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Nitrogen (N) is considered to be the second most limiting factor after water for biomass production in arid and semiarid ecosystems. Biological soil crusts (BSCs) play an important role as N providers, especially in sand dunes. In this study, we looked at the levels of inorganic N forms and the abundance of N-cycle-associated genes in five well-defined BSCs along a transect of a sand dune in the Negev Desert. Four of the crusts are cyanobacterial crusts (with crust A occupying the interdune and the south-facing slope, and the remaining crusts, B, C, D occupying the north-facing slope) and one moss-dominated crusts (E), inhabiting the interface between the north-facing footslope and the interdune, where it benefits from additional water supply by subsurface flow and runoff. Although all crusts contained comparable numbers of the nifH gene (a marker for N2 fixation), the accumulation of inorganic N forms followed the order A ≈ B |
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