Moss-associated N₂ fixation by epiphytic microbes is a key biogeochemical process in nutrient-limited high-latitude ecosystems. Abiotic drivers, such as temperature and moisture, and the identity of host mosses are critical sources of variation in N₂ fixation rates. An understanding of the potential interaction between these factors is essential for predicting N inputs as moss communities change with the climate. To further understand the drivers and results of N₂ fixation rate variation, we obtained natural abundance values of C and N isotopes and an associated rate of N₂ fixation with ¹⁵N₂ gas incubations in 34 moss species collected in three regions across Alaska, USA. We hypothesized that δ¹⁵N values would increase toward 0‰ with higher N₂ fixation to reflect the increasing contribution of fixed N₂ in moss biomass. Second, we hypothesized that δ¹³C and N₂ fixation would be positively related, as enriched δ¹³C signatures reflect abiotic conditions favorable to N₂ fixation. We expected that the magnitude of these relationships would vary among types of host mosses, reflecting differences in anatomy and habitat. We found little support for our first hypothesis, with only a modest positive relationship between N₂ fixation rates and δ¹⁵N in a structural equation model. We found a significant positive relationship between δ¹³C and N₂ fixation only in Hypnales, where the probability of N₂ fixation activity reached 95% when δ¹³C values exceeded − 30.4‰. We conclude that moisture and temperature interact strongly with host moss identity in determining the extent to which abiotic conditions impact associated N₂ fixation rates.

附生微生物对苔藓相关的 N ₂固定是营养有限的高纬度生态系统中的关键生物地球化学过程。非生物驱动因素，如温度和湿度，以及寄主苔藓的特性是 N ₂固定率变化的关键来源。随着苔藓群落随气候变化，了解这些因素之间的潜在相互作用对于预测氮输入至关重要。为了进一步了解 N ₂固定率变化的驱动因素和结果，我们获得了 C 和 N 同位素的自然丰度值以及与¹⁵ N ₂相关的 N ₂固定率在美国阿拉斯加的三个地区收集的 34 种苔藓物种的气体孵化。我们假设 δ ¹⁵ N 值会随着 N ₂固定的增加而增加到 0‰，以反映固定 N ₂在苔藓生物量中的贡献增加。其次，我们假设 δ ¹³ C 和 N ₂固定将呈正相关，因为丰富的 δ ¹³ C 特征反映了有利于 N ₂固定的非生物条件。我们预计这些关系的程度会因寄主苔藓类型而异，反映了解剖结构和栖息地的差异。我们发现我们的第一个假设几乎没有支持，N ₂之间只有适度的正相关关系结构方程模型中的固定率和 δ ¹⁵ N。我们发现仅在 Hypnales 中，δ ¹³ C 和 N ₂固定之间存在显着的正相关，当 δ ¹³ C 值超过 - 30.4‰时，N ₂固定活动的概率达到 95% 。我们得出结论，水分和温度与寄主苔藓的特性密切相关，以确定非生物条件影响相关 N ₂固定率的程度。