Parâmetros fisiológicos do cultivo de milho doce sob influência da deficiência hídrica
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Data
2018-07-30
Autores
Souza, Mara Lúcia Cruz de
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Universidade Estadual Paulista (Unesp)
Resumo
A deficiência hídrica é uma modalidade de estresse físico que afeta o desenvolvimento de diversas culturas agrícolas, causando impactos sociais e econômicos em regiões com baixa disponibilidade hídrica. Diversas pesquisas vêm trazendo como principal foco o estudo da deficiência hídrica na cultura do milho em épocas consideradas críticas a escassez hídrica. O objetivo do presente estudo foi avaliar o comportamento fisiológico e bioquímico de plantas de milho doce sob deficiência durante o estádio vegetativo. A hipótese principal é que as plantas de milho produzirão respostas fisiológicas interativas, no sentido de minorar o impacto dos tratamentos aplicados. O experimento foi conduzido em ambiente protegido em vasos 30L, irrigados via gotejamento, sob delineamento em blocos casualizados em esquema fatorial (3x3) sendo três lâminas de irrigação e três épocas de avaliação em parcelas subdivididas. Os tratamentos foram delimitados com objetivo de simular três níveis de deficiência hídrica (DH): T1 (Tratamento controle) – conduzidos dentro da faixa de umidade ótima para a cultura do milho até o final do ensaio (Tensão de 10 KPa); T2 (Deficiência hídrica moderada-DHM) – Plantas mantidas em tensão mínima de 50 KPa – e T3 (Deficiência hídrica severa-DHS) – Plantas mantidas sob tensão mínima de 70 KPa. As avaliações foram divididas em três épocas durante a imposição do estresse, visando monitorar alterações fisiológicas e bioquímicas das plantas, aos 45, 52 e 59 DAE. Cada tratamento foi composto por 4 repetições e a umidade do solo foi monitorada por tensiometros, mantendo-se os vasos em capacidade de campo até o início dos tratamentos. Quando as plantas entraram majoritariamente em estádio V7, iniciou-se os tratamentos propostos com deficiência hídrica. Neste estádio, realizou-se a primeira coleta (E1) para análise de diferentes parâmetros, as quais consistiram no ponto inicial de avaliações. Sob DH moderada e severa houve alterações dos principais parâmetros fisiológicos e bioquímicos. Os parâmetros de crescimento e biomassa de folhas, caule e raízes foram influenciados pela interação dos fatores lâmina de irrigação e época de avaliação, exceto altura das plantas. O diâmetro colmo não foi influenciado pelos fatores de estudo. As plantas apresentaram decréscimo do CRA nas três épocas avaliadas de acordo com a severidade do estresse. O teor de pigmentos sofreu interferência das épocas e lâminas de irrigação, os quais foram observados decréscimo para clorofila a e b e carotenoides. As plantas apresentaram aumento gradual de perda de eletrólitos nas épocas de avaliação, demonstrando efeito negativo da DH nas membranas celulares. Os parâmetros de trocas gasosas foram afetados pelo nível de DH imposto às plantas. Houve decréscimo das taxas fotossintéticas (A), condutância estomática (gs), transpiração (E) e concentração interna de CO2 (Ci), as quais foram proporcionais entre as variáveis analisadas. As atividades das enzimas antioxidativas (CAT, POD e SOD) aumentaram em resposta à severidade do estresse. Os teores de proteínas reduziram de acordo com as épocas de avaliação e nível de estresse e a atividade da Nitrato Redutase (NR) nas folhas reduziu nas plantas sob DH moderada e severa.
