Taxa–area relationship and neutral dynamics influence the diversity of fungal communities on senesced tree leaves Larry M. Feinstein* and Christopher B. Blackwood Department of Biological Sciences, Kent State University, Kent, Ohio, USA Summary This study utilized individual senesced sugar maple and beech leaves as natural sampling units within which to quantify saprotrophic fungal diversity. Quan- tifying communities in individual leaves allowed us to determine if fungi display a classic taxa–area relation- ship (species richness increasing with area). We found a significant taxa–area relationship for sugar maple leaves, but not beech leaves, consistent with Wright’s species-energy theory. This suggests that energy availability as affected plant biochemistry is a key factor regulating the scaling relationships of fungal diversity. We also compared taxa rank abun- dance distributions to models associated with niche or neutral theories of community assembly, and tested the influence of leaf type as an environmental niche factor controlling fungal community composi- tion. Among rank abundance distribution models, the zero-sum model derived from neutral theory showed the best fit to our data. Leaf type explained only 5% of the variability in community composition. Habitat (vernal pool, upland or riparian forest floor) and site of collection explained > 40%, but could be attributed to either niche or neutral processes. Hence, although niche dynamics may regulate fungal communities at the habitat scale, our evidence points towards neutral assembly of saprotrophic fungi on individual leaves, with energy availability constraining the taxa–area relationship. Introduction Fungal community composition has been shown to be an important factor regulating decomposition (Balser and Fir- estone, 2005; Waldrop and Firestone, 2006). Therefore, our ability to predict decomposition rates and responses to environmental changes may be enhanced with increased understanding of the processes that regulate fungal distributions. Variation in composition of ecological communities is commonly divided into two components: alpha diversity (number and evenness of taxa within a sampling unit) and beta diversity (taxa turnover among areas) (Gaston and Blackburn, 2000). For macroorganisms, it has been frequently observed that there is a correlation between the size of habitat patches or survey areas and the most fundamental measure of alpha diversity, number of taxa detected (Rosenzweig, 1995; Connor and McCoy, 2001; Lomolino, 2001; Drakare et al., 2006). The ‘taxa–area relationship’ (TAR) refers to the shape of the increase in number of taxa with increasing area, and has been most often mod- elled as a power law (S = cA z ) where S is number of species, A is area, c is the intercept in log-log space, and z is a constant related to the rate of species turnover across space (Arrhenius, 1921; Gleason, 1922). Taxa– area relationships have been used to extrapolate species richness (Colwell and Coddington, 1994; He and Leg- endre, 1996; Plotkin et al., 2000), estimate regional diversity inventories (Chong and Stohlgren, 2007), and compare species abundance distributions (May, 1975; Harte et al., 1999; Pueyo, 2006). TARs are also used as an important tool in conservation efforts to protect species from habitat fragmentation and destruction (Faith et al., 2008). Quantifying fungal TARs may help us understand processes regulating fungal community assembly and determine how sampling design affects our ability to detect fungal diversity. Communities in discrete habitat patches (e.g. islands) have proven useful in studying TAR patterns because such communities have well-defined boundaries (Mac- Arthur and Wilson, 1967; Schoener, 1976; Bell et al., 2005). Although a few studies have utilized leaves as discrete habitats for microbial communities (Kinkel et al., 1987; Jacques et al., 1995; Newell and Fell, 1997), most previous molecular studies examining forest floor fungal communities have utilized homogenized mixed ‘grab’ samples of leaves (O’Brien et al., 2005; Neubert et al., 2006; Blackwood et al., 2007a; Keeler et al., 2009; Redford et al., 2010). However, early after leaf fall, individual leaf boundaries must limit the size of fungal Received 29 July, 2011; revised 5 March, 2012; accepted 7 March, 2012. *For correspondence. E-mail feinsteinlm@gmail.com; Tel. (+1) 330 672 3895; Fax (+1) 330 672 3713. Environmental Microbiology (2012) 14(6), 1488–1499 doi:10.1111/j.1462-2920.2012.02737.x © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd