Ectomycorrhizal fungi are shared between seedlings and adults in a monodominant Gilbertiodendron dewevrei rain forest in Cameroon

Abstract

Ectomycorrhizal networks may facilitate the establishment and survival of seedlings regenerating under the canopies of tropical forests and are often invoked as a potential contributor to monodominance. We identified ectomycorrhizal fungi in a monodominant Gilbertiodendron dewevrei (Fabaceae) rain forest in Cameroon, using sporocarps and ectomycorrhizae of three age categories (seedlings, intermediate trees, and large trees) and tentatively revealed nutrient transfer through ectomycorrhizal networks by measuring spontaneous isotopic (13C and 15N) abundances in seedlings. Sporocarp surveys revealed fewer ectomycorrhizal fungal taxa (59 species from 1030 sporocarps) than molecular barcoding of ectomycorrhizal roots (75 operational taxonomic units from 828 ectomycorrhizae). Our observations suggest that ectomycorrhizal fungal diversity is similar to that in other mixed tropical forests and provide the first report of the Tuber‐Helvella lineage in a tropical forest. Despite some differences, all age categories of G. dewevrei had overlapping ectomycorrhizal fungal communities, with families belonging to Thelephoraceae, Russulaceae, Sebacinaceae, Boletaceae, and Clavulinaceae. Of the 49 operational taxonomic units shared by the three age categories (65.3% of the ectomycorrhizal fungal community), 19 were the most abundant on root tips of all categories (38.7% of the shared taxa), supporting the likelihood of ectomycorrhizal networks. However, we obtained no evidence for nutrient transfer from trees to seedlings. We discuss the composition of the ectomycorrhizal fungal community among the G. dewevrei age categories and the possible role of common ectomycorrhizal networks in this rain forest.

Resource acquisition strategies facilitate Gilbertiodendron dewevrei monodominance in African lowland forests

“…Several studies have confirmed the presence of ectomycorrhizal fungi communities in Gilbertiodendron forest (Ebenye et al, 2017;Gérard, 1960;Torti & Coley, 1999). We found significantly higher C:N and C:P ratios in soils from monodominant Gilbertiodendron than mixed forest across our Sangha Trinational study area, with the median C:N ratio in G. dewevrei forest being twice that of mixed forest.…”

“…We find evidence of tight nutrient cycling by G. dewevrei (Cassart et al, 2017;Gérard, 1960;Kearsley et al, 2017) consistent with its association with extremely low base cation soils, providing a competitive advantage over tree species with less nutrient use efficient and conservative strategies. While G. dewevrei has long been recognized as associated with ectomycorrhizal fungi (Ebenye et al, 2017;Gérard, 1960;Hart et al, 1989;Torti & Coley, 1999), we present evidence and arguments for the fundamental role played by this association in facilitating monodominance. Evidence suggests both organic (sensu Phillips et al, 2013) and efficient N and P economies afford an advantage on infertile soils and underpin many of the other traits that have heretofore been associated with this species (Figure 5; also see e.g.…”

“…Citations in Figure: Averill and Hawkes (2016) [Proposed mechanisms that have not been supported in studies: Makana and Thomas (2005) found no evidence to support dense leaf litter preventing seedlings of other species to establish. Ebenye et al (2017) found no evidence that EM hyphal networks facilitate nutrient exchange between adults and seedlings. Torti et al (2001) found that leaf litter decomposition rates are linked to forest type and not species.…”

“…It forms ectomycorrhizal associations (Ebenye et al, 2017;Gérard, 1960;Torti & Coley, 1999), but the ectomycorrhizal status of G. dewevrei is not believed to promote monodominance . Other ectomycorrhizal tree species occur in adjacent mixedspecies forest (e.g.…”

Editorial: Mycorrhiza in Tropical and Neotropical Ecosystems

“…Ectomycorrhizal (EM) associations can influence plant community assembly and facilitate plant coexistence in boreal and temperate regions (van der Heijden et al, 1998), but little is known in tropical and neotropical forests (Bâ et al, 2012; Ebenye et al, 2017). To this end, Essene et al compared assembly patterns of EM fungi in bulk soil to EM root tips collected from three ecologically distinct species of dipterocarp in a Bornean lowland tropical rain forest.…”