Microbial activity in drylands is mediated by the magnitude and frequency of growing season rain events that will shift as climate change progresses. Nitrogen is often co-limiting with water availability to dryland plants. This study investigated how microbes important to the nitrogen (N) cycle and soil N availability varied temporally and spatially in the context of a long-term rainfall variability experiment in the northern Chihuahuan Desert. Specifically, biological soil crust (biocrust) chlorophyll content, fungal abundance, and inorganic N were measured in soils adjacent to individuals of the grassland foundation species, Bouteloua eriopoda, and in the unvegetated interspace at multiple time points associated with experimental monsoon rainfall treatments. Treatments included 12 small weekly (5 mm) or 3 large monthly (20 mm) rain events, which had been applied during the summer monsoon for nine years prior to this study. Additionally, target plant C:N ratios were measured, and ¹⁵N-glutamate was added to biocrusts to determine potential for nutrient transport to B. eriopoda. Biocrust chlorophyll was up to 67% higher in the small weekly and large monthly rainfall treatments compared to ambient controls. Fungal biomass was 57% lower in soil interspaces than adjacent to plants but did not respond to rainfall treatments. Ammonium and nitrate concentrations near plants declined through the sampling period but varied little in soil interspaces. There was limited movement of ¹⁵N from interspace biocrusts to leaves but high ¹⁵N retention occurred in the soils even after additional ambient and experimental rain events. Plant C:N ratio was unaffected by rainfall treatments. The long-term alteration in rainfall regime in this experiment did not change how short-term microbial abundance or N availability responded to the magnitude or frequency of rain events at the end of the growing season, suggesting a limited response of N availability to future climate change.

干旱地区的微生物活动由生长季节降雨事件的数量和频率来调节，降雨事件的数量和频率将随着气候变化的发展而发生变化。氮经常限制旱地植物的水供应。这项研究调查了在北部奇瓦瓦沙漠进行的长期降雨变异性实验中，微生物对氮（N）循环和土壤氮有效性的重要影响如何在时间和空间上变化。具体而言，在与草地基础物种Bouteloua eriopoda相邻的土壤中测量了生物土壤结皮（biocrust）的叶绿素含量，真菌丰度和无机氮。，以及在与实验季风降雨处理相关的多个时间点的无植被空间中。处理包括12次每周小雨（5毫米）或3次每月大雨（20毫米）降雨事件，在本研究之前的九年夏季季风期间应用了这些降雨事件。另外，测量了目标植物的C：N比，并将^15种N-谷氨酸添加到生物结皮中，以确定养分向B. eriopoda转运的潜力。。与周围环境相比，在每周的小雨和每月的大雨中，生物结皮叶绿素的含量最多提高了67％。土壤空隙中的真菌生物量比邻近植物低57％，但对降雨处理没有反应。在采样期间，植物附近的铵和硝酸盐浓度下降，但在土壤间隙中变化不大。¹⁵ N从空间生物结壳到叶片的运动有限，但高¹⁵即使在额外的环境和实验性降雨事件之后，土壤中仍会保留氮。植物C：N的比例不受降雨处理的影响。在该实验中，降雨状态的长期变化并没有改变短期微生物丰度或氮素对生长季结束时降雨事件的强度或频率的响应方式，这表明氮素对未来气候的响应有限。改变。