Mechanisms of severe dieback and mortality in a classically drought-tolerant shrubland species (Arctostaphylos glauca)

PREMISE Mortality events involving drought and pathogens in natural plant systems are on the rise due to global climate change. In the Santa Ynez mountain range in Santa Barbara County, California, USA, big berry manzanita (Arctostaphylos glauca) has experienced canopy dieback related to both a multi-year drought, and infection from fungal pathogens in the Botryosphaeriaceae family. METHODS A full factorial greenhouse experiment with four treatment groups (drought + inoculation; drought – inoculation; watering + inoculation; and control: watering – inoculation) was conducted using N. australe to test the specific influences of drought and fungal infection on A. glauca. Data were collected on stress symptoms, changes in leaf fluorescence and photosynthesis, and mortality. KEY RESULTS A two-way ANOVA showed significant effects of watering and inoculation treatments on net photosynthesis, dark-adapted fluorescence, and disease symptom severity (P < 0.05), and a strong cor...