Characteristics of carbon, nitrogen and phosphorus stoichiometry in litter-root-soil of Pinus sylvestris var. mongolica plantations with different stand ages.

Abstract

To investigate the carbon (C), nitrogen (N), and phosphorus (P) stoichiometry of the litter-root-soil system and the driving factors for their variations in the Pinus sylvestris var. mongolica plantations, we analyzed the contents and stoichiometric ratios of organic carbon, total nitrogen and total phosphorus in litter, roots and soil across 27-year-old (middle-aged), 38-year-old (nearly-mature) and 47-year-old (mature) plantations in Hulunbuir sandy land, with natural forests as a control. The results showed that with increases of stand age, N and P contents showed a trend of decreasing and then increasing in the decomposing layer of the litter, and the C:N and C:P in semi-decomposing layer were significantly higher in near-mature than in middle-aged and mature plantations. The N content in the semi-decomposing layer of litter in natural forests was 17.3% lower than that in plantations. The N:P in the decomposing layer of natural forests was 16.2% lower than that in plantations. With the increases of stand age, root C content showed an increasing trend, and the N content exhibited a decreasing and then increasing trend. Root C:N of middle-aged was significantly lower than that in near-mature plantations. The root C:P of middle-aged and near-mature was significantly lower than that in mature plantations. Root P content was 41.0% higher than that in natural forests. The soil C and P content as well as the C:N and C:P were significantly lower in plantations than in natural forests. The rhizosphere and bulk soils of natural forests with N:P of 3.7 and 3.1 were significantly lower than that of plantations. Cellulase was the main driver of stoichiometric characteristics of litter, while acid phosphatase was the main driver for both root and soil.