The mid-domain effect in ectomycorrhizal fungi: range overlap along an elevation gradient on Mount Fuji, Japan

Abstract

Mid-domain effect (MDE) models predict that the random placement of species' ranges within a bounded geographical area leads to increased range overlap and species richness in the center of the bounded area. These models are frequently applied to study species-richness patterns of macroorganisms, but the MDE in relation to microorganisms is poorly understood. In this study, we examined the characteristics of the MDE in richness patterns of ectomycorrhizal (EM) fungi, an ecologically important group of soil symbionts. We conducted intensive soil sampling to investigate overlap among species ranges and the applicability of the MDE to EM fungi in four temperate forest stands along an elevation gradient on Mount Fuji, Japan. Molecular analyses using direct sequencing revealed 302 EM fungal species. Of 73 EM fungal species found in multiple stands, 72 inhabited a continuous range along the elevation gradient. The maximum overlap in species range and the highest species richness occurred at elevations in the middle of the gradient. The observed richness pattern also fit within the 95% confidence interval of the mid-domain null model, supporting the role of the MDE in EM fungal richness. Deviation in observed richness from the mean of the middomain null estimation was negatively correlated with some environmental factors, including precipitation and soil C/N, indicating that unexplained richness patterns could be driven by these environmental factors. Our results clearly support the existence of microbial species' ranges along environmental gradients and the potential applicability of the MDE to better understand microbial diversity patterns.

Strong effect of climate on ectomycorrhizal fungal composition: evidence from range overlap between two mountains

“…In addition, EM fungal communities may be affected by climate and soil (Cox et al, 2010;Jarvis et al, 2013;Roy et al, 2013). Moreover, EM fungal communities often exhibit spatial structures (Lilleskov et al, 2004;Bahram et al, 2013a;Miyamoto et al, 2014), which may be driven by autocorrelations in environmental factors (Toljander et al, 2006;Tedersoo et al, 2012) or independently by fungal internal factors (e.g., dispersal; Peay et al, 2007). Thus, at larger regional and global scales, whether EM fungal communities are differentiated by hosts, environmental factors or geographical distance is less clear.…”

“…We followed Miyamoto et al, 2014 for the molecular analyses. Briefly, all roots were collected from each soil sample, and EM root tips were classified by their morphological characteristics.…”

“…Field sampling was conducted according to Miyamoto et al, 2014. Briefly, 50 rectangular soil Ectomycorrhizal fungal range overlap Y Miyamoto et al cores (5 Â 5 cm to 10 cm depth) were collected from a 1-ha area at each site.…”

“…In addition, many EM fungi are observed rarely and sporadically because of the inherently limited sampling efforts relative to the entire soil volume (Taylor, 2002). Our previous study (Miyamoto et al, 2014) demonstrated that intensive sampling (many samples from each community) is effective for recording a relatively large number of fungal taxa in a community and for identifying species overlaps among study sites. Consistent sampling across study sites also helps to remove the variations imposed by methodological discrepancies found in many meta-analyses (Nakagawa and Santos, 2012;Tedersoo et al, 2014).…”

“…The data collected were combined with the data from our previous study conducted on Mt. Fuji, which is located B550 km away (Miyamoto et al, 2014). Each elevation gradient encompassed a wide range in climate within a short geographical distance, and different types of forest were present at similar altitudes on both mountains.…”