Plant Power: Opportunities and challenges for meeting sustainable energy needs from the plant and fungal kingdoms

: Bioenergy is a major component of the global transition to renewable energy technologies. The plant and fungal kingdoms offer great potential but remain mostly untapped. Their increased use could contribute to the renewable energy transition and addressing the United Nations Sustainable Development Goal 7 “Ensure access to affordable, reliable, sustainable and modern energy for all.” Current research focuses on species cultivated at scale in temperate regions, overlooking the wealth of potential new sources of small‐scale energy where they are most urgently needed. A shift towards diversified, accessible bioenergy technologies will help to mitigate and adapt to the threats of climate change, decrease energy poverty, improve human health by reducing indoor pollution, increase energy resilience of communities, and decrease greenhouse gas emissions from fossil fuels.

tors based on robust scientific evidence.
Bioenergy is derived from natural resources-predominantly plants and fungi-for generating electricity, cooking, transportation fuel, and domestic heating and cooling (Box 1). Within the last 10-20 years, biofuels and renewable energy sources such as geothermal resources, wind, and solar, have helped to diversify the global energy economy and reduce carbon emissions (IEA, 2019).
Replacing fossil fuels with clean bioenergy significantly reduces air pollution and greenhouse gas emissions (Qin et al., 2015(Qin et al., , 2018. The plant and fungal kingdoms, Plantae and Fungi, respectively, are distantly related (fungi are more closely related to the animal kingdom, Animalia than plants) but ecologically linked as plants depend on endophytic fungi and root mycorrhizae for their very existence (an estimated 90% of plant species have root-based mycorrhizae) and to enhance nutrition, defense, and reproduction (Willis, 2018). The plant kingdom is relatively well understood with ca. 350,000 species (WCVP, 2020) and ca. 10%-20% of "known unknown" species yet to Summary Bioenergy derived from plants and fungi is a major component of the global transition to renewable energy technologies. There is rich untapped diversity in the plant and fungal kingdoms that offers potential to contribute to the shift away from fossil fuels and to address the United Nations Sustainable Development Goal 7 (SDG7) "Ensure access to affordable, reliable, sustainable and modern energy for all." Energy poverty-the lack of access to modern energy services-is most acute in the Global South where biodiversity is greatest and least investigated. Our systematic review of the literature over the last 5 years (2015)(2016)(2017)(2018)(2019)(2020) indicates that research efforts have targeted a very small number of plant species cultivated at scale, mostly in temperate regions. The wealth of potential new sources of bioenergy in biodiverse regions, where the implementation of SDG7 is most urgently needed, has been largely overlooked. We recommend next steps for bioenergy stakeholders-research, industry, and government-to seize opportunities for innovation to alleviate energy poverty while protecting biodiversity. Small-scale energy production using native plant species in bioenergy landscapes overcomes many pitfalls associated with bioenergy crop monocultures, such as biodiversity loss and conflict with food production. Targeted trait-based screening of plant species and biological screening of fungi are required to characterize the potential of this resource. The benefits of diversified, accessible bioenergy go beyond the immediate urgency of energy poverty as more diverse agricultural landscapes are more resilient, store more carbon, and could also reduce the drivers of the climate and environmental emergencies.
In contrast, only 148,000 species of fungi are named and classified (Species Fungorum, 2020) from an estimated 2.2-3.8 million species (Hawksworth & Lücking, 2017). Proportionally, the number of fungal species being used to generate or enhance bioenergy processing would appear to be minimal compared to the plant kingdom which yields primary and derived bioenergy (Box 1) and basic biodiversity research is needed to enable better utilization.
