Disentangling the variability of symbiotic nitrogen fixation rate and the controlling factors

Symbiotic nitrogen (N) fixation (SNF), replenishing bioavailable N for terrestrial ecosystems, exerts decisive roles in N cycling and gross primary production. Nevertheless, it remains unclear what determines the variability of SNF rate, which retards the accurate prediction for global N fixation in earth system models. This study synthesized 1230 isotopic observations to elucidate the governing factors underlying the variations of SNF rate. The SNF rates varied significantly from 3.69 to 12.54 g N m-2 yr-1 across host plant taxa. The traits of host plant (e.g., biomass characteristics and taxa) far outweighed soil properties and climatic factors in explaining the variations of SNF rate, accounting for 79.0% of total relative importance. Furthermore, annual SNF yield contributed to more than half of N uptake for host plants, which was consistent across different ecosystem types. This study highlights that the biotic factors, especially host plant traits (e.g., biomass characteristics an..., The peer-reviewed papers for this synthesis were searched up to September 7, 2022, using Web of Science and China National Knowledge Infrastructure Database. The SNF data were from the field measurements. The strings employed for searching papers are: ((“nitrogen fixation” or “N fixation” or “N2 fixation” or “dinitrogen fixation” or “nitrogenase”) and field). The following criteria were used to sift out the peer-reviewed papers: 1. The SNF rate was measured using 15N isotope method (e.g., 15N natural abundance, and 15N dilution) since these methods guarantee the accuracy of SNF across large spatial/temporal scale than acetylene reduction assay method (Davies-Barnard et al., 2020; Soper et al., 2021); 2. The measurement must be given the unambiguous unit; 3. The studies that plant has been inoculated with specific strains of bacteria (e.g., rhizobium) were excluded; 4. The SNF was measured in the field rather than the laboratory incubation or greenhouse cultivation, and the data from aqu..., , The peer-reviewed papers for this synthesis were searched up to September 7, 2022, using Web of Science and China National Knowledge Infrastructure Database. The SNF data were from the field measurements. The strings employed for searching papers are: ((“nitrogen fixation” or “N fixation” or “N2 fixation” or “dinitrogen fixation” or “nitrogenase”) and field). The following criteria were used to sift out the peer-reviewed papers: 1.The SNF rate was measured using 15N isotope method (e.g., 15N natural abundance, and 15N dilution) since these methods guarantee the accuracy of SNF across large spatial/temporal scale than acetylene reduction assay method (Davies-Barnard et al., 2020; Soper et al., 2021); 2. The measurement must be given the unambiguous unit; 3. The studies that plant has been inoculated with specific strains of bacteria (e.g., rhizobium) were excluded; 4. The SNF was measured in the field rather than the laboratory incubation or greenhouse cultivation, and the data from aque...

共生固氮（Symbiotic Nitrogen Fixation, SNF）可为陆地生态系统补充生物可利用态氮，在氮循环与总初级生产力中发挥决定性作用。然而，当前学界仍未明确调控共生固氮速率变异的核心因素，这一认知缺口阻碍了地球系统模型对全球固氮量的精准预测。本研究整合1230组同位素观测数据，旨在阐明共生固氮速率变异的主控因子。不同宿主植物类群的共生固氮速率差异显著，范围为3.69至12.54 g N m⁻² yr⁻¹。宿主植物性状（如生物量特征与植物类群）对共生固氮速率变异的解释能力远高于土壤属性与气候因子，相对总重要性达79.0%。此外，年共生固氮量可贡献宿主植物超过一半的氮吸收量，这一规律在不同生态系统类型中均保持一致。本研究强调，生物因子尤其是宿主植物性状（如生物量特征……）。

本综合研究所涉及的同行评议文献检索截止至2022年9月7日，检索数据库包括Web of Science与中国知网（China National Knowledge Infrastructure Database）。共生固氮数据均来自野外实地测量。文献检索所用检索式为：(("nitrogen fixation" 或 "N fixation" 或 "N2 fixation" 或 "dinitrogen fixation" 或 "nitrogenase") 且 field)。本研究采用以下标准筛选同行评议文献：1. 共生固氮速率采用15N同位素法（15N isotope method，如15N自然丰度法、15N稀释法）测定，相较于乙炔还原法（acetylene reduction assay），该类方法可保证大时空尺度下共生固氮测定的准确性（Davies-Barnard et al., 2020; Soper et al., 2021）；2. 测定结果需标注明确的计量单位；3. 排除植物接种特定细菌菌株（如根瘤菌（rhizobium））的相关研究；4. 共生固氮测定需在野外开展，而非实验室培养或温室栽培，且排除水生……。

本综合研究所涉及的同行评议文献检索截止至2022年9月7日，检索数据库包括Web of Science与中国知网（China National Knowledge Infrastructure Database）。共生固氮数据均来自野外实地测量。文献检索所用检索式为：(("nitrogen fixation" 或 "N fixation" 或 "N2 fixation" 或 "dinitrogen fixation" 或 "nitrogenase") 且 field)。本研究采用以下标准筛选同行评议文献：1. 共生固氮速率采用15N同位素法（如15N自然丰度法、15N稀释法）测定，相较于乙炔还原法，该类方法可保证大时空尺度下共生固氮测定的准确性（Davies-Barnard et al., 2020; Soper et al., 2021）；2. 测定结果需标注明确的计量单位；3. 排除植物接种特定细菌菌株（如根瘤菌）的相关研究；4. 共生固氮测定需在野外开展，而非实验室培养或温室栽培，且排除水生……。