Epiphytic fungal communities vary by substrate type and at sub-meter
Fungal species have numerous important functions in the environment.
Where these functions occur will depend on how fungi are spatially
distributed, but spatial structures of fungal communities are largely
unknown. This is especially true in hyperdiverse tropical tree canopy
systems, which are understudied using high-throughput sequencing
technology. Here we explore fungal communities in a Costa Rican tropical
rainforest canopy, with a focus on local-scale spatial structure and
substrate specificity of fungi. We sampled 135 locations across five
tree branches and identified fungi from four substrate types: outer host
tree bark, inner bark, dead bryophyte tissue, and living bryophytes.
Samples were located between one centimeter and eight meters apart.
Fungal community composition and diversity varied among substrate types,
even when multiple substrates were in direct contact. Fungi were most
diverse in living bryophytes, with 39% of all fungal OTUs found
exclusively in this substrate, and the least diverse in inner bark.
Fungal communities had significant positive spatial autocorrelation and
distance decay of similarity only at distances less than one meter.
Similarity among samples declines by half in less than ten centimeters,
and even at these short distances, similarities are low with few OTUs
shared among samples. These results indicate that community turnover is
high and occurs at very small spatial scales, with any two locations
sharing very few fungi in common. High heterogeneity of fungal
communities in space and among substrates may have important
implications for the distributions, population dynamics, and diversity
of other tree canopy organisms, including epiphytic plants.