Moisture stress, bradyrhizobia, vesicular-arbuscular mycorrhiza and P-fertilizers effects on soybean growth, nutrient content and phosphatase activity under calcareous soil.

摘要

In a greenhouse experiment, soyabean (cv. Rillito) seed inoculated with Bradyrhizobium were sown in pots in steam-sterilized soil that had been amended with rock phosphate (1 g/kg soil) or superphosphate (0.5 g/kg soil) and inoculated with vesiculararbuscular mycorrhizas (Glomus sp. and Gigaspora sp.). Controls were not inoculated. The pots were watered either at 75% or 25% of soil water holding capacity (not stressed and stressed, respectively). Inoculation with the mycorrhizas or bradyrhizobia increased soyabean shoot and root dry weights compared with uninoculated controls. The greatest increases in root and shoot dry weights were obtained with dual inoculation of mycorrhizas and bradyrhizobia along with application of superphosphate; increases over controls of up to 167% and 400% in non-water stressed and stressed plants, respectively, were obtained. Water stress also reduced nodulation (number and weight per plant). Mycorrhizal colonization was increased by mycorrhizal inoculation and the dual inoculation, and was higher under water stressed than non-stressed conditions. Phosphatase activity in plants decreased under water stress conditions, but was increased by mycorrhizal and dual inoculation. N, P and K concentrations and contents in shoots were increased by P fertilizer application or endophyte inoculation, both in water stressed and non-stressed conditions. The highest shoot N, P and K concentrations and contents were found in plants given superphosphate and the dual inoculation treatment. The highest concentrations of Fe, Mn, Zn and Cu were in plants inoculated with both mycorrhizas and bradyrhizobia. It is concluded that mycorrhizal inoculation increases soyabean resistance to drought, especially when combined with inoculation with bradyrhizobia.