Mycorrhizal dependency, inoculum potential and habitat preference of native woody species in South Brazil

Seedlings from 43 native woody species belonging to different successional groups from the Tibagi River Basin, Parana State, South Brazil were studied to obtain information on the importance of colonization by native arbuscul ar mycorrhizal (AM) fungi. The experiment was carried out in a greenhouse f or 15 to 45 wk, with soil-mix treatments and four successional groups. The mycorrhizal dependency was 90, 48, 12 and 14% of the pioneer, early seconda ry, late secondary and climax species, respectively. The content of P, Ca a nd K was 20, 17 and 23 times greater, respectively, in the leaves of the pi oneer species than in the other successional groups. The colonization by AM fungi in field was studied in seedlings of 36 native woody species collect ed in the interior of the forest of the Mata dos Godoy State Park, and in o pen area at the beginning of arboreal succession. The mycorrhizal colonizat ion in the field was 55.5, 26.9, 6.1 and 2.2% for the pioneer, early second ary, late secondary and climax species, respectively. To assess the mycorrh izal inoculum potential, rhizosphere soil was collected in the interior of the forest and a gap in the same forest and in a cleared area abandoned for natural regeneration. The inoculum potentials and the spore number in the area at the beginning of succession were 5.6 and 53.4 times greater than in the interior of the forest. The results show that the initial growth of th e woody species which take part in the initial phases of succession may be more dependent on the AM fungi, in soils poor in minerals, while those that make up the final succession phases may be less dependent. The potential o f the AM fungi inoculum decreases throughout the successional process and t here is a relation between the inoculum potential found in the field and th e occurrence for the different habitats of the species of adult plants belo nging to different successional groups.