Bioenergy to save the world

Novel Energy Plants Subject Area 5.2

196© Springer-Verlag 2008

Env Sci Pollut Res 1515151515 (3) 196 – 204 (2008)

Area 5.2 • GMOs, Bio-Products, Bio-Processing

Discussion Article

Bioenergy to Save the WorldProducing novel energy plants for growth on abandoned land*

Peter Schröder1*, Rolf Herzig2, Bojin Bojinov3, Ann Ruttens4, Erika Nehnevajova2, Stamatis Stamatiadis5,Abdul Memon6, Andon Vassilev7, Mario Caviezel8 and Jaco Vangronsveld4

1 Helmholtz-Zentrum München, German Research Center for Environmental Health, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany2 Phytotech-Foundation, Quartiergasse 12, 3013 Bern, Switzerland3 Dept. Plant Plant Genetics, Agricultural University of Plovdiv, Mendeleev Str., 4000 Plovdiv, Bulgaria4 Universiteit Hasselt, Campus Diepenbeek, Environmental Biology, Agoralaan, Building D, 3590 Diepenbeek, Belgium5 Soil Ecology and Biotechnology Laboratory, GAIA Environmental Research and Education Center, Kifissia, Greece6 TUBITAK Research Institute for Genetic Engineering and Biotechnology, Gebze, Turkey7 Dept. Plant Physiolgy and Biochemistry, Agricultural University of Plovdiv, Mendeleev Str., 4000 Plovdiv, Bulgaria8 CTU Konzepte Technik und Umwelt, Buerglistr. 29, 8400 Winterthur, Switzerland

* Corresponding author: Prof. Dr. Peter Schröder, Helmholtz-Zentrum-München, German Research Center for Environmental Health,Ingolstädter Landstraße 1, 85764 Neuherberg, Germany ([email protected])

for the fermentation in decentralized biogas reactors, and theresulting nitrogen rich manure can be distributed on the fieldsto improve the soil.

Discussion. Such an approach will open new economic perspec-tives to small farmers, and provide a clever way to self sufficientand sustainable rural development. Together with the presenteconomic reality, where energy and raw material prices havedrastically increased over the last decade, they necessitate thedevelopment and the establishment of alternative concepts.

Conclusions. Biotechnology is available to apply fast breedingto promising energy plant species. It is important that our valu-able arable land is preserved for agriculture. The opportunity toswitch from low-income agriculture to biogas production mayconvince small farmers to adhere to their business and by thatpreserve the identity of rural communities.

Perspectives. Overall, biogas is a promising alternative for thefuture, because its resource base is widely available, and singlefarms or small local cooperatives might start biogas plant op-eration.

Keywords: Agriculture; bioenergy; biogas; biomass; CO2 lev-els; energy plants; fossil fuels; greenhouse gases; Kyoto protocol

OpenChoice

DOI: http://dx.doi.org/10.1065/espr2008.03.481

Please cite this paper as: Schröder P, Herzig R, Bojinov B,Ruttens A, Nehnevajova E, Stamatiadis S, Memon A, VassilevA, Caviezel M, Vangronsveld J (2008): Bioenergy to Save theWorld. Producing novel energy plants for growth on abandonedland. Env Sci Pollut Res 15 (3) 196–204

Abstract

Background and Aim. Following to the 2006 climate summit,the European Union formally set the goal of limiting globalwarming to 2 degrees Celsius. But even today, climate change isalready affecting people and ecosystems. Examples are meltingglaciers and polar ice, reports about thawing permafrost areas,dying coral reefs, rising sea levels, changing ecosystems and fatalheat periods. Within the last 150 years, CO2 levels rose from280 ppm to currently over 400 ppm. If we continue on our presentcourse, CO2 equivalent levels could approach 600 ppm by 2035.However, if CO2 levels are not stabilized at the 450−550 ppmlevel, the consequences could be quite severe. Hence, if we do notact now, the opportunity to stabilise at even 550 ppm is likely toslip away. Long-term stabilisation will require that CO2 emis-sions ultimately be reduced to more than 80% below currentlevels. This will require major changes in how we operate.

Results. Reducing greenhouse gases from burning fossil fuelsseems to be the most promising approach to counterbalance thedramatic climate changes we would face in the near future. It isclear since the Kyoto protocol that the availability of fossil car-bon resources will not match our future requirements. Further-more, the distribution of fossil carbon sources around the globemakes them an even less reliable source in the future. We pro-pose to screen crop and non-crop species for high biomass pro-duction and good survival on marginal soils as well as to pro-duce mutants from the same species by chemical mutagenesis orrelated methods. These plants, when grown in adequate croprotation, will provide local farming communities with biomass

* This work was stimulated by discussions within COST Actions 837 and 859.

