We investigated N2-fixation by moss-cyanobacterial associations in a North American prairie ecosystem, identifying cyanobacteria associated with moss species, and evaluating spatio-temporal dynamics in N2-fixation rates. We confirmed the presence and abundance of N2-fixing cyanobacteria on three moss species (Pleurozium schreberi (Brid.) Mitt., Racomitrium elongatum Frisvoll, Rhytidiadelphus triquetrus (Hedw) Warnst.) using epi-fluorescence light microscopy. To estimate monthly N2-fixation rates on mosses from three sites, we conducted laboratory-based acetylene reduction assays with constant incubation temperatures and natural daylight. We evaluated the relationship between daylength and N2-fixation, and daylength and weather variables. N2-fixation rates varied by species, site, and month. R. elongatum exhibited the highest rates and P. schreberi had the lowest. Rates for R. elongatum and R. triquetrus were positively correlated with daylength, with peaks occurring at 13–14 h daylight, suggesting spring and fall conditions support N2-fixation in this system. Annual median N2-fixation for R. elongatum and R. triquetrus ranged from 0.008–0.124 kg N ha−1 yr−1 based on cover of 11–100%. Our results highlight a previously undescribed source of biological N2-fixation in temperate grasslands. Changes in the distribution or activity of N2-fixing moss-cyanobacterial associations due to management practices and climate change could impact future stand-level nitrogen dynamics.

中文翻译：

---

苔藓蓝细菌协会作为温带草原生物固氮的新来源

我们研究了北美草原生态系统中苔藓-蓝细菌协会对 N2 的固定，确定了与苔藓物种相关的蓝藻，并评估了 N2 固定率的时空动态。我们使用落射荧光显微镜确认了三种苔藓物种（Pleurozium schreberi (Brid.) Mitt.、Racomitrium elongatum Frisvoll、Rhytidiadelphus triquetrus (Hedw) Warnst.）上的 N2 固定蓝细菌的存在和丰度。为了估计来自三个地点的苔藓每月的 N2 固定率，我们在恒定的孵化温度和自然光下进行了基于实验室的乙炔还原分析。我们评估了日长和 N2 固定以及日长和天气变量之间的关系。N2 固定率因物种、地点和月份而异。R. elongatum 表现出最高的比率，而 P. schreberi 最低。R. elongatum 和 R. triquetrus 的比率与日长正相关，峰值出现在日光 13-14 小时，表明春季和秋季条件支持该系统中的 N2 固定。R. elongatum 和 R. triquetrus 的年度中位 N2 固定范围为 0.008-0.124 kg N ha-1 yr-1，基于 11-100% 的覆盖率。我们的结果突出了以前未描述的温带草原生物固氮来源。由于管理实践和气候变化而导致的固氮苔藓蓝细菌协会的分布或活动的变化可能会影响未来的林位氮动态。R. elongatum 和 R. triquetrus 的年度中位 N2 固定范围为 0.008-0.124 kg N ha-1 yr-1，基于 11-100% 的覆盖率。我们的结果突出了以前未描述的温带草原生物固氮来源。由于管理实践和气候变化而导致的固氮苔藓蓝细菌协会的分布或活动的变化可能会影响未来的林位氮动态。R. elongatum 和 R. triquetrus 的年度中位 N2 固定范围为 0.008-0.124 kg N ha-1 yr-1，基于 11-100% 的覆盖率。我们的结果突出了以前未描述的温带草原生物固氮来源。由于管理实践和气候变化而导致的固氮苔藓蓝细菌协会的分布或活动的变化可能会影响未来的林位氮动态。