Crescimento e fisiologia de mudas de mamoeiro (Carica papaya L.) sob estresse salino e doses de N

Abstract

In semi-arid areas, the water used in irrigation almost always has high concentrations of salts that can compromise the soil and, mainly, the growth of crops, causing physiological and nutritional disorders, so the application of nitrogen to improve the nutritional conditions of plants can be a viable alternative to minimize the negative effects of salt stress. In view of the above, this experiment was developed with the objective of evaluating the effects of using doses of nitrogen combined with the electrical conductivity of irrigation water on the production of papaya seedlings. The experimental design was in randomized blocks, combined according to the Central Composite Box experimental matrix, referring to five values of electrical conductivity (0.5; 1.0; 2.25; 3.5 and 4.0 dS m-1) and five doses of nitrogen (0.0; 1.3; 1.8; 3.1 and 3.6 g dm-3), with four repetitions. For the growth variables, plant height, stem diameter, leaf area, relative growth rate of the respective variables, dry mass of the stem, leaves, roots were evaluated, obtaining the total dry mass and the Dickson's quality index. For the physiology, the gas exchanges, the relative nitrogen content were evaluated. Data were subjected to analysis of variance and regression. The dose of 1.8 g dm-3 of N provided better results for the variables height, stem diameter and Dickson's quality index. The largest leaf area was obtained with a dose of 2.1 g dm-3 of N. The increase in N doses contributed to a linear increase in the relative height growth rate. Doses above 2 g dm-3 of N limited leaf, root and total dry matter mass. There was a significant interaction effect (CEai x N) for stem dry matter mass and the dose of 1.8 g dm-3 of N attenuated the effect of salinity up to 2.1 dS m-1. Regarding gas exchange, increasing doses of 3.6 g dm-3 N at levels of 4 dS m-1 of ECai resulted in higher values for the variables intracellular carbon concentration (Ci), internal/external carbon ratio (Ci/ Cref) transpiration (E) and stomatal conductance (gs). Greater efficiency was observed in the fluorescence and photosynthesis rates under N fertilization. Higher foliar levels of N were found under doses of 3.2 g dm-3 of N and 4 dS m-1 of electrical conductivity of irrigation water.