Introduction

The World Energy Outlook 2006 (www.IEA.org) specifiesthat the world will have to face two energy-related threats:the first of not having adequate and secure supplies of en-ergy at affordable prices and the second of environmentalharm caused by consuming too much of it. Hence, the G8-leaders postulated the need to decrease fossil-energy demandin favour of geographic fuel-supply diversity. Mitigating cli-mate-destabilising emissions is more urgent than ever. They

Subject Area 5.2 Novel Energy Plants

Env Sci Pollut Res 1515151515 (3) 2008 197

called on the IEA to "advise on alternative energy scenariosand strategies aimed at a clean, clever and competitive en-ergy future" (IEA 2006). Although the outlook paints a darkpicture of the development until 2030, it makes a clear state-ment that biofuels and renewables could make up to 12%of the global energy budget if the right measures be taken.But the report does also state clearly that increasing fooddemand, which competes with biofuels for existing arableand pasture land, will constrain the potential for biofuelproduction. Hence, it is clear that sustainable and efficientbiomass production must not proceed on valuable arableland but on so far neglected and set aside plots. This meansthat solutions have to be proposed for soils that have beenabandoned, e.g. because they may be degraded, polluted ornon-exploited, relatively poor soils.

Similarly, the EREC (European Renewable Energy Council)concludes that adopting the targets for the share of bioenergywill be the basis for the continuation of a sustainable EUenergy policy, as well as a precondition for establishing asustainable, competitive and secure energy mix for the fu-ture (EREC 2006).

In 2003, the European Commission initiated the EuropeanTechnology Platform 'Plants for the Future' as a stakeholderforum on plant genomics and biotechnology. This platformis supported by the European Commission and major pub-lic and private stakeholders. It is coordinated by EPSO(www.epsoweb.org/catalog/tp/), whose high-ranking plantphysiologists sketched their opinion about future develop-ments in food and energy crops. They claim that we pres-ently do not fully exploit the potential in plants, and thatthe world can be supplied with sufficient nutrients and en-ergy when biotechnology of plants is boosted (http://www.europabio.org/relatedinfo/Plantgenbrochure.pdf). It is nec-essary to note that generation of genetically modified plantsis just one biotechnology, the use of which is controversiallydiscussed with view to safety of global food and feed supply(Young 2003, 2004, Gaugitsch 2004). Providing the worldwith bioenergy using more conventional ways of classicalbreeding is another option which has been postulated evenearlier. Ambitious papers on the production of plant-derivedenergy from green and animal manure have been publishedas early as in the 1980s (Drake 1983, Long 1984). Progressis likely to result from a combination of plant breeding, plantand microbial metabolic engineering, and chemical engineer-ing, hence delivering fuel with a much smaller ecologicalfootprint (Abraham 2007). European border countries andcountries of the Mediterranean will encounter particularproblems when trying to adopt bio-energy plants to fightclimate change, because their production systems are con-centrated in areas of high fertility and water availability.Hence, substituting crops for energy plants will lead to short-age in food production and soil resources.

1 Bioenergy Options

The use of bio-based strategies to fulfil our energy demandsis most promising. Recent literature has already identifiedseveral crops, amongst them maize, wheat, potatoes, rape-seed and others, that can be produced on European arableland to substitute fossil fuels and make the European energy

market more independent. Bio-ethanol production, biodiesel(i.e. rapeseed oil methyl ester) and biogas (i.e. methane andaliphatic gases) from plant sources are in the focus of inter-est (Young 2003). In fact, production of energy crops is al-ready ongoing, and technologies for bio-fuel production areestablished in richer countries. However, explicit accountingfor CO2 at each stage of the production process is essential todecide for the most environment-friendly alternative (Rabl etal. 2007). Biogas produced from animal manure, wastes andfresh biomass ranks amongst the most sustainable energyforms, especially because of its potential production in small,decentralized units that require no big transport infrastruc-ture. Hence, it may be an alternative of incredible potentialfor rural areas of low standards and with lacking infrastruc-tures where it will deliver heat, gas to be stored and electri-cal energy to small farms and communities.

As reviewed by Markard et al. (2002), biogas from agricul-ture has many ecological advantages. Being renewable, itmay substitute fossil energy carriers, and will also reduceemissions of methane gas from 'natural' (i.e. uncontrolled)decomposition processes of organic matter. Hence, biogasproduction can mitigate greenhouse gas emissions.

