Estresse osmótico na germinação, crescimento e nutrição mineral da gliricídia (Gliricidia sepium Jacq. Walp).

Abstract

Water stress and soil salinity in the Brazilian semi-arid northeastern region are limiting factors for plant growth. Two experiments were carried out to evaluate the effects of the osmotic stress in germination, growth and mineral nutrition of Gliricidia sepium plants. The experiments were carried out in the Laboratory of Botany and in a nylon screenhouse in the Academic Unit of Forest Engineering, of the Federal University of Campina Grande, in PatosPB. In the first experiment, the tolerance of Gliricidia sepium seeds to water and salt stresses during germination was evaluated. Seed germination were observed in four 100-seed replications in polyethylene glycol (PEG-6000) or sodium chloride (NaCl) solutions with four osmotic potentials levels (0; -0.5; -1.0 and -2.0 MPa), arranged according to a completely random design, simulating water and salt stresses, respectively. Each 100-seed replication consisted of a gerbox placed in a BOD germinator, adjusted to 30ºC. The number of germinated seeds was counted every day, and germination percentage and germination velocity index were estimated from these data. Percentage germination of the control seeds averaged 94%, and reduced to 77.6% and 44.3% in -1.0 MPa NaCl and PEG solutions, respectively. No germination was observed at -2.0 MPa. Germination velocity index showed the same trend. Gliricidia sepium seeds showed less tolerance to water stress than to salt stress. To evaluate the growth and mineral nutrition of seedlings of Gliricidia sepium under salt stress, an study was carried out in a nylon screenhouse. Seeds were sown in 'Leonard' pots, containing Hoagland & Arnon nutritive solution with four NaCl levels (0, 100, 200 and 400 mmol L-1) and four replications (1 plant/pot), arranged according to a completely random design. At day 60 after seedling emergency, data on plant height, root, stem and leaf dry matter, and nutrient (N, P, K, Ca, Mg, S and Na) accumulation in plant tissue were collected. All variables were negatively affected by NaCl levels present in the nutritive solution, except Na, especially in the root tissue. Gliricidia sepium showed to be sensitive to salinity.