Application of the thermal time model for different Typha domingensis populations

Cattail (Typha domingensis Pers.) is a perennial emergent plant which is used in Green Floating Filters (GFFs), one of the most innovative systems of wastewater treatment to bioremediate eutrophic waters and produce biomass as biofuel feedstocks. The establishment of cattails in GFFs depends on the seed germination and plant responses under conditions of a new habitat. This study analysed the germination responses of four different populations of cattails through a thermal time model to know their basic parameters of germination and which population would be more adapted to the conditions tested.

Seeds from the Badajoz (Ba), Cuenca (Cu), Madrid (Ma), Seville (Se) and Toledo (To) populations were exposed to different thermal regimes (constant, and alternating temperatures between 15 and 30 °C) and different darkness treatments (between 0 and 20 days with 24 h dark photoperiod, then exposed to light with 12 h light/dark photoperiod) to determine the parameters of the thermal model from germination levels in each treatment. To population was used to validate the thermal time parameters of other populations. Regardless of the other parameters, no germination occurred in total darkness. The mean value of base temperature (T_b) was 16.4 ± 0.2 °C in all treatments. Optimum temperature (T_o) values in Ma and Ba were 25 °C, and those in Cu and Se were 22.5 °C. The germination response decreased when the temperature approached T_b and increased when it was close to T_o. In comparison to alternating temperatures, constant temperatures had the highest germination response and lowest thermal time (θ_T(50)). Darkness treatments had a direct relationship with θ_T(50). The population origin also affected seed germination; Cu had the highest values of T_o and germination response but had a lower θ_T(50), which coincides with the lowest mean ambient temperatures.

According to these results, the germination response of cattails was high in all populations under optimal conditions but was affected to a greater or lesser extent depending on thermal regimes, darkness treatments, and populations. The thermal time model allowed us to determine that T_o was between 22.5-25 °C and that Cu is the best population regarding the germination response under the conditions tested.