Biogas production also reduces unpleasant odours in agricul-ture in the vicinity of populated areas. Moreover, the residualbiomass possesses improved fertiliser quality and can be re-distributed to fields more accurately than untreated organicwaste. Of course, efficient fertilising reduces agrochemicalpollution of surface and ground waters (Schulz & Eder 2001).

Biogas also has social benefits. Its production will generatealternative sources of income especially in the agriculturalsector of poorer countries and for smaller local companies.This is of particular significance in remote or economicallyunderdeveloped regions. Additionally, strengthening tradi-tional agriculture has a socio-cultural dimension as typicalcultural landscapes may be preserved, even if new plants areintroduced and new products are harvested. The opportu-nity to switch from low-income agriculture to biogas pro-duction may convince small farmers to adhere to their busi-ness and by that preserve the identity of agricultural commun-ities. Overall, biogas is a promising alternative for the fu-ture, because its resource base is widely available, and evensingle farms or small local cooperatives could start biogasplant operation.

1.1 Upcoming concepts for energy plants

Technologies to produce bioenergy from plants, their by-products and from manure are well established, but the cropplants under consideration have been specifically selectedfor decades to yield optimum nutrient content for food andfeed, and hence produce high value protein, oil or carbohy-drate. It is not sustainable and not cost-effective, to fermentand end-oxidize these plants at relatively low economic yield.Hence, producing bioenergy from food and forage cropsmust be seen critically. As long as our concepts for energyplants are based on high yield cereals and other quality live-stock feed, the cost of the energy produced will remain fartoo high to become competitive. If Europe is to compete ona global scale, it needs novel plants to produce cheap biom-ass and green manure, but to leave our food base untouched.


198 Env Sci Pollut Res 1515151515 (3) 2008

The most abundant source of bioenergy is where most ofthe fixed carbon is deposited – the cell wall. New technolo-gies have to be developed to modify cell wall compositionto create a 'feedstock' that is more readily converted intofuels. Research on the production of novel energy plantsrequires (a) identification of plant species or mutants pro-ducing biomass with the optimum composition for thebioenergy market, e.g. biogas, (b) testing the agronomic ca-pabilities of the chosen species, (c) studying how to producebioenergy from the chosen species to exploit their potential,and (d) testing their performance on marginal or abandonedland in order to present sustainable and economically at-tractive alternatives to stake-holders. Only if these condi-tions are met, bioenergy plants will succeed, biotechnologywill be strengthened, and we will successfully contribute tosolve the world's energy problem.

1.2 Production base for energy plants

Growing plants for biofuel production on the same, alreadylimited available agricultural areas, will potentially increasefood and fodder prices. This will be more pronounced in thepoorer countries and less developed agricultural regions,which will leave them with even fewer chances to developsustainable production systems. This is especially true in theMediterranean where agricultural food production isstrongly limited by water availability and soil quality. Thelack of financial resources on farms in these countries leadsto neglecting the production base and the soil, which ulti-mately increases soil degradation. As a result, such areasusually become abandoned and set aside – they are in factwithdrawn from the food production. It turns out that thepresent development is at the verge of becoming non-sus-tainable, similar to our previous behaviour in other economicareas. Taking all of the above into account, the only wayout of this dilemma is to identify promising species and breednovel plants suitable to produce readily digestible carbohy-drate, protein and oil, to be finally cropped on abandonedmarginal and degraded agricultural land or so far unexploitedsoils, to enhance their capacity to build up biomass, and

provide them with resistance against pests. When farmersstart growing novel energy plants in crop rotation with lo-cal plants and leguminous species, they will enlarge the lo-cal production base (Fig. 1).

Therefore, fast breeding methods must be employed to fur-ther develop these novel plants with traits essential for thebioenergy industry. These cultures of novel plants will re-quire novel plant protection measures as well as crop rota-tion protocols to ensure sustainable productivity. After har-vest, the biomass will feed local biogas production in thedry fermentation process. The electricity system of the lo-cal community will be stabilized at low cost, and the pro-cess heat can be used in households. Consequently, digestedsolid residues will be used to ameliorate the land and im-prove the soil quality. Such knowledge-based biotechnolo-gies will provide farming communities with opportunitiesto increase energy and food availability, reduce energy costsand increase quality of life, conserve fossil fuel reserves,fight climate change and create new economic opportuni-ties for small farms.

