Nitrogen status of Pinus radiata seedlings after undercutting: changes in total, soluble, and insoluble nitrogen

Changes in total, soluble, and insoluble nitrogen and chlorophyll concen-trations in Pinus radiata D. Don seedlings were monitored for 56 days after a single undercutting (root pruning). After undercutting there was a marked reduction in total soluble and insoluble shoot nitrogen concentration. Some of this mobilised nitrogen contributed towards lateral root growth while 15 % was lost, possibly from the damaged root as exudate. Twenty-one days after under-cutting, total seedling nitrogen content began to improve, coinciding with lateral root dry matter gains. By 56 days, undercut seedling nitrogen content approached that at Day 0, while control seedlings had acquired an additional 20.6 mg nitrogen. Lateral root dry weights and nitrogen content of undercut seedlings were higher than those of control plants after 56 days. However, soluble nitrogen concentration in lateral roots of undercut seedlings was not significantly different from the controls, although total and insoluble nitrogen concentrations were significantly below control plant values. There was no significant difference in chlorophyll concentration of needles between control and undercut seedlings