## 1 Introduction  
In Europe, more than 13,638 biogas plants (72%) utilize the agricultural feedstocks out of 18,943 biogas plants [1], among which corn (_Zan mays_ L) silage is the major feedstock [2]. While corn silage is the most widely used energy crop for biogas production, there is interest in using other sources of plant biomass for environmental, economic, and societal reasons [3]. For example, _Plnramites australis_ (Cav.) Trin. ex Steud. (common need) is a perennial invasive wetland plant species in North America that produces substantial quantities of biomass of up to 30 h\({}^{-1}\) y\({}^{-1}\)[4]. While all parts of the common need can be used for both biogas and biofent production [5], the estimated biogas yields reported in the literature are only 150 L kg\({}^{-1}\) volatile solids (VS) of fresh material compared to grass and pig manure that yield more than 280 and 340 L kg\({}^{-1}\) VS, respectively [4, 6]. The issues of low degradability and poor conversion to biogas are also applicable to other potential energy crops, such as _Miscantlus_ and _Arundo donax_ L. [7, 8]. In nature, one of the most efficient systems for unlocking the energy found in lignocellulosic substrates is the rumen animals such as cattle and sheep. While the stepwise fermentation process (hydrolysis, acidification, acetogenesis, methanogenesis) that occurs during anaerobic digestion (AD) is crudely similar to the digestive process in the rumen, it is far less efficient [9]. One reason for the reduced efficiency of AD compared to the rumen likely lies in differences in the microbial populations between these two environments. The anaerobic digestive system of the rumen has been extensively studied, and anaerobic fungi (AF) are known to be involved in the digestion of the most recalcitrant lignocellulosic within the rumen [10]. Anaerobic fungi use rhizoids to physically penetrate and disrupt the lignin layer of lignocellulosic, while also enzymatically degrading plant cell walls using a diverse suite of extracellular hydrolytic enzymes, including cellulases, hemicellulose, pectinases, and phenolic acid esterases [11]. Some of the extracellular hydrolytic enzymes produced by these organisms are freely released into the milieu; others are bound to the cellular surface as components of multienzyme cellulosomes [12]. Using feruloyl esterase activity, AF cleaves the bonds between hemicellulose and lignin, increasing the access of microbial enzyme to hemicellulose. Although AF are known to degrade lignin, they do not utilize the lignin themselves [13]. While AF are known to play an essential role within the rumen, their presence, abundance, and activity level in AD is not well understood. Bioaugmentation involves adding specific microorganisms into a system or process in order to improve its efficiency [14]. Several studies have been conducted using bioaugmentation with bacteria or fungi as a pretreatment for the hydrolysis of lignocellulosic substrates prior to AD [12]. In one study, the addition of thermophilic _Geobacillus_ sp. strain AT1 to a biogas reactor using sewage sludge as substrate resulted in a 210% increase in bio-gas production due to the protease activity of the microbe [15]. In another study, 22 isolates of white rot fungi were used individually to pretreat wheat straw, with the greatest lignin degradation and subsequent increase in biogas yield (from 0.293 L g\({}^{-1}\) to 0.343 L g\({}^{-1}\)) obtained from an isolate of _Pleutrotus florida_[16]. Recently, studies utilizing AF to improve biogas production and speed up substrate degradation have been reported [17; 18; 19]. To date, isolates of the genera _Anaeromyces_, _Neocallimastix_, and _Pironyces_ have been added to AD systems in an effort to improve lignocellulosic degradation and ultimately improve methane yield [18; 19]. A previous study [18] demonstrated increased biogas yields from different substrates, such as maize silage, anaerobic sludge, and microcrystalline cellulose, with bioaugmentation of AF in fed batch semicontinuous digesters.