New neotropical sebacinales species from a Pakaraimaea dipterocarpacea forest in the Guayana Region, Southern Venezuela: structural diversity and phylogeography.

Pakaraimaea dipterocarpacea, a member of the Dipterocarpaceae endemic in the Guayana region, is associated with a diverse community of ectomycorrhizal (ECM) fungi. Amongst the 41 ECM fungal species detected in a 400 m2 P. dipterocarpacea ssp. nitida plot in Southern Venezuela, three species belonged to the Sebacinales. We tested whether ECM anatomotype characterization can be used as a feasible element in an integrative taxonomy in this diverse fungal group, where the relevance of fruitbody morphology for species delimitation seems limited. Using a combination of ECM morpho-anatomical characterizations and phylogenetic analyses based on nuclear ITS and LSU sequences, we report three new species. The main distinguishing features of Sebacina guayanensis are the yellowish cell walls together with conspicuous undifferentiated, uniform compact (type B) rhizomorphs. Staghorn-like hyphae are characteristic of S. tomentosa. The combination of clusters of thick-walled emanating hyphae, including hyphae similar to awl-shaped cystidia with basal dichotomous or trichotomous ramifications, and the presence of type B rhizomorphs were characteristic of a third, yet unnamed species. The three species belong to three different, possibly specifically tropical clades in Sebacinales Group A. The geographic distribution of phylogenetically related strains was wide, including a Dicymbe forest in Guyana and an Ecuadorian rainforest with Coccoloba species. We show that ECM morpho-anatomy can be used, in combination with other analyses, to delineate species within Sebacinales Group A. In addition to phylogenetic information, type B rhizomorphs observed in different Sebacinales clades have important ecological implications for this fungal group. The phylogeography of Sebacinales suggests that dispersion and host jump are important radiation mechanisms that shaped P. dipterocarpacea ECM fungal community. This study emphasizes the need for more sequence data to evaluate the hypothesis that phylogeographic relationships between neo- and paleotropical ECM fungal species could be attributed to the vicariance of cross-continental hosts such as the Dipterocarpacae.

Ectomycorrhizal symbiosis of tropical African trees.

The diversity, ecology and function of ectomycorrhizal (EM) fungi and ectomycorrhizas (ECMs) on tropical African tree species are reviewed here. While ECMs are the most frequent mycorrhizal type in temperate and boreal forests, they concern an economically and ecologically important minority of plants in African tropical forests. In these African tropical forests, ECMs are found mainly on caesalpionioid legumes, Sarcolaenaceae, Dipterocarpaceae, Asterpeiaceae, Phyllantaceae, Sapotaceae, Papilionoideae, Gnetaceae and Proteaceae, and distributed in open, gallery and rainforests of the Guineo-Congolian basin, Zambezian Miombo woodlands of East and South-Central Africa and Sudanian savannah woodlands of the sub-sahara. Overall, EM status was confirmed in 93 (26%) among 354 tree species belonging to EM genera. In addition, 195 fungal taxa were identified using morphological descriptions and sequencing of the ML5/ML6 fragment of sporocarps and ECMs from West Africa. Analyses of the belowground EM fungal communities mostly based on fungal internal transcribed spacer sequences of ECMs from Continental Africa, Madagascar and the Seychelles also revealed more than 350 putative species of EM fungi belonging mainly to 18 phylogenetic lineages. As in temperate forests, the /russula-lactarius and /tomentella-thelephora lineages dominated EM fungal flora in tropical Africa. A low level of host preference and dominance of multi-host fungal taxa on different African adult tree species and their seedlings were revealed, suggesting a potential for the formation of common ectomycorrhizal networks. Moreover, the EM inoculum potential in terms of types and density of propagules (spores, sclerotia, EM root fragments and fragments of mycelia strands) in the soil allowed opportunistic root colonisation as well as long-term survival in the soil during the dry season. These are important characteristics when choosing an EM fungus for field application. In this respect, Thelephoroid fungal sp. XM002, an efficient and competitive broad host range EM fungus, possessed these characteristics and appeared to be a good candidate for artificial inoculation of Caesalps and Phyllanthaceae seedlings in nurseries. However, further efforts should be made to assess the genetic and functional diversity of African EM fungi as well as the EM status of unstudied plant species and to strengthen the use of efficient and competitive EM fungi to improve production of ecologically and economically important African multipurpose trees in plantations.

Pakaraimaea dipterocarpacea is ectomycorrhizal, indicating an ancient Gondwanaland origin for the ectomycorrhizal habit in Dipterocarpaceae.

