Effect of inoculation time on camptothecin content in arbuscular mycorrhizal Camptotheca acuminata seedlings Effect of arbuscular mycorrhiza on camptothecin content in Camptotheca acuminata seedlings Effect of co-cultivation time on camptothecin content in Camptotheca acuminata seedlings after inoculation with arbuscular mycorrhizal fungi EFFECTS OF ARBUSCULAR MYCORRHIZAL FUNGI ON THE GROWTH AND ABSORPTION OF NITROGEN AND PHOSPHORUS IN CAMPTOTHECA ACUMINATA SEEDLINGS Effect of nitrogen on camptothecin content in Camptotheca acuminata seedlings