Differences in physiological responses to infection by Ceratocystis tsitsikammensis, a native ophiostomatoid pathogen, between a native forest and an exotic forestry tree in South Africa

•First record of the physiological responses of a native and an exotic tree to infection by Ceratocystis tsitsikammensis.•Native tree (Virgilia divaricata) changes its N economy in infected plants.•Invasive tree (Acacia mearnsii) changes its biomass allocation, to below ground storage in response to infection.•Support is found for use of lesion length as proxy for disease development.•These results have important conservation and economic implications.

The native forest-tree pathogen Ceratocystis tsitsikammensis infects native trees (e.g. Virgilia divaricata) and Acacia mearnsii, an invasive alien and important forestry tree in South Africa. We explored the physiological effects of infection by this fungus on these two tree species, within the context of the Biotic Resistance Hypothesis (BRH). The effects of infection on physiological and resource capture parameters were measured, in conjunction with lesion length. Infected V. divaricata trees changed their N economy by relying more on soil derived N and less on biological nitrogen fixation. Infected A. mearnsii trees altered their biomass allocation into below ground investments. The species responded differently to infection, hence it was not clear which was most negatively affected. Results do support numerous studies that base tests of pathogenicity on lesion length. These results hold important conservation and economic relevance as A. mearnsii is both an invasive tree species and a forestry tree.