Background/Question/Methods Fungi that live asymptomatically within plant leaves, foliar endophytes (FE), can play important roles in plant defense from herbivores and pathogens and reach hyper-diverse levels in tropical forests. However, we still have a poor understanding of the major factors affecting woody-plant FE diversity and spatial distribution. Previous research on woody-plant FE in other systems provides evidence for host specific effects. Also, moisture commonly limits fungal growth, especially in arid regions. To investigate how host species identity and precipitation affect FE communities, I conducted a study of the FE in major, riparian woody-plant species in Arizona. At three sites representing a precipitation gradient, I quantified the FE communities associated with Quercus turbinella, Fraxinus velutina and Populus fremontii using a combination of molecular and culture-based techniques.

Results/Conclusions These species varied greatly in the percent of colonized leaf segments (i.e. FE abundance). Quercus turbinella had the highest abundances on average with 67% leaf segments colonized, which was 2X greater than F. velutina (29%) and 16X greater than P. fremontii (4%). Although Q. turbinella had the highest diversity (average four species), their FE communities were dominated by one species, representing 50% of all isolates. Fraxinus velutina had an average species richness of two, and was also dominated by another single species (32% of all isolates). Populus fremontii had a diffuse community composed of single isolates of only six species. Statistical analyses of the FE morphospecies data indicate that plant species was a strong predictor of FE abundance, diversity and community composition. Precipitation was positively correlated with FE diversity, but not abundance or community structure. The small effect of precipitation is surprising, given that water is generally an important factor for fungal dispersal and growth. Together these results suggest that: 1) different woody-plant species harbor distinct FE communities and 2) the effects of precipitation are likely over-ridden or modulated by plant species effects.