ABSTRACT Biological nitrogen fixation (BNF) is an important nitrogen source for both N2-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N2-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with 15N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N2 fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant−1, which was significantly lower than that of the CN (6.18 mg N plant−1) and HW (8.01 mg N plant−1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant−1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.

中文翻译：

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N2 固定和转移到邻近植物的数量，但不是比例，因草原土壤而异

摘要 生物固氮 (BNF) 是自然和管理生态系统中固氮植物及其邻近植物的重要氮源。生物固氮可能因土壤条件而异，但缺乏关于不同土壤对混合草丛中固氮剂 N 贡献的影响的知识。在这项研究中，使用三种草地土壤评估了来自红三叶草的 BNF 的数量和比例。三个土壤样品，Hallsworth (HH)、Crediton (CN) 和 Halstow (HW) 系列，是从英国德文郡的三个草原地点收集的。进行了 15N 自然丰度的盆栽实验，以估计红三叶草的 BNF，以及在草 - 三叶草系统中从红三叶草转移到非 N2 固定草的 N 比例。结果表明，HH土壤中来源于大气的红三叶草中的BNF为2.92 mg N plant-1，显着低于CN（6.18 mg N plant-1）和HW（8.01 mg N plant-1）土壤。来自 BNF 的草中的氮在 HH 土壤中为 0.46 mg N plant−1，显着高于 CN 和 HW 土壤中的氮。然而，在土壤中来自 BNF 的红三叶草和草的 N 含量百分比在比例上没有显着差异，分别为 65%、67%、65% 和 35%、27%、31%，在 HH、CN、和硬件，分别。我们的观察表明，红三叶草的 BNF 量在草地土壤中有所不同，来自 BNF 的 N 量转移到邻近植物，这与生物量生产有关。