Data from: Biological soil crusts modulate nitrogen availability in semi-arid ecosystems: insights from a Mediterranean grassland

Biological soil crusts (BSCs) greatly influence the N cycle of semi-arid ecosystems, as some organisms forming them are able to fix atmospheric N. However, BSCs are not always taken into account when studying biotic controls on N cycling and transformations. Our main objective was to understand how BSCs modulate the availability of N in a semi-arid Mediterranean ecosystem dominated by the tussock grass Stipa tenacissima. We selected the six most frequent soil cover types in the study area: S. tenacissima tussocks (ST), Retama sphaerocarpa shrubs (RS), and open areas with very low (BS), low (LC) medium (MC) and high (HC) cover of well developed and lichen-dominated BSCs. The temporal dynamics of available N dynamics followed changes in soil moisture. Available NH4+-N did not differ between microsites, while available NO3--N was substantially higher in the RS than in any other microsite. No significant differences in the amount of available NO3--N were found between ST and BS microsites, but these microsites had more NO3--N than those dominated by BSCs (LC, MC and HC). Our results suggest that BSCs may be inhibiting nitrification, and highlight the importance of this biotic community as a modulator of the availability of N in semi-arid ecosystems.生物土壤结皮（Biological Soil Crusts, BSCs）对半干旱生态系统的氮循环具有显著调控作用，因其组成组分中的部分生物可固定大气中的氮素。然而，在探究氮循环与转化的生物调控机制时，生物土壤结皮往往未被充分纳入研究考量范畴。本研究的核心目标是解析生物土壤结皮如何调控以丛生禾草细茎针茅（Stipa tenacissima）为优势种的地中海半干旱生态系统中的氮素有效性。我们选取了研究区域内6种最常见的土壤覆盖类型：细茎针茅丛生斑块（ST）、球果鹰爪豆（Retama sphaerocarpa）灌丛（RS），以及发育良好、以地衣为主导的生物土壤结皮覆盖度分别为极低（BS）、低（LC）、中（MC）和高（HC）的裸地区域。有效氮的时间动态变化与土壤水分的变化趋势高度一致。不同微生境下的铵态氮（NH₄⁺-N）有效含量无显著差异；而硝态氮（NO₃⁻-N）有效含量在RS样地中显著高于其余所有微生境。细茎针茅丛生斑块（ST）与裸地（BS）样地的有效硝态氮含量无显著差异，但二者的有效硝态氮含量均高于以生物土壤结皮为主导的LC、MC及HC样地。本研究结果表明，生物土壤结皮可能对硝化过程具有抑制作用，同时凸显了该生物群落在半干旱生态系统氮素有效性调控中的重要价值。