Crescimento e trocas gasosas de mudas de Microdesmia rigida (Benth.) Sothers & Prance mantidas sob sombreamento.

Abstract

Due to the importance of light intensity in the growth of seedlings during the nursery phase, and the lack of information in this regard in oiticica plants (Microdesmia rígida), this work aimed to evaluate the effect of shading on growth and gas exchange of plant seedlings. The research was conducted at the Forest Nursery of the Academic Unit of Forest Engineering, at the Rural Health and Technology Center of the Federal University of Campina Grande (CSTR / UFCG) (Centro de Saúde e Tecnologia Rural da Universidade Federal de Campina Grande), Campus in Patos. Levels of 0% (full sun), 50% and 70% of shading were evaluated, arranged in a completely randomized design (DIC), with four replications of 15 plants. The growth parameters of the seedlings and physiological evaluated were: height, absolute growth rate, diameter, height/diameter ratio, leaf area, root-shoot ratio, Dickson's quality index (DQI), sweating rate, stomatal conductance, rate photosynthesis, internal CO2 concentration, levels of chlorophyll a, b and total. Shading promoted a reduction in the rate of transpiration, an increase in the stomatal conductance of plants at 30 and 60 days after the beginning of treatments, and in the rate of photosynthesis of plants, at 90 days. The internal CO2 concentration increased with shading, except at 60 days, when there was a decrease as the incident light intensity decreased. Regarding the concentration of pigments, for chlorophyll a no differences were observed between the 50% shading and full sun treatment; however, chlorophyll b and total chlorophyll were higher in the treatment with 70% shading. In relation to growth, shaded environments provided an increase in plant height, stem diameter, leaf area, in addition to greater accumulation of dry mass, and IQD. It is recommended to produce oiticica (Microdesmia rígida) seedlings under 50% shading during the nursery phase, as this condition provides the achievement of better seedling quality indexes.