Rising global demand for palm oil for food and biofuels had stimulated the conversion of 2.3 million ha of peat swamp forest for oil palm plantations by 2010 on the Malay Peninsula, Borneo, and Sumatra (Koh, Miettinen, Liew, & Ghazoul, 2011). Biofuel crop plantations are likewise implicated of deforestation in the Amazon in South America, despite cattle farming and soy cultivated for animal feed accounting for over 80% of pasture expansion in the period 2005-2013 (Barona, Ramankutty, Hyman, & Coomes, 2010;da Costa, Matricardi, Pedlowski, Cochrane, & Fernandes, 2017;Gollnow, Hissa, Rufin, & Lakes, 2018;Pendrill, Persson, Godar, & Kastner, 2019). Modeling simulations with an increased global ethanol demand by 2030 predict sugarcane driving expansion of agriculture into the natural vegetation of the Cerrado and Amazon (van der Hilst, Verstegen, Woltjer, Smeets, & Faaij, 2018). In the short term, the direct impact of biofuel production on deforestation in the Amazon will likely be amplified following the lifting in 2019 of a ban on sugarcane cultivation in the Amazon, to boost biofuel production (Ferrante & Fearnside, 2020). Wood fuel harvesting is a FIGURE 1 The iconic NASA "Earth at Night" 2016 satellite image provides a compelling illustration of energy poverty (https://earth obser vatory.nasa.gov/featu res/Night Light s/page3.php). Approximately 11% of the global population, mostly in the Global South, do not have access to electricity, which includes 56% in sub-Saharan Africa, 37% in Oceania (excluding Australia and New Zealand), 9% in Central and Southern Asia, 5% in Northern Africa and Western Asia, 2% in Eastern and South-Eastern Asia, Latin America and the Caribbean, while the populations of Europe and North America all have access to electricity (United Nations, 2019)

Box 1 What is plant power?
Through photosynthesis, plants possess the remarkable ability to locally reduce entropy by capturing solar energy to build complex molecules from simple ones. Humans release this bioenergy using a range of technologies, the simplest of which is igniting fuel between the stones of a hearth to provide energy for cooking and warmth. Archaeological evidence suggests that the controlled use of fire has been used for at least 350-400 thousand years by several Homo species (H. erectus, H. neanderthalensis, H. sapiens) (MacDonald, 2017;Sandgathe & Berna, 2017). Modern technologies to release "plant power" fall broadly into two categories: thermal and biological, and each requires different feedstock.
Liquid biofuels. Bioethanol accounts for two-thirds of liquid biofuels used in the transportation sector globally (OECD and FAO, 2019). It is derived from fermented high sugar crops (beets, Beta vulgaris L., Amaranthaceae; sugarcane, Saccharum officinarum L., Poaceae) and starchy crops (wheat; maize, Zea mays, both Poaceae). An array of cellulose-rich biomass feedstocks (corn stover; switchgrass, Panicum virgatum L., Poaceae; Miscanthus; wood chips) are used in second generation technologies which generate biofuels using fermentation or thermal processes. For biodiesel production, plants containing high yields of extractable lipids are required and the suitability of the feedstock is contingent on the fatty acid chain length and saturation of the lipids (Demirbas, 2010; Pinzi, Mata-Granados, Lopez-Gimenez, Luque de Castro, & Dorado, 2011;Wahyudi, Widodo, & Wijayanti, 2018). Oil content is therefore not necessarily a direct indication of biodiesel suitability. The main sources of biodiesel are vegetable oils (soybean, Glycine max (L.) Merr., Leguminosae; palm, Elaeis, Arecaceae; and rapeseed, Brassica napus Vilm., Brassicaceae) and waste cooking oils (OECD & FAO, 2019).
Emerging sources. A significant new supply chain based on wet feedstocks such as invasive aquatic plants (e.g. water hyacinth, Pontederia crassipes (=Eichhornia crassipes, Pontederiaceae) is emerging in the Global South; plant material cleared from large water bodies that would usually be left to decompose can instead be processed to yield thermal energy, electricity, and bioethanol (Patel, 2012;Santibañez-Aguilar, Ponce-Ortega, González-Campos, Serna-González, & El-Halwagi, 2013;Varanasi, Kumari, & Das, 2018). In dry environments, fast-growing succulent plant species suitable for cultivation on marginal soils with limited irrigation hold promise as bioenergy feedstocks (Yang, Lu, et al., 2015;. Also as succulence, plants that utilize the crassulacean acid metabolism photosynthesis pathway exhibit improved heat/drought durability and water-use efficiency. Genera such as Agave spp. (Asparagaceae) and Opuntia spp. (Cactaceae) have been highlighted for their potential as bioenergy feedstocks in drylands that far exceeds current production levels (Davis, Kuzmick, Niechayev, & Hunsaker, 2017;Davis et al., 2014Davis et al., , 2019Mason et al., 2015). Plants with enhanced heat/ drought resistance will help to reduce global production requirements of Triticum spp.
