Diversity and dynamics of mycorrhizal associations in tropical rain forests with different disturbance regimes in South Cameroon

The present study documents the occurrence of mycorrhizal associations in the rain forests of south Cameroon. All species investigated are mycorrhizal. Most timber species form arbuscular mycorrhiza, but some timber species, which usually occur in clumps, form ectomycorrhiza. Species diversity of ectomycorrhizal fungi in the undisturbed rain forest is substantial, with more than 125 species having been recorded. Inoculum potential of arbuscular mycorrhizal and ectomycorrhizal fungi is high in the undisturbed rain forest. The shifting cultivation cycle increases inoculum potential of arbuscular mycorrhizal fungi, but lowers inoculum potential of ectomycorrhizal fungi to various extent.On sites of forestry practices (skid trails, landings) inoculum potential of arbuscular mycorrhizal and ectomycorrhizal fungi is very substantially reduced and recovery rates are low. Mycorrhizal colonisation and seedling growth are positively correlated with mycorrhiza inoculum potential. Inoculum potential of arbuscular mycorrhizal fungi and performance of seedlings of arbuscular mycorrhizal trees can be boosted after inoculum addition. Both inoculum quantity and inoculum quality are important criteria for inoculation practices. Ectomycorrhizal inoculum potential cannot be increased through inoculum addition and management of the intact ectomycorrhizal network is necessary for maintenance of the ectomycorrhizal tree species.Key words : Arbuscular mycorrhiza, ectomycorrhiza, disturbance, rain forest, diversity, inoculum potential, Cameroon, forestry practices</p

Habitat and diversity of ectomycorrhizal fungi in forests of South Cameroon

Information is lacking on habitat and diversity of ectomycorrhizal (ECM) fungi of African humid forests. For three years, mushroom excursions were carried out in four sites with contrasted soil and altitude characteristics of South Cameroon, during wet seasons. Collected fungi were described in fresh state and dried exsiccates examined for microscopic description before morpho-anatomical identification. ECM fungi abundantly fruited exclusively in mixed caesalp, monodominant Gilbertiodendron and Uapaca forest clumps, independently of elevation, rainfall, topography and soil texture. 21 ECM tree species in 11 genera belonging to two families, Ceasalpiniaceae and Phyllanthaceae, dominated ECM forest clumps. More than 100 putative ECM fungal species in 27 genera were identified and assigned to seven families and one super family group. Members of Russulaceae and Amanitaceae recruited the highest number of ECM taxa, followed by species of Boletoids and Cantharellaceae. Paxillus, Clavulina, Coltricia, Scleroderma, Cortinarius and Inocybe genera contained limited species. 12 ECM fungal species were locally edible, including Lactarius gymnocarpus and all chanterelles. Though, species richness was very large in a mountainous area, all four sites shared a substantial large number of ECM mushroom species. Low plant diversity but high fungal richness recommends ECM forest clumps for biodiversity sanctuaries

Growth response of three native timber species to soils with different arbuscular mycorrhizal inoculum potentials in south Cameroon

After tropical forest disturbance, mycorrhizal inoculum could be insufficient. Increasing mycorrhizal density through inoculum addition is then crucial for successful regeneration of deforested lands. Greenhouse bioassays were set up to determine the effectiveness of native arbuscular mycorrhizal fungi in soils from different disturbance stages on the growth of three important timber species, Terminalia superba, Distemonanthus benthamianus, and Entandrophragma utile. Soils were collected from late and early successional forest stands, fields of food crops, fallow of Chromolaena odorata, skid trails, bare soil landings, and landings with the pioneer tree Musanga cecropioides. These soils were used to grow seedlings without or with addition of an inoculum collected under the grass Paspalum conjugatum. The extent to which seedlings responded to indigenous inoculum and inoculum addition varied with tree species and with mycorrhizal inoculum potential. After inoculum addition, Terminalia strongly increased root colonization with a small increase in shoot dry weight and Distemonanthus hardly increased root colonization but showed a strong increase in shoot dry weight. Entandrophragma increased both root colonization and shoot dry weight. Plant biomass was lower in soils with low inoculum potential such as late successional stands, skid trails, and both kinds of landings; the mycorrhizal inoculation effect was then large. Plant biomass was high in agricultural fields and fallow; mycorrhizal inoculation effect was sometimes even negative. These data indicate that low inoculum might limit plant re-establishment after disturbance and that mycorrhizal inoculation has a potential for improving seedling establishment on deforested land

