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Tedersoo L.,University of Tartu | Bahram M.,University of Tartu | Jairus T.,University of Tartu | Bechem E.,University of Buea | And 8 more authors.
Molecular Ecology | Year: 2011

Mycorrhizal fungi play a key role in mineral nutrition of terrestrial plants, but the factors affecting natural distribution, diversity and community composition of particularly tropical fungi remain poorly understood. This study addresses shifts in community structure and species frequency of ectomycorrhizal (EcM) fungi in relation to host taxa, soil depth and spatial structure in four contrasting African ecosystems. We used the rDNA and plastid trnL intron sequence analysis for identification of fungi and host plants, respectively. By partitioning out spatial autocorrelation in plant and fungal distribution, we suggest that African EcM fungal communities are little structured by soil horizon and host at the plant species and family levels. These findings contrast with patterns of vegetation in these forests and EcM fungal communities in other tropical and temperate ecosystems. The low level of host preference indirectly supports an earlier hypothesis that pioneer Phyllanthaceae may facilitate the establishment of late successional Fabaceae and potentially other EcM host trees by providing compatible fungal inoculum in deforested and naturally disturbed ecosystems of tropical Africa. © 2011 Blackwell Publishing Ltd. Source

The overexploitation of natural resources, resulting in an increased need for arable lands by local populations, causes a serious dysfunction in the soil's biological functioning (mineral deficiency, salt stress, etc.). This dysfunction, worsened by the climatic conditions (drought), requires the implementation of ecological engineering strategies allowing the rehabilitation of degraded areas through the restoration of essential ecological services. The first symptoms of weathering processes of soil quality in tropical and Mediterranean environments result in an alteration of the plant cover structure with, in particular, the pauperization of plant species diversity and abundance. This degradation is accompanied by a weakening of soils and an increase of the impact of erosion on the surface layer resulting in reduced fertility of soils in terms of their physicochemical characteristics as well as their biological ones (e.g., soil microbes). Among the microbial components particularly sensitive to erosion, symbiotic microorganisms (rhizobia, Frankia, mycorrhizal fungi) are known to be key components in the main terrestrial biogeochemical cycles (C, N and P). Many studies have shown the importance of the management of these symbiotic microorganisms in rehabilitation and revegetation strategies of degraded environments, but also in improving the productivity of agrosystems. In particular, the selection of symbionts and their inoculation into the soil were strongly encouraged in recent decades. These inoculants were selected not only for their impact on the plant, but also for their ability to persist in the soil at the expense of the residual native microflora. The performance of this technique was thus evaluated on the plant cover, but its impact on soil microbial characteristics was totally ignored. The role of microbial diversity on productivity and stability (resistance, resilience, etc.) of eco- and agrosystems has been identified relatively recently and has led to a questioning of the conceptual bases of controlled inoculation in sustainable land management. It has been suggested that the environmental characteristics of the area to rehabilitate should be taken into account, and more particularly its degradation level in relation to the threshold of ecological resilience. This consideration should lead to the optimization of the cultural practices to either (i) restore the original properties of an ecosystem in case of slightly degraded environments or (ii) transform an ecosystem in case of highly degraded soils (e.g., mine soils). In this chapter, we discuss, through various examples of experiments conducted in tropical and Mediterranean areas, the performance of different strategies to manage the microbial potential in soils (inoculation of exotic vs. native species, inoculation or controlled management potential microbial stratum via aboveground vegetation, etc.) based on the level of environmental degradation. © 2013 Académie des sciences. Source

Henry C.,Montpellier SupAgro | Raivoarisoa J.-F.,Ambatovy | Razafimamonjy A.,Ambatovy | Ramanankierana H.,Center National Of Recherches Sur Lenvironnement | And 3 more authors.
Forest Ecology and Management | Year: 2015

Ecological restoration in severely disturbed environments can fail because of lack of knowledge of the functioning of the original ecosystem. Nevertheless, facilitating establishment between plant species can help accelerate ecological succession, especially in stressful environments. Mycorrhizal symbiosis plays a key role in plant growth, particularly in harsh environments, and could also play a role in facilitation between plants, as mycorrhizal fungi can form a mycelial network that simultaneously interacts with the root systems of several plant species. In a high-elevation Malagasy tropical rainforest on acidic and iron-rich soil surrounding an active mining site, four genera of ectomycorrhizal plants are locally abundant: Leptolaena, Sarcolaena, Uapaca and Asteropeia. A floristic survey showed that only Asteropeia seedlings can grow on bare soil. Molecular analysis of ectomycorrhizal fungi ITS rDNA enabled us to describe ectomycorrhizal communities and their distribution among these four plant genera. Russulaceae, Boletales, Cortinariaceae and Thelephoraceae are abundant in these forests. There is extensive sharing between ectomycorrhizal communities associated with Asteropeia mcphersonii and other ectomycorrhizal plants. There are also many mycorrhizal fungi species which are common to ectomycorrhizal communities of seedlings and adult trees. This abundance of generalist fungi allows us to envisage the use of A. mcphersonii in the ecological restoration of the mine site. Planting ectomycorrhizal fungi in the bare soil at the beginning of ecological restoration could allow them to grow, thereby establishing a source of inoculum to colonize other ectomycorrhizal plants and consequently facilitate their establishment. © 2015 Published by Elsevier B.V. Source

