Mycorrhizal colonization and mycotrophic growth of native woody species as related to successional groups in Southeastern Brazil

Differences in arbuscular mycorrhizal colonization, mycotrophic growth and response to superphosphate were studied in seedlings of 28 native woody species belonging to different successional groups in woodland fragments in the state of Minas Gerais, Southeastern Brazil. The experiment was carried out in a glasshouse in plastic bags filled with a soil-mix composed of soil + burnt rice shell (6:1 v/v) amended or not with superphosphate (Control, P) and infested or not with a mixture of arbuscular mycorrhizal (AM) fungi Glomus etunicatum Becker and Gerdermann and Gigaspora margarita Becker and Hall (M) and co-application of P and M (MP), with 10 replications per species. Successional groups were represented by 8, 5, 4 and 11 species of pioneers, early secondary, late secondary and climax species, respectively. It was found that dry matter yield of climax species was 6.8-fold higher than the pioneer ones in control treatments. However, pioneers were markedly more responsive to soil-mix treatments than climax ones. Based upon shoot dry matter, overall response for M, P and MP overcontrols was 813, 575 and 1688% for pioneers and 0, 48 and 106% for climax ones. Mycorrhizal effects were much greater in soil-mix with no added P than when superphosphate was added. They were maximum and consistent among pioneers and markedly diminished in climax species in which positive response to M was found in only 27% of the species of this group. AM colonization ranged from 0 to 81% of the root length colonized and it was inversely related to succession and directly related to mycorrhizal response. Growth responses to soil-mix treatments were inversely related to seed weight and to succession. Pioneer species have light seeds, high susceptibility to infection and colonization rate and are responsive to both mycorrhiza and superphosphate, whereas, late successional species are more dependent upon their seed reserves than upon AM and superphosphate for initial growth. However, late successional species may become myconhiza-dependent in later growth stages. The Glomalean fungi and soil phosphorus are important factors in light of the forest ecology and reforestation technology in low-fertility soils in the tropics. (C) 1998 Elsevier Science B.V.