1.3 Plant breeding options

Selection of desirable traits from conventional Mendelianbreeding under field conditions takes several years and manyplant generations to accomplish the goal. Conventionalmutagenesis and in vitro selection can considerably shortenbreeding times and complement field selection. With a viewto legal and societal restrictions, conventional breeding (suchas mutagenesis or in vitro breeding) could be a promisingalternative to genetic transformation for the improvementof yield and other traits of high yielding crops. Those classi-cal non-GM techniques are free from safety regulations inthe EU Member States, and will allow one to screen & de-velop mutants under greenhouse and field conditions.

Mutagenesis – Mutation techniques have often been used toimprove yield, oil quality, disease, salt and pest resistance incrops, or to increase the attractiveness of ornamental plants.In some economically important crops (e.g. barley, durumwheat and cotton) mutant varieties nowadays occupy themajority of cultivated areas in many countries (Maluszynskiet al. 1995). Mutagenesis has also played an important rolein improving agronomic characteristics of Helianthus an-nuus L., one of the most important oil seed crops in theworld. Osorio et al. (1995) have reported an increased vari-ability in the oil fatty acid composition of sunflower mu-tants, obtained from seeds mutagenised with ethylmethane-sulphonate (EMS). New sunflower mutants with enhancedbiomass production and oil content were obtained byChandrappa (1982) after mutagenesis with EMS or diethylsulphate (DES). Kübler (1984) has obtained sunflower mu-tants of M2 and M3 generations with high linoleic acid con-tent for diet food and mutants with high oleic acid contentfor special purposes like frying oils after EMS mutagenesis.Nehnevajova et al. (2007) used chemical mutagenesis toimprove yield and metal uptake of sunflowers. In the sec-ond mutant generation sunflowers were obtained with im-proved yield (6–9 x), metal accumulation (2–3 x) and metalextraction efficiency (Cd 7.5 x, Zn 9.2 x; Pb 8.2 x) on asewage sludge contaminated field. Whereas the best sun-

Fig. 1: View of an agricultural region of northern Greece. Different soilcolours depict fertile and infertile areas. Abandoned land with eroded andlow organic matter soil is more obvious around the area closest to thephotographer



flower mutant could produce 26 t of dry matter yield perha, control sunflower inbred lines produced only 3 t drymatter per ha and year in the same experimental site. Theseresults demonstrate that EMS mutagenesis can lead to en-hanced biomass production and partially to improved metalaccumulation in sunflowers (Fig. 2).

Moreover, classical mutagenesis has also been used to getnew mutant variants with reduced metal accumulation traits.Nawrot et al. (2001) have obtained barley mutants with anincreased level of tolerance to Al toxicity. Ma et al. (2002)have shown a rice mutant defective in Si uptake and Navarroet al. (1999) have isolated mutants of Arabidopsis thaliana,cdht 1 and cdht4, which accumulated 2.3 times less Cd thancontrol plants exposed to 150 µM CdCl2.

Mutation breeding has a long history with cotton wherenewly developed genotypes occupy significant cultivated areain several countries (Maluszynski et al. 1995). Initially, theefforts were concentrated towards improving either fibrequality or the pest resistance of the crop. With the more andmore widespread use of cotton oil for dietary purposes, in-terest has increased in modifying its fatty acid composition(Abo-Hegazi et al. 1991, Bhat and Dani 1993). However,

no attempts have yet been made to improve the energeticvalue of the plant with the view of biofuel production.

Attempts to characterize cotton biomass for energy produc-tion were so far mainly targeted towards biomass burning(Liao et al. 2004) or for biodiesel production through cata-lytic pyrolysis (Putun et al. 2006). Mutation breeding willtherefore add yet another option to the possible uses of thecrop, making its cultivation profitable on poor, degradedand/or polluted soils. This will be supported by the growinginterest in cultivating energy crops in southern Europe, wherethe expansion in the last decade was aimed mainly towardslow-input cropping systems. The development of new cottonmutants, better adapted for biogas production under low-in-put cropping systems, could provide a new pathway in the useof this traditional crop besides its much more obvious butmuch more resource-hungry use for fibre production.

In vitro breeding (somaclonal variation – spontaneous muta-tions). Plant biotechnology involving modern tissue culture,using somaclonal variation and in vitro selection, offers theopportunity to develop new germplasm, better adapted to end-user demands (Alibert et al. 1994). Somaclonal variation canresult in a range of genetically stable variations similar to

Fig. 2: Chemical mutagenesis with ethyl metane sulfonate (EMS) as a promising approach for the production of novel plant varieties. EMS alters basesof the DNA by alkylating individual segments which leads to mispairings



variations induced with chemical mutagens (Skirvin et al.1993, Jain et al. 1998). Somaclonal variation and in vitroselection seem to be also appropriate to develop plant vari-ants with enhanced survival under adverse conditions (Herziget al. 1997, Guadagnini et al. 1999, Nehnevajova et al. 2006).

