Growth of spinach plants (Spinacia oleracea L.) exposed to excess zinc and manganese

Increased anthropogenic inputs of heavy metals in agricultural soils lead to worrisome effects on the water, soil, and plants. A greenhouse study was conducted in Tunja, Colombia to determine the effects of excess Zn and Mn on leaf area, root length, dry matter production and partitioning, root to shoot ratio, specific leaf weight, water uptake, and agronomic water use efficiency in spinach seedlings (Spinacia oleracea L. hyb. Marimba). Seedlings were grown floating on a complete nutrient solution in 4 L glass containers. Concentrations of 40 mg L-1 Mn, 40 mg L-1 Zn, 80 mg L-1 Mn, 80 mg L-1 Zn and combinations thereof were added to the solution, with a control treatment receiving no excess Zn or Mn. Zn at 40 mg L-1 reduced leaf area by 78.82% in relation to the controls; 40 mg L-1 Mn increased leaf area by 35.23%. Plants exposed to 80 mg L-1 Zn with 80 mg L-1 Mn increased allocation of biomass to leaves by 45.05% as compared to the control plants. Addition of 80 mg L-1 Zn and 40 mg L-1 Mn + 80 mg L-1 Zn led to an increase of 9.24 and 29.75%, respectively, in dry matter allocation to stem + petioles. Roots were affected the most by excess Mn and Zn, alone and in combination. While addition of 40 or 80 mg L-1 of Mn reduced total root length by 45.06 and 81.64%, respectively; while Zn concentrations of 40 or 80 mg L-1 reduced total root length by 88.78 and 98.07%, respectively.