A influência da hidratação descontínua de sementes e dos ciclos de rega em mudas no comportamento germinativo e no potencial alelopático de espécies exóticas invasoras da Caatinga

Abstract

Biological invasion is one of the main causes of biodiversity loss worldwide. Certain characteristics can increase invasiveness, such as the presence of hydration memory in seeds and the allelopathic potential of the plant. This is the ability to release allelochemicals that affect the development of target species in the environment and can be influenced by environmental conditions such as discontinuous seed hydration and irrigation cycles in seedlings. This thesis aims to understand the influence of these environmental conditions on the germination behavior and allelopathic potential of invasive exotic species in the Caatinga biome. In this sense, this work has three chapters, the first of which is dedicated to verifying whether the germination of seeds of the invasive species Neltuma juliflora (Sw.) Raf., Sylva Tellur. var. juliflora is favored in situations of water deficit when subjected to discontinuous hydration. Among the results, I observed that the germination behavior of the species, through the measured parameters, was altered due to the passage through hydration and dehydration (HD) cycles of the seeds. Thus, the species benefits from the hydration memory of the seeds under water deficit conditions during the invasion process, demonstrating an invasive characteristic. In the second and third chapters, I analyzed how the passage through water deficit cycles and irrigation cycles in seedlings of Leucaena leucocephala (Lam.) de Wit (Fabaceae) and N. juliflora influences allelopathy during germination and initial development of a model species (in the laboratory) and a native species (in the laboratory and in a greenhouse), respectively. In the second chapter, I observed that the allelopathy of L. leucocephala was favored by the passage through these previous cycles, while N. juliflora did not show alterations in its allelopathy. Finally, the third chapter showed that, despite the native species being tolerant to allelopathic stresses, extracts of L. leucocephala in laboratory experiments influenced the germination time of the batch, while in the greenhouse, the effects occurred in various ways, such as a decrease in seedling emergence and the length of the roots. This thesis demonstrates that the presence of hydration memory in seeds of N. juliflora and L. leucocephala, when subjected to discontinuous hydration, can be a characteristic of invasiveness. Furthermore, allelopathy is a dynamic process influenced by previous conditions, so its invasive potential can increase in environments that naturally present situations similar to discontinuous hydration and irrigation cycles.