Growth and functional characteristics of young Bertholletia excelsa plants grown in association with an N2-fixing tree under fertilization

Abstract

Mixed plantations that include N2-fixing trees have several benefits, both above and below ground, that can favor the growth of economically valuable trees. However, for species native to the Amazon, it is not yet clear what the optimal combination of species that enhances crop productivity is. In order to better understand the association between B. excelsa and T. vulgaris, two different chapters were proposed for this thesis. In Chapter 1, we evaluated the effects of the planting systems and fertilization on the edaphoclimatic variables, growth and the morphophysiological characteristics of the model species, B. excelsa. It was observed that the association between B. excelsa and T. vulgaris reduced light availability and soil temperature, while at the same time increased soil moisture and CO2 efflux. The higher phosphorus content in the soil was due to NPK fertilization directed at this nutrient. The plants of B. excelsa cultivated in the pure plantation + liming + NPK system showed the highest growth rates and greatest biomass stocks. The higher P content associated with higher light availability were the factors that most contributed to the growth and carbon gain of the species in this system. In Chapter 2, we sought to understand the effects of planting systems, fertilization and seasonality on carbon and nitrogen metabolism in B. excelsa. To do this, we evaluated metabolic responses over two years (2021-2022), covering seasonal periods of rainfall and drought. We observed a dynamic in the concentration of soluble sugars, starch and other organic compounds such as amino acids and proteins. By analyzing seasonal variations, we were able to conclude that B. excelsa modulates its metabolism, especially in relation to glucose and amino acids, as an adaptive mechanism to improve its osmoregulation capacity and protect itself against the lower availability of water during the dry season in the Amazon. Overall, the growth of the B. excelsa plants under pure planting + liming + NPK were influenced by changes in the microclimate of the plantation, availability of foliar N, P and K, leaf morphology, improved photosynthetic performance, and changes in carbon and nitrogen metabolism. It can be concluded that, although the association between B. excelsa and T. vulgaris improved the microclimate of the plantation, the fertilized pure plantation presented the highest photosynthesis and greatest biomass gain, indicating that, in addition to P, light directly affects the growth of B. excelsa.