Abstract. Representing biological nitrogen fixation (BNF) is an important challenge in the incorporation of nitrogen (N) cycling in land models. Initial representations of BNF in land models applied simplified phenomenological relationships. More recent representations of BNF are mechanistic and include the dynamic response of BNF to N limitation of plant growth. However, they generally do not include the competitive dynamics between N-fixing and non-fixing plants, which is a key ecological mechanism that determines ecosystem-scale symbiotic BNF. Furthermore, asymbiotic BNF is generally not included in land models. Here, we present LM4.1-BNF, a novel representation of BNF (asymbiotic and symbiotic) and an updated representation of N cycling in the Geophysical Fluid Dynamics Laboratory Land Model 4.1 (LM4.1). LM4.1-BNF incorporates a mechanistic representation of asymbiotic BNF by soil microbes, a representation of the competitive dynamics between N-fixing and non-fixing plants, and distinct asymbiotic and symbiotic BNF temperature responses derived from corresponding observations. LM4.1-BNF makes reasonable estimations of major carbon (C) and N pools and fluxes and their temporal dynamics, in comparison to the previous version of LM4.1 with N cycling (LM3-SNAP) and to previous representations of BNF in land models generally (phenomenological representations and those without competitive dynamics between N-fixing and non-fixing plants and/or asymbiotic BNF). LM4.1-BNF can be applied to project the dynamic response of vegetation to N limitation of plant growth and the degree to which this will constrain the terrestrial C sink under elevated atmospheric CO2 concentration and other global change factors.

中文翻译：

---

土地模型中生物固氮和固氮植物与非固氮植物之间竞争态氮的新颖表示（GFDL LM4.1-BNF）

摘要。代表生物固氮（BNF）是将氮（N）循环纳入土地模型的重要挑战。BNF在土地模型中的初始表示应用了简化的现象学关系。BNF的最新代表是机制性的，包括BNF对植物生长的N限制的动态响应。但是，它们通常不包括固氮植物和非固氮植物之间的竞争动态，这是决定生态系统规模共生BNF的关键生态机制。此外，土地模型通常不包括非共生性BNF。在这里，我们介绍LM4.1-BNF，这是地球物理流体动力学实验室土地模型4.1（LM4.1）中BNF（非共生和共生）的一种新颖表示形式，以及N循环的更新表示形式。LM4。1-BNF结合了土壤微生物对非共生BNF的机械表征，对固氮植物和非固氮植物之间竞争动态的表征以及从相应观察中得出的独特的非共生和共生BNF温度响应。与先前版本的带有N循环的LM4.1（LM3-SNAP）和之前的BNF在陆地上的表示相比，LM4.1-BNF对主要的碳（C）和N池和通量及其时间动态进行了合理的估计。通常建立模型（现象学表示以及那些在N固定和非固定植物和/或非共生BNF之间没有竞争动态的现象）。LM4。