Trocas gasosas, crescimento e resposta bioquímica de cultivares de soja submetidas ao déficit hídrico no solo

Abstract

This work aimed to evaluate the gas exchange, growth and biochemical activity of soybean cultivars submitted to water deficit in the soil, represented by fraction of transpirable soil water (FTSW). Three experiments were carried out (E1) with sowing on 11/19/2018, (E2) sown on 12/28/2018 and (E3) sown on 10/09/2019. The experiments were carried out in 8-liter pots filled with soil material and arranged inside a “sheltered screened” structure. The soybean cultivars used were BMX GARRA IPRO, DM 66I68 RSF IPRO and NA 5909 RG. In each experiment, a completely randomized design was used, in a 3x2 two-factor arrangement, with factor A being the three soybean cultivars and factor B being water regimes, irrigated - IR, and not irrigated - NI. The available water, represented by FTSW and transpiration, were measured daily during the period of imposition of the water deficit in each experiment, by weighing the vessels. Each experiment ended when all plants with water deficit showed relative transpiration (RT) ≤ to 10% of the transpiration of the pot plants without water deficit. In E1 and E2 the leaves dried in the oven were ground and reserved for analysis to determine nitrogen content (total N), in these experiments biochemical analyzes and activities of antioxidant enzymes in the leaves of the plants were also performed. The data of the variables obtained in the plants were analyzed using ANOVA and using the software SISVAR version 5.6. The means were compared by the Skott knott test at the level of 5% error significance (p < 0.05). The estimated FTSW thershold values, in which transpiration begins to be affected (FTSWc), were 0.33, 0.29 and 0.31 in E1, 0.35, 0.41 and 0.43 in E2 and 0.31, 0.49 and 0.45 in E3 respectively, for the cultivar BMX GARRA, DM 66I68 and NA 5909. In E1 the non-irrigated plants reduced the total nitrogen accumulation in the leaves by 20.2%, whereas in E2 the cultivar NA 5909 exhibited a total N content in the leaf tissue 22.2% higher in relation to cultivar BMX GARRA and 13.9% higher than the DM 66I68. It is observed that the activity of Superoxide dismutase (SOD) in plants under water deficit conditions increased 19.8% in E1 and 30.2% in E2 in cultivar NA 5909. The Guaiacol peroxidase (POD) activity showed a significant increase 113% in E1 in cultivar NA 5909 of NI plants and in E2 the activity of this enzyme increased by 83% in DM 66I68 in NI plants. The cultivars DM 66I68 and NA 5909 present a more efficient stomatal control, conserving water in the soil for a longer time, being more tolerant to water deficit.