Measuring transpiration responses to summer precipitation in a Mediterranean climate: a simple screening tool for identifying plant water‐use strategies

Rainfall utilization by vegetation is a complex function of the timing and magnitude of rain events, soil properties, evaporative demand and aboveground and belowground plant functioning. Understanding these interactions is highly relevant to a number of ecological problems, including salinization of cleared agricultural land in southern Australia. Ameliorative revegetation efforts require information on plant water‐use strategies; we used sap‐flow recordings to screen a range of species and identify four types of response to a large summer rainfall event: (1) no response, (2) delayed response, (3) small, rapid response and (4) large, rapid response. Proteaceous shrub species (e.g. Isopogon gardneri) rapidly increased transpiration up to five‐fold. Other shrubs such as Allocausarina campestris (Casuarinaceae) only increased transpiration two‐fold due to partial summer dormancy. Deep‐rooted Eucalyptus species (Myrtaceae, e.g. E. wandoo) were sufficiently reliant on antecedent soil water that they did not respond to summer precipitation. One hemi‐parasite species Nuytsia floribunda (Loranthaceae) required over 2 weeks to fully respond to rainfall, possibly due to water storage and changes to the hydraulic pathway. We discuss these results in terms of the ‘threshold‐delay’ model and the role of this screening method in assisting revegetation strategies.