Biological soil crusts affect small-scale spatial patterns of inorganic N in a semiarid Mediterranean grassland

The influence of biological soil crusts (BSCs) on the small-scale spatial distribution of inorganic nitrogen (N) in drylands is largely unknown, despite their known impact and importance on the N cycle in these environments. We evaluated how perennial plants and BSCs affected small-scale spatial patterns of soil inorganic N (ammonium and nitrate) availability in a semiarid grassland from Spain. The data were analyzed by using geostatistical methods. The range of semivariograms for ammonium and nitrate, and the coefficient of variation of nitrate, were lower in BSC-dominated microsites than in plant-dominated microsites. Our results suggest that BSCs modulate the small-scale spatial pattern of inorganic N, producing more homogeneous conditions for spatial distribution of inorganic N forms than microsites provided by plants. These results may have important repercussions for the foraging strategies and ability of plant roots to uptake N.