Abstract
One-year-old sugi (Cryptomeria japonica D. DON) seedlings were potted in April, ammonium (NH4 series) and nitrate nitrogen (NO3 series) were applied separately in July. Soil moisture was controlled under dry or wet conditions. Contents of inorganic nitrogen and free amino-acids were determined for three weeks after the application of nitrogen. Ammonium was not found in the roots with neither series. Ammonium might be assimilated immediately to amino-acids in roots. Nitrate was found in roots with the NO3 series. A little nitrate nitrogen might be translocated from roots to shoots when nitrate was accumulated in the roots, but most of nitrate was reduced in roots. Large amounts of free amino-acids were found in the roots with the NH4 series rather than in those with the NO3 series. In shoots, free amino-acids increased soon after the nitrogen applications in the wet conditions of both series. The increments of amino-acids in shoots continued until the end of the experiment with the NH4-wet series. Nitrate accumulation in roots with the NO3 series might show that nitrate reduction is the rate-limiting factor in the process of nitrate utilization. The influences of soil moisture on nitrate reduction rarely were observed under the condition of -0.035 MPa. However, this soil moisture deficit was considered as influencing nitrate absorption, and ammonium absorption or amino-acids translocations from roots to shoots also might be influenced.
