Arbuscular mycorrhizal fungi (AMF) are important components of soil microbiota in the rhizosphere. The diversity and dynamics of AMF may have a marked impact on the structure and diversity of associated plant communities, both in the natural and agricultural ecosystems. As part of the effort to evaluate the potential role of arbuscular mycorrhizal fungi in the regeneration of secondary forest, we studied the extent of mycorrhizal association in a tropical secondary forest of Southern China.
Rhizosphere soil samples of 26 different plants species in 13 families were randomly collected from soil cores of 030 cm depth in a tropical secondary forest of Xishuangbanna, Southwestern China. The study site consisted of nutrient-deficient ferralsol. Total nitrogen (N) was between 0.751.9 g/kg, with an average of 1.2 g/kg. Total phosphorus (P) ranged from 0.92 to 8.3 mg/kg, with an average of 2.6 mg/kg. Exchangeable potassium (K) was 41.0139.2 mg/kg, with an average of 81.7 mg/kg. Organic carbon was 11.830.4 g/kg, with an average of 18.7 g/kg. The arbuscular mycorrhizal association of these 26 plant species and the spore density of AMF in the rhizosphere soils were analyzed. All 26 plant species were infected with arbuscular mycorrhizal fungi that belonged to eleven species, i.e. Glomus geosporum, G. fasciculatum, G. aggregatum, G. constrictum, G. etunicatum, G. mosseae, G. microcarpum, Gigaspora margarita, Scutellospora calospora, Acaulospora scrobiculata and Acaulospora laevis. The AMF spore density ranged from 13 to 29 per 100 g soil, with an average of 19. The highest and lowest spore density belonged to Olea rosea Craib (Oleaceae) and Pithecolobium clypearia Benth. (Papilionaceae), respectively. The species richness was between 4 and 9 per plant species with an average of 6. The highest ones were Schizomussaenda dehiscens (Craib) H.L. Li (Rubiaceae) and Elaeocarpus prunifolioides Hu (Elaeocarpaceae); the lowest one was Macaranga kurzii (Kuntze) Pax & Hoffm. in Engl. (Euphorbiaceae). The frequency of AMF species ranged from 26.9% to 100%, with an average of 53.8%; the highest and lowest frequency belonged to G. geosporum and Scutellospora calospora, respectively. The relative abundance［12］ of AMF species was between 3.0% (G. etunicatum) to 26.5% (G. geosporum). Shannon-Weiner index and species evenness index of AMF was 0.94 and 0.93, respectively.
The presence of coenocytic hyphae, intercellular hyphae or intracellular hyphal coils, arbuscules, and/or vesicles in the root cortex was used to assign AM fungal colonization. Percent root length with hyphae in 26 plant species ranged from 8.6 to 16.2, with an average of 11.1%; the lowest and the highest one was Castanopsis hystrix Miq. (Fagaceae) and Olea rosea Craib (Oleaceae), respectively. Percent root length with vesicles ranged from 19.2 to 24.4, with an average of 22.7; the lowest one was Macaranga kurzii (Kuntze) Pax & Hoffm. in Engl. (Euphorbiaceae) and the highest ones belonged to Castanopsis hystrix Miq. (Fagaceae), Itea macrophylla Wall. (Escalloniaceae), Homalium ceylanicum Gagnep. (Samydaceae) and Elaeocarpus prunifolioides Hu (Elaeocarpaceae). Percent root length with arbuscules ranged from 13.6, Pithecolobium clypearia Benth.(Papilionaceae), to 20.9, Schima wallichii Choisy (Theaceae), with an average of 17.1; the AMF colonization was between 44.8%, Pithecolobium clypearia Benth.(Papilionaceae), to 56.5%, Macaranga kurzii (Kuntze) Pax & Hoffm. in Engl. (Euphorbiaceae), with an average of 50.9%. AMF were found in 50.9% of plant roots with Glomus and Acaulospora as the dominant genera. Our data suggest a high presence of arbuscular mycorrhizal association in tropical secondary forest of Xishuangbanna.