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

CyanobacteriaMichen 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 cyanobacterium
Microcoleus vaginatus on sandy soils were the most susceptible
to disruption; crusts on gypsiferous soils were the
least susceptible. Crusts where the soil lichen Collema tenax
was 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 ecosystems.