Ecofisiologia do coqueiro gigante sob diferentes condições de umidade e salinidade do solo no litoral Oeste do Estado do Ceara

Abstract

The plants grow and reproduce in a complex environment, composed of a multiplicity of factors, consequence of several physiological processes, controlled by the environmental conditions and genetic characteristics of each species. In this context, the objective was to characterize the ecophysiological behavior of the giant coconut tree in different developmental environments and epochs of evaluation, in the West Coast of the State of Ceará, Brazil. It was adopted the statistical model of measures repeated in time, in a split-split scheme, the installments being composed of the evaluation periods (dry season: October 2016 and September 2016; rainy season: April 2016 and March / April 2017); and subplots for four environments (Irrigado, Sequeiro, Foreiro and Preamar) with ten replications referring to the ten useful plants of each environment. At each evaluation date, leaf gaseous gas exchange evaluations were performed and samples of the same leaves were collected for nutritional evaluation, content of organic solutes and Na and Cl accumulation in the leaf surface. Soil samples were also collected to determine the soil moisture and electrical conductivity profile. The presence of abiotic stress factors for the coconut palm culture characterizes two of the four environments evaluated, being the salinity and the water excess characteristic of the environment Preamar and the water deficit characterizing the environments of Sequeiro. The Foreiro environment, despite the proximity of the ocean, presents no limitation from the point of view of soil salinity, and higher moisture in the lower layers of the soil profile significantly reduce the influence of the dry season on the rates of liquid photosynthesis. The Preamar environment, although presenting an intrinsic relationship with the sea, did not present high levels of salts in the soil. The sea air causes accumulation of Na and Cl on the coconut leaf surfaces in all environments, highlighting those closest to the sea. The giant coconut tree in the rainy season adjusts the metabolism to survive the dry conditions which favors the development of the species. Higher carbohydrate levels were observed in environments under abiotic conditions. No relationship was observed between proline accumulation in leaves and factors of abiotic stress present in the studied coconut cultivation environments.