SURVIVAL OF PROPAGULES OF ARBUSCULAR MYCORRHIZAL FUNGI IN SOILS IN EASTERN AUSTRALIA USED TO GROW COTTON

Soil-borne spores and hyphae of arbuscular mycorrhizal fungi are impor tant propagules in cracking clay soils of northern NSW, Australia. In these soils, senescent roots were uncommon. Although c. 4-200 spores g (-1) soil were found, less than 6% established arbuscular mycorrhizas in trap plants, and this percentage declined over 24 months. Using tet razolium red as a vital stain, 16-21 % of spores from held soils were found to be viable in fresh soil and 6-7 % after 24 months of storage. Using fluorescein diacetate, the length of stained hyphae of c. 0 5 m g(-1) soil was shown to be halved over 32 wk. The density of viable p ropagules of arbuscular mycorrhizal fungi in soil declined over time a nd was reduced by severe disturbance. The fungi that survived to 12 mo nths included a species thought to form dormant spores, while those in itiating infection after 24 months, did not.