Determination of carbon and dissolved organic nitrogen accumulation in oriental spruce (picea orientalis (L.) peterm.) stands at different stand development ages and sites

Carbon and nitrogen are fundamental elements sustaining matter cycling in forest ecosystems, and plants can directly utilize organic nitrogen compounds such as free amino acids in addition to inorganic nitrogen. This study investigated the variation of carbon, nitrogen, and free amino acid contents stored in roots, forest floor, and soil of Oriental spruce stands in relation to elevation, site quality, and stand development stages, using correlation and multivariate analysis of variance. The mean amounts of organic carbon and nitrogen stored in the soil were 78.43 and 4.80 t/ha, respectively. Forest floor biomass, carbon, and nitrogen stocks were 11.04, 3.45, and 0.12 t/ha, while root biomass carbon and nitrogen stocks were 14.66, 4.24, and 0.09 t/ha, respectively. Soil ammonium, nitrate, and total mineral nitrogen contents were 7.23, 4.45, and 11.68 kg/ha, respectively. The soil free amino acid contents (kg/ha) were 0.040 (alanine), 0.037 (arginine), 0.039 (asparagine), 0.041 (aspartic acid), 0.041 (glycine), 0.037 (glutamine), 0.042 (glutamic acid), 0.040 (histidine), and 0.041 (leucine). Overall, carbon, nitrogen, and amino acid contents in Oriental spruce stands varied with elevation, stand development stage, site quality, and soil properties.