Exogenous ABA Optimized Nitrogen Distribution During Nitrogen Imbalance Supply in Populus cathayana

Nitrogen (N) and abscisic acid (ABA) are important nutrients and signaling molecules in regulating plant growth and stress responses. Although the crosstalk between ABA and N has been widely noted, our understanding of the process and mechanism underlying their interaction remains limited. Here, we found that exogenous ABA influenced the growth and N utilization efficiency (NUE) of Populus cathayana depending on N supply level. Integrated transcriptome analysis identified a substantial number of overlapping differentially expressed genes in the leaves following both exogenous ABA treatment and N deficiency, indicating potential crosstalk between ABA and N signaling pathways. Cross-treatment experiments demonstrated that ABA significantly enhanced biomass accumulation and NUE in poplar under N-deficient and N-excessive conditions. Elemental analysis further revealed that ABA significantly altered N distribution among leaves. Additionally, asparagine synthetase (EC 6.3.5.4), a key enzyme in N assimilation, was significantly induced by both ABA and N availability, contributing to N distribution and influencing aboveground growth in P. cathayana. Furthermore, genes associated with N metabolism and transport, such as PcASN1, PcNRT2.5, PcNRT3.1, PcNPF4.1 and PcGDC1, were found to be co-regulated by N and ABA. Therefore, these results reveal a mechanism by which ABA enhances N utilization, pointing to a new strategy for optimizing poplar NUE.