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The present work was carried out to quantify camelina germination niche under salinity and temperature ( T) stress using halotime and halothermal time models. Seed germination ( SG) time courses were recorded at six constant temperatures (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, and 30 °C) and at each of the following levels of NaCl concentrations (0, 50, 100, 150, 200, and 250 mM). Halotime model could well describe the germination time courses across a range of NaCl concentrations ( R2 = 0.79–0.91). The median base NaCl concentration was approximately constant (231 mM) at suboptimal T followed by a linear decrease, with the rate of 17.4 mM °C−1, under supra-optimal T. However, the germination rate increased with increasing T, reaching its maximum at a fixed optimum temperature ( To = 20 °C), independent of NaCl concentration. Then it decreased linearly for T > To and intercepted the x-axis at the ceiling temperature values of 33.5 °C, 30 °C, 28 °C, 25 °C, and 22 °C under 0, 50, 100, 150, and 200 mM NaCl, respectively. Consequently, based on model estimation the adequate soil T for SG of camelina should be in the range of 0.4 °C–33.5 °C, and the To is 20 °C. Besides, the salinity should be less than 231 mM.

Camelina (Camelina sativa (L.) Crantz; Brassicaceae) is known as an important and low-input oilseed crop, which is widely used in the production of biopolymers, biofuels, cosmetics, food, and feed. One of the main problems of camelina cultivation is related to seed size which can directly influence its germination, seedling growth, and development. Therefore, this study was performed to evaluate the effect of temperature (T) and water potential (ψ) on camelina germination behavior using population-based threshold models as the first study in this case. For this purpose, camelina seeds were incubated at eight Ts (5, 10, 15, 20, 25, 30, 35, and 40 °C) and at each of the following five levels of ψs (0, –0.25, –0.50, –0.75 and –1 MPa). The results illustrated that T, ψ and T × ψ significantly affected germination characteristics of camelina. The ψb(50) value remained constant at Ts ≤ 20 °C (−1.29 MPa), afterward increased linearly to −0.81 and −0.41 MPa at 25 and 30 °C, respectively. The thermal time model also showed that the ψ levels did not affect the value of Tb at sub-optimal Ts (Tb = 1.5 °C), while Tc(50) decreased linearly with decreasing ψ, with the rate of 11.3 °C per MPa at supra-optimal Ts, conforming with the results obtained by the hydrothermal time model. This decrease in germination capacity at Ts above To was due to the shifts in the ψb(50) (become more positive), reflecting a decrease in GR50 as a result of thermoinhibition which could be considered as an adaptive strategy under stress conditions. The cardinal Ts for camelina germination at 0 MPa were estimated 1.5 °C for Tb, 20.0 °C for To, and 34.4 °C for Tc. Consequently, camelina could be marked as a cold-tolerant plant and suitable for cultivation in arid regions due to the high resistance to low water potential (ψb(50) = −1.29 MPa).