The effect of agricultural practices on the development of indigenous arbuscular mycorrhizal fungi. II. Studies in experimental microcosms

Two glasshouse experiments were performed to assess the development and met abolic activity of mycorrhizas formed by isolates of arbuscular mycorrhizal fungi (AMF) from three different genera, Acaulospora, Gigaspora and Glomus on Desmodium ovalifolium L. plants. In the first experiment the effect of disturbance of a pre-established extra-radical mycelium (ERM) was studied. In the second experiment the effect of phosphate addition as either organic matter (OM) or fertiliser was studied. Disturbance of a pre-established ER M reduced the formation of mycorrhizas by Gigaspora rosea (BEG111) and incr eased that by Glomus manihotis (BEG112) on D. ovalifolium plants. Acaulospo ra tuberculata (BEG41) failed to form mycorrhizas in the experiment. Either Gi. rosea (BEG111) or G. manihotis (BEG112) appeared to be the major compo nent of the colonisation resulting from treatments with combinations of two or three of the AMF and determined the sensitivity of these treatments to disturbance of a pre-established ERM. The addition of phosphate fertiliser (10 mg P kg(-1)) reduced mycorrhiza formation by each species of AMF compar ed with the addition of OM (10 mg P kg(-1)). This work indicates that AMF f rom different genera respond differently to management by agricultural prac tices when in association with a tropical legume. Clearly, there is potenti al to alter the formation of mycorrhizas of AMF from different genera, thro ugh the use of agricultural practices. The significance of the development and metabolic activity of mycorrhizas formed by AMF from different genera f or plant growth is discussed.