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.

Lijiao Wang,Ping Liu,Jincheng Han,Lei Yu,Yutao Wang,Xin Jing

doi:10.7717/peerj.11873

Abstract

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.

Highlights

The forest ecosystem is an important part of the terrestrial ecosystem and the Earth’s biosphere
The objectives of this study were to test the following three hypotheses: (1) assuming that the carbon distribution of P. tabuliformis plantations was age-dependent, the carbon content of the plant organs would change with the different needs of the plants at different growth stages; (2) assuming that the C: N: P stoichiometric characteristics of the soil are highly dependent on stand age and soil depth, the passing of time and change in plant growth requirements would mean that the carbon, nitrogen, and phosphorus elements in all soil layers would change and accumulate to different degrees; and (3) from the growth cycle of young forest (YF) to over-mature forest (OMF), soil C: N: P stoichiometry would significantly affect plant carbon distribution
The present study was consistent with the previous research have found that the total carbon (TC), total nitrogen (TN), and total phosphorus (TP) content of soil in OMF was the highest (Zhao et al, 2012).The results of the present study showed that the surface layer (0–20 cm) had the highest TC and TN content, showing the phenomenon of ‘‘surface accumulation,’’ which is consistent with the results of previous studies and might be related to the high activity of soil surface soil microorganisms (Wang & Zheng, 2018)

Summary

Introduction

The forest ecosystem is an important part of the terrestrial ecosystem and the Earth’s biosphere. Forest ecosystem carbon storage accounts for approximately 56% of the terrestrial ecosystem carbon storage, of which forest vegetation carbon storage accounts for more than 80% of the global vegetation carbon storage, and the forest soil carbon pool accounts for more than 40% of the global soil carbon pool (Brown, Schroeder & Kern, 1999; Houghton et al, 2001; Yang et al, 2019). The three nutrient elements interact with each other during cycling, and nitrogen and phosphorus affect carbon fixation in soil (Han et al, 2005)

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