Abstract
Ectomycorrhizal (ECM) plants and fungi can be diverse and abundant in certain tropical ecosystems. For example, the primarily paleotropical ECM plant family Dipterocarpaceae is one of the most speciose and ecologically important tree families in Southeast Asia. Pakaraimaea dipterocarpacea is one of two species of dipterocarp known from the Neotropics, and is also the only known member of the monotypic Dipterocarpaceae subfamily Pakaraimoideae. This Guiana Shield endemic is only known from the sandstone highlands of Guyana and Venezuela. Despite its unique phylogenetic position and unusual geographical distribution, the ECM fungal associations of P. dipterocarpacea are understudied throughout the tree’s range. In December 2010 we sampled ECM fungi on roots of P. dipterocarpacea and the co-occurring ECM tree Dicymbe jenmanii (Fabaceae subfamily Caesalpinioideae) in the Upper Mazaruni River Basin of Guyana. Based on ITS rDNA sequencing we documented 52 ECM species from 11 independent fungal lineages. Due to the phylogenetic distance between the two host tree species, we hypothesized that P. dipterocarpacea would harbor unique ECM fungi not found on the roots of D. jenmanii. Although statistical tests suggested that several ECM fungal species did exhibit host preferences for either P. dipterocarpacea or D. jenmanii, most of the ECM fungi were multi-host generalists. We also detected several ECM fungi that have never been found in long-term studies of nearby rainforests dominated by other Dicymbe species. One particular mushroom-forming fungus appears to be unique and may represent a new ECM lineage of Agaricales that is endemic to the Neotropics.
Highlights
Ectomycorrhizal (ECM) fungi are a diverse functional group of mutualistic root symbionts that enhance host plant nutrient acquisition, protect against root disease, and mitigate the effects of abiotic stresses [1,2]
Because tropical habitats are often challenging to access, there are still major gaps in our understanding of the ecology, biogeography, and host preferences of tropical ECM fungi and plants
The co-occurrence of these two distantly related, Guiana Shield endemic, ECM-forming tree species in close proximity to our previous study sites provided a unique opportunity to further explore fungal host preferences and beta diversity of ECM fungi in this remote neotropical region
Summary
Ectomycorrhizal (ECM) fungi are a diverse functional group of mutualistic root symbionts that enhance host plant nutrient acquisition, protect against root disease, and mitigate the effects of abiotic stresses [1,2]. In the Neotropics, several unrelated plant genera have independently evolved the ability to form ECM symbioses with fungi: Pakaraimaea (Dipterocarpaceae), Quercus (Fagaceae), Coccoloba (Polygonaceae), Aldina (Fabaceae subfamily Papilionoideae), Dicymbe (Fabaceae subfamily Caesalpinioideae), Gnetum (Gnetaceae) and at least three genera in the Nyctaginaeae (Pisonia, Neea, and Guapira) [4,7,9,10,11,12] These primarily lowland neotropical ECM plants are highly variable in terms of growth habit and geographic distribution. In the Pakaraima Mountains of Guyana [9] Further explorations in this region identified the nearby Pegaima savanna-forest mosaic as a habitat where the leguminous ECM tree, Dicymbe jenmanii Sandw., co-occurs with the dipterocarp P. dipterocarpacea. The co-occurrence of these two distantly related, Guiana Shield endemic, ECM-forming tree species in close proximity to our previous study sites provided a unique opportunity to further explore fungal host preferences and beta diversity of ECM fungi in this remote neotropical region. We asked the following questions: 1) Do ECM fungi exhibit marked host preferences for either one or the other plant species?, 2) Does P. dipterocarpacea host ECM fungal species not found on leguminous trees of the region? and, 3) Are the dominant ECM fungi in this dipterocarp-dominated forest different from those of the Fabaceae-dominated ECM communities in nearby rainforests?
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