Functional Influences of Cryptobiotic Surface Crusts in an Alpine Tundra Basin of the Olympic Mountains, Washington, U.S.A

Layers of cryptobiotic organisms (lichens, mosses, fungi, algae, cyanobacteria) on the soil surface are common features of undisturbed sites in cold deserts, semi-arid grasslands, and arctic and alpine communities. Little is known about the relationship between these crusts and flowering plant communities in alpine ecosystems. This study compared the soil environment, associated plant temperature patterns and crust atmospheric nitrogen fixation activity in an alpine site with two different types of cryptobiotic crusts and one site without crusts. When compared to the noncrusted site, both types of crusts were associated with changes in soil texture, increased soil organic matter (52 and 314%), increased late summer soil moisture (56 and 419%), and increased soil nitrogen and phosphorus. Soil surfaces and near surface soils at midday were cooler by 5 to 8 degree C under moss-dominated crust and 10 to 11 degree C cooler under fruticose lichen dominated crust as compared to noncrusted surfaces. However, foliage temperatures of adult Douglasia laevigata cushions did not differ in these three sites. Cooler and moister surface conditions associated with the crusts may influence seedling establishment and have less effect on adult plants with established root systems. Despite greater soil nitrogen concentrations in the two different crust sites, leaf nitrogen concentration was 25 to 44% lower in leaves of plants growing with crusts compared to the same species growing in the noncrusted site. Competition for nutrients at the crust sites may offset greater nutrient concentrations in soils. Knowledge of specific functional attributes of different cryptobiotic surfaces will be important for the development of management and restoration plans in alpine ecosystems.