Amelioration of manganese toxicity in young rice seedlings with potassium

A hydroponic experiment was conducted in a control led-temperature glasshouse for 14 days to study the effect of additional potassium (K) on the amelioration of manganese (Mn) toxicity in young rice (Oryza sativa L. cv. Kakehashi) seedlings. Reduced growth, rolling of old leaves, brown spots and interveinal chlorosis on young leaves, and root browning were the main symptoms of Mn toxicity in plants grown with high Mn (1.0 mM) and adequate K (1.0 mM). Application of additional K (10 mM) to the nutrient solution increased chlorophyll concentration and dry matter yields of plants grown in high Mn, but did not restore dry matter accumulation to the level achieved in the control plants. Plants grown in 1.0 mM Mn and 10 mM K had lower tissue Mn concentration on a dry matter basis than plants grown in 1.0 mM Mn and 1.0 mM K and did not show leaf injury symptoms, but still showed root browning;, however, the accumulation (per plant basis) of Mn was approximately the same, indicating that additional K increased the tolerance of the plant to high Mn. The concentration and accumulation of iron (Fe) in shoots of plants grown at 1.0 mM K with 1.0 mM Mn was lower than in the control plants, indicating an inhibition of Fe translocation to shoots by high Mn. Additional K increased both concentration and accumulation of Fe in shoots and roots of plants grown in high Mn. The higher phosphorus (P), K, zinc (Zn), and copper (Cu) concentrations in shoots and roots of plants grown in 1.0 mM Mn and 1.0 mM K could be a concentration effect because of severe growth reduction, while lower calcium (Ca) and magnesium (Mg) concentrations were probably due to competition with Mn at the absorption sites. Additional K further decreased Ca and Mg concentrations, indicating possible interference of K with the absorption and physiological availability of Ca and Mg. Additional K increased K concentrations and decreased P, Cu, and Zn concentrations in shoots and roots of plants grown with high Mn. These results suggest that additional K can partially alleviate the symptoms of Mn toxicity and Mn-induced Fe deficiency in rice seedlings and significantly improve plant growth.