalues suggest that, in ∼90 years, water useby biofuel crops could exceed the total waterbeing used now by global croplands (GEMIS2009). Therefore, whether extensively or inten-sively produced, biofuels will contribute to fu-ture water shortages and quality problems due tomore LU and chemical inputs.

The overall environmental impact of bioen-ergy production is largely determined by thescale of direct and indirect LUC, whether fortotal GHG balance or the conservation of natu-ral resources and biodiversity. If land is fertileenough to grow DECs, it should be suitable togrow food crops as well (Altson et al. 2009).However, if DECs are grown on land that is un-suitable for crop production, they will be de-pendent on chemical inputs and irrigation; thesefactors will disrupt the energy balance and wouldlead to N2O emissions with the potential to over-compensate all GHG gains.

Herbaceous perennial grasses may provideimproved soil structure and function, whichwould reduce runoff and erosion risk. Grass-land ecosystems are usually more biodiversity-

friendly than cropping systems. Perennial poly-cultures offer a low-input, less polluting, andmore efficient alternative to annual monoculturesfor bioenergy production. The use of diverse na-tive perennial grasses may be a viable alterna-tive to monocultures of grass species as theyrequire fewer inputs, promote biodiversity, andreduce the risk of becoming invasive (Tilmanet al. 2006; Rowe et al. 2009). However, non-native grass species may have invasive traitsand can result in reduced biodiversity and in-creased fire hazards. Large-scale deployment ofDECs could accelerate and worsen the currentunsustainable trends of deforestation and deple-tion of natural resources; deforestation accountsfor 20% of worldwide GHG emissions (Ferreet al. 2005; Carroll and Somerville 2009). Also,many of the SRC plantations established todayare causing a range of environmental and so-cial problems, including loss of biodiversity, soilerosion, and displacement of local people (Rock-wood et al. 2008). However, there is a large bodyof data suggesting that the C benefits of bio-fuels will be eliminated, if not reversed; if in-tact, C-rich managed or natural ecosystems areconverted to biofuel production (Barbara 2007;Johnston et al. 2009).

Life cycle analysis

Energy cropping systems vary with respect tolength of plant life cycle, yields, feedstock con-version efficiencies, nutrient demand, soil C in-put, and N losses. These factors affect the magni-tude of the components contributing to net GHGfluxes and nutrient losses (Adler et al. 2007).Assessment of the GHG implications of LU andLUC to growing DECs is a very complex andcontentious issue. Life cycle analysis (LCA) isused to examine the validity of bioenergy as ameans to reduce GHG emissions (Adler et al.2007; Rowe et al. 2009). Searchinger et al. (2008)were the first to analyze the C emissions of cornethanol and account for LUC. They concludedthat adding 10.8 Mha to grow more corn forethanol would double C emissions relative to




fossil fuel over 30 years. A similar LCA study(Fargione et al. 2008) concluded that the produc-tion of food-crop ethanol in the United States,Brazil, and Southeast Asia would induce LUCthat increase C emissions from 17 to 420 timesthe annual C savings of biofuels, depending onLUC assumptions.

The Global Emission Model for IntegratedSystems (GEMIS 2009), used in conductingLCA, maintains a database for energy, mate-rial, and transport systems and includes the to-tal life cycle in its calculations of impacts. TheGlobal Emission Model for Integrated Systems(GEMIS) database covers efficiency, power, di-rect air pollutants, GHG emissions, solid wastes,liquid pollutants, and LU for each process. MostLCA studies reported mixed results of net reduc-tions in GHG emissions and fossil energy con-sumption when ethanol and biodiesel are used toreplace fossil fuels (GEMIS 2009). A few studiesexamined impacts of LUC on local air pollution,acidification, eutrophication, and ozone deple-tion, and concluded that the positive impacts onGHG emissions may carry an additional environ-mental cost (Barbara 2007; Rowe et al. 2009).Several LCA studies concluded that bioenergyis the superior LU option delivering the greatestmitigation benefits where DEC growth rates arehigh, biomass is used efficiently, initial C stocksare low, and a long-term view is taken (Bren-des et al. 2003). Land converted from row cropsto perennial DECs showed an increase in C se-questration of up to 1.1 t C/ha during five years;other studies reported increases in soil C at ratesof 0.2–1.0 t C/ha/yr for several decades (Adleret al. 2007). Nevertheless, the positive impactson GHG emissions may carry a cost in other en-vironmental areas, so that a much more carefulanalysis is needed to understand the trade-offs inany particular situation (Searchinger et al. 2008).

