PS 2-30 - Biocrust community responses to nitrogen deposition in dry and wet alpine meadows

Monday, August 7, 2017
Exhibit Hall, Oregon Convention Center
Caroline A. Havrilla1, Halle L. Bramer1, Nichole N. Barger1 and Amber C. Churchill1,2, (1)Ecology and Evolutionary Biology, University of Colorado Boulder, Boulder, CO, (2)INSTAAR, University of Colorado Boulder, Boulder, CO

Biocrusts, soil microbial communities consisting of varying assemblages of cyanobacteria, algae, bryophytes, and lichens, occur globally in diverse terrestrial ecosystems, and support critical ecosystem processes. While biocrust ecology in dryland ecosystems is increasingly well documented, we know surprisingly little about biocrusts in alpine ecosystems. Alpine ecosystems are experiencing elevated levels of anthropogenic nitrogen (N) deposition, and are expected to be highly sensitive to this stressor. Empirical evidence suggests alpine plant communities respond to increased N inputs, however, to date, biocrust responses to N deposition remain largely unexplored. Thus, the aims of this study were to: (1) compare biocrust community composition in two alpine community types (dry and wet meadows); and (2) assess biocrust responses to N deposition. To achieve these aims, we first measured and compared percent ground cover of biocrust mosses, lichens, and vascular plants between dry and wet meadows. To characterize biocrust community responses to N deposition, we then measured percent cover of lichens, mosses, and plants in dry and wet meadow plots receiving one of four N addition treatments: (i) Control; 0 kgN ha-1yr-1, (ii) 3 kgN ha-1yr-1, (iii) 12 kgN ha-1yr-1, or (iv) 30 kgN ha-1yr-1 following two (2015) and three (2016) years of N addition.


Study results showed biocrust cover differed significantly between dry and wet meadows with moss cover 5-fold lower, and lichen cover 12-fold higher in the dry versus wet meadow. These differences may be attributed to environmental differences such as greater water availability in the wet meadow relative to the dry meadow. Results from the N addition experiment indicate N addition treatments affected moss, lichen, total biocrust, and vascular plant cover in the dry meadow. Specifically, relative to control plots, moss cover increased in plots receiving moderate (12 kgN ha-1yr-1) N addition, while lichen cover and total biocrust cover decreased in plots receiving moderate (12 kgN ha-1yr-1) and high (12 and 30 kgN ha-1yr-1) N addition. Additionally, vascular plant cover increased in high N addition (30 kgN ha-1yr-1) plots. These results suggest N addition may facilitate moss growth, while posing barriers to lichen growth and survival in dry meadows. Contrastingly, in the wet meadow, there were no significant effects of N addition on moss, lichen, total biocrust, or vascular plant cover. Overall, study results indicate biocrust community composition differs between dry and wet alpine meadows, and suggest N deposition may differentially impact biocrust community structure and cover within these alpine communities.