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

摘要

Cyanobacterial-lichen soil crusts can be a dominant 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 investigated. Surface disturbances reduced nitrogenase activity by 30–100. Crusts dominated by the cyanobacteriumMicrocoleus vaginatuson sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichenCollema tenaxwas present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated by cyanobacteria with or without heterocysts. Consequently, anthropogenic surface disturbances may have serious implications for nitrogen budgets in these ecosystem