Bryo-tic resource pulses and community and ecosystem level processes

Background/Question/Methods

The effects of vascular plants on ecosystem processes have been well studied, but despite the potential of bryophytes to punch well above their biomass their effects on ecosystems have received less attention.  Bryophytes may affect ecosystems in substantially different ways than vascular plants due to their exceptional absorptive capacity which allows them to accumulate nutrients from precipitation, canopy throughfall, cyanobacterial associations, and litter.  Perhaps more importantly, unlike vascular plants bryophytes undergo dehydration and rehydration cycles during which their cells become “leaky” and release large pulses of cellular constituents.

I measured total amounts of carbon and nitrogen released from eight moss species after rehydration from a desiccated state.  I also explored how bryo-tic pulses from one of these species affect co-existing vascular plants and modify interactions among plants.  In common garden and field experiments, I investigated direct and indirect interactions between a native moss (Syntrichia ruralis) and two vascular plants, Festuca idahoensis and the exotic invader Centaurea stoebe.  Centaurea (spotted knapweed) is widely distributed across North America and can displace native biota and alter biogeochemical cycling.  

Results/Conclusions

When compared to constantly hydrated mosses, mosses that were desiccated and rehydrated released significantly more carbon and nitrogen– from 2 to 31 percent more carbon.  The most common moss species in grasslands dominated by Festuca and Centaurea, Syntrichia, lost the least amount of carbon and nitrogen upon rehydration.  Nevertheless in demographic surveys, Centaurea and Syntrichia were positively associated, suggesting the potential for facilitative interactions.  In a field experiment, Syntrichia produced more biomass when grown with Centaurea.  Syntrichia kept soils wetter for longer but did not facilitate Centaurea in the field.  Conversely in a greenhouse experiment, Syntrichia increased Centaurea biomass but did not affect Festuca.  However, when Centaurea and Festuca were grown together, Syntrichia did not facilitate the invader.  In a second greenhouse experiment, rehydration leachate (the bryo-tic resource pulse) from Syntrichia had no effects on Festuca or Centaurea when grown alone, but facilitated Festuca when grown with Centaurea.  These results indicate that a native moss may alter interactions between vascular plant species via different mechanisms, which result in different outcomes, and potentially affect the course of invasions.