Airborne fungal spore dispersal and trait diversity in coastal mixed-evergreen forests in California

Background/Question/Methods

Airborne fungal spore abundance in tropical forest ecosystems is stratified. A higher density of spores is found in the still, dark, and moist understory compared to the windy, light, and dry conditions of the forest canopy. This spatial stratification suggests that spore dispersal is influenced by abiotic site factors and that species may be dispersal limited. Moreover, once spores are discharged, spore traits such as size or ornamentation may restrict or facilitate spore movement. Although previous studies characterize fungal spore dispersal dynamics in tropical forests, spore dynamics in temperate forests is still largely unknown. This study examines the spatial dynamics of airborne spores in a temperate coastal mixed-evergreen forest in California. We ask: is there is a difference in 1) aerospora density and 2) spore trait morphology from the forest floor into the canopy? Spores from different fungal species were collected at the University of California, Santa Cruz Upper Campus Reserve in April-June 2012. Adhesive spore traps were attached to 1m vertical steel posts and at 1m intervals onto 30m ropes. The ropes were launched into the forest canopy using a crossbow at 15 replicate forest sites.  Spore density and traits are characterized by imaging of spores under a light microscope and analyzed using the software analysis tool imageJ^®. Traits measured include spore diameter, shape, outer ornamentation, cell wall thickness, and presence/absence of melanin. Spore samples are identified under a light microscope and through DNA barcoding methods to identify cryptic species.   

Results/Conclusions

Fungal species collected and identified under a light microscope include: Botrytis cinerea and Aspergillus sp., two common forest molds and Phythophthora ramorum, the oomycete fungal pathogen responsible for sudden oak death.  Preliminary results suggest that at least 12 distinct spore trait morphologies exist across sites. In the 1m diameter vertical post transects, there is a higher density of spores closer to the soil (0.2m from the forest floor) compared to 1m in the air. This initial result suggests that there is some evidence for vertical stratification in airborne spore density in mixed-evergreen forests.