Efeitos de variações na luminosidade no crescimento vegetativo de Chamaecrista rotundifolia (Pers.) Greene, uma herbácea perene da Caatinga.

Abstract

Light variations in the Caatinga are due to habitat fragmentation and natural variation in the tree canopy, which influence the growth and development of herbaceous plants. Aiming to understand the strategies of Chamaecrista rotundifolia (Pers.) Greene, a perennial herb from the Caatinga, with variation in light, this study hypothesizes that, as this factor decreases, there is a reduction in the area, longevity and production of leaves of this species. Individuals clustered in clearings, and a total of 400 seeds were randomly collected in the Caatinga fragment of the Agronomic Research Institute (IPA), Caruaru-PE. The seeds were germinated and 120 viable seedlings were placed in 4 treatments (T) with different percentages of light: T100: full sun, T70: 70%, T50: 50%, T30: 30%; 30 reps each; duration of 6 months. We measured the length and width of previously marked leaves on a weekly basis, so that we could measure the relative growth rate in leaf area (FCRAf), using specific allometric equations for this species. We measured longevity (LF) and total leaf production (PTF). We evaluate the results using GLMs (Generalized Linear Models). We found that there were no very significant differences in relative leaf growth rates between the light availability treatments. The lowest total leaf production (TFP) was similar between T30 and T50, differing from the other treatments. Compared to T100, there was a reduction in sheet production of up to 91.64% observed in T30. In addition to the higher leaf production at T100, we observed that this treatment also had the highest leaf abscission (PEF) values during monitoring. With more than 97% loss in T30 when compared to T100. And as for leaf longevity, we found that only 8% was explained by the reduction in light availability. All vegetative characteristics analyzed were plastic, with greater emphasis on the plasticity index of the relative distance of the attributes: number of leaves (0.73), height (0.68) and diameter (0.56), respectively, more plastics during the study. Extreme variations in luminosity normally have a negative impact on the primary metabolism of plants, however, specifically for this species from the Caatinga, the increase in this factor proved to be advantageous for its success in growth and establishment in this stochastic environment. Thus, added to its low nutritional requirement and large production of biomass and nutrient deposition in the soil, the species C. rotundifolia proved to be an excellent pioneer species, which can be used in the restoration of degraded environments.