Effects of arbuscular mycorrhizal inoculation and fertilizer on production of Castanopsis acuminatissima saplings for forest restoration in northern Thailand

ABSTRACT: Castanopsis acuminatissima is a native tree species, used to restore evergreen forest ecosystems in northern Thailand. To accelerate tree seedling growth, experiments were performed to determine the efficacy of inoculating C. acuminatissima seedlings with arbuscular mycorrhizal (AM) fungi, produced on sorghum (Acaulospora elegans, Glomus etunicatum, Glomus mosseae). The effects of AM inoculation, together with application of phosphate fertilizer (KH2PO4) on seedlings, in a P-deficient soil were determined under greenhouse conditions. Increasing P-application greatly enhanced seedling growth (maximum at 250 mg kg-1 soil). Growth was most rapid with G. etunicatum-colonized plants together with P-application (40.8 cm). Much lower growth was recorded with non-AM plants without P added (14.4 cm). In a second experiment, seedlings were grown in forest soil, with a slow-release fertilizer (NPK), with or without AM inoculation. Seedling growth was significantly enhanced by the fertilizer, but not by the fungi. Greatest height increase was found with non-AM plants that received fertilizer (14.5 cm tall), whereas lower height was recorded for non-AM plants with no fertilizer added (10.9 cm). AM inoculation  enhanced seedling growth more in P-deficient soil than in forest soil, due to differences in the abilities of AM species to establish a symbiosis. Therefore, for efficient sapling production, the soil properties and the fertilizer regimen should be evaluated, along with secondary effects caused by changes in mycorrhizal association.