Nitrogen use by Pinus densiflora trees growing on a Mt. Fuji lava flow

Abstract

To quantify the nitrogen (N) use by Pinus densiflora trees growing on an infertile lava surface, N pools, N requirement and N uptake through fine roots and N deposition from the atmosphere were estimated. The N requirement and the N uptake of fine roots were 55.5 kg N ha⁻¹ year⁻¹ and 39.7 kg N ha⁻¹, respectively. Thus, the ratio of N uptake to N requirement of the fine roots was 71.5%. Including fine-root contribution, the total N requirement of the P. densiflora trees was 98.6 kg N ha⁻¹ year⁻¹, and the total N uptake was 64.2 kg N ha⁻¹ year⁻¹. Thus, the N uptake of the P. densiflora trees was 64.1% of the N requirement, indicating that P. densiflora trees growing on an infertile lava surface obtain some of their N from below-ground organic material layers every year and the contribution of N storage in trees for their growth is not any higher than indicated in previous reports that excluded fine-roots contribution. The wet N deposition of our research forest was only 5.8% of the N requirement of the P. densiflora trees and only 8.9% of the N uptake. Movement of the below-ground organic material layer N concentrations in the F- and L-layers coincides with needle development and fine-root growth, suggesting the possibility that P. densiflora trees extract N from the organic N of those layers for growth.