Malosma laurina Dieback Associated with Fungal Induced Loss in Hydraulic Conductivity and Photosynthesis

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Research Poster

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Widespread Malosma laurina (Laurel Sumac) dieback is occurring throughout the Santa Monica Mountains. M. laurina is a keystone species within the SMM and its deep roots provide necessary slope stability to the hillsides; therefore, M. laurina’s health is of ecological importance. This study examines whether M. laurina dieback is associated with decreased stem water transport due to the prevalence of a pathogenic fungus within the water transport tissue. Stem samples from dieback and healthy control M. laurina were cultured for fungal growth. 100% of samples from water transport tissue from dieback adult plants contained a fungal pathogen from the genus Botryosphaeria; whereas, 0% of adult healthy plants contained the fungus. The hydraulic conductivity, a measurement of stem water transport, was significantly lower in dieback M. laurina as compared to control M. laurina. Water potentials at predawn (Ψpd) and midday (Ψmd) were lower (more negative) for dieback M. laurina than healthy M. laurina. Double staining of dieback and control M. laurina suggest that a physical blockage is the mechanism of decreased stem water transport. The results of the pathogen cultivation support the hypothesis that a fungus is influencing hydraulic constriction in dieback of M. laurina and reduced photosynthetic rates.

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