Fast breeding using molecular markers. Molecular markersare capable of providing efficient means for streamliningand speeding the breeding process. However, such markershave never been used for selecting of traits related to biogasproduction. An attempt to identify such markers in a modelplant, well adapted to the conditions of South-Eastern Eu-rope, will be of paramount importance. Cotton combinesseveral essential characteristics for such kind of work: 1.irradiation mutagenesis is well documented to induce largenumbers of genetic modifications in a single treatment inthis crop, thus increasing chances that traits related to im-proved biogas production will be affected; 2. the identifica-tion of the most appropriate techniques and tools has al-ready been a major subject of research (Bojinov and Lacape2003, Lacape et al. 2003) and 3. the identification of DNA-based markers, linked to improved biomass characteristicsfor biogas production, bears the potential to tremendouslyfacilitate future breeding programmes, aiming at develop-ing specialized varieties.

2 Helping Plants to Do the Job

2.1 Identification of stress tolerance of both existing cropsand newly bred genotypes

The molecular and biochemical mechanisms of plant adapta-tion to stress conditions are still poorly understood and sig-nalling pathways involved remain unclear (Dat et al. 2000,Schröder 2001). However, adaptation to environmentalchanges is crucial for plant growth and survival. When grow-ing energy plants on marginal land in low-input systems, theymay suffer from various stresses such as drought, heat, patho-gens, nutrient deficiency or metal toxicity. Hence, currentlycultivated crops, bred for productivity in high input croppingsystems will prove unsuitable on poor and abandoned soils.

In recent years, reactive oxygen species (ROS) have beensuggested to act as intermediate signalling molecules to regu-late gene expression (Mittler 2002, Mittler et al. 2004,Messner and Schröder 1999, Schröder et al. 2001, 2002). Inthis function, ROS have been proposed as a central compo-nent of plant adaptation to both biotic and abiotic stresses(Dat et al. 2000). These ROS are partially reduced forms ofatmospheric oxygen (3O2) and can be very toxic since theyattack several cell constituents such as proteins, lipids, ornucleic acids (Foyer and Noctor 2005). Many stresses, in-cluding drought, heavy metals, salt stress, heat shock orpathogen attack enhance the production of ROS (Mittler2002). The use of ROS as signalling molecules suggests thatduring the course of evolution plants were able to achieve ahigh degree of control over ROS levels. The steady statelevel of ROS in the different cellular compartments is there-fore controlled by an interplay between different ROS-pro-ducing and ROS-scavenging mechanisms (including enzy-matic and non-enzymatic reactions). Oxidative stress andoxidative damage occur when both types of mechanisms arestrongly imbalanced in the plant.

Several studies have demonstrated effects of oxidative, stress-related responses (e.g. ROS-scavenging enzymes such asSOD, APOD, CAT, GST, GPOD, enzymes of ascorbate-glu-tathione pathway,….) and on other stress or housekeepingproteins (e.g dehydrin, actin, histone) in sunflower or tobaccoexposed to drought, heat shock or metals at the metabolomiclevel (Bueno et al. 2002, Gallego et al. 1996, Zhang and Kirk-ham 1996), as well as at the transcriptomic level (Kiani et al.2007, Rizhsky et al. 2002). It is clear that oxidative, stress-related responses will influence plant performance and even-tually lead to an accumulation of unwanted phenolic metabo-lites in the plant material. Hence, differences in stress resistanceof various plant genotypes have to be evaluated with specificemphasis on the differences between parental genotypes andmutants, after exposure to increasing stress levels (drought,heat shock and/or metals).

