Efeito de diferentes níveis de sombreamento nos atributos vegetativos e reprodutivos de herbácea da caatinga

Abstract

Variations in the availability of light inside dry forests regulate the vegetative and reproductive development of herbaceous species. Many of these species adjust themselves tolerating the different luminosity conditions, changing their physiological, phenological, anatomical and morphological processes. Thus, we hypothesize that the increase in light availability in dry forests triggers greater vegetative and reproductive growth of herbaceous plants, favoring their survival. In this work we aim to understand the adjustments that occur in the phenological, vegetative morphological and reproductive responses of Talinum triangulare (Jacq.) Willd in different light conditions. Our expectations are that reductions in vegetative growth, and lower production of leaves, flowers, fruits and seeds, as well as delays in phenological responses, occur through the reduction of light availability, that is, in greater shading. For this study we selected as a model the geophilic herbaceous Talinum triangulare (Jacq.) Willd. The seeds of this species were collected in the caatinga in Caruaru, conducted to the laboratory and applied pre-germinative treatments (chemical scarification and immersion in water) to overcome dormancy. After the germination in the BOD chamber, the seedlings were transplanted to polyethylene bags containing soil from the same place of origin as the seed collection. Transplanted seedlings were placed in greenhouse for 15 days for acclimatization and on the 16th day they were submitted to four treatments of different light availability by shading: T1: full sun (control); T2: 30%; T3: 50% and T4: 70% shading, with 30 replicates per treatment. The plant growth in height, diameter and accumulated number of leaves produced were measured every 6 months. At the end of the experiment, one leaf of each plant per treatment was removed to measure the leaf area. The number of flowers and fruits produced to measure the total production was counted daily. Seeds of 60 fruits were counted per treatment, stipulating the value for the total fruits produced. The ratio fruit / flower (Fr / Fl) and fruits / seeds (Fr / S) was measured in each treatment for the total production. At the end of the experiment, the plants were separated into leaves, stems and roots, dried in greenhouses and weighed to obtain the biomass accumulated in the plants. Our results showed that the plants submitted to the treatment of higher luminosity (T1) presented higher growth in height and diameter, greater accumulation of biomass, besides the greater production of leaves, flowers, fruits and seeds. However, there was a lower leaf area in T1 compared to the other shade treatments. There were no differences in vegetative phenological responses, only temporal delays in the reproductive phenophases between treatments. Confirming our expectations, we verified that the greater availability of light favors the growth and reproduction of T. triangulare and consequently the greater shading reduces the growth and prolongs the vegetative phase, delaying the reproductive responses. Thus, we expect the development and establishment of this species to be favored by the increase of direct light intensity in the dry forest soil, whether mediated by changes in the climate or by increasing modification of anthropogenic origin.