Abstract
Large-scale Quercus variabilis natural secondary forests are protected under the Natural Forest Protection (NFP) program in China to improve the ecological environment. However, information about nutrient characteristics and carbon (C) storage is still lacking. Plant biomass and C, nitrogen (N) and phosphorus (P) stoichiometry of tree tissues, shrubs, herbs, litter, and soil were determined in young, middle-aged, near-mature and mature Quercus variabilis secondary forests in the Qinling Mountains, China. Tree leaf N and P concentrations indicated that the N-restricted situation worsened with forest age. The per hectare biomass of trees in decreasing order was near-mature, mature, middle-aged, then young stands. The majority of the biomass was in the stems (44.88–48.15%), followed by roots (24.54–28.68%), and branches (10.15–14.16%), and leaves made up the lowest proportion (2.86–3.55%) of trees. C storage at plant layer increased significantly with age, reaching maximum values in near-mature stand (100.4 Mg·ha−1) and then decreasing in mature stands. Soil C storage at a depth of 0 to 100 cm was 82.8, 96.8, 85.8, 104.2 Mg·ha−1, and C storage of forest ecosystem was 122.8, 163.0, 184.9, 178.3 Mg·ha−1 in young, middle-aged, near-mature, mature stands, respectively. There were significant correlations between biomass and C, N, P stoichiometry in different layers, especially in young stands.
Highlights
Carbon (C), nitrogen (N), and phosphorus (P) are key elements to living organisms, and their ratios are a useful indicator of nutrient limitation in terrestrial ecosystems and ecosystem function [1,2].Nutrient concentrations and their ratios generally change with plant growth, as plants have different photosynthetic capabilities and nutrition requirement at different growth stages [3]
C is fixed through photosynthesis which leads to the accumulation of C storage in plant biomass
Tree leaf N and P, stem N, and branch P concentration decreased, while root C concentration increased with age
Summary
Carbon (C), nitrogen (N), and phosphorus (P) are key elements to living organisms, and their ratios are a useful indicator of nutrient limitation in terrestrial ecosystems and ecosystem function [1,2] Nutrient concentrations and their ratios generally change with plant growth, as plants have different photosynthetic capabilities and nutrition requirement at different growth stages [3]. Forests 2017, 8, 281 rate related to the N and P use efficiency [6,7], and N:P ratios can be used to infer potential nutrient limitations on terrestrial primary productivity [8,9] Such changes have typically been found in some annual species or perennial species which have a growing season or year [3]. These changes in perennial species are more complex because of their longer lifespan and continual usage of nutrients
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