Effect of temperature and water potential on Capparis spinosa seed germination: Quantification of the cardinal temperatures and hydrothermal time

This study was conducted to quantify the germination response of Capers Capparis spinosa L. to temperature and water potential. The seeds were germinated at seven temperatures (5, 10, 15, 20, 25, 30, and 35 °C) and six water potentials (zero, -0.3, -0.6, -0.9, -1.2 and -1.5 MPa). Increased water potential and temperature decreased germination percentage and increased germination time. The results revealed that the dent-like function (RMSE = 0.24, R2 = 0.82, and r = 0.86) is suitable for describing the response to temperature and water potential. Based on the dent-like model base, optimum and ceiling temperatures were estimated as 8.81 to 11/13, 21.30 to 24.88, and 35.22 to 37.55 °C, respectively. Biological hours for the control treatment (zero potential water) were calculated as 52.11 hours. The hydro time constant for SSG (θH), the middle value for the base water potential (Ψb(50)), the standard deviation in base water in the water potential (σyb), and the thermal time constant for SSG (θT) spanned the values of 0.63–243.48 MPa h, −0.3–2.59 bar and 343.3–1344.3 °C h, respectively. The hydrothermal time parameters were 445.12 bar °C h, −2.274 MPa, and 8.28 °C for θHT, and Ψb(50), Tb in temperatures and water potentials, respectively.