ABSTRACT The use of dark septate fungi (DSE) to promote plant growth can be beneficial to agriculture, and these organisms are important allies in the search for sustainable agriculture practices. This study investigates the contribution of dark septate fungi to the absorption of nutrients by rice plants and their ensuing growth. Four dark septate fungi isolates that were identified by Internal transcribed spacer phylogeny were inoculated in rice seeds (Cv. Piauí). The resulting root colonization was estimated and the kinetic parameters Vmax and Km were calculated from the nitrate contents of the nutrient solution. The macronutrient levels in the shoots, and the NO3--N, NH4+-N, free amino-N and soluble sugars in the roots, sheathes and leaves were measured. The rice roots were significantly colonized by all of the fungi, but in particular, isolate A103 increased the fresh and dry biomass of the shoots and the number of tillers per plant, amino-N, and soluble sugars as well as the N, P, K, Mg and S contents in comparison with the control treatment. When inoculated with isolates A103 and A101, the plants presented lower Km values, indicating affinity increases for NO3--N absorption. Therefore, the A103 Pleosporales fungus presented the highest potential for the promotion of rice plant growth, increasing the tillering and nutrients uptake, especially N (due to an enhanced affinity for N uptake) and P.

RESUMO. O nitrogênio é essencial para o crescimento e desenvolvimento das plantas e tem influência direta na produção de grãos e conteúdo de óleo. O boro tem sido bastante estudado no cultivo de girassol, devido a alta exigência desta cultura por este nutriente. Este trabalho teve por objetivo avaliar o efeito de nitrogênio e boro na produção de grãos e óleo em plantas de girassol. O experimento foi conduzido em casa de vegetação utilizando-se dois híbridos: BRS 321 e Neon. N e B foram aplicados em solução nutritiva: B + 50 N (2,49 kg de B ha-1 e 10 kg de N ha-1 no plantio e 40 kg de N ha-1 suplementar); B + 10 N (2,49 kg de B ha-1 e 10 kg de N ha-1 no plantio); 50 N (sem B e 10 kg de N ha-1 no plantio e 40 kg de N ha-1 suplementar); 10 N (sem B e 10 kg de N ha-1 no plantio). Ao final do ciclo foi analisado os teores de N e B total em todas as partes das plantas, produção de grãos por capítulo e teor de óleo. A combinação entre o fornecimento de B com a maior adubação nitrogenada foi essencial para a produção de óleo pelo híbrido BRS 321. Em relação à produção de grãos com menor adubação nitrogenada Neon apresentou a melhor resposta à aplicação B.

ABSTRACT. Nitrogen is essential for plant growth and development and directly influences both grain production and oil content. Boron has been studied in sunflower cultivation due to high demand of this culture for this nutrient. This study aimed to evaluate the N and B differential supply effect on the grain and oil production of sunflower plants. The experiment was conducted in a greenhouse and used two sunflower hybrids: BRS 321 and Neon. N and B were applied via nutritive solution according to the following treatments: B + 50 N (2.49 kg ha-1 B and 10 kg ha-1 N at planting and 40 kg ha-1 B as additional fertilization); B + 10 N (2.49 kg ha-1 B and 10 kg ha-1 N at planting); 50 N (0 B and 10 kg ha-1 N at planting and 40 kg ha-1 N as additional fertilization) and 10 N (0 B and 10 kg ha-1 N at planting). Analyses of total N and B in all collected plant parts were performed, as well as measurements of grain production for each chapter and oil extraction at the end of the cycle. The association between B fertilization and a greater amount of N fertilization was essential to BRS 321 oil production. Regarding grain production at lower levels of N fertilization, Neon presented the best response to B application.

RESUMO O girassol é uma oleaginosa de grande importância agroenergética e o nitrogênio é considerado um dos fatores limitantes para seu crescimento e produção. O objetivo deste trabalho foi avaliar a absorção de nitrogênio (alto e baixo suprimento de nitrato e amônio) e determinar os parâmetros cinéticos (Km e Vmax) de absorção desses íons em plantas de girassol (híbrido Neon). O experimento foi conduzido em câmara de crescimento utilizando-se sistema hidropônico. Foram aplicados os seguintes tratamentos: 0,2 e 2,0 mmol L-1 de N-NO3- e N-NH4+. Foram determinados os parâmetros cinéticos (Km e Vmax) da absorção de nitrato e amônio, bem como as frações solúveis (N-NO3-. N-NH4+, N-amino e açúcares) e N-total em diferentes tecidos das plantas de girassol. As plantas cultivadas com amônio exibiram maior Vmax quando comparadas com as cultivadas com nitrato. Altas doses de amônio provocaram redução no volume radicular e as plantas supridas com 2,0 mmol L-1 de N-NO3- produziram maior biomassa de raízes e parte aérea. Os maiores teores de N-NO3- foram encontrados nos pecíolos. Analisados em conjunto, os dados sugerem maior potencial de utilização de N nítrico como fonte de nitrogênio para a adubação nitrogenada no cultivo de girassol.

ABSTRACT Sunflower plants are source of oilseeds with great importance for agroenergy. Nitrogen deficiency is considered one of the factors limiting growth and yield. The objective of this study was to assess the nitrogen uptake (high and low supply of nitrate and ammonium) and to determine the uptake kinetics parameters (Km and Vmax) of these ions in sunflower plants (Neon hybrid). The experiment was carried out in a growth chamber using a hydroponic system. The following treatments were applied: 0.2 and 2.0 mmol L-1 of N-NO3- and N-NH4+. The two kinetics parameters (Km and Vmax) involved in the uptake of nitrate and ammonium were determined, as well as the soluble fractions (N-NO3-, N-NH4+, amino-N and sugars) and total N, in different plant tissues. The plants grown with ammonium showed higher Vmax than those cultivated with nitrate. High ammonium rates caused reduction of root volume and the plants supplied with 2.0 mmol L-1 of N-NO3- produced more biomass from the roots and aerial part. The highest concentrations of NNO3- were found in the petioles. Analyzed together, the data suggest a greater potential for use of nitric-N as a nitrogen source for fertilization in the cultivation of sunflower.