Ecological stoichiometry has been widely applied in aquatic ecosystems, but has limited implications in terrestrial ecosystems. The pot experiments with Trifolium repens L. were conducted to demonstrate the relations between C: N: P, biological components and growth rate of clover colonized by arbuscular mycorrhizal (AM) fungi. The results showed that for mycorrhizal clover, N, P concentrations increased with increasing growth rate, in support of the Growth Rate Hypothesis (GRH). Mycorrhizal clover had higher P and RNA concentrations than non-mycorrhizal clover, indicating that the increase in P concentration would invest more RNA to meet the synthesis of protein. Results also indicated that the increase in N concentration with rapid growth rate may be attributed to the increase in the concentration of protein N. Underlying mechanisms driving the association of C: N: P with growth rate for symbiotic partners should help elucidate the allocation of major nutrients to cellular organs and trophic dynamics in terrestrial ecosystems.

SUMMARYCommunities of arbuscular mycorrhizal fungi (AMF) were surveyed in different South Australian ecosystems. The soil was wet-sieved for spore extraction, followed by the determination of presence and abundance of AMF species as well as the percentage of root colonization. Mycorrhizal associations were common and there was substantial fungal diversity in different ecosystems. Spores were most abundant in the permanent pasture system and less abundant under continuous wheat. The incidence of mycorrhizal associations in different plant species and the occurrence of Arum-and Paris-type colonization generally conformed with previous information. Spores of seventeen AMF were verified throughout seasonal changes in 1996 and 1997 in the permanent pasture and on four host species (Lolium perenne, Plantago lanceolata, Sorghum sp. and Trifolium subterraneum), set up with the same soils under greenhouse conditions. Glomus mosseae was the dominant spore type at all sampling times and in all trap cultures. Mycorrhizal diversity was significantly affected by different sampling times in trap cultures but not in field-collected soil. P. lanceolata, Sorghum sp. and T. subterraneum as hosts for trap cultures showed no differences in richness and diversity of AMF spores that developed in association with their roots. Abundance and diversity were lowest, however, in association with L. perenne, particularly in December 1996. Results show that the combination of spore identification from field-collected soil and trap cultures is essential to study population and diversity of AMF. The study provides baseline data for ongoing monitoring of mycorrhizal populations using conventional methods and material for the determination of the symbiotic effectiveness of AMF key members.Index terms: trap cultures, Glomus, Gigaspora.

A systematic application of the fungicide benomyl was used to follow up the suppression of arbuscular mycorrhizal (AM) colonization and to determine its fungitoxic activity and persistence at different depths. Repeated applications of benomyl reduced AM colonization mainly in the upper 0-4 cm layer of the treated soils. Furthermore, AM colonization decreased with soil depth. The activity and persistence of this fungicide was reduced over small changes in depth in the first 10 cm of the soil profile beneath a semiarid herbland at Brookfield Conservation Park (South Australia). Repeated applications of the fungicide only slightly increased the levels of toxicity in the soils, probably because of biodegradation of the fungicide in soils with a recent history of exposure to the fungicide. The decline in fungicide activity at depth was correlated with a decline in the suppressive effect of the fungicide on the activity of AM fungi.Résumé : Une application systématique du fongicide Bénomyl a été utilisée pour suivre la suppression de la colonisation par les mycorhizes arbusculaires (MA) ainsi que pour déterminer son activité fongicide et sa persistance à différentes profondeurs. Des applications répétées de Bénomyl réduisaient la colonisation par les MA principalement dans la couche supérieure de 0-4 cm des sols traités. En outre, la colonisation par les MA diminuait en fonction de la profondeur du sol. L'activité et la persistance de ce fongicide étaient progressivement réduites avec la profondeur dans les 10 premiers centimètres de sol sous une formation végétale herbacée semi-aride dans le Brookfield Conservation Park (Australie du Sud). Des applications répétées du fongicide n'augmentaient que légèrement les niveaux de toxicité des sols, probablement à cause de la biodégradation de ce fongicide dans les sols récemment exposés au fongicide. Le déclin de l'activité du fongicide en profondeur était corrélé avec un déclin de l'effet suppresseur du fongicide sur l'activité des champignons MA.

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