Quantifying water use in a plant–fungal interaction

Fungal rust galls are parasitic fungi on Acacia host plants. The amount of water required by fungal parasites has yet to be widely measured. Sap flow instrumentation was installed on branches of Acacia implexa to measure water use of a fungal rust gall. Host water use was also measured. Partial regression analysis, using gall sap flow against environmental variables, was performed to determine a possible driving mechanism of gall sap flow. Following the removal of galls from branches, sap flow immediately returned to, and stayed at, zero flow. Gall sap flow was 4.63 % of total host tree sap flow on a daily and cumulative basis. Vapour pressure deficit explained the greatest amount of variation in gall sap flow, suggesting gradients of water potential was the driving mechanism of water use. This study demonstrated that instruments which can measure low sap flow can be used to quantify fungal water use.

► The quantity of water a fungus parasitises from its host plant is measured.
► In this study, a fungal rust gall parasitised 4.63% of host tree water use.
► A gradient of water potential from the host to the fungus was the driving mechanism of water flow.