Glomalean mycorrhizal fungi from tropical Australia I. Comparison of the effectiveness and specificity of different isolation procedures

A comparison of different methods for isolation of vesicular-arbuscular myc orrhizal (VAM) fungi into open-pot cultures was undertaken as part of a stu dy of the diversity of these fungi. Four different isolation techniques usi ng spores separated from soil, soil trap cultures, root samples, or transpl anted seedlings grown in intact soil cores were used to obtain as many fung i as possible from each site. Isolation methods were compared using paired samples from the same locations within natural (savanna, rocky hill, wetlan d, rainforest) and disturbed (minesite) habitats in a seasonally dry tropic al region in the Northern Territory of Australia. There were large differen ces in (i) the efficiency (rate of increase in mycorrhizal colonisation), ( ii) the proportion of successful cultures, (iii) fungal diversity (number o f fungal species in each culture) and (iv) specificity (identity of species isolated) between these four procedures. However, the less-efficient proce dures generally resulted in a higher proportion of cultures of one fungus, which could be used without further isolation steps. Most species of Scutel lospora, Acaulospora and Gigaspora were obtained primarily from field-colle cted spores, but only 50% of these culture attempts were successful. Spores from these initial cultures produced mycorrhizas much more rapidly and suc cessfully when used to start second-generation cultures. Several species of fungi, rarely recovered as Living spores from field soils, were dominant i n many trap cultures started from soil or roots. Most of these fungi were G lomus species, that were first distinguished by colonisation patterns in ro ots and eventually identified after sporulation in second- or third-generat ion trap cultures. These experiments demonstrated that glomalean fungi in t he habitats sampled belonged to two functional categories, based on whether or not spores were important propagules. The "non-sporulating" fungi were dominant in many trap cultures, which suggests that these fungi had higher total inoculum levels in soils than other fungi. Pot-culturing methods prov ided additional information on fungal diversity which complemented spore oc currence data obtained using the same soil samples and provided valuable ne w information about the biology of these fungi.