Functional influences of cryptobiotic surface crusts in an alpine tundra basin of the Olympic Mountains, Washington, USA

Layers of cryptobiotic organisms (lichens, mosses, fungi, algae, cyanobacte ria) on the soil surface are common features of undisturbed sites in cold d eserts, semi-arid grasslands, and arctic and alpine communities. Little is known about the relationship between these crusts and flowering plant commu nities in alpine ecosystems. This study compared the soil environment, asso ciated plant temperature patterns and crust atmospheric nitrogen fixation a ctivity in an alpine site with two different types of cryptobiotic crusts a nd 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 nitro gen and phosphorus. Soil surfaces and near surface soils at midday were coo ler by 5 to 8 degreesC under moss-dominated crust and 10 to 11 degreesC coo ler under fruticose lichen dominated crust as compared to noncrusted surfac es. However, foliage temperatures of adult Douglasia laevigata cushions did not differ in these three sites. Cooler and moister surface conditions ass ociated 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 con centration was 25 to 44% lower in leaves of plants growing with crusts comp ared to the same species growing in the noncrusted site. Competition for nu trients at the crust sites may offset greater nutrient concentrations in so ils. Knowledge of specific functional attributes of different cryptobiotic surfaces will be important for the development of management and restoratio n plans in alpine ecosystems.