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Na agricultura, além da disponibilidade da água, a disponibilidade de nitrogênio é geralmente considerada o fator mais limitante para o crescimento de plantas no seu ambiente natural. Apesar de sua importância e de ser requerido em quantidades significativas pelos seres vivos, este elemento é encontrado na natureza em abundância em uma forma quimicamente muito estável (predominantemente na forma de gás nitrogênio, N2), fazendo-se necessária a transformação para uma forma “combinada” com o hidrogênio (H2) que facilite sua assimilação. As plantas podem adquirir o nitrogênio “combinado” a partir de diferentes fontes sintéticas (processo Haber Bosch) e naturais, como os raios; e a fixação biológica de nitrogênio (FBN). A FBN constitui a principal via de incorporação do nitrogênio à biosfera, tornando-se um processo biológico determinante para a vida na terra, de igual importância a fotossíntese e a respiração. Com o intuito de reduzir os efeitos adversos dos fertilizantes sintéticos, manter e aumentar a fertilidade dos solos, contribuir com a nutrição das culturas e melhor aproveitar a FBN, têm-se avaliado o potencial dos fertilizantes biológicos. Neste contexto, o potencial de organismos fixadores de nitrogênio que habitam a filosfera de culturas hortícolas é ainda pouco conhecido. Neste trabalho, testou-se a aplicação de um bioestimulante comercial com microrganismos que colonizam a filosfera na cultura da alface (Lactuca sativa L.) e avaliou-se a capacidade de fixação de nitrogênio do microrganismo e sua contribuição para a cultura. O experimento decorreu no município de Bragança, região de Trás-os-Montes, nordeste de Portugal. Para a condução do experimento utilizou-se um delineamento fatorial com dois fatores: fertilização nitrogenada, com quatro níveis de fator (D1, D2, D3 e D4, a que correspondem 0, 0,33, 0,66 e 1,32 g N vaso-1); e um produto comercial com Methylobacterium symbioticum, com dois níveis de fator (Com e Sem). De cada tratamento foram incluídas quatro repetições. Realizaram-se dois ciclos de cultivo. Ao longo do experimento determinou-se a intensidade da cor verde das folhas. As plantas foram coletadas e levadas a estufa, até atingirem peso constante, pesadas, moídas, e levadas ao laboratório para determinação da biomassa produzida e avaliação da composição elementar dos tecidos. De modo geral, os resultados permitiram atribuir ao tratamento Com Microrganismo um incremento na produção de matéria seca (11,4 contra 9,8 g vaso-1 no primeiro ciclo e 14,6 contra 10,7 g vaso-1 no segundo ciclo), área foliar (99,4 dm² contra 69,3 dm² no primeiro ciclo) e índice de clorofila (medido por leituras SPAD, nos valores de 27,8 contra 25,0 no primeiro ciclo) em comparação com as plantas de alface não inoculadas. Para os demais parâmetros avaliados (teor de nitratos e macro e micronutrientes nos tecidos), apesar dos valores não diferirem estatisticamente, os resultados obtidos nas plantas com microrganismo mantiveram uma tendência favorável quando comparados ao tratamento sem microrganismo. Ainda assim, recomenda-se a realização de novos estudos para avaliar a eficácia do produto comercial à base de Methylobacterium symbioticum para esta e outras culturas.
