Effect of Temperature, Water Potential and Salinity on Seed Germination of Four Native Perennial Grasses of the Monte (Argentina)

Abstract

Seed germination is critical for successful restoration in degraded desert ecosystems. This study aimed to determine thermal requirements and tolerance limits to water and salt stress of four key forage species: Aristida mendocina, Digitaria californica, Pappophorum caespitosum, and Leptochloa crinita. Controlled laboratory experiments were conducted to evaluate constant temperature regimes (5, 15, 20, 25, 30, 35, 40, and 45°C), one alternating-temperatures regime (45-15°C), water potentials (0, -0.38, -0.58, -0.97, -1.30, -1.52, and -1.77 MPa) simulated with Polyethyleneglycol (PEG) solutions, and NaCl concentrations (0.1, 0.3, and 0.5 M). We recorded final germination percentage and germination rate (Maguire Index). The species exhibited different environmental plasticity. L. crinita and P. caespitosum showed the broadest thermal ranges, achieving optimal germination (>80%) between 25 and 35°C. P. caespitosum demonstrated the highest tolerance to salinity and water stress, being the only species capable of germinating in 0.5 M NaCl solutions (20%) and at -1.77 MPa (20%). In contrast, *A. mendocina* and *D. californica* were the most sensitive; the former restricted its optimum to 20-30°C, and both reduced their germination by half with just 0.1 M NaCl. Highlights: All four C4 grasses germinate between 15 and 40 °C. Pappophorum caespitosum is highly tolerant to drought and salinity. Aristida mendocina and Digitaria californica have low tolerance to salinity. Leptochloa crinita showed intermediate tolerance to drought and salinity. Establishing tolerance thresholds enables genotype selection for ecological restoration.