Water deficiency (WD) is a form of physical stress that affects the development of several agricultural crops, causing social and economic impacts in regions with low water availability. Several researches have been focusing on the study of water deficiency in maize crop in phenological stages critical to water scarcity. The aim of the present study was to evaluate the physiological and biochemical responses of sweet corn plants growing under water deficiency during the vegetative stage. The main hypothesis is that corn plants will produce interactive physiological responses, in order to reduce the impact of applied treatments. The experiment was conducted in protected environment in 30 L pots, irrigated via drip irrigation, under a randomized block design in a factorial scheme (3 x 3), three irrigation levels and three evaluation periods in subdivided plots. The treatments were delimited with the objective of simulating three levels of water deficiency: T1- Control (10 KPa) - conducted within the optimum humidity range for the maize crop until the end of the experiment; T2- Moderate water deficiency (50 KPa) and T3- Severe water deficiency (70 KPa). The evaluations were divided in three seasons during the imposition of stress treatments, aiming to monitor the physiological and biochemical changes of the plants at 45, 52 and 59 DAE (days after seed emergence). Each treatment was composed of 4 replicates and the soil moisture was monitored by tensiometry, maintaining the vessels in field capacity until the beginning of the treatments. When the plants entered the V7 stage, the proposed treatments with water deficiency were started. At this stage, the first collection (E1) was performed to analyze different parameters, which consisted of the initial point of evaluations. Under moderate and severe WD there were alterations of the main physiological and biochemical parameters. The growth and biomass parameters of leaves, stem and roots were influenced by the interaction of the factors of irrigation depth and time of evaluation, except for plant height. The stem diameter was not influenced by the studied factors. The plants presented a decrease of relative water content (RWC) in the three evaluated seasons according to the severity of the stress. The pigments content was influenced by irrigation times and water depths, which showed a decrease for chlorophyll a and b and also carotenoids. The plants presented a gradual increase of electrolyte loss in the evaluation periods, demonstrating the negative effect of WD on the cell membranes structures. The gas exchange parameters were affected by the level of WD imposed on the plants. There was a decrease in photosynthetic rates (A), stomatal conductance (gs), transpiration (E) and internal CO2 concentration (Ci), which were proportional among the variables analyzed. The specific activities of the antioxidative enzymes (catalases, peroxidases and superoxide dismutases) increased in response to the severity of water stress. Protein contents reduced according to the evaluation and stress levels and Nitrate Reductase (NR) activity in leaves reduced in plants under moderate and severe WD.
Water deficiency (WD) is a form of physical stress that affects the development of several agricultural crops, causing social and economic impacts in regions with low water availability. Several researches have been focusing on the study of water deficiency in maize crop in phenological stages critical to water scarcity. The aim of the present study was to evaluate the physiological and biochemical responses of sweet corn plants growing under water deficiency during the vegetative stage. The main hypothesis is that corn plants will produce interactive physiological responses, in order to reduce the impact of applied treatments. The experiment was conducted in protected environment in 30 L pots, irrigated via drip irrigation, under a randomized block design in a factorial scheme (3 x 3), three irrigation levels and three evaluation periods in subdivided plots. The treatments were delimited with the objective of simulating three levels of water deficiency: T1- Control (10 KPa) - conducted within the optimum humidity range for the maize crop until the end of the experiment; T2- Moderate water deficiency (50 KPa) and T3- Severe water deficiency (70 KPa). The evaluations were divided in three seasons during the imposition of stress treatments, aiming to monitor the physiological and biochemical changes of the plants at 45, 52 and 59 DAE (days after seed emergence). Each treatment was composed of 4 replicates and the soil moisture was monitored by tensiometry, maintaining the vessels in field capacity until the beginning of the treatments. When the plants entered the V7 stage, the proposed treatments with water deficiency were started. At this stage, the first collection (E1) was performed to analyze different parameters, which consisted of the initial point of evaluations. Under moderate and severe WD there were alterations of the main physiological and biochemical parameters. The growth and biomass parameters of leaves, stem and roots were influenced by the interaction of the factors of irrigation depth and time of evaluation, except for plant height. The stem diameter was not influenced by the studied factors. The plants presented a decrease of relative water content (RWC) in the three evaluated seasons according to the severity of the stress. The pigments content was influenced by irrigation times and water depths, which showed a decrease for chlorophyll a and b and also carotenoids. The plants presented a gradual increase of electrolyte loss in the evaluation periods, demonstrating the negative effect of WD on the cell membranes structures. The gas exchange parameters were affected by the level of WD imposed on the plants. There was a decrease in photosynthetic rates (A), stomatal conductance (gs), transpiration (E) and internal CO2 concentration (Ci), which were proportional among the variables analyzed. The specific activities of the antioxidative enzymes (catalases, peroxidases and superoxide dismutases) increased in response to the severity of water stress. Protein contents reduced according to the evaluation and stress levels and Nitrate Reductase (NR) activity in leaves reduced in plants under moderate and severe WD.
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Palavras-chave
Estresse abiótico, produção de culturas, metabolismo, fotossíntese