In contrast with normal onshore winds, Santa Ana winds bring dry, hot air towards the coast, originating from inland mountains and deserts. Fungal spores in dust can be dispersed by these winds. Fungi perform many ecosystem functions, including decomposing plant material, increasing plant growth, and causing disease in humans and agricultural crops.
We hypothesized: 1) Fungal community composition will shift during Santa Ana Occurrences (SAOs), because the source of fungal biomass in air changes. 2) Airborne spore concentration will be positively correlated to temperature and negatively correlated to relative humidity because compared to onshore winds SAOs carry more spores via dust entrained by winds. 3) Fungal pathogens will be the most abundant functional group during SAOs because fungal pathogens tend to rely on air dispersal more than decomposers or symbionts.
From March to September 2015, we deployed a high-volume sampler to collect particulate matter smaller than 2.5 microns. We used barcoded ITS2 primers and sequenced with the Illumina Mi-Seq to determine fungal community composition. We used FUNGuild to assign functional groups (e.g., pathogens, decomposers, symbionts). Climate factors, including temperature, relative humidity, wind speed, wind direction, and rainfall were taken from a weather station 2.5 mi away from the sampler.
Results/Conclusions
Airborne fungal community composition significantly shifted during SAOs (F = 2.16, p = 0.006). Spore concentration (F = 1.66, p = 0.04), relative humidity (F = 1.79, p = 0.018) and wind speed (F = 1.44, p = 0.097*) also structured community composition. We found a significant increase in spore concentration during SAOs (F = 10.46, p = 0.005) while spore concentration decreases with relative humidity (F = 30.14, p < 0.001). Decomposers were the most abundant functional group during SAOs, and pathogens were more abundant during onshore winds. Overall, these results supported our first and second hypothesis. We did not find support for our third hypothesis. Climate models predict more intense SAOs with lower relative humidity and higher wind speeds, therefore it is highly likely dispersing fungal communities in the future will be decomposer dominated. *marginally significant