Predição da germinação de sementes para quatorze espécies do Cerrado em função da temperatura e superação de dormência física com ajuste de modelo hidrotérmico em Bowdichia virgilioides

Abstract

Seed germination is a decisive process, since the establishment and seedling survival depend on environmental factors after germination. Soil temperature and water potential are the main environmental regulators of germination and can be used in models to describe germination patterns, as well as provide fundamental parameters to predict occurrence of plants in different ecosystems. Also, predict germination and vulnerability of species in altered habitats, especially in case of future climate changes in the environment. Temperature also affects seed physical dormancy (PY) and determines the time and rate of permeable seeds. The objective was to quantify seed germination of 14 species occurring in the Cerrado based on thermal time and to evaluate the risk of species survival in global climate change scenarios; propose hydrothermal models to predict germination of Bowdichia virgilioides seeds; to quantify the thermal requirement for breaking PY in B. virgilioides seeds based on a thermal model and to relate the seed coat polymorphism with germinative characteristics. Seeds were collected in the warmer regions of the Cerrado, Mato Grosso state, in the Central Brazil region and placed to germinate in incubators. In the case of the 14 species, seeds were placed at constant temperatures of 10 to 50 °C and evaluated every hour or day. Germination rate (R (g)), based on the germination time of 50% of the seeds (T50) were used to determine cardinal temperatures. Germination predictions were made based on the IPCC scenarios of increasing global temperature. The base temperature (Tb) varied from 3.5 to 16.5 °C; maximum temperature (Tmax), from 35 to 50 °C and optimum temperatures (To) from 30 to 35 ° C. The estimated thermal time varied from 484 °C hour to 400 °C day at sub-optimal temperatures and 108 °C hour at 126 °C day at supra-optimum temperatures. The results of this study suggest that non-dormant seeds after dispersal may in the future be the most vulnerable in the Cerrado. For B. virgilioides, the seeds were incubated at temperatures of 10 to 40 °C and water potentials of 0.0; -0.2; -0.4; -0.6; and -0.8 MPa. Thermal time, hydro time and hydrothermal time models were developed from the T50. The estimated medium Tb was 12 °C for all water potentials; Tmax varied from 35 to 40 °C. Ψb ranged from -0.73 to -0.85 MPa at sub-optimal temperatures and was -0.39 MPa at supra-optimal temperatures. Hydro time was between 17.51 and 1.70 MPa, with the lowest value estimated at 30 °C and the hydrothermal time was 31.3 MPa ° C day. B. virgilioides seeds had their PY break quantified at constant and alternating temperatures, and were also subjected to relative air humidity of 10 to 100% in an incubator at 35 °C and at room temperature. The Tb for breaking PY in the fractions of 20 to 60% of the seeds was 22.9 °C and the thermal time was 58.12 to 206.25 °C day. Freshly dispersed seeds do not need two steps to break dormancy, however, in relative air humidity less than 75%, they decrease sensitivity.