Soil surface disturbances in cold deserts: effects on nitrogenase activity in cyanobacterial-lichen soil crusts

Abstract

CyanobacteriaMichen soil crusts can be a domi- nant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was inves- tigated. Surface disturbances reduced nitrogenase activity by 30-100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most sus- ceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema te- nax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of ni- trogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated by cya- nobacteria with or without heterocysts. Consequently, anthropogenic surface disturbances may have serious im- plications for nitrogen budgets in these ecosystems.