Effects of different magnesium nutrition on root growth and physiological characteristics of rice

Magnesium (Mg) is one of the essential nutrients for higher plants. It plays an essential role in photosynthesis and many other metabolic processes. Rice (Oryza sativa L.) plants were grown in hydroponics culture at three Mg2+ levels under a greenhouse conditions to investigate the effects of different Mg concentrations on root growth, Mg uptake and some related physiological characteristics of rice. The results showed that root dry matter weight, root to shoot ratio, total root length, root activity, bleeding sap flow rate, the concentrations of total free amino acids and Mg in bleeding sap, Mg influx rate and Mg uptake rate of rice were significantly related to Mg supply levels. At low Mg2+ supply (0.05 mmol/L), rice plants partitioned larger proportion of dry matter to the roots causing to an increase of total root length and root to shoot dry weight ratio before Mg deficiency in rice leaves, which might be one of adaptive low-Mg-stress mechanisms of rice at early growth stage. Moderate Mg2+ supply (1.0 mmol/L) was able to promote plant growth and development, increase dry matter yield, and enhance root activity and bleeding sap rate as well as the total free amino acids contents. Root activity and amino-synthesized power might be restrained to a certain extent by low or high levels of Mg2+ (5.0 mmol/L). The results also showed that Mg uptake, Mg concentrations in the bleeding saps, average Mg influx rate and the Mg uptake rate were significantly increased with an increase of Mg2+ concentrations in the nutrient solution.