What lies beneath: A continental survey of ectomycorrhizal fungal spore banks

Background/Question/Methods

Ecologists have long acknowledged the importance of seed banks, yet despite the fact that many plants rely on mycorrhizal fungal partners for survival and growth, the structure of ectomycorrhizal fungal spore banks is known primarily from the western USA. As secondary successional habitats become more common due to anthropogenic disturbances, it is important to consider what ectomycorrhizal fungal (EMF) partners may survive in the soil as recalcitrant spores. To investigate EMF diversity and to test the importance of biogeography and plant host on structuring fungal communities, soils were collected in a replicated nested sampling design in forests across Alaska, California, Florida, Minnesota, Mississippi, and North Carolina.  Fresh soils and root tips were sequenced immediately using 454 pyrosequencing at each of 13 sampling locations within a plot.  Additional soil cores were sieved and dried, then used in a bioassay with a common non-native pine host in addition to native pine hosts to detect EMF species that are able to persist in the soil as recalcitrant propagules.  With this design we produced the first continental view of ectomycorrhizal sporebanks, and we tested the importance of plant host and biogeography in structuring these assemblages.

Results/Conclusions

Currently we have analyzed samples from Alaska, California, and North Carolina. A total of 142,962 raw sequence reads with average read length of approximately 600 bp were acquired to distinguish approximately 203 operational taxonomic units half of which were considered to be ectomycorrhizal fungi and half were considered to be root endophytes.  Principle coordinates analyses on community similarity indices indicates that biogeography has a strong effect on structuring the species composition of fungi in ectomycorrhizal spore banks, while identity of plant bioassay host appears to have a limited effect. The most common known ectomycorrhizal genera in all three regions were: Tuber, Wilcoxina, Tomentella, Sebacina, Rhizopogon, Suillus, Thelephora, Cenococcum, and Amphinema.  Thus, a limited number of EMF genera are represented in the responsive spore bank, and the regional structure seen appears to be driven by species-level differences within these common genera. As additional samples are analyzed we expect to obtain a refined view of the patterning of EMF spore banks within North America, create new basic knowledge on fungal diversity, and answer important questions on the relative importance of neutral versus niche processes on structuring ectomycorrhizal fungal spore bank assemblages.