Survival of propagules of arbuscular mycorrhizal fungi in soils in eastern Australia used to grow cotton

Abstract

SUMMARYSoil-borne spores and hj^phae 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~^ 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~^ 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.

Patterns of arbuscular mycorrhiza down the profile of a heavy textured soil do not reflect associated colonization potential

“…Alternatively, colonization at depth might have arisen from hyphae or spores in soil or senescent roots. Hyphae growing from colonized senescent roots can establish mycorrhizas (Tommerup & Abbott, 1981), although McGee et al (1997) concluded that senescent roots made a negligible contribution to the colonization of plants and our results support that conclusion. It is unlikely that fresh roots intercepted senescent roots colonized by AM fungi by following previous lines of root growth.…”

Propágulos de fungos micorrízicos arbusculares em solos deficientes em fósforo sob diferentes usos, da região semi-arida no nordeste do Brasil

“…McGee, et al (1997), utilizando o mesmo método, encontraram 20 % de esporos viáveis em amostras de solo recém-coletadas, que diminuíram para 6-7 % após dois anos de estocagem. No presente estudo, o período de estocagem foi ao redor de um ano.…”

High densities of arbuscular mycorrhizal fungi maintained during long fallows in soils used to grow cotton except when soil is wetted periodically

“…The small volume of soil should not affect the initiation of infection, or the initial spread of infection within the roots. It is likely that the small volume of soil affected the shoot growth of the seedlings, and the data obtained do not indicate the mycorrhizal effect on plant growth which we have demonstrated elsewhere (Pattinson et al, 1997).…”

“…It IS likely that the soils contained more propagules tban were necessary to initiate maximum rates of infection as suggested by McGee et al (1997). Tbe result of excess propagules would be to mask effects of factors tbat deplete the number of propagules.…”

“…Thus the survival of spores and hyphae in soil during the fallow will determine the propagule density of AM fungi following cotton. \'^iability of AM fungi can decline over time (Thompson, 1987;McGee et al, 1997), be reduced by cultivation or disturbance (Evans & Miller, 1988, 1990Fairchild & Miller, 1988, 1990Jasper, Abbott & Robson, 1989;McGonigle, Evans & Miller, 1990;McGee et al, 1997), environmental factors such as soil temperature and relative humidity (Sylvia & Schenck, 1983;Daft, Spencer & Thomas, 1987;Ruiz-Lozano & Azcon, 1996), and application of pesticides (Trappe, Molina & Castellano, 1984) and perhaps fertilizers (Johnson & Pfleger, 1992). The rate or extent to which each factor affects \'iability of AA'I fungi is unclear.…”