Description:
<jats:title>Abstract</jats:title><jats:p>This study aimed to evaluate the effects of phosphorus (P) deficiency on the lateral root growth of <jats:italic>Fraxinus mandshurica</jats:italic> seedlings and to reveal the potential molecular mechanisms involved. <jats:italic>F. mandshurica</jats:italic> seedlings were treated with various concentrations of P (0, 0.5, 1, and 2 mM KH<jats:sub>2</jats:sub>PO<jats:sub>4</jats:sub>) for 15 d. The growth of lateral roots was quantified by the number of lateral roots, total root length, total root surface area, and root : shoot ratio. Additionally, the levels of endogenous hormones and acid phosphatase were determined in the lateral roots of <jats:italic>F. mandshurica</jats:italic> seedlings using enzyme‐linked immunosorbent assay (ELISA). The transcription of 17 <jats:italic>FmWRKYs</jats:italic> and <jats:italic>FmPHR1</jats:italic> was detected in the lateral roots of <jats:italic>F. mandshurica</jats:italic> seedlings using quantitative real‐time PCR (qRT‐PCR). <jats:italic>F. mandshurica</jats:italic> seedlings under P deficiency (0 mM) exhibited significantly higher number of lateral roots, total root length, total root surface area, and root : shoot ratio than those under P supply. P deficiency significantly decreased the levels of indole‐3‐acetic acid, brassinolide, and ethylene, and increased the levels of gibberellins 3, cytokinin, abscisic acid, and acid phosphatase in the lateral roots of <jats:italic>F. mandshurica</jats:italic> seedlings when compared to seedlings with P supply. In addition, the transcription of four <jats:italic>FmWRKYs</jats:italic>, including <jats:italic>FmWRKY6, FmWRKY23, FmWRKY44</jats:italic>, and <jats:italic>FmWRKY71</jats:italic>, as well as <jats:italic>FmPHR1</jats:italic> were significantly higher in the lateral roots of <jats:italic>F. mandshurica</jats:italic> seedlings under P deficiency compared to seedlings treated with 1 mM P. Phosphorus deficiency promoted the lateral root growth of <jats:italic>F. mandshurica</jats:italic> seedlings and this process may be associated with the up‐regulation of <jats:italic>FmWRKY6, FmWRKY23, FmWRKY44, FmWRKY71</jats:italic>, and <jats:italic>FmPHR1</jats:italic>.</jats:p>