Direct uptake and rapid decrease of organic nitrogen by Wollemia nobilis

Organic nitrogen (N) can be directly taken up by many plants, particularly under low-temperature and N-limited conditions. The natural environment of Wollemia nobilis, shady conditions and shallow, acidic soils with high organic matter, led to the hypothesis that organic N might be a potential N source, although this species is living in a subtropical area. A pot experiment was carried out to investigate whether W. nobilis seedlings have the capability to take up intact organic N and whether the uptake of organic N contributes significantly to N acquisition for W. nobilis. Three 15N-labeled N forms, ammonium (NH4-N), nitrate (NO3-N), or glycine, were injected into soils separately, and the tissues of plants were then harvested 6 and 48 h after injection. Our results demonstrated that W. nobilis, a subtropical species, has the capability to take up intact glycine as indicated by the enrichment of 13C and 15N in fine roots at a nearly 1:1 ratio. The uptake rate of glycine-N was faster than that of inorganic N, but which was only restricted in the short term (6 h). The absorbed glycine-N reduced quickly (in 48 h), indicating that organic N uptake did not contribute greatly to N acquisition for W. nobilis.