Plant Architecture, Growth and Biomass Allocation Effects of the Invasive Pathogen Myrtle Rust (austropuccinia Psidii) on Australian Myrtaceae Species after Fire

In 2010, the parasitic fungus Austropuccinia psidii (myrtle rust) was detected in Australia. Austropuccinia psidii infects immature growth of myrtaceous species. Many of Australia's myrtaceous species occur within fire-prone vegetation communities and have the capacity to resprout after fire. Therefore, it is likely that new post-fire growth may be vulnerable to A. psidii infection, causing subsequent flow-on effects to species' persistence and community dynamics. The aim of this study was to test the impacts of A. psidii on native Australian Myrtaceae species after fire. We grew eight native susceptible species in a glasshouse experiment before burning them and inoculating the resprouting new growth of half the plants with A. psidii. We assessed the effect of A. psidii on the architecture, growth and biomass allocation of our study species. Although general patterns were observed across species, results were found to be species-specific. Austropuccinia psidii significantly reduced the height of two of the eight species (Callistemon citrinus and Eucalyptus moluccana), but none of the species had increased branching. As expected, specific leaf area was lower (9%) in inoculated plants - although only significant for C. citrinus and E. dalrympleana - and leaf biomass was greater (15%), but significant for Angophora costata only. Finally, biomass allocation did not significantly differ between infection treatments. We can conclude that the effect of A. psidii infection on fire-damaged plants has significant impacts on plants at the species level, which may have flow-on effects at the community level, especially after repeated infections. Furthermore, these impacts may be exacerbated in the future under climate change, as the predicted increase in frequency and intensity of fires across Australia will result in more frequent new growth availability, providing more opportunities for A. psidii infection.