(wheat) and Zea mays (maize), both used for bioenergy feedstocks, which have already been linked to climate change (Field, Barros, Dokken, & Mach, 2014;Lobell, Schlenker, & Costa-Roberts, 2011). High carbohydrate content feedstocks are favored for fermentation, although pre-treatment is necessary to hydrolyze structural carbohydrates into fermentable sugars. Anaerobic digestion yields biogas (a mixture of methane and carbon dioxide) from feedstocks containing high carbohydrate, fat, and protein content such as agricultural and municipal waste, animal and human wastes. Anaerobic digestion is widely used in Asia, notably China and India, where millions of small-scale community anaerobic digester systems are in operation (Ahammad & Sreekrishnan, 2016), and it has potential in Africa to replace wood and charcoal cooking fuels. However, significant cultural and socio-economic barriers to household adoption of biogas technology persist, from awareness to installation of digesters, training and market opportunities (Clemens, Bailis, Nyambane, & Ndung'u, 2018;Rupf, Bahri, de Boer, & McHenry, 2015). In the northern hemisphere, anaerobic digestion has been implemented at large scales for treatment of sludge, food waste, and agricultural waste, generating combined heat and power or upgraded to produce bio-methane for the gas grid or transport. major threat to forests in some areas, and has been exaggerated by land-use change leading to wood fuel scarcity. In wood fuel depletion hotspots (Bailis, Drigo, Ghilardi, & Masera, 2015) such as Nepal and Uganda, unsustainable forest harvesting supports 82%-90% of energy used, respectively, yet the majority of the population in both countries experience energy poverty (Baral et  Traditional wood fuels account for 1.9%-2.3% (1.0-1.2 Gt CO 2 e yr −1 ) of global CO 2 emissions (Bailis et al., 2015) (and see Box 2). Unsustainable wood fuel harvesting is even more prevalent in the Earth's drylands, where water scarcity constrains the prevalence of trees in the landscape. Drylands occupy ca. 41% of global land area (Mortimore, 2009) and overlap with regions affected by energy poverty, particularly in Africa (United Nations, 2019). For example, A similar situation affects the development of new bioenergy sources derived from the algae kingdom. Micro-and macroalgae produce "third generation" biofuels, including renewable aviation fuel, bio-coal, and biogas, and are also used to capture, remove or transform pollutants such as excess nutrients and heavy metals from wastewater, and CO 2 from exhaust gases. Algae grow faster than terrestrial crops, but economic viability remains a challenge due to high processing costs preventing the wide-scale implementation of third generation energy solutions including algae, and advanced and lignocellulosic feedstocks (EPA, 2020). And yet, the species diversity and technological advances make algae a likely resource (Guarnieri & Pienkos, 2015;Guiry, 2012), like fungi, to yield major breakthroughs for sustainable bioenergy supplies in the future.

Box 2 Assessing the diversity of plant power
We assessed the diversity of energy plants and research efforts within the last 5 years to characterize their potential and possible drawbacks. We identified 2,582 species representing 1,909 genera in 188 plant families used for "fuel" from plant use records in the literature, standardized according to the Economic Botany Data Standard (Cook, 1995), and maintained in a database at the Royal Botanic Gardens, Kew, using the World Checklist of Vascular Plants taxonomy (Diazgranados et al., 2020;WCVP, 2020). This resource is comprehensive but not exhaustive, as many fuel plants likely remain under-documented, notably in the tropics (Cámara-Leret & Dennehy, 2019). To accommodate incompleteness and possible geographical biases, known fuel species, including both native and introduced species, were mapped at Level 3 of the World Geographical Scheme for Recording Plant Distributions (WGSRPD) (Brummitt, 2001) (Figure 2a). The phylogenetic distribution of known fuel species was visualized ( Figure 3) on a recent phylogeny of seed plants produced from DNA sequence data retrieved from the National Center for Biotechnology Information (NCBI) repository (Smith & Brown, 2018) comprising 449 plant families. The proportion of fuel species per family was optimized on the phylogeny using the contMap function in the R package PHYTOOLS (Revell, 2012).