2.2 Promoting plant growth by rhizosphere processes

The plant genome is often considered to completely regu-late plant productivity and stress resistance. However, mu-tualistic micro-organisms have the potential to affect plantproductivity and even stress resistance. N2-fixing rhizobialive in association with the roots in specialized structures(nodules) and provide nitrogen to their host. Hence, legu-minous cultures can help to enrich the poor soil with nitro-gen, a property which makes these crops very suitable totake part in the rotation schemes of energy crops on mar-ginal lands. The potentially beneficial effects of plant-mi-crobe interactions on plant growth and tolerance are welldocumented (Hall 2002, Herrera et al. 1993, Mastretta etal. 2006). Mycorrhiza, as well as plant associated bacteria(rhizosphere or endophytic), can contribute to the nutrientsupply of their plant hosts, which is important for optimalplant growth in normal conditions, but also for improvingplant survival in hostile environments (Requena et al. 1997).Previous research with tobacco has already demonstratedgrowth increases, after inoculation with selected bacterialstrains. Exploitation of the possibilities of microbial asso-ciations therefore opens new perspectives for the improve-ment of yield and the increase of stress tolerance of energycrops grown on marginal land. Endophytic bacteria havepreviously been isolated from tobacco plants and seeds grownon metal contaminated soil in Northern Europe (Mastrettaet al. 2006). Reinoculation experiments showed that posi-tive effects on growth were observed in (sterile) plants withseed endophytes, while endophytes isolated form wholeplants on the contrary caused growth reductions. Mecha-nisms by which endophytic bacteria can promote plantgrowth include, e.g. biological nitrogen fixation, synthesisof phytohormones, or more particular properties such asmetal tolerance or xenobiotic degradation pathways (Lode-wyckx et al. 2001, Mastretta et al. 2006, Barac et al. 2004).An exploitation of such microbial associations opens per-spectives for yield improvement and increases stress toler-ance of energy crops grown on marginal land. Characteriz-ing novel plants in this way will allow not only to drawconclusions about the genotypes under investigation, but alsoto gain more insight in the regulation and sequence of eventsoccurring in plants in response to environmental changes.



2.3 Best practice in agronomy

Monocultures of bioenergy crops are particularly vulnerablewhen cultivated on infertile soils and potential exposure todrought stress, pest and/or pathogen attacks. All forms ofagriculture cause changes in the balances and fluxes of pre-existing ecosystems, thereby limiting resiliency functions. Theintensive agriculture in some regions, with its strong reduc-tion of landscape structures and vast decoupling of energyand matter cycles, has caused stress and degradation of theproduction base; massive influence has also been exerted onneighbouring compartments. To overcome the economic,social and political inadequacies leading to ecological deg-radation during energy plant production, it is of paramountimportance to transpose available knowledge on sustainableproduction systems, including remote sensing technologies,into knowledge-based practical instructions and politicalregulations on a regional scale. Thus, applied research for asustainable and ecologically compatible land use is ever soimportant (Schröder et al. 2004).

Studies with remote sensing have demonstrated the relation-ship between canopy spectral reflectance and biomass pro-duction of some major crops (Pinter et al. 2003). Reflec-tance data are typically derived from aircraft or satelliteimages in the visible and NIR ranges of the spectrum andsubsequently transformed into vegetation indices (i.e. NDVI).However, the availability of this information by airborneplatforms is constrained by weather conditions, revisit fre-quency and elaborate data processing. On the other hand,proximal sensors are an emerging technology designed toovercome the limitations of current instrumentation by de-livering real-time data of high spatial resolution that can beused in site-specific management. Proximal sensors wererecently used successfully for the prediction of biomass inirrigated corn, cotton and vineyards (Bausch and Delgado2003, Stamatiadis et al. 2004, 2006). The application ofthis technology is expected to provide valuable managementtools for increasing biomass production of energy crops.

Plant stress tolerance under field conditions may also besuccessfully evaluated using photosynthetic parameters, suchas leaf gas exchange and chlorophyll fluorescence. Theirchanges through stress development give a very good esti-mate about tolerance capacity. As non-destructive measures,these parameters have the advantage to provide reliable andfast information about plant behaviour at complex stressconditions. This was demonstrated in a screening study withcotton genotypes from different species grown under rainfed conditions in Bulgaria (Bojinov et al. 2000).

Agricultural production systems have to be chosen that di-minish soil and fertility losses, ensure water availability andfight pathogens. Farm practices that prevent erosion willhelp to protect soils and water quality. Sustainable agricul-ture will be achieved only when information about hetero-geneity of soil-plant systems is available and appropriateplans are developed and implemented at the level of the lo-cal farm and the region. In order to make the production ofnovel energy plants possible, it is of utmost importance todevelop adequate management systems. These should lowerproduction costs, reduce pollution of surface and ground-

water, reduce pesticide residues in food, reduce a farmer'soverall risk, and increase both short- and long-term farmprofitability (Parr et al. 1990).

