Thesis (Ph.D.)--Chulalongkorn University, 2008

Ectomycorrhizal (ECM) community structure was investigated in a dry dipterocarp forest in Nan province and Dipterocarpus alatus plantation in Chachoengsao province between 2005 and 2006. Aboveground, 30 ECM species in the natural dipterocarp forest and 9 ECM species in the D. alatus plantation were observed in both years. The dominant ECM species were Russula spp. in the forest and Scleroderma columnare and Russula siamensis in plantation. Underground, ECM morphotypes were identified by morphological and molecular analysis. Twelve ECM morphotypes found in the forest was higher than 4 morphotypes in the plantation. Tomentella spp. and Cenococcum geophilum were dominant in the forest whereas S. columnare and R. siamensis were dominant in the plantation. This indicated that species composition of the underground ECM community did not correlate with aboveground sporocarps community in the native dipterocarp forest whereas correlate in the D. alatus plantation. The effect of soil properties including moisture content, organic matter and pH on ECM community were studies. The ECM community structure significantly varied depending on soil moist content. An experiment was conducted to determine the effect of 3 selected ectomycorrhizal fungi including Astraues asiaticus, A. odratus and Pisolithus abditus on the growth of 7 dipterocarp species; Shorea siamensis, S. roxburghii, S. farinose, Dipterocarpus intricatus, D. obtusifolius, D. alatus and Hopea odorata. The selected ECM species colonized seedling of all dipterocarp species ranging from 26.27% to 74.13% and stimulated growth of the seedlings more than non inoculated seedlings with increasing shoot height, stem diameter and shoot dry weight up to 51.94%, 50.11%, and 64.38%, respectively. This study wouldd be an important step towards understand fundamental characteristics of the ECM community in dipterocarp forest and the use of selected ECM fungi for reforestation and afforestation in Thailand