The influence of fire frequency an arbuscular mycorrhizal colonization in the shrub Dillwynia retorta (Wendland) Druce (Fabaceae)

Fire regimes have three inter-related components that can affect population dynamics: frequency, intensity and season. However, there has been little effort to study the effects of any of these components on arbuscular mycorr hizas (AM). In order to examine the long-term effects of fire frequency on AM colonization, the roots of Dillwynia retorta were examined at 32 sites s upporting Hawkesbury Sandstone vegetation in the Sydney region of southeast ern Australia. These sites were representative of the broad-scale variabili ty in fire frequencies with respect to the length and timing of inter-fire intervals found in the Sydney region during the previous 30 years. The leng th of the shortest inter-fire interval was significantly correlated with to tal AM colonization, and the length of the longest inter-fire interval was related to the arbuscular colonization. The length of the most-recent inter -fire interval and the time since the shortest inter-fire interval were not related to AM colonization in D. retorta. Furthermore, AM colonization was directly related to the local abundance of the host plant. indicating that the effects of fire frequency on AM colonization are likely to occur indir ectly via direct effects on the host plant. Canonical correspondence analys is demonstrated that the presence and abundance of alternate potential host s had no influence on mycotrophy in D. retorta. Thus, the impact of fire on D. retorta was probably the main factor influencing its mycorrhizal status in relation to fire history.