Background: The Dirigent (DIR) gene family is pivotal for lignin polymerization and stress adaptation in plants, yet its systematic characterization in Sorghum bicolor (S. bicolor), a critical bioenergy crop, remains underexplored. Methods: Leveraging the S. bicolor genome database, we conducted a genome-wide identification, phylogenetic classification, and expression profiling of the DIR gene family. Evolutionary dynamics, gene structure variations, promoter cis-regulatory elements, and spatiotemporal transcriptome patterns were analyzed using bioinformatics and experimental validation (RT-qPCR). Results: A total of 53 SbDIR genes were systematically identified, exhibiting uneven chromosomal distribution. Phylogenetic analysis clustered them into five clades (DIR-a, DIR-b/d, DIR-c, DIR-e, DIR-f), with subfamily-specific exon number variations suggesting functional divergence. Evolutionary studies revealed tandem duplication (TD) as the primary driver of family expansion, accompanied by strong purifying selection. Promoter analysis highlighted abundant hormone- and stress-responsive cis-elements. Tissue-specific RNA-seq data revealed root-enriched expression of SbDIR2/4/18/39/44/53, implicating their roles in root development. Notably, SbDIR39 and SbDIR53 were significantly upregulated (2.8- and 5-fold, respectively) under 150 mM NaCl stress, underscoring their stress-responsive functions. Conclusions: This study provides the first comprehensive atlas of the DIR gene family in S. bicolor, elucidating its evolutionary mechanisms and tissue-specific/stress-induced expression profiles. Key candidates (SbDIR39/53) were identified as promising targets for molecular breeding or CRISPR-based editing to enhance stress resilience in S. bicolor. These findings lay a foundation for translating genomic insights into agronomic improvements.

Soil fertility has an important impact on orchard yield and quality, and sandy soil limits the economic yield of orchards due to its low water and fertilizer retention capacity. Although biochar and alfalfa planting have been widely utilized separately in soil improvement, few studies have examined the effects of combined alfalfa planting and biochar application on jujube orchard soils. This study investigates the effects of alfalfa planting alone and alfalfa planting combined with different levels of biocarbon addition on soil properties. A field experiment was conducted in a jujube orchard in Yanchuan County, Shaanxi Province, with four treatments: clear tillage control (CK), alfalfa planting only (B1), alfalfa planting + 1.5 kg·m⁻² biocarbon (B2), and alfalfa planting + 3 kg·m⁻² biocarbon (B3). The results show that planting alfalfa significantly increased soil moisture content (SMC) and soil organic matter (SOM) content by 27.79% and 17.65%, respectively, and biochar addition significantly increased soil carbon, nitrogen, and phosphorus content by 8.11–37.7%, enhanced the soil moisture content (SMC) by 98.13–100.22%, promoted the growth of alfalfa, and increased vegetation cover (p < 0.05). The combination of biochar and alfalfa improves soil fertility more effectively than alfalfa alone. It can increase the soil N and P nutrient contents, improve soil available nutrients, promote alfalfa growth in a short period, and provide a feasible solution for soil improvement in the future.