Fire disturbance represents a major driver of soil nitrogen (N) distribution in many arid and semiarid grasslands. The spatial patterns of soil N and δ 15 N at microsite scale following fires, however, are rarely studied. Here we investigated the spatial distribution of soil N and soil δ 15 N before and within three years after a prescribed fire in a grassland-shrubland ecotone in the northern Chihuahuan Desert. The spatial heterogeneity of soil N decreased significantly after the fire, with the autocorrelation distance increasing from 1.55 m to over 3 m, and the spatial dependence index decreasing from 99% to 73%. Soil δ 15 N was autocorrelated at 0.44 m after the fire, a much smaller scale that is similar to recovered grass patches, suggesting grasses tend to control the soil N cycling rather than shrubs. Different from the overall content of soil N, which merely changed before and after fire, soil δ 15 N increased substantially after the fire. We argued that high temperature and increased soil moisture at grass microsites post-fire may lead to an enhanced mineralization rate and 15 N-enriched soil ammonium at grass microsites, which further stimulates the rapid recovery of grasses after the fire.

火灾是许多干旱和半干旱草原土壤氮素分布的主要驱动力。但是，很少研究火灾后土壤微尺度上的土壤氮和δ15 N的空间格局。在这里，我们调查了北部奇瓦瓦沙漠草原-灌木丛过渡带规定的火灾发生前和发生后三年内土壤N和δ15 N的空间分布。火灾后土壤氮的空间异质性显着降低，自相关距离从1.55 m增加到3 m以上，空间依赖指数从99％降低到73％。火灾后0.45 m处的土壤δ15 N是自相关的，其规模小得多，类似于回收的草块，这表明草倾向于控制土壤的氮循环而不是灌木。与土壤N的总含量不同（仅在燃烧前后发生变化），土壤δ15 N在燃烧后显着增加。我们认为，火灾后草微场所的高温和土壤水分的增加可能导致矿化速率提高，草微场所的土壤中富含15 N的土壤铵，这进一步刺激了火灾后草的快速恢复。