One important trait of mutants intended for low-input sys-tems of South-Eastern Europe is their stress resistance towater shortage. Water stress will not only induce stomatalclosure and limit photosynthetic activity, but also limit min-eral N uptake and crop growth. The interaction betweenwater availability and nutrient uptake is a crucial elementthat needs to be taken into account when testing the abilityof new mutants to adapt to water-deficient environments.This can be achieved in site of specific field plot experimentsthat combine different irrigation and fertilization rates in asplit-plot experimental design to yield best practise recom-mendations for a given region. The natural abundance ofthe stable isotopes of carbon (δ13C) and nitrogen (δ15N) inplant tissues has been used as integrated indicators of waterstress and N nutrition, respectively. In the case of 13C, theisotopic signal has been generally used to identify differencesin water stress over large topographic gradients or betweenmutants. For estimation of productivity potentials (Laithaand Marshall 1994), in the case of δ15N, the isotopic signalhas been used to identify N uptake of the source fertilizer.Recent evidence indicates that the combined isotopic signalin the leaves is sensitive enough to identify water- or nutri-ent-stressed plants over short distances within single fields.This finding is significant when considering that conven-tional analytical methods may be unable to detect such smallspatial differences in plant stress or nutrient deficiencies. Thisnovel approach of interpreting isotopic data will be an im-portant tool to explore biomass variation in the cultivationof energy plants.

3 Producing Biogas

With fossil-based fuel prices steadily rising as the resourcesdiminish, bioenergy will grow steadily and is fast becom-ing an energy industry factor, currently accounting foraround 3% of US energy production. By 2030 it shouldhave reached more than 10% in Europe. Moreover, as theEU and other countries stimulate research on energy pro-duction by legislation and corresponding incentives sup-porting Green Energy, investments into biogas productionwill become safe ground for agricultural communities.Modern dry fermentation has processing and technical ad-vantages over the liquid fermentation process currently usedfor producing biogas.

3.1 Reactor types and research needs

State-of-the-art digestion systems for energy crops are so-called aqueous digesters, i.e. energy crops are shredded andfed into digesters with a large amount of additional waterleading to a concentration of usually below 5% dry sub-stance in the reactor. This leads to large volumes of the di-gestion vessels since the residence time needs to be held atapprox. 40 days in order to fully convert the digestible or-ganic matter. The reactor type is – according to text books –an agitated vessel and thus operates always at a minimumconcentration of organic matter.



Newer technology – so called dry digestion, does not diluteorganic matter with water but keeps the organic matter un-mixed with already digested matter and, thus, keeps the or-ganics concentration always as high as possible. Using sucha plug flow type reactor results in lower volumes due to themuch higher concentration of organics, which range fromapprox. 35% to 12% between the feeding stage and thefinal stage of the process. An intercomparison shows thatthe plug flow type is very successful for organic waste appli-cation because of its rigidness against inhibition and sidereactions. These benefits are combined with the shorter resi-dence time of the reactor to boost its economic value. How-ever, only little experience is available with running this re-actor type on energy crops (Fig. 3).

The energetic quality of the biogas depends on the fermen-tation process and on the characteristics of the actual sub-strate fed into the reactor. The challenge of optimal biogasproduction is to maintain a stable anaerobic digestion pro-cess and the technical solutions to achieve that are limited.Instead, it requires good quality energy plant material, ac-curacy, perseverance and experience on the side of the plantoperators. The above hindrances are further complicated bythe lacking technical protocols tackling these problems. Thebasic substrate for biogas production should be organic sub-stances derived from plant matter, although other organicwastes might be added to the reactor. Residues of vegetableor animal fat are of particular interest in this respect, asthey have high calorific values and thus enable high biogasyields. This co-digestion might also be beneficial forstabilising the fermentation process. It is known that inhib-iting reactions may be caused by side products of the reac-tions or by ingredients originating from the crops. Monodigestions are particularly difficult due to the lack of traceminerals and – during dry digestion – the possibility of highsalt concentration leading to high osmotic pressures, whichmight kill or seriously damage them. Using new energy cropsmay therefore lead to unexpected problems in the process(e.g. unexpectedly high heavy metal concentrations that couldnot be predicted by numerical approaches [Mohammed and

Markert 2006, Fränzle and Markert 2007]), which mightlower gas production rates as compared to the conventionalindustrial environment. Hence, it is crucial to scrutinize thedigestion process for the new plants, because if digestion isdeteriorated by unexpected metabolites, they may not beuseful, although they seemed promising at first glance.

