Acetylene reduction by cryptogamic crusts from a blackbrush community as related to resaturation and dehydration

N 2 fixation Microcoleus and Scytonema dominated cryptogamic crusts as related to the resaturation-dehydration phenomenon was estimated using the acetylene reduction assay. The mean maximum fixation rates were estimated to be 6.3 nmol N 2 m −2 s −1 for Microcleus and 9.4 nmol N 2 m −2 s −1 for Scytonema crusts. Nitrogen inputs were estimated to be 0.7–3.6 kg N 2 ha −1 yr −1 for a relic community, 0.4–2.0 kg N 2 ha −1 yr −1 for a light grazing community, and 0.02–0.17 kg N 2 ha −1 yr −1 for moderate and heavily grazed communities.