Silício na atenuação dos efeitos da salinidade em alface hidropônica

Abstract

In the semiarid most groundwater is saline and, when used in crop irrigation, may limit growth. Silicon (Si) softens the effect of saline stress on plants. With the objective of evaluating the potential of Si to attenuate the effects of salinity on hydroponic lettuce, four experiments were conducted in a completely randomized design, in a factorial scheme, with four replications. In the first (i) five lettuce cultivars (Repolhuda Todo Ano, Grandes Lagos Americana, Great Lakes 659, Lucy Brown and Crespa Repolhuda) were tested and five salinity levels (0, 50, 100, 150, 200 mM NaCl) were tested. In the second (ii), two lettuce cultivars (Great Lakes 659 and Lucy Brown) and six different combinations of NaCl and Si in the nutrient solution (0 mM Na2SiO3 + 0 NaCl, 6.0 mM Na2SiO3 + 0 mM NaCl, 0 mM Na2SiO3 + 150 mM NaCl, 6.0 mM Na2SiO3 + 150 mM NaCl, 0 mM Na2SiO3 + 200 mM NaCl, 6.0 mM Na2SiO3 + 200 mM NaCl). In these two, the germination and initial growth of the seedlings were evaluated. In third (iii), at lettuce was cultivated in a hydroponic system using five levels of Si (0, 2, 4, 6, 8 mM) in the nutrient solution, where phytotechnical variables, gas exchange and post-harvest. In quart (iv) three salinity levels of the hydroponic solution (1.65, 3.65, 7.65 dS m-1) and two of Si (0 and 2 mM) were used. Gas exchanges, chlorophylls, enzymatic and non-enzymatic antioxidants were evaluated. There was a reduction in germination of all cultivars at the highest salinity levels, from 100 mM NaCl. The 'Lucy Brown' was the most tolerant at the highest levels of NaCl and the 'Grandes Lagos Americana' and 'Great Lakes' the most sensitive. When Si was added to the NaCl solution, the effects of saline stress were reduced. The addition of small doses of Si influenced the variables photosynthesis, soluble solids and titratable acidity. Salinity reduced all variables related to plant growth. Titratable acidity, soluble solids, vitamin C and total chlorophyll increased with salinity. The enzymes peroxidase of ascorbate and peroxidase guaiacol had their activity increased with both saline and Si stress. Silicon attenuated the effects of salinity on germination and initial growth of lettuce seedlings, however, on plants under hydroponic cultivation, although it had positive effects on physiology, this was not effective in attenuating the effects of saline stress, since its use did not result in increases of fresh and dry mass.