In agriculture, in addition to water, nitrogen availability is generally considered the most limiting factor for plant growth in their natural environment. Despite its importance and being required in significant quantities by living beings, this element is found in nature in abundance in a chemically very stable form (predominantly in the form of nitrogen gas, N2), making it necessary to transform into a form “combined” with hydrogen (H2), that facilitates its assimilation. Plants can acquire “combined” nitrogen from different synthetic (Haber Bosch process) and natural sources, such as lightning; and biological nitrogen fixation (BNF). The BNF constitutes the main way of incorporation of nitrogen into the biosphere, becoming a biological process determinant for life on earth, of equal importance to photosynthesis and respiration. To reduce the adverse effects of synthetic fertilizers, maintain and increase soil fertility, contribute to crop nutrition, and make better use of BNF, the potential of biological fertilizers has been evaluated. In this context, the potential of nitrogen-fixing organisms that inhabit the phyllosphere of horticultural crops is still poorly understood. In this work, the application of a commercial biofertilizer with microorganisms that colonize the phyllosphere in the lettuce crop (Lactuca sativa L.) was tested and the nitrogen fixation capacity of the microorganism and the increase in production of this crop evaluated. The experiment took place in the municipality of Bragança, region of Trás-os-Montes, northeast of Portugal. In the experiment, a factorial design with two-factors was used: nitrogen fertilization, with four-factor levels (D1, D2, D3 and, D4, corresponding to 0, 0.33, 0.66, and, 1.32 g N pot-1); and commercial product with Methylobacterium symbioticum with two-factor levels (With and Without). From each treatment, four replicates were included. Two cultivation cycles were carried out. Throughout the experiment, the intensity of the green color of the leaves was determined. The plants were collected and taken to the greenhouse until they reached constant weight, weighed, ground, and taken to the laboratory to determine the biomass produced and evaluate the elemental composition of the tissues. In general, the results allowed to attribute to the treatment with microorganism an increase in the production of dry matter (11.4 against 9.8 g vase-1 in the first cycle and 14.6 against 10.7 g vase-1 in the second cycle), leaf area (99.4 dm² versus 69.3 dm² in the first cycle) and chlorophyll index (measured by SPAD readings, in the values of 27.8 versus 25.0 in the first cycle) compared to uninoculated lettuce plants. For the other parameters evaluated (nitrate content, and macro and micronutrients in the tissues), although the values did not differ statistically, the results obtained in plants with microorganism maintained a favorable trend when compared to the treatment without microorganism. Even so, further studies are recommended to evaluate the effectiveness of the commercial product based on Methylobacterium symbioticum for this and other cultures.
In agriculture, in addition to water, nitrogen availability is generally considered the most limiting factor for plant growth in their natural environment. Despite its importance and being required in significant quantities by living beings, this element is found in nature in abundance in a chemically very stable form (predominantly in the form of nitrogen gas, N2), making it necessary to transform into a form “combined” with hydrogen (H2), that facilitates its assimilation. Plants can acquire “combined” nitrogen from different synthetic (Haber Bosch process) and natural sources, such as lightning; and biological nitrogen fixation (BNF). The BNF constitutes the main way of incorporation of nitrogen into the biosphere, becoming a biological process determinant for life on earth, of equal importance to photosynthesis and respiration. To reduce the adverse effects of synthetic fertilizers, maintain and increase soil fertility, contribute to crop nutrition, and make better use of BNF, the potential of biological fertilizers has been evaluated. In this context, the potential of nitrogen-fixing organisms that inhabit the phyllosphere of horticultural crops is still poorly understood. In this work, the application of a commercial biofertilizer with microorganisms that colonize the phyllosphere in the lettuce crop (Lactuca sativa L.) was tested and the nitrogen fixation capacity of the microorganism and the increase in production of this crop evaluated. The experiment took place in the municipality of Bragança, region of Trás-os-Montes, northeast of Portugal. In the experiment, a factorial design with two-factors was used: nitrogen fertilization, with four-factor levels (D1, D2, D3 and, D4, corresponding to 0, 0.33, 0.66, and, 1.32 g N pot-1); and commercial product with Methylobacterium symbioticum with two-factor levels (With and Without). From each treatment, four replicates were included. Two cultivation cycles were carried out. Throughout the experiment, the intensity of the green color of the leaves was determined. The plants were collected and taken to the greenhouse until they reached constant weight, weighed, ground, and taken to the laboratory to determine the biomass produced and evaluate the elemental composition of the tissues. In general, the results allowed to attribute to the treatment with microorganism an increase in the production of dry matter (11.4 against 9.8 g vase-1 in the first cycle and 14.6 against 10.7 g vase-1 in the second cycle), leaf area (99.4 dm² versus 69.3 dm² in the first cycle) and chlorophyll index (measured by SPAD readings, in the values of 27.8 versus 25.0 in the first cycle) compared to uninoculated lettuce plants. For the other parameters evaluated (nitrate content, and macro and micronutrients in the tissues), although the values did not differ statistically, the results obtained in plants with microorganism maintained a favorable trend when compared to the treatment without microorganism. Even so, further studies are recommended to evaluate the effectiveness of the commercial product based on Methylobacterium symbioticum for this and other cultures.
Description
Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do Paraná
Keywords
Lactuca sativa L. Methylobacterium symbioticum Agricultura sustentável Biofertilizantes Bioestimulantes Fixação biológica de nitrogênio.