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Guarana is a plant native to the Amazon region that produces the fruit known as guarana. Guarana production is carried out by small farmers and is a source of income for thousands of people in rural and urban areas. The interference caused by the competition between weeds and guarana is an important limiting factor of its production. Despite its economic and social importance, there are few studies on the management of weeds in this species. Thus, this research aimed to study the effects of weed interference on guarana yield in different periods. This study was performed in Maués, AM, in the 2014 and 2015 seasons. The experimental design was a randomized block design with eight treatments and four blocks. Treatments consisted of a combination of four different periods of control or coexistence with weeds (March to May, June to August, September to November, and December to February). Weed community was composed of 23 weed species belonging to 12 botanical families, with Paspalum virgatum being the species with the highest importance value index (55.74%). Weed coexistence with guarana from June to August provided the lowest yields (156.16 kg ha-1 of grains) when compared to weed control in the same period (309.05 kg ha-1 of grains). Weed interference from June to August reduced guarana yield by 50%.

We subjected seedlings from three tree species from the semi-arid ''Caatinga'' biome to water deficiency and rehydration. The species were Bauhinia monandra K. and Hymenaea courbaril L., (both Fabaceae), and Tabebuia aurea (Bignoniaceae). Seedlings were kept under water restriction until photosynthesis decreased to values around zero. Plants were rehydrated and photosynthesis measured until its values reached values of well-watered plants. We measured leaf water potential, maximum quantum yield, and chlorophyll index on (1) the first day of the experiment; (2) when photosynthesis decreased to around zero; and (3) after photosynthesis recovery. We then determined biomass and leaf area. To avoid water deficiency B. monandra and T. aurea (but not H. courbaril) reduced their leaf area resulting in lower biomass accumulation. The chlorophyll index was also not affected in H. courbaril, but it was lower for the other two species under stress. Maximum quantum yield was equally decreased in all the tree species as a mechanism to decrease light damage of photosynthetic apparatus. Drought differentially affected the vegetative growths of B. monandra, T. aurea, and H. courbaril when time and intensity were considered, affecting leaf area status leading to the leaf biomass decrease. Decreases in soil moisture led to decreased gas exchange. However, leaves were positively acclimated using chlorophyll strategies by lowering the light harvest in photosystems, which protect photosynthetic reaction centers.

Tabebuia aurea (Benth. & Hook. f. ex S. Moore) (Bignoniaceae) is a boreal species common in Brazil. It is used for ornamental parks and along sidewalks. Its timber is also used for furniture. The objective of this study was to evaluate the effect of nursery shading on the growth and photosynthesis of T. aurea and their photosynthetic adaptation after being transferred to direct sunlight. The T. aurea seedlings were grown under 0, 50, 70 or 95% shade. The photosynthetic active radiation and leaf gas exchange were measured over two distinct periods: 51 (young seedlings) and 70 days after having been sown under each shade treatment. Immediately after the measurements were taken, the seedlings were transferred into full sunlight and the measurements were repeated two times after 15 min and 3 days under ambient sunlight. T. aurea seedlings showed satisfactory growth up to 50% shade in the nursery, which could be verified both by growth measurement and by total biomass accumulation. Shading greater than 70% reduced the number of leaves, the leaf area and the stem diameter in relation to plants exposed to full sunlight. The results suggest that T. aurea seedlings should be grown under full sunlight or under shading up to 50% to maximize their growth in the nursery and to minimize stress when transferring the seedlings to their final planting sites.Key words: Bignoniaceae, nursery, Atlantic Forest, leaf gas exchangeAdaptações morfológica e fotossintética de plântulas de Tabebuia aurea no viveiro RESUMO Tabebuia aurea (Benth. & Hook. f. ex S. Moore) (Bignoniaceae) é uma espécie arbórea comum no Brasil, utilizada para fins ornamentais de calçadas e parques cuja madeira é usada para fabricação de móveis. O objetivo deste estudo foi avaliar o efeito do sombreamento no crescimento e na fotossíntese de mudas de T. aurea e sua adaptação fotossintética após transferência ao sol pleno. As plântulas de T. aurea foram cultivadas sob 0, 50, 70 e 95% de sombreamento. Sob cada condição de sombreamento foram avaliadas a radiação fotossinteticamente ativa e as trocas gasosas das folhas aos 51 (plântulas jovens) e após 70 dias após a semeadura das sementes sem o uso de luz artificial; logo em seguida as plântulas foram transferidas para o sol pleno e nova medidas foram feitas após 15 min e 3 dias da transferência para a nova condição. As plântulas de T. aurea apresentaram crescimento satisfatório até o nível de 50% de sombreamento no viveiro que pôde ser verificado tanto pelo crescimento como pelo acúmulo de biomassa total. O sombreamento acima de 70% reduziu o número de folhas, área foliar e o diâmetro do coleto em relação às plantas expostas ao pleno sol. Os resultados sugerem que plântulas de T. aurea devem ser cultivadas em sol pleno ou com sombreamento de até 50% para maximizar o crescimento no viveiro e minimizar o estresse de transferência das mudas para o local de plantio definitivo.Palavras-chave: Bignoniaceae, produção de mudas, Floresta Atlântica, plântulas, trocas gasosas foliar

A colheita mecanizada da cana-de-açúcar altera a composição da flora infestante, com predominância de espécies da família Convolvulaceae. O uso de combinações de herbicidas pode aumentar a eficiência no controle destas plantas daninhas. Sendo assim, objetivou-se com esse trabalho avaliar a eficiência de sulfentrazone, hexazinone, amicarbazone e suas associações em diferentes doses, no controle de espécies de corda-de-viola, em aplicações sobre a palhada de cana-de-açúcar. Para isso, foram conduzidos seis experimentos em casa-de-vegetação onde cada experimento caracterizou-se pelo uso de um herbicida ou suas associações, assim definidos: sulfentrazone, hexazinone, amicarbazone, sulfentrazone + hexazinone, sulfentrazone + amicarbazone e hexazinone + amicarbazone. Em cada experimento foi utilizado o delineamento inteiramente casualizado em esquema fatorial 4x8, com três repetições. Os fatores analisados foram: quatro espécies de corda-de-viola (Ipomoea nil, Ipomoea hederifolia, Merremia aegyptia e Ipomoea quamoclit) e oito doses dos herbicidas (0; 6,25; 12,5; 25; 50; 100; 200 e 400% da dose recomendada para a cultura da cana-de-açúcar). As associações sulfentrazone + hexazinone, sulfentrazone + amicarbazone e hexazinone + amicarbazone em doses menores do que a recomendada pelo fabricante, aplicadas sob condições de palhada de cana-de-açúcar, são eficientes no controle de corda-de-viola.