Ação de microrganismos e da alternância de temperatura na superação da dormência exógena de sementes florestais amazônicas

Abstract

The dormancy is a property of the seed which slows the germination until the environmental conditions are favorable to the seedling establishment. Its cause can be on the bud development (endogenous) or on the involucre characteristics (exogenous). Technological procedures as dawns, endocarp removal, chemical and mechanical scarification and immersion in hot water were already performed in labs or nurseries, being efficient on overcoming the seeds’ exogenous dormancy of various species. However, to understand the environmental factors evolved on the dormancy breaking and germination in the nature is fundamental for understanding the species life cycle. The alternating temperature and the ground microorganisms’ action are frequently mentioned on the literature as a factor of exogenous breaking in the nature, whereas for the microorganisms’ action, there are few scientific results which demonstrate effective participation. The objective of this work was to compare the influence of these two factors for breaking the exogenous dormancy of amazon forest’s seeds, considering the difference between physical dormancy, caused by the involucre impermeability, and the mechanical dormancy, caused by its hardness. Germination experiments were performed with four amazon forest’s species which have physical dormancy (Ochroma pyramidale, Enterolobium schomburgkii, Parkia pendula and Dinizia excelsa) and five which have mechanical dormancy (Byrsonima crassifolia, Eugenia stipitata, Minquartia guianensis, Bertholletia excelsa and Astrocaryum aculeatum). It was used the vermiculite substratum super thin. For verifying the effect of the thermal alternating, three conditions of temperature were tested: constant (25ºC) and alternating every 12 h with amplitude of 10 ºC (20/30 ºC) and of 20ºC (15/35 ºC), with photoperiod of 12 h. Disinfection of the seeds procedure was performed with the sequence immersion in solution of detergent, alcohol and sodium hypochlorite for the microorganisms’ removal. Parallel, it was studied the effect the presence of microorganisms on the compost activator Fert Bokashi®, in constant temperature of 25 ºC, using solution of 0, 1, 10 and 100 mL/L of distilled water on the substratum’s first wetting. The germination was weekly followed and the final average percentage were calculated, the average time and the Germination Speed Index. The experimental design was entirely randomized, with 4 repetitions from 50 to 100 seeds, according to the species, and the data were evaluated by Variance Analysis and Kruskal-Wallis Test. The species with the same type of dormancy showed different responses. Seeds of Ochroma pyramidale (physical dormancy) and Bertholletia excelsa (mechanical dormancy), showed greater final germination with thermal alternating between 15 and 35 ºC. Minquartia guianensis (mechanical dormancy) reacted positively to the microorganisms’ effect (10 mL/L). Eugenia stipitata (mechanical dormancy) showed high rate of germination (> 90%) under all tested conditions, but without reduction along the germination period. There wasn’t dormancy breaking and the germination was low in all the treatments applied to the physical dormancy species Parkia pendula, Dinizia excelsa and Enterolobium schomburgkii and on the mechanical dormancy species Astrocaryum aculeatum and Byrsonima crassifolia. Isolating the factors thermal alternating and microorganisms in lab, there were simplifications concerned to wetting and luminosity, which also interfere. The thermal alternating on the nature is usually associated to higher water stress and light incidence than the constant temperature. On the complexity of forest ecosystem, there may be more than one indispensable factor for germination. Thus, it was not possible to perform generalizations concerned to the fundamental environment factor for breaking the dormancy on the nature considering only the type of dormancy the seeds showed, the thermal alternating and the microbial action.