Modeling germination and shoot-radicle elongation of Ambrosia artemisiifolia

Laboratory studies were conducted to describe germination and seedling elon gation of Ambrosia artemisiifolia L. (common ragweed) seed. The germination process was tested for the interaction of temperature and water potential across eight thermo-periods (7.5, 12.5, 17.5, 22.5, 27.5, 32.5, 37.5, and 4 2.5 C) and 12 water potentials (0, -0.03, -0.06, -0.1, -0.2, -0.4, -0.6, -0 .9, -1.2, -1.5, -1.8, and -2.1 mPa). The rate of seedling shoot and radicle elongation was described as a function of temperature and rested for eight day:night temperature treatments (10:5, 15:10, 20: 15, 25:20, 30:25, 35:30 , 40:35, and 45:40 C). The rate of germination was mathematically modeled b y a Welbull function. Probit analysis was used to determine the cardinal te mperatures (base, optimum, and maximum) and base water potential (psi(b)). The base temperature (T-b), optimum temperature (T-opt), maximum temperatur e (T-max) and psi(b) for A. artemisiifolia germination were estimated as 3. 6, 30.9, and 40 C and -0.8 mPa, respectively The rates of shoot and radicle elongation were described by regression models. The T-b, T-opt, and T-max for shoot and radicle elongation were estimated as 7.7 and 5.1, 29.5 and 31 .4, and 43.0 and 44.3 C, respectively. A mathematical model describing the process of A. artemisiifolia seed germination in terms of hydrothermal time (theta(HT)) was derived. The theta(HT) model described the phenology of A. artemisiifolia seed germination using a single curve generated from the re lationship of temperature and water potential. This model can help in predi cting germination and emergence of A. artemisiifolia under field conditions . Nomenclature: Ambrosia artemisiifolia L. AMBEL, common ragweed.