Physiological strategies explain mortality differences amongst ecologically and culturally significant Australian desert plants following a hotter drought

Jaylen David Nicholson , Rita Okai, Andrea Leigh , Danielle Way , Nicholas Macgregor , Rebekah Robertson, Samuel Merson , Tracey Guest, Adrienne Nicotra 

Climate change-induced drought and heatwave events (hotter droughts) are causing mass plant dieback events globally. Recently, Uluru-Kata Tjuta National Park (UKTNP) in central Australia saw a widespread plant dieback (mortality) event, resulting in negative impacts to the ecosystems and concern and a desire to understand more about the underlying causes of mass plant death from Anangu (Traditional Owners). We measured morphological and physiological traits that were hypothesised to drive physiological mechanisms underpinning the patterns of dieback observed at UKTNP in culturally important species chosen by Anangu. Maintenance of leaf relative water content (RWC) was the leaf trait that best predicted dieback severity, with all low dieback severity species exhibiting drought-avoidance strategies, where RWC was maintained between spring and summer. Most moderate and high dieback severity species exhibited drought-tolerance strategies, evidenced by large declines in seasonal RWC compensated by higher wood densities. However, two small shrub species with high dieback severity likely died due to failure of different physiological mechanisms - one of hydraulic failure and one of carbon starvation - highlighting the importance of considering species-specific trait combinations to understand drivers of mortality. Hotter drought events in central Australia are likely to impact not only plant communities, but Anangu culture.