Influência da disponibilidade hídrica, fotoperíodo e temperatura na atividade cambial em Cordiera concolor (Rubiaceae)
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Data
2016-12-02
Autores
Lara, Natália Oliveira Totti de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Em ambientes tropicais, a disponibilidade hídrica é um dos principais fatores que interferem na atividade cambial das espécies vegetais. Estudos recentes, em campo, indicam também o comprimento do dia e a temperatura como sinalizadores importantes da atividade cambial nestas espécies. Este estudo experimental visa contribuir para o entendimento da influência dos fatores abióticos, água, comprimento do dia e temperatura, na atividade cambial em plantas com um ano de idade de Cordiera concolor (Cham.) Kuntze (Rubiaceae). A espécie, sempre-verde e arbustiva, é nativa, comum no cerrado paulista, e possui camadas de crescimento demarcadas por faixas marginais de parênquima axial. Realizamos dois experimentos (n=45 plantas cada um), sob regime hídrico controlado e sob comprimento do dia e temperatura naturais, um no início da primavera, quando o fotoperíodo aumenta de 11 para 12 horas e a temperatura média é de 19,9ºC e outro no final do verão, quando o fotoperíodo diminui de 12 horas para 11 horas e a temperatura média é de 23,9ºC, ambos durante cinco semanas. Cada experimento continha os mesmos três tratamentos hídricos, com 15 plantas cada, obtidos a partir de uma curva de retenção hídrica de solo de cerrado sensu stricto: saturação hídrica (21% de umidade), capacidade de campo (8% de umidade) e deficiência hídrica (3% de umidade). Ao final de cada semana, sorteamos três plantas de cada tratamento e coletamos a região mais desenvolvida do eixo caulinar. Obtivemos secções transversais e longitudinais tangenciais e radiais seriadas para análise da atividade cambial. Atribuímos presença/ausência da atividade cambial através da visualização de figuras mitóticas e paredes recém-formadas observadas na zona cambial. Para a avaliação das paredes recém-formadas, amostramos quinze fileiras sequenciais radiais na zona cambial e contamos todas as paredes recém-formadas localizadas nesta região. Analisamos os dados a partir de modelos lineares generalizados (GLM) o que nos permitiu observar que no início da primavera, independentemente da quantidade de água, a atividade cambial é intensificada com o aumento do fotoperíodo. No final do verão, a quantidade de água influencia na atividade cambial, onde observamos que (i) as plantas submetidas à saturação hídrica apresentaram atividade cambial que se prolongou ao longo das semanas; (ii) as plantas em capacidade de campo entraram em dormência ao longo das semanas e (iii) as plantas em deficiência hídrica apresentaram dormência cambial desde a primeira semana. A temperatura não foi um sinalizador importante para a atividade cambial em nenhum dos dois períodos. Adicionalmente observamos a formação e a diferenciação das células parenquimáticas que compõem a faixa marginal no início do período de atividade cambial, sendo esta, portanto, inicial. Concluímos que a disponibilidade hídrica não influencia a atividade cambial no período em que o comprimento do dia aumenta ao longo das semanas. Já, no período em que o comprimento do dia diminui, a água tem maior influência nas plantas, modificando a relação da dormência cambial com o comprimento do dia.
In tropics, the water availability is one of the main factors interfering in the cambial activity of plants. Recent studies, in the field, also indicate that day length and temperature are important signals of the cambial activity in tropical plants. This experimental study aims to contribute for understanding the role of these abiotic factors (water, day length and temperature) on cambial activity in 1-year-old plants of Cordiera concolor (Cham.) Kuntze (Rubiaceae). This species, evergreen and shrubby, is native and common in Cerrado of São Paulo, and have growth layers demarcated by axial parenchyma marginal bands. We conducted two experiments (n = 45 plants, each), under controlled water regimes and under natural day length and temperature, one in early spring, when the day length increases from 11 hours to 12 hours and mean temperature is 19,9ºC and another in late summer, when day length decreases from 12 hours to 11 hours and mean temperature is 23,9ºC, both for five weeks. Each experiment contained the same three water treatments, obtained from a water retention curve of cerrado soil, with 15 plants each: waterlogging (21% moisture), field capacity (8% moisture) and water deficit (3% moisture). At the end of each week, we randomly selected three plants of each treatment and collected the most developed region of the main stem. We obtained transverse and tangential and radial sections for cambial activity analyses. We identified cambial activity by mitotic figures and the presence of recently formed periclinal cell walls. We used fifteen sequential radial rows in the cambial zone to count the newly formed periclinal cell walls. We analyzed the data using generalized linear models (GLM) which allowed us to observe that in early spring, regardless of the amount of water, the cambial activity is increased by day length. In late summer, the amount of water influences the cambial activity, which we observed that (i) plants subjected to waterlogging had their cambial activity prolonged throughout the weeks; (ii) the plants in field capacity had their cambium dormant over the weeks and (iii) the plants in water deficit presented cambial dormancy since the first week. The temperature was not an important signal for cambial activity in both periods. Additionally, we observed, in the beginning of cambial activity, the production and differentiation of the parenchyma cells that compound the marginal bands, which means that the bands are initial. We conclude that water availability does not influence the cambial activity in the period when the day length increases over the weeks. In the period when the day length decreases, the water has greater influence on plants, modifying the relation of the cambial dormancy with the day length.
In tropics, the water availability is one of the main factors interfering in the cambial activity of plants. Recent studies, in the field, also indicate that day length and temperature are important signals of the cambial activity in tropical plants. This experimental study aims to contribute for understanding the role of these abiotic factors (water, day length and temperature) on cambial activity in 1-year-old plants of Cordiera concolor (Cham.) Kuntze (Rubiaceae). This species, evergreen and shrubby, is native and common in Cerrado of São Paulo, and have growth layers demarcated by axial parenchyma marginal bands. We conducted two experiments (n = 45 plants, each), under controlled water regimes and under natural day length and temperature, one in early spring, when the day length increases from 11 hours to 12 hours and mean temperature is 19,9ºC and another in late summer, when day length decreases from 12 hours to 11 hours and mean temperature is 23,9ºC, both for five weeks. Each experiment contained the same three water treatments, obtained from a water retention curve of cerrado soil, with 15 plants each: waterlogging (21% moisture), field capacity (8% moisture) and water deficit (3% moisture). At the end of each week, we randomly selected three plants of each treatment and collected the most developed region of the main stem. We obtained transverse and tangential and radial sections for cambial activity analyses. We identified cambial activity by mitotic figures and the presence of recently formed periclinal cell walls. We used fifteen sequential radial rows in the cambial zone to count the newly formed periclinal cell walls. We analyzed the data using generalized linear models (GLM) which allowed us to observe that in early spring, regardless of the amount of water, the cambial activity is increased by day length. In late summer, the amount of water influences the cambial activity, which we observed that (i) plants subjected to waterlogging had their cambial activity prolonged throughout the weeks; (ii) the plants in field capacity had their cambium dormant over the weeks and (iii) the plants in water deficit presented cambial dormancy since the first week. The temperature was not an important signal for cambial activity in both periods. Additionally, we observed, in the beginning of cambial activity, the production and differentiation of the parenchyma cells that compound the marginal bands, which means that the bands are initial. We conclude that water availability does not influence the cambial activity in the period when the day length increases over the weeks. In the period when the day length decreases, the water has greater influence on plants, modifying the relation of the cambial dormancy with the day length.
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Palavras-chave
Cerrado, Câmbio vascular, Comprimento do dia, Regime hídrico controlado, Temperatura