Crescimento, ecofisiologia e eficiência do uso de nutrientes de Tachigali vulgaris L. G. Silva & H. C. Lima fertilizado na Amazônia Oriental.

Abstract

Studies that address the behavior, initial development, ecophysiology, uptake and efficiency of nutrient use of native Amazonian trees as a function of fertilization are extremely important to support actions for the recovery and management of degraded areas. The use of native forest species, whether for timber production or the recovery of degraded areas, is still hampered by the lack of information on their nutritional requirements for the establishment and development of plants in the field. The adequate supply of nutrients, such as phosphorus (P) and potassium (K) can favor different mechanisms of plant growth, such as photosynthetic performance, effectively contributing to the establishment of plants in the field, because it acts in the expression of phenotypic plasticity in relation to the tolerance of plants to limiting conditions of primary resources (water, light and nutrients), contributing to incorporate degraded areas to productive processes. Tachigali vulgaris L. G. Silva & H. C. Lima - Fabaceae is a pioneer species that often initiates secondary succession in open areas, and is ideally considered for reforestation due to its high capacity for biomass production, rapid growth under adverse conditions, and high resistance to environmental disturbances. Its wood has similar characteristics to eucalyptus wood, regarding calorific value and weight and volume yield in the carbonization process, being considered promising for energy plantations in the Brazilian Amazon and bordering regions. In this sense, the objective of this thesis was to evaluate the response to fertilization with phosphorus and potassium on growth, ecophysiology and nutrient use efficiency in T. vulgaris plantation in the Eastern Amazon. Chapter 1 evaluated the effect of P and K fertilization on gas exchange in T. vulgaris; chapter 2 investigated the effect of seasonal precipitation on gas exchange in T. vulgaris fertilized with P and K, using multivariate statistics; and chapter 3 evaluated the influence of fertilization with different levels of P and K on growth and nutrient use efficiency in T. vulgaris plantation. The experiment was installed in March 2016 at the experimental station of the Federal Rural University of the Amazon, in the municipality of Igarapé-Açu/PA. Three doses of P (0, 65.22 and 130.44 kg ha-1) and three doses of K (0, 100 and 200 kg ha-1) were applied in a 3 x 3 factorial scheme and randomized block design. Spot measurements of gas exchange were performed in April and November 2018 with an infrared gas analyzer. Growth parameters, nutrient concentration in biomass, nutrient use efficiency (EUN) and biological use coefficient (CUB) were also evaluated. Potassium fertilization in T. vulgaris plantation provided positive increases (approximately 30%) in net photosynthesis rate per unit leaf area. The other gas exchange variables, such as gs, Ci, E, ΦC, EUA and EiUA, were also favored with the dose of 78.2 g kg-1 of K, suggesting the role of K in the regulation of physiological processes essential for plant growth, such as the opening and closing of stomata. Factor analysis and principal components analysis allowed the initial reduction of 8 variables of gas exchange to 2 and 3 principal components, in the periods of high and low rainfall, respectively. Seasonality influenced the behavior of physiological variables and consequently their grouping within each principal component. T. vulgaris responded positively to fertilization with P and K in the morphological variables of growth in diameter and height, gas exchange, nutrient concentration in aboveground biomass, EUN and CUB, and could double the productivity in volume and wood biomass at the age of three years. The higher CUBP, CUBK and CUBMg found represent values compatible with the critical CUB levels defined for biomass production of the eucalyptus stem. The woody compartments of T. vulgaris showed the highest CUB values, something quite desirable and of great interest for forestry. Due to the natural genetic variability within the stand from native seeds, it is recommended, for future studies with the species, to consider the planting age factor to evaluate the relative export of nutrients in the harvests performed. It is hoped that more studies will be conducted with the species, due to its enormous silvicultural potential, in order to encourage the use of T. vulgaris in programs to recover degraded areas and in energy plantations in the Amazon.