نقش شیمی خاک و مناطق گیاهی در پروش قارچ در سه جنگل بارانی پانامایی The role of soil chemistry and plant neighbourhoods in structuring fungal communities in three Panamanian rainforests

Introduction Many lowland tropical rainforests are strongly phosphorus (P) depleted (Sollins 1998; Mirmanto et al. 1999; Vitousek et al. 2010; Wright et al. 2011) and they harbour some of the highest plant diversity on the planet (Wright 2002). Biotic forces, including plant-associated soil fungi, play a key role in promoting plant diversity (Klironomos 2002; Bell, Freckleton & Lewis 2006; Petermann et al. 2008; Mangan et al. 2010; *Correspondence author. E-mail: jonesfr@science.oregonstate.edu Schnitzer & Klironomos 2011). Fungi interact with plant communities in mutualistic, pathogenic, and commensal ways (Rosenblueth & Mart
ınez-Romero 2006; Smith & Read 2008b; Van Der Heijden, Bardgett & Van Straalen 2008; Dodds & Rathjen 2010). Fungi play critical roles in ecosystem processes including decomposition and nutrient cycling, and they have been hypothesized to play a critical role in the maintenance of plant diversity via pathogen-mediated negative density dependent survival (Janzen 1970; Connell 1971; Augspurger 1983; Clark & Clark 1984; Carson et al. 2008; Timothy Paine et al. 2008; Hol et al. 2013; Bagchi et al. 2014; Comita et al. 2014; but also see Hyatt et al. 2003) and plant-soil feedbacks (Bever 2002; Mangan et al. 2010; Philippot et al. 2013). Despite their recognized role in these processes, the relative importance of the abiotic and biotic drivers of soil fungal community structure and diversity in lowland tropical forests remains poorly understood. Soil properties can determine soil fungal communities and host-microbe interactions (Lauber et al. 2008; Vinale et al. 2008). For example, arbuscular mycorrhizal (AM) fungi (subphylum Glomeromycotina) form associations with 80% of plant species worldwide (Wang & Qiu 2006; Brundrett 2009), and enhance the uptake of water, inorganic P, and other relatively immobile nutrients by effectively increasing root surface area and therefore increasing the volume of soil explored (Smith, Anderson & Smith 2015). The symbiosis between plants and AM fungi can be facultative and dependent on the plant’s soil nutrient requirements and resource availability (Heijden & Kuyper 2001; Lambers et al. 2008; Dumbrell et al. 2009; Albornoz et al. 2016a). Similarly, P and other soil properties can affect non-AM fungal communities, such as ectomycorrhizal fungi (Albornoz et al. 2016b), saprophytic fungi (Kerekes et al. 2013), and pathogens (Toljander et al. 2006; Tedersoo et al. 2016). Nevertheless, fungi are only partially driven by soil properties, and other factors, such as biotic interactions, simultaneously structure fungal communities. Plant communities can also affect their associated fungal communities (Johnson et al. 2004; Prescott & Grayston 2013) due to differences in fungal host specificity, defined as the taxonomic range of plant host species (Molina & Trappe 1982; Botnen et al. 2014). For example, obligate pathogens experience high selection pressure to infect hosts and reciprocal natural selection can occur between hosts and pathogens. This leads to an ‘evolutionary arms race’ between pathogen effectors and plant immunity genes, resulting in increased host specificity of pathogens (Jones & Dangl 2006; Dodds & Rathjen 2010; Brown & Tellier 2011). In contrast, AM fungi are thought to be generalists in forming host associations (i.e. a broad range of hosts; Davison et al. 2015) compared to other fungal groups such as saprophytes, pathogens, and endophytes (Tedersoo et al. 2010). Because of the host specificity that many fungal clades exhibit, they are thought to be strongly coupled with plant communities (Davey et al. 2015; Gao et al. 2015). However, the effects of plant community composition relative to soil chemistry in structuring fungal communities remains largely unknown, and studies that quantitatively determine the relative impact of each are scarce.