Importance of the ectomycorrhizal network for ectomycorrhiza formation and seedling survival in rain forests of South Cameroon

An investigation was undertaken at two sites in south Cameroon to assess the importance of living roots of adult trees as sources of inoculum for survival, ectomycorrhizal colonisation and growth of seedlings of Paraberlinia bifoliolata. One-month-old seedlings of Paraberlinia bifoliolata, isolated from or in contact with roots of adult target trees, were transplanted in concentric circles 5, 10, 15, and 30 m away from the stem bases of four adult tree species (Afzelia bipindensis, Brachystegia cynometroides,Paraberlinia bifoliolata and Tetraberlinia bifoliolata). After 4 and 8 months, survival, ectomycorrhiza formation and seedling height were observed; plant biomass was determined after 8 months. After 4 months, there was no difference in seedling survival between seedlings in contact with roots of adult trees and isolated seedlings. The number of ectomycorrhizal seedlings was higher among seedlings in contact with adult trees than among isolated seedlings. After 8 months, both seedling survival and ectomycorrhiza formation were higher in seedlings in contact with roots than in isolated seedlings. Seedling survival and ectomycorrhiza formation were highest under Brachystegia. The fraction of surviving seedlings that had formed ectomycorrhizas was lowest under Afzelia. The fraction of surviving seedlings that were ectomycorrhizal declined monotonically towards the edge of the crown projection. Biomass of seedlings in contact with adult trees was significantly higher than that of isolated seedlings. This difference was consistent for all four tree species. The height of seedlings did not vary with the treatment

Growth response of Pterocarpus soyauxii and Lophira alata seedlings to host soil mycorrhizal inocula in relation to land use types.

Deficiency in mycorrhizal inoculum in soils due to land use types (LUT) can be alleviated by quantity and quality inoculum addition. A bioassay was carried out to determine how host soil mycorrhizal inoculum influenced mycorrhizal colonization, carbon allocation and partitioning of seedlings of two native timber species of Cameroon humid forest. Seedlings of Pterocarpus soyauxii and Lophira alata were raised for six months on surface soils (0 - 20 cm) collected from early secondary forests and LUT derived from slash-and-burn agriculture and selective logging. Mycorrhizal inoculation effect (MIE) was derived. Seedlings were mainly colonized by members of the Glomaceae and Gigasporaceae, respectively, as shown by molecular typing. They generally performed poorly in soils with indigenous inoculum. But addition of soil inoculum from P. soyauxii trees favored nodulation, significantly increased mycorrhizal colonization and total biomass but decreased root-to-shoot ratios, resulting in large and positive MIE, irrespective of LUT. ln contrast, host soil inoculum of L. alata did not affect fractional mycorrhizal colonization but significantly increased total biomass and resulted in high carbon allocation to roots in low and sometimes negative MIE. Therefore, seedlings' responses to mycorrhizal inoculum depend on host soil inoculum and that could be critical for successful rejuvenation of tropical trees

Knowledge and utilization of edible mushrooms by local populations of the rain forest of South Cameroon

Indigenous knowledge of edible fungi and their utilization by local populations were investigated in southern Cameroon from 1996 to 1999. Some 100 participants from the major ethnic groups, comprising Bantu farmers and Bagyeli (Pygmy) hunter-gatherers, were interviewed. Mushroom usage by 30 families, (319 persons), was monitored daily for over a year. Mushroom knowledge among both groups was extensive. Over 50 vernacular names were provided by respondents. In Bantu households, women and children, and to some extent hunters, harvest mushrooms. In contrast, the whole Bagyeli household participates. Bantu harvest mushrooms preferentially in secondary forests while Bagyeli collect them predominantly in primary forests. Mushroom consumption is low for both groups, 1.1 and 1.4 kg of fresh mushrooms per person per year, respectively, a rate that is much lower than in central and eastern Africa. The apparent discrepancy between extensive mushroom knowledge and rather infrequent mushroom consumption probably relates to the social valuation of mushrooms

Managing mycorrhiza in tropical multispecies agroecosystems

This paper focuses on the role of mycorrhizal fungi in multispecies agroecosystems and the importance of the mycorrhizal network. The methods for arbuscular mycorrhizal research and the concepts of mycorrhizal responsiveness are briefly discussed. Also covered are the benefits of a perennial mycorrhizal system in multispecies agroecosystems, mycorrhizas in models of nutrient uptake and nutrient cycling, and the management perspectives for arbuscular mycorrhizal associations