Exploring the community ecology of geothermal mosses: Do invertebrates impact moss genetic diversity?

Background/Question/Methods

Few organisms are capable of thriving at Earth’s thermal extremes, yet those that do remain relatively unexplored, particularly those engaged in complex, multi-trophic communities.  While few vascular plants can survive in geothermal soils, non-vascular mosses are often found in some of the hottest regions of geothermal systems. We investigated the community ecology of geothermal mosses at Lassen Volcanic National Park, CA, in particular, asking what biotic and abiotic factors are driving this understudied, extreme ecosystem.  We established study sites along an existing geothermal moss-community temperature gradient using the ubiquitous model moss species, Ceratodon purpureus as a focal species. We hypothesized that genetic variation of C. purpureus would vary across this temperature gradient, with little to no genetic variation in the most extreme sites, and that community structure and function would correlate with genetic variation. To test our hypotheses, we estimated genetic variation in C. purpureus and profiled the invertebrate communities as well as fungal biomass, soil organic matter, and nutritive properties of the soil-moss complex across the geothermal gradient, obtaining a snapshot of the moss ecosystem.

Results/Conclusions

We found significant trends in the biotic and abiotic factors influencing moss-dominated communities along a geothermal gradient.  We found that geothermal C. purpureus is not simply clonal, and that genetic variation exists primarily within localized populations, not among them.  The study site with the greatest moss genetic diversity fell in the center of the temperature gradient and correlated positively with invertebrate diversity, fungal biomass and soil organic matter, presumably indicating a “hot spot” for community diversity and productivity.  This study begins to unravel and reconnect the multi-trophic factors driving geothermal moss communities.   Our results indicate both intuitive and surprising ecological correlations, and present the intriguing prospect that the universal moss-microarthropod relationship may be affecting moss genetic diversity as well as driving functional community ecology.