Characteristics of Carbon and Nitrogen Dynamics in a Small Watershed of Aged Japanese Cedar and Cypress Stands in the Northern Kanto Region, Japan.

Abstract

To clarify the characteristics of carbon (C) and nitrogen (N) dynamics in a small watershed of aged (94 year-old) Japanese cedar (Cryptomeria japonica) and cypress (Chamecyparis obtusa) stands in the northern Kanto region, amounts of net N mineralization and CO₂ efflux in soil were measured. The amounts of inorganic N, the rate of net N mineralization and CO₂ efflux were greater in the lower slope of the cedar stand than in the upper slope of the cypress stand. The amounts of inorganic N had a positive correlation with the rate of CO₂ efflux. These suggested that there was inorganic N retention when the CO₂ efflux rate was high, especially in the lower slope of the cedar stand. The amounts of net N mineralization and the consumption of water-soluble organic carbon (WSOC) had a positive correlation, which suggested the effect of C characteristics on net N mineralization in the soil. In the cedar stand, the amount of inorganic N supply was greater than N uptake, and the ratios of C to N assimilation and soil respiration to inorganic N supply were smaller than in the cypress stand. Therefore, the aged artificial forest on a fertile site, such as the cedar stand on a lower slope position, has a risk of N discharge from the forest ecosystem.