Crescimento e respostas ecofisiológicas de bertholletia excelsa bonpl. cultivada em diferentes sistemas de plantio sobre área alterada

Abstract

Due to the high rates of altered or degraded areas in the Amazon region, planned and effective actions are needed for their recovery and to extend the benefits of the initiative to the population and the forest production chain. Forest plantations can be a viable alternative to meet such demand, and plantation systems that involve the intercropping of plants of different species or successional groups can be even more successful for this purpose. Thus, the objective of this work was to investigate the aspects of the sites and the ecophysiological and growth responses of Bertholletia excelsa cultivated in different planting systems on an altered area. The study was carried out in experimental plantations located at the Federal University of the South and Southeast of Pará, in the municipality of Marabá-PA. The following treatments were applied to these plantings: 1 - pure planting of B. excelsa; 2 - mixed planting with the consortium between B. excelsa and Ingá (Inga edulis); 3 - agroforestry system with the association between B. excelsa, ingá, cocoa (Theobroma cacao), banana (Musa sp.), corn (Zea mays) and beans (Vigna sp.). From these treatments, survival rates and growth were determined in the period between October 2020, June 2021 and September 2021. The treatments were compared regarding changes in resource availability (water, light and nutrients) and efficiency in the use of these resources, survival and growth, leaf morphology, and physiological responses such as gas exchange, chloroplast pigment content, nutritional status and leaf water status. The adopted experimental design was in randomized blocks (DBC), with three treatments and five replications. Over the 20 months of experimentation, there were no differences between treatments regarding the availability of water, light and nutrients, except for the availability of magnesium (Mg) in the soil, which was higher in agroforestry systems. Plants from agroforestry systems had higher levels of Mg in the leaves and no differences were found in the concentration of chloroplastic pigments, however it was found that seedlings planted in agroforestry systems have higher values of photosynthesis, stomatal conductance and transpiration and also greater efficiency in use of N and K, while seedlings planted in pure planting showed greater efficiency in water use. The highest survival rates were observed in the agroforestry system and mixed planting. The treatments did not differ in terms of growth rates. The best ecophysiological responses for B. excelsa were observed respectively in agroforestry and mixed planting systems, mainly in relation to gas exchange, leaf gain and nutrient use efficiency, reflecting the greater survival of the species in these planting systems.