Abstract：
Biological nitrogen fixation (BNF) provides a globally important input of nitrogen (N); its quantification is critical but technically challenging. Leaf reflectance spectroscopy offers a more rapid approach than traditional techniques to measure plant N concentration ([N]) and isotopes (δ15N). Here we present a novel method for rapidly and inexpensively quantifying BNF using optical spectroscopy. We measured plant [N], δ15N, and the amount of N derived from atmospheric fixation (Ndfa) following the standard traditional methodology using isotope ratio mass spectrometry (IRMS) from tissues grown under controlled conditions and taken from field experiments. Using the same tissues, we predicted the same three parameters using optical spectroscopy. By comparing the optical spectroscopy-derived results with traditional measurements (i.e. IRMS), the amount of Ndfa predicted by optical spectroscopy was highly comparable to IRMS-based quantification, with R2 being 0.90 (slope=0.90) and 0.94 (slope=1.02) (root mean square error for predicting legume δ15N was 0.38 and 0.43) for legumes grown in glasshouse and field, respectively. This novel application of optical spectroscopy facilitates BNF studies because it is rapid, scalable, low cost, and complementary to existing technologies. Moreover, the proposed method successfully captures the dynamic response of BNF to climate changes such as warming and drought.
摘要：
生物固氮（BNF）是全球重要的氮（N）输入，它的量化至关重要，但在技术上具有挑战性。叶片反射光谱为传统技术提供了一种快速的方法来测量植物N浓度（[N]）和同位素（δ15N）。在这里，我们提出了一种使用光谱学快速，廉价地定量BNF的新方法。我们测量了植物[N]，δ15N,以及使用同位素比质谱（IRMS）的标准传统方法从受控条件下生长的组织中提取的大气固定（Ndfa）中的N量。使用相同的组织，我们用光谱学预测了同样的三个参数。通过将光谱学得出的结果与传统测量结果(即，IRMS)，通过光谱学预测的Ndfa的量与基于IRMS的定量非常可比，对于温室和田间种植的豆类，R2分别为0.90（斜率=0.90）和0.94（斜率=1.02）（预测豆类δ15N的RMSE分别为0.38和0.43），分别。这种光谱学的新应用促进了BNF研究，因为它是快速的，可扩展，低成本,是对现有技术的补充。此外，所提出的方法成功地捕获了BNF对气候变暖和干旱等气候变化的动态响应。