Economic sustainabilityof biofuels

Similar to food crops, the economic sustainabil-ity of biofuels depends on the cost of production,

the market price they command, existing poli-cies, tariffs, and mandates (IFPRI 2007; Young2009). In particular, the long-term sustainabilityof corn ethanol depends on its ability to deal withvolatility in fossil fuel and corn prices; whereas,that of cellulosic ethanol depends on the cost ofgrowing DECs, and the development of a com-mercially viable conversion and production tech-nology. However, DECs need to be competitivewith conventional crops nationally, and in caseof free trade in biofuels, internationally (Khannaet al. 2009). For example, corn ethanol in theUnited States would need to compete with theless costly and less C- and energy-intensive sug-arcane ethanol from Brazil.

The effects of future expansion of biofuelson food prices are difficult to predict or isolate;however, the growing reliance on food-basedbiofuels has already created considerable con-cern and controversy about their impact on foodprices, soil and water resources, and the environ-ment. Prices of corn, soybean, and rapeseed inthe United States and Europe increased dramati-cally due to the exhaustion of their stocks in thebioenergy industry. Although rising crop pricesmay contribute to improved welfare on the farm,they may also be capitalized into land rents andthe price of other inputs, thus reducing the benefitto farmers (IFPRI 2007). The worldwide rise incommodity prices between 2005 and 2008 wastriggered by a threefold rise in the share of cornused for ethanol production in the United Statesto 30%, while land area under corn increasedby 15% (Khanna et al. 2009). A wide range ofnegative impacts of biofuel production on cropand food prices has been reported in the litera-ture (Searchinger et al. 2008). Corn ethanol, forexample, was reported to be responsible for asmall fraction (3%) of the 43% increase in worldfood prices in 2008 (Hochman et al. 2008). How-ever, the World Bank (unpublished report) at-tributed 70% of the 140% increase in world foodprices (2002–2008) to biofuels; whereas, Roseg-rant (2008) attributed 39% of food price increaseduring the same period to biofuel demand. Nev-ertheless, the effect of higher food prices will,




necessarily, vary across countries depending onwhether these are food exporting or importingcountries.

Conclusions

DECs are set to increase in the developing aswell as the developed world and dedicated en-ergy cropping systems are expected to help off-set GHG emissions and contribute positively toGCC adaptation and mitigation efforts. How-ever, quantifying that offset is complex and con-tentious. A combination of larger yields andmore efficient processing methods are needed tomaximize the environmental benefits of DECs;they have the added benefit of providing certainecosystem services, including C sequestration,biodiversity enrichment, salinity mitigation, andenhancement of soil and water quality. The valueof these services will depend on the particularbioenergy system in question and the referenceLU that it displaces.

New genetic resources need to be evaluatedfor their potential prior to being released, and thecrops that would eventually serve as sources ofbiofuels will likely be highly genetically modi-fied from existing DEC species. Genetic modifi-cations will help simplify and streamline indus-trial processes to breakdown cellulose, hemicel-lulose, and lignin. Genetically modified DECs,which include dormant cellulose-degrading en-zymes, are a potential goal of genetic research.Nothing is known about the impact of their de-ployment at a large scale into ecosystems; there-fore, ecological concerns, as well as their im-pact on LUC and food production, should beaddressed before they are released to farmers.Research on direct production of hydrocarbonsfrom plants or microbial systems is needed todevelop energy crops with higher photon conver-sion efficiency, can couple CO2-neutral biofuelproduction with C sequestration, and producenontoxic and highly biodegradable biofuels.LCA is needed to help validate bioenergy asa means of reducing GHG emissions, and as acomprehensive strategy to understand direct andindirect impacts and interactions of a wide range

of factors on the environment. This analysis isessential in order to ensure that DECs have apositive and sustainable impact on GCC adapta-tion and mitigation efforts.

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Crop Adaptation to Climate Change (Yadav/Crop Adaptation to Climate Change) || Energy Crops to Combat Climate Change