Investigating niche partitioning of ectomycorrhizal fungi in specialized rooting zones of the monodominant leguminous tree Dicymbe corymbosa

Abstract

Temperate ectomycorrhizal (ECM) fungi show segregation whereby some species dominate in organic layers and others favor mineral soils. Weak layering in tropical soils is hypothesized to decrease niche space and therefore reduce the diversity of ectomycorrhizal fungi. The Neotropical ECM tree Dicymbe corymbosa forms monodominant stands and has a distinct physiognomy with vertical crown development, adventitious roots and massive root mounds, leading to multi-stemmed trees with spatially segregated rooting environments: aerial litter caches, aerial decayed wood, organic root mounds and mineral soil. We hypothesized that these microhabitats host distinct fungal assemblages and therefore promote diversity. To test our hypothesis, we sampled D. corymbosa ectomycorrhizal root tips from the four microhabitats and analyzed community composition based on pyrosequencing of fungal internal transcribed spacer (ITS) barcode markers. Several dominant fungi were ubiquitous but analyses nonetheless suggested that communities in mineral soil samples were statistically distinct from communities in organic microhabitats. These data indicate that distinctive rooting zones of D. corymbosa contribute to spatial segregation of the fungal community and likely enhance fungal diversity.

Ectomycorrhizal associations in the tropics – biogeography, diversity patterns and ecosystem roles

“…By contrast, studies in the Guiana Shield employing above‐ and belowground sampling found that D. corymbosa ‐dominated forests on both sand and lateritic soils had similar ECM fungal communities (Smith et al ., ). Broader geographical overlap also was found in the ECM fungi symbiotic with canopy trees D. corymbosa , D. altsonii , Dicymbe jenmanii , Aldina insignis and Pakaraimaea dipterocarpacea (Smith et al ., , ; Henkel et al ., ).…”

“…Differences in enzymatic capabilities among ECM fungi could impact nutrient cycling because species with higher enzymatic capabilities may mine organic N and P and further slow the decomposition of residual soil organic matter (Lindahl & Tunlid, ). Furthermore, co‐occurrence of ECM fungal species with different suites of enzymes and different substrate preferences may promote niche partitioning, species packing and higher local ECM fungal diversity (Smith et al ., ). Further studies on this topic are needed to establish the role of different species and functional groups in nutrient cycling, as well as their responses to anthropogenic ecological impacts.…”

“…Despite extensive root tip sampling and fruiting body surveys in Dicymbe forests of Guyana, there are no records of ECM Pezizales (e.g. Henkel et al ., ; Smith et al ., ) and only a few ECM Pezizales have been reported from tropical Africa (Tedersoo et al ., 2012a). By contrast, some Mexican tropical dry forests dominated by Quercus host a high diversity of ECM Pezizales and may be biodiversity hotspots for these fungi (García‐Guzmán et al ., ).…”

“…In a more intensive study, Smith et al . () examined ECM fungi from D. corymbosa root tips inhabiting aerially trapped litter, decayed wood, humus‐rich root mounds and mineral soil. They found ECM fungi on roots in all strata and detected significant turnover of ECM fungal communities, particularly in the mineral soil, indicative of some degree of niche differentiation.…”

“…Smith et al . (, , ) found that co‐occurring species of Fabaceae and P. dipterocarpacea harbored many of the same ECM fungi across multiple sites in Guyana, suggesting that host preferences are weak in that region. Peay et al .…”