Soil-borne spores and hyphae of arbuscular mycorrhizal fungi are important 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 tetrazolium red as a vital stain, 16–21 % of spores from field 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 propagules of arbuscular mycorrhizal fungi in soil declined over time and was reduced by severe disturbance. The fungi that survived to 12 months included a species thought to form dormant spores, while those initiating infection after 24 months, did not.

Comparative measurements of gas-exchange, acid accumulation and chlorophyll a fluorescence of different species of Clusia showing C3 photosynthesis, or crassulacean acid metabolism, at the same same field site in Venezuela

Errors occurred in Figures 3 and 4:

Figure 3(a) y-axis: for JO2 read JCO2

Figure 4(a) y-axis: for JO2 read JCO2

This symposium, the third in the annual series initiated by the Trustees of The New Phytologist, shall consist of discussions and 13 presentations about the impacts of nitrogenous compounds dispersed via the atmosphere, and of ozone as a secondary pollutant.