We further explored regional geographical patterns in the diversity of fuel plant species by evaluating the list of fuel taxa against the World Checklist of Vascular Plants (WCVP, 2020) ( Figure 2b). Because fuel species richness is largely related to overall plant diversity and the area of a region, we also measured the proportion of fuel plant species per WGSRPD Level 3 region compared to the total number of vascular plant species [(number of fuel species)/(total number of fuel species)]. Lastly, we compared the geographic distribution of introduced fuel species versus all fuel species to detect patterns in the origins of fuel species. We found that a higher diversity of native fuel species, and fewer introduced species, are used in regions with greater plant diversity, such as sub-Saharan Africa ( Figure 2c). Introduced fuel species are, overall, more common in the northern hemisphere.
We applied a systematic review approach to evaluate current research (2015-2020) on the plant and fungal kingdoms as sources of bioenergy. We defined three questions: "How are fungi enhancing bioenergy recovery from plants?", "What are the risks and benefits of using plants for energy?", and "How are new sources of energy from plants identified?" For each question, keyword searches (Methods S1) were carried out in English in two bibliographic databases (Scopus, http://scopus.com/ and Web of Science, ht t p:// webof knowl edge.com/). References were screened by title and abstract ( Figure 4a). The results (Table S1) showed that research into plants and fungi for bioenergy spans plant science, agricultural, environmental and energy science, yet research efforts across these disciplines focus narrowly on bioenergy species already in use (Figure 4c), and on temperate crops ( Figure 4b). Hence, research efforts within the past 5 years have overlooked the biodiversity-rich regions where energy poverty is most acute and where there is arguably the greatest potential for emerging technologies to use plants and fungi, including species whose energy potential have not yet been unlocked (Antonelli, Smith, & Simmonds, 2019).
in the dryland areas of eastern Uganda, 98.8% of households use fuelwood for cooking and preserving food, mostly from Acacia spp.
Bioenergy landscapes have the potential to foster synergies between biodiversity, food, and energy production (Werling et al., 2014). One promising concept is the community-based "energy garden," pioneered by the Hassan Biofuels Park in southern India which gave rise to significant changes in national and state biofuel policy and legislation (Gowda, Prasanna, Kumar, & Haleshi, 2014).
This approach identifies sustainable plant materials within the community and matches them to technologies supplying local bioenergy. It combines the cultivation of predominantly indigenous fuel plants on marginal or degraded land with the management of community forests, clearing invasive species, and use of agricultural and household waste to supply biomass for accessible energy processing technologies. Besides energy security, the system protects biodiversity, and improves food security (through agricultural productivity and ecosystem services such as pollinator provision) and water management (through erosion control) (Pariyar et al., 2016). The energy garden concept has been transferred to rural communities in Nepal (Pariyar et al., 2016). However, in order to ultimately displace fossil fuel combustion and reach net zero carbon emissions globally, some bioenergy solutions must also be scalable.
Agroecosystem modeling in France, for instance, emphasized local factors such as soil type, meteorological data, and previous landuse largely impacting crop performance, and determined that using three biomass sources would use <3% of regional agricultural land and reduce greenhouse gas emissions by 60% (Dufossé, Drouet, & Gabrielle, 2016).
This review assesses the current role of the plant and fungal kingdoms in energy security and the potential for these natural resources to be developed in response to SDG 7 (United Nations, 2015). We focus on opportunities for local-scale interventions most relevant to addressing energy poverty at the community level. We summarize sources of bioenergy and associated technologies for deriving bioenergy from plants (Box 1) and fungi. Research trends are evaluated in a systematic literature review of plant-derived bioenergy (Box 2), as well as the lessons to be learned and approaches to accelerate development of new feedstocks for the future. Lastly, we recommend priorities for research and development that will help to harness the potential of the plant and fungal kingdoms for alleviating energy poverty while protecting and benefitting biodiversity and the ecosystem services they provide.  The emergence of flex crops, cultivated for multiple purposes, have helped to reduce food versus fuel tensions in the bioenergy sector, but have been implicated in "land-grabbing" and major changes in land use, as investment funds move globally seeking high returns from commodities (Borras, Franco, Isakson, Levidow, & Vervest, 2016). The demand for flex crops is driven by major consumer and processing regions such as Europe, which are unlikely to meet their own regional demand for non-food crops, and rely heavily on imports from other world regions (two-thirds of the cropland required to meet the EU's non-food biomass consumption is in other regions, mostly in China, the US, and Indonesia). The land-use impacts will require targeted policy making to avoid negative consequences being passed to low-income nations (Bruckner et al., 2019). Such impacts have been exemplified by a reduction in the European demand for palm oil in response to policy change governing sustainable biofuels in Europe that had a marked impact on the Indonesian supply chain, although these have not curtailed its environmental impact (Hinkes, 2019). Demands for biofuel have driven the conversion of agricultural land to maize in North America and sugarcane in South America, creating tensions with food production, deforestation and exposing plant-derived bioenergy as not necessarily "clean" nor "green." Bioethanol derived from maize has a high carbon footprint due to the fossil fuel-derived fertilizers required for its cultivation (Fairley, 2011;Mekonnen et al., 2018;Stehfest, Ross, & Bouwman, 2010), whereas the sugarcane industry has a lower carbon footprint because the bagasse waste product from the initial energy recovery is then used to cogenerate heat and electricity displacing energy required for bioethanol production (Mekonnen et al., 2018), even taking into consideration carbon emissions from crops burned prior to harvest (de Figueiredo, Panosso, Romão, & La Scala, 2010).

