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.