Light regulates tropical symbiotic nitrogen fixation more strongly than soil nitrogen

Nitrogen limits primary production in almost every biome on Earth1,2. Symbiotic nitrogen fixation, conducted by certain angiosperms and their endosymbiotic bacteria, is the largest potential natural source of new nitrogen into the biosphere3, influencing global primary production, carbon sequestration and element cycling. Because symbiotic nitrogen fixation represents an alternative to soil nitrogen uptake, much of the work on symbiotic nitrogen fixation regulation has focused on soil nitrogen availability4,5,6,7,8. However, because symbiotic nitrogen fixation is an energetically expensive process9, light availability to the plant may also regulate symbiotic nitrogen fixation rates10,11. Despite the importance of symbiotic nitrogen fixation to biosphere functioning, the environmental factors that most strongly regulate this process remain unresolved. Here we show that light regulates symbiotic nitrogen fixation more strongly than does soil nitrogen and that light mediates the response o...氮几乎限制了地球上几乎所有生物群系（biome）的初级生产（primary production）1,2。由特定被子植物（angiosperms）及其内共生细菌（endosymbiotic bacteria）所介导的共生固氮（symbiotic nitrogen fixation），是向生物圈（biosphere）输入新生氮的最大潜在自然来源3，对全球初级生产、碳封存（carbon sequestration）及元素循环（element cycling）均具有深远影响。由于共生固氮可作为植物吸收土壤氮的替代途径，此前绝大多数关于共生固氮调控机制的研究均聚焦于土壤氮有效性（soil nitrogen availability）4,5,6,7,8。然而，共生固氮属于能量高成本的生理过程9，因此植物可获取的光照资源或同样会调控共生固氮速率（symbiotic nitrogen fixation rates）10,11。尽管共生固氮对生物圈功能至关重要，但目前学界仍未明确对该过程调控作用最强的环境因子（environmental factors）。本研究表明，相较于土壤氮，光照对共生固氮的调控作用更为显著，且光照会介导响应o...