FROM PLANT TO POWER
Electricity generated directly from biomass from major agricultural crops is more efficient than producing biofuel, and tends to be more

Monocots
Ma.  Possible tensions between bioenergy production and water resource availability is one area in which new water-efficient feedstocks could expand the potential for developing bioenergy technologies, particularly in dryland environments. Prosopis (Fabaceae) trees are associated with N-fixing bacteria, and have been found to maintain higher productivity under drought and heat stress in comparison with other widely recommended species for arid lands (Leucaena leucocephala, Parkinsonia aculeata, Prosopis tamarugo, Cercidium floridium, and Olneya tesota) and could act as a source of biomass, wood, and food products in drylands (Felker, 1998;Felker, Cannell, Clark, & Osborn, 1983). More recently, xeric plants that use Crassulacean acid metabolism (CAM) have been considered for their potential as sustainable dryland bioenergy feedstocks. Their lower water requirements per unit of dry biomass than C 3 and C 4 crops as well as their water storage capacity help them overcome the limitation of intermittent water availability (Borland, Barrera Zambrano, Ceusters, & Shorrock, 2011). Agave (Asparagaceae) and Opuntia (Cactaceae) species can operate at near-maximum productivity with low water requirements (Borland et al., 2011;Borland, Griffiths, Hartwell, & Smith, 2009) and exhibit lower greenhouse gas emissions and nitrogen leaching than maize . Opuntia ficus-indica and Euphorbia tirucalli (Euphorbiaceae) have also been considered potential bioenergy crops and been determined to produce promising yields with low rainfall (Mason et al., 2015) but require careful consideration of the potentially negative ecological impact of introducing invasive species outside their natural range (Grace, 2019). In a global scale GIS-based productivity model, simulations for the year 2070 on low-grade land suggested that Opuntia ficus-indica alone has the capacity to meet extreme bioenergy scenarios (>600EJ yr −1 ) and is highly resilient. Opuntia ficus-indica and Agave tequilana (both CAM) outperformed the C 4 bioenergy crop Panicum virgatum in modeled arid zones (latitudinal range 30°S-30°N) (Owen, Fahy, & Griffiths, 2016). Agave bioenergy production systems have been determined by life cycle analysis to provide increased energy outputs and greenhouse gas offsets compared to maize or switchgrass (Yan, Tan, Inderwildi, Smith, & King, 2011) as well as being far more water efficient (Davis, LeBauer, & Long, 2014) due to the high water content of their tissues, and relative ease with which tissue is digested (Yang, Lu, et al., 2015;.

Rosids Asterids
The establishment of new bioenergy feedstocks and crops is dependent on agricultural, economic, and social factors (IEA, 2019) beyond the immediate tensions with food, water, and biodiversity.
