我国农林业生产中氮素利用效率普遍较低，是限制我国农林业可持续化发展的重要原因。杨树的快速生长需要大量的氮素，但是人们对光信号调控林木氮素吸收同化的分子机制却知之甚少。本研究拟以杨树光敏色素互作因子4（phytochrome-interacting factor 4，PtPIF4）为研究对象，利用转基因技术和CRISPR-Cas9技术分别构建PtPIF4超表达系和敲除系，分析其在不同光周期下的表型。利用非损伤微测技术及15N标记技术,分析PtPIF4转基因相关材料及野生型根系对氮素吸收的能力。同时，利用生理生化技术，分析PtPIF4转基因相关材料及野生型根系和叶中氮素代谢相关代谢物含量及酶活性。利用RNA-seq和ChIP-seq技术解析PtPIF4调节杨树氮素吸收的转录调控网络及分子遗传机制。本研究将为遗传改良林木氮素利用效率提供理论依据，为我国人工林的氮肥管理提供实践依据。

The nitrogen use efficiency in agricultural and forestry production is generally low in China, which has limited the sustainable development of agroforestry in China. The fast growth of poplar requires large amounts of nitrogen, however, the molecular mechanisms by which light signal regulates nitrogen uptake and assimilation in woody plants are largely unknown. In this study, we will establish over-expression and knockout lines of poplar phytochrome-interacting factor 4 (PtPIF4) using transgenic technique and CRISPR-Cas9 technique, and characterize the phenotypes of the transgenic lines under different photoperiod conditions. Meanwhile, non-invasive micro-test technology and 15N labeling technology will be used to evaluate the nitrogen uptake capacity in PtPIF4 transgenic plants and wild type. Metabolites and enzymes related to nitrogen metabolism will be measured using physiological and biochemical technologies. Furthermore the RNA-seq and ChIP-seq technologies will be used to reveal the transcriptomic regulatory network mediated by PtPIF4 underpinning nitrogen uptake and assimilation in poplar. This study will provide theoretical basis for genetic breeding of woody plants with high nitrogen use efficiency, and practical evidence for nitrogen management of forest plantations in our country.