Ecofisiologia de rebrotas de Bertholletia excelsa Bonpl. em plantio florestal submetido ao desbaste

Abstract

The species Bertholletia excelsa has economic and social importance in the North Brazil region. Added to various performance characteristics of this species, studies demonstrate the potential for the same composition of forest plantations. Recently, some scientific studies highlighting their ability to emit sprouts, a characteristic that would, depending on the force and silvicultural measures, the restoring coppicing system. This system can be a good idea to avoid additional costs and problems, such as predation by rodents that feed on the endosperm in the seedlings of this species. In this condition, research on the influence of physical factors of the environment on the performance of growth and functional characteristics in Bertholletia excelsa coppice of regrowth are important for obtaining better results in your driving. In General, works highlight the relevance of genetic factors or environmental, operational and physiological determinants for the success of the coppice. Thus, this study aimed to investigate the growth above-ground and functional characteristics of regrowth of Bertholletia excelsa growing in the understory of a plantation on the effect of the following factors: I) diameters of stumps; II) light gradients - photosynthetically active radiance (PAR) and III) progression of the dry season in a year of El Niño in interaction with the treatment of reduction of stems. To this end, in order to analyze the effect of the factors I and II, was measured biometrically all coppice regrowth in a forest planting thinning, in a total of 251, these stumps when absent (shoots) have been classified as dead, subsequently, took place the draw of four coppice regrowth by diameter class, with amplitude between classes of five centimeters and full range from zero to thirty centimeters with independence between the diameter of the stumps in relation of photosynthetically active radiation and the height of the stumps. Levels of photosynthetically active radiance were measured on the tops of the shoots, leaf area, leaf mass per area ratio (LMA), leaf nutrient content, leaf water potential, leaf gas exchange and chlorophyll a fluorescence. For factor II, stumps were selected samples with the same number of sprouts (3 stems), similar as average height and average diameter of the regrowth and stumps of diameter between 6 and 10 centimeters. These samples were subjected to reduction of stems, making the treatments T1 (1 stem), T2 (2 stems) and T3 (3 stems). These measured the height and diameter of the sprouts in July, October and December, the leaf functional characteristics (specific leaf weight, leaf nutrient content, leaf water potential, gas exchange, fluorescence and chloroplastid pigments) were obtained in the same months biometrics in a year characterized as El Niño. The diameter of the stump was negatively related to survival and positively and not linear with the number of sprouts, growth, carbon sequestration, stomatal conductance, leaf area and leaf mass area ratio. The N content and Fe both the mass base had a linear relationship with the diameter of the stumps. While the photosynthetically active irradiance on the tops of the shoots was growing and non-linear relationship with the above-ground growth and phosphorus content (base area) and linear with ratio of leaf mass area (LMA), N content (base area), carbon fixation and stomatal conductance. In the experiment III, in October there was an increase contents P, N and K compared to July as a possible response of leaf ontogeny and chl a/chl b ration as a possible response to higher irradiance. The progression of the dry season resulted in lower growth above ground in the period from October to December compared to previous period (July to October), lower stomatal conductance, internal carbon concentration, carbon and increased fixation on the intrinsic efficiency in water use in December, reducing the levels of N and P and maintenance of K, as a possible result of the reduced availability of water in the soil. The thinning treatment did not result in significant gains in height and diameter of the dominant shoot and leaf functional characteristics and not interacted with the progression of dry season. Given the above, it is concluded that the diameter of the strains, irradiance levels and changes modulated by the progression of the dry period in the last months of measurement interfere with restored growth, conditioned by foliar functional characteristics and should be considered for conduction Bertholletia excelsa coppice growing in the understory of a plantation after thinning.