Ecofisiologia de mudas de figueira (Ficus carica L.) em estresse salino

Abstract

The fig tree (Ficus carica L.) is a fruitful species with great worldwide expansion and that presents high productive potential in the semiarid conditions. In these conditions, the alternative sources, such as wells and dams, offer water with high salt content, whose effects are harmful to crops. The salinity is a stress factor that alters plant growth and development by limiting vegetal production. The aim of this work was to evaluate the ecophysiology of fig tree seedlings (Ficus carica L.) seedlings in saline stress. The experiment was conducted in a nursery of seedlings, located in the semi-arid region of Rio Grande do Norte, using a completely randomized experimental design with twelve replicates. The seedlings were submitted to increasing levels of electrical conductivity (ECa) (0.5, 1.5, 3.0, 4.5 and 6.0 dS m-1) in irrigation water. 77 days after the treatments initiation, it was evaluated the potential leaf water in predawn and midday, the photosynthesis rates, the stomatal conductance, transpiration, internal CO2 concentration and transpiration daily curve. 80 days after the treatments initiation, it was collected four plants per treatment, and evaluated the number of leaves, leaves areas, plant height, and stem diameter. Plants were fractioned (roots, stem, leaves), dried and weighted. It was also selected four plants per treatment, which were taken to microscopic analysis, in order to determinate stomatal density, length, and diameter, and trichomes density and height in both leaf sides. The data was submitted to an F test and regression analysis. The salinity reduced the water potential at both evaluated times (before sunrise and noon), photosynthesis, stomatal conductance, internal CO2 concentration and daytime transpiration of fig trees at 77 days. It was also observed the reduction in the number of leaves and leaf area, as well as the length and diameter of the stem at 80 days. There was also the decrease of all biomasses (root, stem, leaf and total) with the increase of salinity. On the adaxial side of the leaf, no stomata were found and the number and size of the trichomes were not affected by the salinity. In the abaxial face, a reduction in stomatal density, stomata size (smaller longitudinal and transverse diameter), and number and length of the trichome were observed, with increased salinity. Was observed osmotic adjustment in the seedlings, where they accumulated solutes (soluble sugars, soluble proteins and proline) to keep water potential levels low in order to absorb water from the soil. The increase of salinity in irrigation water negatively interferes in the gas exchange and the growth and development of Figueira cv. "Roxo de Valinhos", irrigation water can be used, with electrical conductivity of up to 1.5 dS m-1 in the production of seedlings