Study On The Characteristics Of Nitrate Accumulation And Assimilation In Toona Sinensis

Characteristics of nitrate accumulation and assimilation of Toona sinensis were studied in this paper, for the purpose of understanding how to reduce the accumulation of nitrate in Toona sinensis. Results are as follows:1. Nitrate metabolism characteristics of Toona sinensis: Nitrate reductase activity and concentrations of amino acid in leaves of Toona sinensis were higher than those in the roots in either 0.1 or 5 mmol/L NO₃^--N supply. There was no difference in the content of NO₃^- between the leaves and roots at 0.1mmol/L NO₃^--N. The content of NO₃^- in leaves was lower than that in the roots at 5 mmol/L NO₃^--N, which indicates that higher concentration of NO₃^--N supply may enhance the nitrate reductase activity in leaves, increase NO₃^--N assimilation efficiency, thus increasing the content of free amino acids in leaves. The opposite process may be true in the root.2. The effects of NaCl, molybdenum (Mo) and manganese (Mn) on nitrate metabolism in Toona sinensis: salinity (40 mmol/L NaCl) had no significant effect on the contents of chlorophyll, but decreased the net photosynthetic rate at either 0.1 or 5 mmol/L NO₃^--N supply. Leaf nitrate reductase activity enhanced and the NO₃^- content in leaves decreased at 40 mmol/L NaCl NaCl to some extent. The decrease of NO₃^- content in leaves may be due to the antagonism between Cl- and NO₃^- during ion uptake in the roots. The increase of nitrate reductase activity under salinity may be probably due to the reason that the storage of NO₃^- in the vacuole was replaced by Cl-, i.e., NO₃^- in the vacuole can effuse into cytoplasm, thus inducing higher nitrate reductase activity. Anyway, salinity can increase the nitrate reductase activity and reduce NO₃^- content in leaves and roots of Toona sinensis to some extent.Either Mo or Mn supply increased nitrate reductase activity of Toona sinensis, decreased nitrate content to some extent. The supply of 0.002% Mo increased nitrate reductase activity, and decreased the nitrate content was low in leaves with a supply of 0.002% Mo. Supply of 0.02% and 0.05% Mn increased nitrate reductase activity of leaves, and NO₃^- content in leaves was low with a supply of 0.05% Mo. The compound supply of either 0.001% Mo + 0.01% Mn or 0.001% Mo + 0.01% Mn increased nitrate reductase activity, while NO₃^- content in leaves was low at those treatments. In conclusion, proper concentration of Mo and Mn compound may increase nitrate reductase activity, and reduce NO₃^- content in leaves of Toona sinensis.