Societal issues such as market access, finance, and policy frameworks determine whether new bioenergy technologies and feedstocks will become established. Market linkages, access to institutional support, and micro-finance stimulate farmers' investment and adoption of sustainable technologies policies and programs (Shiferaw, Okello, & Reddy, 2009). In rural Ethiopia, factors such as trust in government support, credit constraints, market access, and spouse education influence farmers' uptake of sustainable agricultural practices being adopted (maize-legume rotation, conservation tillage, animal manure use, improved seed, and inorganic fertilizer use) (Teklewold, Kassie, & Shiferaw, 2013). Wealthy, educated, young male farmers are most likely to adopt new technologies in Ethiopia, as they are able to afford the risk if the technology fails (Melesse, 2018). However, barriers such as the complex bureaucratic governance structure and misalignment of policies can undermine all these interventions, as has been shown in Indonesia (Bößner et al., 2019). Governance and policy are crucial to encourage transition to bioenergy and reduce people's dependence on non-renewable energy sources, particularly as population growth increases energy needs. Many countries in sub-Saharan Africa (Mohammed, Mokhtar, Bashir, & Saidur, 2013) and India (Luthra, Kumar, Garg, & Haleem, 2015) have national renewable energy policies but not fully formed regional policies.

Afforestation in countries such as Madagascar and Ethiopia with
Grevillea species (Proteaceae, native to Australia) for primary fuel has resulted in unexpected land transformation due to the preferences of local people for native rather than exotic species ( (Devappa, Roach, Makkar, & Becker, 2013). Jatropha curcas can be invasive outside its native range (Prentis et al., 2009) and future climate scenarios will increase its invasive potential (Dai et al., 2018). By comparison, a sustainable seed oil industry has been successfully established in East Africa based on the indigenous tree species Croton megalocarpus Hutch. (Euphorbiaceae). The species is used as a biofuel for electricity (Jacobson, Shr, Dalemans, Magaju, & Ciannella, 2018). One micro-enterprise, EcoFuels Kenya (efk.co.ke), sources > 3,000 tonnes of wild-collected nuts per year through a proprietary collection network. Processing of the nuts yields seedcake which is used as animal feed and husks pressed into briquettes are sold to the coal firing industry.
With increasing awareness of the climate crisis, attention is turning to carbon capture technologies in addition to renewable energy production. To date, plants have provided large-scale solutions to reducing atmospheric carbon dioxide such as forests (Bonan, 2008;Kukrety, Wilson, D'Amato, & Becker, 2015) and grasslands with belowground biomass (Scurlock & Hall, 1998). Improving carbon storage potential is now a breeding target for perennial fast-growing bioenergy crops such as Miscanthus, which store carbon in long, lignified roots and do not require annual ploughing (Christensen, Laerke, Jørgensen, & Kandel, 2016;Xue, Lewandowski, & Kalinina, 2017).
Miscanthus has even been proposed to be substituted for maize on currently available croplands in the US, potentially using half the land and one-third of the water to produce the same amount of bioethanol, which could be further improved with advanced biofuel conversion technology (Qianlai Zhuang, Qin, & Chen, 2013). There has been significant research into the role of perennial plants such as Miscanthus in enhancing carbon capture and storage (e.g., Agostini, Gregory, & Richter, 2015), although in the context of energy crops this has tended to concentrate on the restricted set of species listed in Box 1 and shown in Figure 4c. This research suggests that while currently used perennial energy crops may not impact soil organic carbon levels (Ferchaud, Vitte, & Mary, 2016;Ye & Hall, 2020), they do positively impact carbon draw-down and storage within the plant, but choice of species is critical to achieve carbon capture outcomes (Di Vita, Pilato, Pecorino, Brun, & D'Amico, 2017). We propose that a diversity-driven approach to plant and fungal energy sources could also involve research to identify novel perennial taxa that simultaneously maximize carbon capture and storage while a standing crop.
Plant roots appear to differentially take up carbon (Kell, 2012) and increased atmospheric CO 2 appears to disproportionately increase biomass and yield in tuberous crops such as cassava (Manihot esculenta, Euphorbiaceae) (Rosenthal et al., 2012) that can be used in energy production (Okudoh, Trois, Workneh, & Schmidt, 2015). Perennial plants also often offer advantages including year-round harvesting, better abiotic and biotic stress resilience, and supply of a broader range of ecosystem services when compared with shorter lived plant species (Borrell, Biswas, Goodwin, & Blomme, 2019). High value co-products may increase the feasibility of certain biofuels. Biodiesel production generates ca. 10% glycerol as the main byproduct (Yang, Hanna, & Sun, 2012) that is often considered a waste product. However, crude glycerol has been investigated as a source of reduced carbon for the model diatom Phaeodactylum tricornutum and did not reduce photosynthetic capacity, or cell growth, suggesting crude glycerol could be used to increase biodiesel production or other co-products from P. tricornutum (Villanova et al., 2017). The production of microalgal biofuels could also become more feasible if produced alongside high value co-products in a biorefinery producing multiple products from microalgae such as proteins, pigments, vitamins, and antioxidants (Chew et al., 2017;Li, Liu, Cheng, Mos, & Daroch, 2015).  (Alston, Mabry, & Turner, 1963) and phylogenetic (Rønsted et al., 2012) (Guiry, 2012). For the fungal kingdom, with <5% of species scientifically identified and named (Hawksworth & Lücking, 2017;Willis, 2018), biological screening programs, focused on ecological and environmental parameters rather than traits in known species, will be the most viable option for discovering new useful properties in the asyet undocumented species. In the bioenergy sector, fungi are mainly used in the pre-treatment of lignocellulosic biomass and expansion of these applications may be one of the most rewarding research areas.

