Plant Debris and Its Contribution to Ecosystem Carbon Storage in Successional Larix gmelinii Forests in Northeastern China

How C: N: P stoichiometry in soils and carbon distribution in plants respond to forest age in a Pinus tabuliformis plantation in the mountainous area of eastern Liaoning Province, China

Carbon distribution in plants and ecological stoichiometry in soils are important indicators of element cycling and ecosystem stability. In this study, five forest ages, young forest (YF), middle-aged forest (MAF), near-mature forest (NMF), mature forest (MF), and over-mature forest (OMF) in a Pinus tabuliformis plantation were chosen to illustrate interactions among the C: N: P stoichiometry in soils and carbon distribution in plants, in the mountainous area of eastern Liaoning, China. Carbon content was highest in the leaves of MAF (505.90 g⋅kg-1) and NMF (509.00 g⋅kg-1) and the trunks of YF (503.72 g⋅kg-1), MF (509.73 g⋅kg-1), and OMF (504.90 g⋅kg-1), and was lowest in the branches over the entire life cycle of the aboveground components (335.00 g⋅kg-1). The carbon content of the fine roots decreased with soil layer depth. In YF, MAF, and NMF carbon content of fine roots at 0.5 m was always higher than that of fine roots at 1 m; however, it was the opposite in MF and OMF. The carbon content of the leaves changed with forest age; however, carbon content of branches, trunks and fine roots did not change significantly. Soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) content was highest in the OMF. Soil TC, TN and AP content, and TC: TN, TC: TP and TN: TP ratio decreased with increasing soil depth. Soil TC, TN, and TP content had a significant effect on the carbon content of fine roots (p < 0.05). The leaf carbon content and soil element content changed obviously with forest age, and the soil TN, TP and AP increased, which might reduce the carbon content allocation of fine roots.