Impacts of chloride de-icing salt on bulk soils, fungi, and bacterial populations surrounding the plant rhizosphere

This study was conducted to investigate the dynamic changes of bulk soil and microbial populations in the surrounding plant rhizosphere under the influence of chloride de-icing salt. Each experimental plant was given 0.25 L de-icing salt solution with an irrigation concentration of 200 g/L, once every 3 days for 27 days. Samples were taken weekly from each soil layers (0-15 cm, 15-30 cm and 30-45 cm). The results revealed that de-icing salt led to different effects in different soil layers in one month. A trend of increasing electric conductivity (EC) values, Na+ concentrations, and Cl- concentrations in the upper soil layer, compared with the other two soil layers, was apparent, which proved a stronger effect of de-icing salt on the upper soil layer. Soil cation exchange capacity (CEC) decreased with the accumulation of the de-icing salt. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that de-icing salt decreased the Shannon diversity (H) and Evenness (E) of fungal populations in three soil layers and led to a decrease of bacterial H in the upper soil layers. However, a contrary trend for H and E of bacterial populations was seen in the middle and lower soil layers. Both the unweighted pair group mean average (UPGMA) cluster and canonical correspondence analysis (CCA) analysis indicated that the bacterial populations were more stable than the fungal populations in response to salinity stress. CCA analysis showed the dynamic changes of microbial populations and the soil properties (EC, CEC, Na+ and Cl-) were strongly correlative. The microbial populations were obtaining a new dynamic equilibrium at the end of the study. The dominant microbial populations were originally Crepidotus, Metarhizium, Penicillium and Acidobacterium, but converted to Pythium, Boletaceae, Cystofilobasidiales, Phacidium, Acidobacterium, Pseudomonas and Chloroflexi with the addition of de-icing salt. The obtained results suggest that the uses of chemical agents leading to soil salinization, such as de-icing salt, can destroy the micro-ecosystem of bulk soil surrounding plant rhizosphere and influence soil health. (C) 2013 Elsevier B.V. All rights reserved.