The lignin deposition responses of different poplar root systems to salt stress.

Salt stress significantly constrains plant growth and development, with the root system serving as the primary organ for sensing and responding to salinity. Poplar (Populus spp.), a widely cultivated tree species, plays a pivotal role in urban greening, windbreak and sand fixation, and various economic sectors. Six poplars as experimental materials to analyze lignin deposition in the root system and variations in the casparian strip under salt stress. Lignin enrichment and changes in the casparian strip are as follows: P. alba × P. glandulosa '84K' showed the most pronounced changes, followed by P. cathayana and P. tremula × P. alba, then P. deltoids × P. euramericana 'Nanlin895', Populus × euramaricana 'Bofeng 3 hao' and P. simonii. Transcriptome sequencing revealed the molecular mechanisms in the 84K poplar and P. simonii with the greatest and smallest lignin increase, respectively. The results reveal that 84K poplar and P. simonii mainly regulate the accumulation of lignin through phenylalanine metabolism, starch and sucrose metabolism, as well as the MAPK signaling pathway under salt stress. This study provides critical theoretical support for elucidating the molecular response mechanisms of root lignin and the casparian strip under salt stress.