Harinantenaina Rakotondraibe L.,Ohio State University | Rasolomampianina R.,Center National Of Recherches Sur Lenvironnement | Park H.-Y.,Ohio State University | Li J.,Ohio State University | And 9 more authors.
Bioorganic and Medicinal Chemistry Letters | Year: 2015

In continuation of our ongoing search for bioactive compounds from microbial extracts, we performed antiproliferative and/or antimalarial assays on extracts of 806 microbial species isolated from Madagascan marine organisms, on 1317 species isolated from Madagascan soil samples and on a Streptomyces species (S.4) from a marine sponge collected from the Florida Keys. This work identified active extracts from four Streptomyces isolates (S.1, S.2, S.3 and S.4). The extracts of Streptomyces S.1 and S.2 showed antiproliferative activity against the A2780 ovarian cancer cell line, while those of S.3 and S.4 displayed both antiproliferative and antimalarial activity. Bioassay-guided fractionation coupled with dereplication of the active extracts led to the identification and isolation of nonactin (1), monactin (2), dinactin (3), ±-nonactic acid (4), toyocamycin (5), piperafizine A (6) and a new dipeptide named xestostreptin (7). The structures of all isolated compounds 1-7 were elucidated by analyses of their NMR spectroscopic and mass spectrometric data, and were confirmed by comparison with the data reported in the literature. Compound 6 was crystallized and subjected to X-ray diffraction analysis to confirm its structure as piperafizine A (6). Compounds 1-3 displayed strong antiproliferative activity against A2780 ovarian cancer cells (IC50 values of 0.1, 0.13 and 0.2 μM, respectively), A2058 melanoma cells (IC50 values of 0.2, 0.02 and 0.02 μM, respectively), and H522-T1 non small-cell cancer lung cells (IC50 values of 0.1, 0.01 and 0.01 μM, respectively), while compounds 4 and 7 exhibited weak antiplasmodial activity against the Dd2 strain of Plasmodium falciparum, with IC50 values of 6.5 and 50 μM, respectively. © 2015 Elsevier Ltd. All rights reserved. Source

Baohanta R.,Center National Of Recherches Sur Lenvironnement | Thioulouse J.,CNRS Biometry and Evolutionary Biology Laboratory | Ramanankierana H.,Center National Of Recherches Sur Lenvironnement | Prin Y.,Montpellier SupAgro | And 8 more authors.
Biological Invasions | Year: 2012

The objectives of this study were to determine the impact of two exotic tree species (pine and eucalypts) on the early growth of Uapaca bojeri (an endemic tree species from Madagascar) via their influence on soil chemical, microbial characteristics, on ectomycorrhizal fungal community structures in a Madagascarian highland forest and to test the ability of an early-successional ectomycorrhizal shrub, Leptolena bojeriana, to mitigate the impacts of these exotic species. Finally, we hypothesized that L. bojeriana could act as a natural provider for ectomycorrhizal propagules. Soil bioassays were conducted with U. bojeri seedlings grown in soils collected under the native tree species (U. bojeri and L. bojeriana) and two exotic tree species (Eucalyptus camaldulensis and Pinus patula) and in the same soils but previously cultured by L. bojeriana seedlings. This study clearly shows that (1) the introduction of exotic tree species induces significant changes in soil biotic and abiotic characteristics, (2) exotic-invaded soil significantly reduces the early growth and ectomycorrhization of U. bojeri seedlings and (3) L. bojeriana decreased these negative effects of the exotic tree species by facilitating ectomycorrhizal establishment and consequently improved the U. bojeri early growth. This study provides evidence that L. bojeriana can facilitate the ectomycorrhizal infection of U. bojeri and mitigates the negative effects of the introduction of exotic tree species on the early growth of the native tree species. From a practical point of view, the use of ectotrophic early-successional shrub species should be considered to improve forest resaturation after exotic invasion. © 2012 Springer Science+Business Media B.V. Source

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