This study aimed to explore the effects of different types and concentrations of salt stress on the seed germination of Pennisetum alopecuroides, and clarify the molecular mechanism underlying the “low-promotion and high-inhibition” effect of Na⁺ concentration on seed germination. The fingdinga are expected to provide a theoretical basis for the cultivation of P. alopecuroides in saline-alkali land and the breeding of salt-tolerant varieties.

Seeds of the ornamental-fodder dual-purpose P. alopecuroides line "Langyan No. 1" were used as experimental materials. Different concentration gradients were set for six types of salts, inciuding NaCl, MgSO₄, NaHCO₃, KCl, Na₂SO₄, and mixed salt (NaHCO₃:NaCl:Na₂SO₄=1:15:84). Germination-related indicators (germination energy, germination rate, bud length, and root length) were determined, and the membership function method was employed to evaluate the impact of different salt treatments on seed germination. Additionally, stress physiological indicators were measured, and transcriptome sequencing was performed on P. alopecuroides seeds treated with CK (control), 10 mmol·L^-1 NaCl, and 100 mmol·L^-1 NaCl for 3 days. Metabolic pathways and candidate genes involved in low-concentration Na⁺-promoted germination were analyzed, and the reliability of sequencing data was verified by qRT-PCR.

Low concentrations of NaCl (10-25 mmol·L^-1) and Na₂SO₄ (10 mmol·L^-1) could promote seed germination, with significantly higher germination energy and germination rate than the control group, and the relative salt injury rate was 0. In contrast, high-concentration salts (≥100 mmol·L^-1) inhibited germination, among which NaHCO₃ showed the strongest inhibitory effect (no seed germination was observed at 200 mmol·L^-1). For stress physiological indicators, low-concentration NaCl stress significantly increased the activities of superoxide dismutase (SOD) and catalase (CAT), as well as the content of proline (Pro); while high-concentration NaCl stress significantly induced the accumulation of malondialdehyde (MDA). Transcriptome analysis identified 14259 differentially expressed genes (DEGs) in total. DEGs associated with low-concentration NaCl-promoted germination were mainly enriched in the oxidative phosphorylation pathway. Genes such as PPA and ATPeV1D in this pathway were positively correlated with germination indicators, whereas genes like ATPeF0A and ND1 were positively correlated with relative salt injury rate and MDA content. The inhibitory effect of high Na⁺ concentration on seed germination was mainly achieved by downregulating the expression of genes related to germination-promoting hormone synthesis pathways and upregulating the expression of genes involved in germination-inhibiting hormone synthesis pathways. qRT-PCR verification confirmed the reliability of the transcriptome data.

Under salt stress, Na⁺ concentration exerts a “low-promotion and high-inhibition” effect on seed germination of Pennisetum alopecuroides. Low-concentration of neutral sodium salts (NaCl, Na₂SO₄) can promote germination, while high-concentration salts (especially the alkaline salt NaHCO₃) exhibit inhibitory effects. The salt tolerance mechanism of Pennisetum alopecuroides is associated with the regulation of antioxidant enzyme activities, proline accumulation, and the expression of genes in pathways such as oxidative phosphorylation.