Thermal-biological aspects of germination of seeds in tropical forest tree species

The present study was carried out with the objective of evaluating the ecological and applied aspects of temperature in the germination of Colubrina glandulosa (Rhamnaceae), Chloroleucon dumosum (Fabaceae), Enterolobium contortisiliquum (Fabaceae), Mimosa bimucronata (Fabaceae) and Sapindus saponaria (Sapindaceae). Then we assessed germination, average germination time, germination uniformity and germination activation energy as a function of temperatures. The experiment was conducted at the Plant Propagation Laboratory, on the Engineering and Agricultural Sciences Campus, at the Federal University of Alagoas, Rio Largo, AL, Brazil. The experimental design was completely randomized with four replications of 25 seeds per treatment. The data were subjected to analysis of variance and the means were compared using the Tukey test at 5% probability. The isothermal incubation was performed in Biochemical Oxigen Demand (B.O.D.) germination chamber, at constant temperatures of 5, 10, 15, 20, 25, 30, 35 and 40 ºC and alternating at 20-30 ºC. The seeds of C. glandulosa, C. dumosum, E. contortisiliquum and M. bimucronata germinated in the range of 10 ºC ≤ T ≤ 35 ºC, and S. saponaria germinated in the range of 20 ºC ≤ T ≤ 35 ºC. We found that seeds in the optimal temperature range has unimodal distribution of relative frequency, concentrating germination in the shortest time. The activation energy was positive in the range of 10 ºC ≤ T ≤ 30 ºC, with an inversion of the signal at a temperature of 35 ºC. The studied species had a wide range of temperature tolerance and the speed was curvilinearly dependent on them. The germination process is predominantly endergonic