Crescimento inicial, trocas gasosas e mecanismos protetores de Cedrela fissilis Vell. em função das disponibilidades hídricas e sombreamentos

Abstract

During your life cycle, the plants not always they find favorable environmental conditions for your metabolism and growth. Soil water availability and shading are abiotic factors that can become stressful to the unadapted or tolerant plant and may limit its growth and development by requiring the plant to adopt anatomical, morphological and physiological adjustments to ensure its survival. The objective of this work was to evaluate the parameters of initial growth, photosynthetic metabolism, antioxidant enzymes and morphoanatomy of Cedrela fissilis Vell. under different water availability and levels of shading. The seedlings were cultivated under flooding for 0, 10, 20, 30 and 40 days and under natural environmental conditions receiving only rainwater (control). Both conditions of water availability were conducted in full sun (0% shading level) and under cover of 30% and 70% shading. The flood simulation was performed with water 5 cm above the surface of the substrate in tarpaulin pools. Gas exchange, quantum efficiency of photosystem II, activity of antioxidant enzymes, initial growth and foliar anatomy were evaluated. There was a reduction in the rates of photosynthesis, transpiration and stomatal conductance during the 40 days of evaluation. The instantaneous efficiency of water use (EUA), intrinsic water use efficiency (EIUA) and the carboxylation efficiency of Rubisco (A/Ci) were higher at the 70% shade level. Plants grown in full sunlight showed lower potential quantum efficiency of photosystem II (Fv/Fm) and internal CO2 concentration (Ci). The highest activities of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) were observed at 40 days for all cultivation conditions, being higher in flooded plants. There was an increase in height, stem diameter, root length (CR), leaf area (AF), shoot dry mass (MSPA) and root (MSR), Dickson Quality Index (IQD) and density stomatal (DE) during the 40 days of evaluation, being the highest values in the control seedlings in relation to the wetlands. The stomatal opening (AE) decreased in all treatments, being lower in floodplains regardless of the level of shading. The stomatal index (IE) decreased in the full sun and the paliçadic parenchyma (PP), adaxial cuticle (Cad) and the abaxial cuticle (Cab) decreased with increasing shading intensity. The abaxial epidermis (Eab) was thicker at 40 days at the 70% shading level, the adaxial epidermis (Ead) in this same period was higher in the full sun condition and the lachrymal parenchyma (PL) at 40 days was higher in the intensity of 30% shade. Thus, C. fissilis seedlings are sensitive to soil flooding for up to 40 days, especially if flooding is associated with greater light availability. The seedlings present greater efficiency of gas exchange and antioxidant activity when flooding is associated with 70% shading, where they presented higher growth and responses that induced anatomical changes. The control seedlings obtained better results of initial growth and seedling quality. Young plants of C. fissilis showed high sensitivity to flooding and high levels of luminosity, and the symptoms are aggravated when the factors are associated.