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

Samenvatting

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.