Physiological and transcriptomic analyses elucidate the effects of nitrogen form ratios on strawberry growth and development.

In protected strawberry cultivation, the application of a mixture of ammonium (NH₄⁺) and nitrate (NO₃⁻) nitrogen typically yields better plant growth and development compared to treatments using either nitrogen form alone. To elucidate the underlying physiological and molecular mechanisms, this study employed 'Benihoppe' strawberry (Fragaria × ananassa Duch.) as plant material. Under a constant total nitrogen concentration (6 mmol/L), treatments with different ammonium-to-nitrate ratios (NH₄⁺:NO₃⁻) were established. Through the determination of physiological indices and endogenous hormone levels, combined with transcriptome analysis, we systematically investigated the regulatory role of nitrogen form ratios on strawberry growth. The 7:3 NH₄⁺:NO₃⁻ ratio treatment (CL₂) significantly promoted plant height and petiole growth, increased fruit yield, but had no significant effect on fruit size. During the green fruit stage, this treatment notably increased the levels of auxin, cytokinin, and gibberellin. Transcriptome analysis revealed a significant enrichment in plant hormone signal transduction pathways, with related differentially expressed genes (AUX/IAA, SAUR, GH3, CRE1, and B-ARR) being markedly regulated. This study proposes that a 7:3 ammonium-to-nitrate ratio helps regulate strawberry growth and improve yield, with the underlying mechanism likely involving the coordinated regulation of plant nitrogen uptake and hormone signaling, thereby providing a theoretical basis for precise nitrogen fertilization management in protected strawberry cultivation.