Morfofisiologia e metabolismo antioxidante de mudas de Cedrela fissilis Vell. sob disponibilidades hídricas e luminosas

Abstract

Cedrella fissillis Vell. is a native tree species of great relevance to the national and international timber industry, in addition to presenting significant ecological potential. Its high economic value has led to intense exploitation, resulting in this species being designated as vulnerable. In this context, deeper knowledge about the responses that C. fissilis seedlings present when subjected to different cultivation conditions becomes essential for the preservation, use and cultural management of this species. In recent years, the occurrence of climate variations has intensified, and such variations cause plants to be exposed to adverse and extreme conditions. Among the abiotic factors that interfere with the growth and development of plants, water and light availability stand out. It is essential to verify which species are tolerant, and for what periods they can withstand water and light variations without compromising their growth and development. Therefore, we aimed to evaluate the impacts of exposure time to different water and light availability and the interaction of these factors on the photochemical activity and initial growth of C. fissilis, and also to verify whether shading can mitigate the effects of water stress on the cultivation of C. fissilis, facilitating the action of protection mechanisms and maintaining the quality of the seedlings. The seedlings were subjected to combinations of three shading levels – SH (0%, 30% e 70%) and three water regimes based on the water holding capacity (WHC) of the substrate, constituting nine cultivation conditions: T1 – 0% SH + 40% WHC; T2 – 0% SH + 70% WHC; T3 – 0% SH + 100% WHC; T4 – 30% SH + 40% WHC; T5 – 30% SH + 70% WHC; T6 – 30% SH + 100% WHC; T7 – 70% SH + 40% WHC; T8 – 70% SH +70% WHC; T9 –70% SH + 100% WHC. The first chapter addressed the characteristics of gas exchange, chlorophyll a fluorescence and chlorophyll index, which were evaluated at 15, 30, 45 and 60 days of cultivation, as well as destructive characteristics of relative water content and growth, which were evaluated at 15 and 60 days. It was found that C. fissilis seedlings are sensitive to water deficit, here represented by 40% WHC, regardless of the exposure time, and when grown in full sun, even with variations in radiation, the stressful effects were enhanced, acting synergistically. The condition that provided the best gas exchange erformance and the greatest accumulation of total dry mass for C. fissilis seedlings was 30% shading combined with 100% WHC. The second chapter explores the responses of C. fissilis with regard to photochemical activity, water content, antioxidant metabolism and seedling quality. The evaluations of these characteristics were carried out in two different periods: at 15 and 60 days. C. fissilis seedlings respond to extremes of combined water and light availability and among the cultivation conditions studied, the combination of moderate shading (30% SH) with greater water availability (100% WHC) reduced damage to the photosynthetic apparatus and provided better seedling quality with increased exposure time. Excessive light caused damage to gas exchange and photosystem II and reduced seedling quality under 0% SH conditions. Seedlings grown under full sun and low water availability (0% SH + 40% WHC) did not show good quality. We conclude that C. fissilis seedlings adapt to different growing conditions through adjustments in their physiology and metabolism.