Mapas de calor e componentes principais na termobiologia de sementes do semiárido

Abstract

Deforestation, predatory agriculture, and excessive grazing are significant issues affecting semi-arid regions. Consequently, studies focusing on the conservation and management of native tree species are crucial. These studies aid in developing protocols that assist in the recovery and preservation of these ecosystems. Leucaena leucocephala and Pterogyne nitens, both members of the Fabaceae family, are recognized for their ecological and agricultural functions. This study aimed to evaluate the germination thermobiology of L. leucocephala and P. nitens seeds under varying temperatures using heat maps and principal component analysis (PCA), and to identify their main implications for the restoration of degraded environments. The experiment was conducted at the Phytotechnics Laboratory on the Campus of Engineering and Agricultural Sciences - UFAL. Seed lots from Caatinga areas, collected at different times in the upper hinterlands of Alagoas state, were used. The physiological potential of the seed lots was assessed using a completely randomized design (CRD). Treatments consisted of constant isothermal incubation temperatures: 5, 10, 15, 20, 25, 30, 35, and 40 °C, tested for both species. Each treatment had four replicates of 25 seeds, totaling 64 experimental units. Germinated seeds were counted daily, starting from the fourth day for L. leucocephala and the seventh day for P. nitens after the germination test setup, lasting ten and fifteen days, respectively. The variables analyzed were germinability, first germination count, germination speed index, germination synchrony index, seedling length, and seedling dry mass. For data analysis, the 'Multivariate Analysis' package in RStudio (version 4.4.1) was used. The Principal Components (PCA) and HeatPlot functions were applied to understand the correlation among different variables and the indirect impact of temperatures on the physiological potential of the seeds. Additionally, the similarity between different temperature regimes was identified based on the set of evaluated variables. L. leucocephala seeds germinated between 15 and 35 °C. PCA revealed that a temperature of 35 °C provided a higher germination speed, meaning this temperature favored faster and more uniform germination. However, the dendrogram ranked 20 and 25 °C as the most promising temperatures for greater seedling length and biomass accumulation, suggesting enhanced seedling development under these conditions. P. nitens seeds, on the other hand, germinated between 15 and 40 °C, demonstrating thermal plasticity. Temperatures of 30 and 35 °C promoted greater germination synchrony, and the dendrogram classified the thermal range of 20 to 35 °C as the most favorable for the development of P. nitens. Germination of both species was reduced at 15 and 40 °C, likely due to thermal stress associated with suboptimal or supraoptimal temperatures for germination.