The consistent association of Paleotropical Dipterocarpaceae with ectomycorrhizal (ECM) fungi suggests that ECM status is an ancestral character in the family. Despite its distinctive morphology, Pakaraimaea dipterocarpacea, a Neotropical Dipterocarpaceae endemic to the Guayana Region, is phylogenetically related to the Paleotropical Dipterocarpaceae. The confirmation of P. dipterocarpacea ECM status would indicate that Paleotropical Dipterocarpaceae and P. dipterocarpacea probably had a common ECM ancestor. Mycorrhizal colonization of P. dipterocarpacea was assessed, and ECMs were recorded using histological and molecular methods. P. dipterocarpacea was highly colonized by typical ECMs, and several ECM fungal taxa belonging to Clavulinaceae, Sebacinaceae, Cortinariaceae and Amanitaceae were identified. This paper provides the first documented evidence of ECM in a neotropical genus of Dipterocarpaceae and indicates that ECMs possibly evolved in Gondwana in ancestors of Dipterocarpaceae before the separation of South America from Africa by the Atlantic, c. 135 million years ago. The observation of Sebacinaceae and Clavulinaceae suggests that broad host range fungi are important components of P. dipterocarpacea ECM communities.

Foliar 15N natural abundance indicates phosphorus limitation of bog species.

Foliar delta15N, %N and %P in the dominant woody and herbaceous species across nutrient gradients in New Zealand restiad (family Restionaceae) raised bogs revealed marked differences in plant delta15N correlations with P. The two heath shrubs, Leptospermum scoparium (Myrtaceae) and Dracophyllum scoparium (Epacridaceae), showed considerable isotopic variation (-2.03 to -15.55 per thousand, and -0.39 to -12.06 per thousand, respectively) across the bogs, with foliar delta15N strongly and positively correlated with P concentrations in foliage and peat, and negatively correlated with foliar N:P ratios. For L. scoparium, the isotopic gradient was not linked to ectomycorrhizal (ECM) fractionation as ECMs occurred only on higher nutrient marginal peats where 15N depletion was least. In strong contrast, restiad species (Empodisma minus Sporadanthus ferrugineus, S. traversii) showed little isotopic variation across the same nutrient gradients. Empodisma minus and S. traversii had delta15N levels consistently around 0 per thousand (means of -0.12 per thousand and +0.15 per thousand respectively), and S. ferrugineus, which co-habited with E. minus, was more depleted (mean -4.97 per thousand). The isotopic differences between heath shrubs and restiads were similar in floristically dissimilar bogs and may be linked to contrasting nutrient demands, acquisition mechanisms, and root morphology. Leptospermum scoparium shrubs on low nutrient peats were stunted, with low tissue P concentrations, and high N:P ratios, suggesting they were P-limited, which was probably exacerbated by markedly reduced mycorrhizal colonizations. The coupling of delta(15)N depletion and %P in heath shrubs suggests that N fractionation is promoted by P limitation. In contrast, the constancy in delta15N of the restiad species through the N and P gradients suggests that these are not suffering from P limitation.

Abundance and characteristics of Pisolithus ectomycorrhizas in New Zealand geothermal areas.

Pisolithus is restricted in New Zealand to geothermal areas where it associates with Kunzea ericoides var. microflora (prostrate kanuka) and occasionally Leptospermum scoparium. Here we describe for the first time the ectomycorrhizal morphotypes of three New Zealand Pisolithus species and report the frequency and abundance of these morphotypes against other mycorrhizal fungi associated with these hosts in New Zealand geothermal areas. The three Pisolithus species form typical ectomycorrhizal associations with Kunzea ericoides var. microflora, and one also was observed forming typical ectomycorrhizal associations with Leptospermum scoparium. Although the morphotypes from the three Pisolithus species share many morphological and anatomical characteristics, they vary with regard to the abundance of rhizomorphs. The common occurrence of Pisolithus fruiting bodies at the geothermal sites was matched by frequent and abundant Pisolithus ectomycorrhizas. Pisolithus ectomycorrhizas were frequent (100% of soil cores) and abundant (between 55 and 88% of ectomycorrhizal tips) associates of prostrate kanuka in hot (50 C at 8 cm depth), highly acidic and N depleted soils. The levels of arbuscular mycorrhizal colonization of prostrate kanuka were lower than on K. ericoides and L. scoparium on cooler soils. The stressful conditions where prostrate kanuka dominates probably favor Pisolithus over the mycorrhizal fungi occurring in cooler geothermal areas. Questions about how several genetically similar Pisolithus species co-occur on prostrate kanuka in geothermal areas without mutual competitive exclusion are discussed.

Genetic diversity of Pisolithus in New Zealand indicates multiple long-distance dispersal from Australia.

• Pisolithus is a common ectomycorrhizal (EcM) associate of prostrate kanuka Kunzea ericoides var. microflora (Myrtaceae) in New Zealand geothermal areas. Here, we report the genetic diversity and phylogeny of Pisolithus and interpret the results in relation to the origin of this fungus in New Zealand. • We determined the genetic variation of Pisolithus on the basis of ITS gene sequences and spore morphology. • We identified three Pisolithus species in New Zealand, each matching Australian species associated with eucalypts and acacias. All three species co-occurred locally in thermal areas, with two species sometimes colonizing root tips in the same soil volume, indicating co-occurrence of species on a smaller scale. • We propose that Pisolithus fungi were introduced to New Zealand from Australia by trans-Tasman airflow during recent geological times. The success of this long-distance dispersal of EcM fungi may be related to the capacity of kanuka to act as a 'nurse plant' for wind-blown spores.