FROM PLANTS
The identification of fungal species new to science will likely reveal yet more species suitable for bioenergy applications.

BIOENERGY PRODUCTION
The fungal kingdom is one of the most promising untapped natural resources for addressing global energy challenges. Fungi enhance bioenergy recovery from biomass and are able to utilize the waste products of bioenergy processes to produce yet more bioenergy, such as waste glycerol from biodiesel production (Fakankun, Mirzaei, & Levin, 2019), seafood processing plant effluent (Cheirsilp, Suwannarat, & Niyomdecha, 2011), and waste coffee pulp (Menezes et al., 2013). The basidiomycete white-rot fungi are the most widely used for delignification of bioenergy feedstocks, as they completely mineralize lignin in aerobic conditions (Saritha & Arora, 2012).
Recently, the addition of rumen liquid has been found to improve the efficiency of biogas production by anaerobic fungi typical of grazing animal digestive tracts (Gruninger et al., 2014;Nagler, Kozjek, Etemadi, Insam, & Podmirseg, 2019).

RECOMMENDATIONS
The plant and fungal kingdoms have untapped potential to address energy poverty (SDG 7) and diversify the bioenergy sector with sustainable, local sources of feedstock matched to emerging tech-

nologies. Established supply chains from North America and South
America currently dominate global bioenergy production, and regions with the highest energy security and least biodiversity currently support intensive research efforts on a few well-known plant species.
Opportunities abound to refocus research and development toward the most appropriate species and renewable technologies to address energy poverty and enhance global access to clean, green bioenergy.
We make the following recommendations to stakeholders in the bioenergy sector to harness the potential of plants and fungi to reduce energy poverty in an environmentally sustainable way: Researchers and funding bodies should scale efforts to identify new sources of bioenergy from native plant species in the Global South where energy poverty is most acute and plant diversity exceptionally rich (see Box 2). Efforts should focus particularly on sub-Saharan Africa and Oceania (excluding Australia and New Zealand). We emphasize the importance of screening programs with different approaches to optimize the identification of plant and fungal species new to science with potential as native feedstocks in multipurpose systems. Accurately identified reference collections in botanic gardens and seed banks, as well as fungal culture libraries and algal collections, are invaluable for accelerating these studies.
Species which can be grown on degraded or marginal lands, or harvested during invasive plant clearance efforts, should be prioritized.
Industry should prioritize investment in technologies developed for native species and multi-purpose systems, which provide the full spectrum of ecosystem services in bioenergy landscapes such as foods, carbon storage, shade, water management, air quality, pollinator support, and biocultural value. Modeling using natural capital approaches should be used to select species and ecosystems.
Technologies minimizing waste from bioenergy production processes, or high-yielding native plants, fungi or offshore-cultivated algae, are priorities to reduce the impact of bioenergy production on land use and terrestrial biodiversity, as explained in Section 3, above.
Governments and international aid programs should urgently prioritize the implementation of energy-efficient stoves in households, and ovens for small-scale industries, where timber and charcoal extraction is linked to high levels of biodiversity loss and poverty.
Partnerships with communities, researchers, and industry, supported by governments, are needed to embed clean and green bioenergy technology, educate communities about sustainable harvesting, and provide training to manage infrastructure. Policy frameworks at the local and national level are needed to embed bioenergy technologies with financial incentives. These could include subsidies, micro-finance, crop insurance, assured markets and minimum support prices declared by government for compulsory farming of bioenergy crops such as pulses or oilseeds.