4 Conclusions

In the European Union, biomass is regarded the most prom-ising renewable energy option for the closer future (Euro-pean Commission 1997, Wellinger et al. 1991). Biogas inparticular has received considerable attention as a renew-able energy carrier with a huge potential for the Europeanmarket. Being usually produced by anaerobic digestion ofwet agricultural products (including manure), the most wide-spread use of biogas is seen in the decentralised generationof electricity and heat to cover local demand. Excess elec-tricity can even feed into local electricity networks. Alterna-tively, biogas can be added to the natural gas grid for powergeneration or heating purposes, or as a vehicle fuel. So far,biogas potential has been exploited to various extents andin different ways in different countries and regions. In Aus-tria, Germany and Switzerland numerous biogas plants havebeen established, and the United Kingdom, France, the Neth-erlands, Denmark, Sweden and Belgium are also starting tofurther this technology (Abraham et al. 2007). However,most southern European countries, and especially new EUmember states have not adopted this promising way to im-prove local energy production. It is therefore necessary toevaluate the potential of abandoned soils in South-EasternEurope to grow plants that produce sufficient biomass atlow costs, as a sustainable energy supply to poorer regions.The importance of the matter is hardly taken into accountin the 7th Framework Program of the EU: Although high-tech solutions for growth of biomass are presently availableall over Europe, their sustainability is usually not achieved,resilience to numerous parameters is questionable, and clear-cut evidence is presented in EU papers that these technicalsolutions are too expensive for many communities.

Besides scientific progress, it will be of high importance tostrengthen the European Research Area (ERA) by interna-tional cooperation to achieve common and well-developedstrategies that respond to global change issues of high pub-lic concern such as energy plant and biogas production. Thesestrategies should be applicable in all member states, and notonly to those with lower net income. Cost effectiveness, re-liability, long-term sustainability, resilience and reasonableinput of resources are key characteristics of biogas produc-tion. Breeding new plants by a fast-track-breeding approachbased on mutagenesis, aiming at the development of newgenotypes which are particularly adapted to marginal soils,and resistant to the extreme climatic conditions in southernEurope is one of the most promising alternatives to conven-tional breeding, and also to GMO approaches. The exploi-tation of plant-microbial interactions as an alternative/complement to chemical fertilisers to improve yield of plantsis well known in organic farming, and it should be appliedin energy plant production, as well as in the evaluation of

Fig. 3: Flow chart of the biogas production process in a dry fermentationreactor



stress resistance of new plants by metabolomic and tran-scriptomic analyses.

Further, and to not fall back into the mistakes of the agricul-tural production in the 1970s and 1980s, it will be impor-tant to optimize rotation schemes and soil management prac-tices for the specific condition met in a region (Wei and Zhou2006), hand in hand with an optimisation of crop mixturesin bio-reactors for optimal energy production.

5 Perspectives

Europe is one of the leading players in the advancement oftechnologies and related environmental applications. Euro-pean remote sensing satellites cover all of the Earth's cli-matic zones, while European ground-based, air-based andocean-based monitoring devices serve users by providing highquality observation data in areas as diverse as urban plan-ning, adaptation to and mitigation of climate change, disas-ter reduction, disease control and humanitarian relief. Wewill have to focus our work on the exploration of the finiteand irreproducible resources, that is the land and the soils,and on their sustainable exploitation for food and energy(Haber 2007). Research on bioenergy plants and fossil fuelreduction is one of the major aims for the next decade, andthis cannot be achieved by small groups or single institu-tions. With view to the impact in our information society,it is necessary to include as many stakeholders and group-ings as possible in successful developments. Through theEuropean Union's exhaustive efforts to promote greaterawareness of science in society, results emanating from itsenvironmental research initiatives may also have knock-oneffects on the day-to-day decisions made by industry, com-merce and Europe's citizens – the ultimate goal being tofind a sustainable balance. Especially teams that includescientists from associated countries or new member stateswill influence this development by working together andinvestigate burning topics, with the aim of producing newenvironmental tools and technologies to promote sustain-able development. This will help to establish rules and regu-lations for biogas production in the EU core countries andin the countries that will enlarge the ERA, and they willraise interest for the technologies by improving publicawareness of the green technology used to protect our mostvaluable resource, the climate. SME partners involved willespecially result in an enlarged cooperation and technologytransfer across Europe, thus confirming the role of Europeas a leader in the export of innovative and environmentallyfriendly environmental technologies at affordable costs andhigh efficiency worldwide.

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Received: June 15th, 2007Accepted: March 1st, 2008

OnlineFirst: March 2nd, 2008

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