Germination responses of Physorhynchus chamaerapistrum to abiotic stressors: implications for semiarid rangeland restoration

Understanding seed germination responses to environmental factors is crucial for predicting plant establishment and distribution. This study investigated the effects of constant (5, 10, 15, 20, 25, 30, 35, 40 and 45 °C) and alternating temperature (25/15, 30/20, 35/25, and 40/30°C; day/night) regimes, osmotic potential (0, − 0.2, − 0.4, − 0.6, − 0.8, − 1.0, and − 1.2 MPa), and salinity (0, 50, 100, 150, 200, 250, 300, and 350 mM) on seed germination of Physorhynchus chamaerapistrum , a rangeland species native to semi-arid regions. Under constant temperatures, germination occurred across a broad range (10–40 °C), with optimum performance between 15 and 30 °C. Maximum germination percentage (88%) was achieved at 30 °C, while the highest germination rate (15.26 seeds/day) occurred at 25 °C, with model predictions indicating peak germination rates at 23.76 °C. Alternating temperature regimes revealed highest germination (88%) at 25/15°C and germination rate at 30/20°C, with rapid decline at elevated temperatures (18% at 40/30°C), Osmotic stress experiments demonstrated germination tolerance to − 0.2 MPa (95%), with 50% inhibition occurring at − 0.61 MPa and complete inhibition at − 1.2 MPa. Salinity trials showed linear germination decline with increasing NaCl concentrations, from 90% at 0 mM to complete inhibition at 350 mM, with 50% germination rate reduction at 90 mM. Mean germination time increased substantially under all stress conditions, reaching maximum values of 8.64 days at − 0.84 MPa osmotic potential and 6.06 days at 244 mM of salinity. These findings demonstrate that P . chamaerapistrum has a distinct thermal range favorable for germination and exhibits progressively reduced germination under increasing osmotic and salinity stress. The lower GR₅₀ relative to the threshold for final germination indicates that germination rate is particularly sensitive to salinity. The identified thermal, osmotic, and salinity thresholds provide species-specific benchmarks that may inform future seed-based restoration studies in semi-arid rangelands. However, their implications for field establishment and grazing management require validation under natural conditions.