Heavy metals pollution in low quality water irrigated soil and their impact on bacterial abundance and diversity in the rhizosphere of Swiss chard (Beta Vulgaris L.) seedlings

Abstract

Substandard irrigation water impacts the chemical characteristics of soil, which may subsequently modify the shape of soil bacterial communities. Five categories of water, including the river water (RW), acid mine drainage (AMD), untreated wastewater (UTWW), treated wastewater (TWW), and tap water (TW), were utilized as irrigation water samples. Soil and water samples were examined for heavy metals, such as Chromium (Cr), Cobalt (Co), Zinc (Zn), Arsenic (As), Cadmium (Cd), and Lead (Pb), using ICP-MS. The V1-9 region of bacterial 16S rRNA was PCR-amplified to evaluate the effects of heavy metals in low-quality irrigated soil on bacterial diversity and abundance in the rhizosphere of Swiss chard seedlings. Approximately 88.9% of heavy metals in water, with concentrations ranging from 0.03 to 432.8 mg/L, were detected at low levels in TW. Conversely, about 83.3% of heavy metals, with the concentrations between 0.38 and 553.78 mg/kg, were detected at low levels in TW irrigated soil (TS1). The electrical conductivity (EC), pH, and organic matter (OM) fluctuated based on the irrigation water and soil samples. Bacterial diversity and abundance in soils differed according on the quality of irrigation water samples. Blastoccus, Microlunatus, Nocardioides, Solirubrobacter, and Streptomyces exhibited higher relative abundance in soil subjected to low-quality water compared to soil irrigated with TW (TS1). Redundancy analysis (RDA) demonstrated that bacterial community structure in the rhizosphere of Swiss chard seedlings were influenced by heavy metals, EC, pH and OM. This indicates that the introduction of heavy metals into the soil can select sensitive bacteria, whereas soil OM can supply nutrients that enhances resistant/tolerant bacterial multiplication, thereby influencing seedling growth.