Nitrogen and Phosphorus Distribution and Relationship in Soils and Plants under Different Aged Chinese Fir Plantation

Zhen’An Yang,Zhibin Luo

doi:10.3390/f12091271

Abstract

As essential nutrients for plant growth and development, the balance of nitrogen (N) and phosphorus (P) between soils and plants is a key component to ecosystem stability. In this study, we examined the distribution of nutrients in the soils and different organs of Chinese fir (Cunninghamia lanceolata) in Hunan Province, southern China. Additionally, we investigated the nutrient concentrations in soil layers (0–80 cm depth) and in plant organs, and the total biomass of 10-, 20-, and 30-year-old plantations. The results suggested that the nutrients in the soil were aggregated in the surface layer. The highest and lowest values of N concentrations in 0–80 cm soil layers and P concentrations in 0–40 cm soil layers were both in 30-year-old plantations and 20-year-old plantations, respectively. Nitrogen in the organs of Chinese fir in all plantations and P concentrations in the organs of 20- and 30-year-old trees decreased in the following order: leaves, fine roots, coarse roots, and stems. Total biomass (N and P pools of four organs) increased consistently with stand age increase, and N and P pools were the highest in leaves and stems, respectively. There were significant, positive correlations between N and P in the soil (0–80 cm), and organs, respectively, and also between N concentrations of fine roots and that of 0–10 and 10–20 cm soil, respectively. In Chinese fir plantations, concentrations of nutrients in specific tree organs and the soil were correlated positively, which can only partially explain the balance of nutrients within the plant–soil ecosystem. This study suggested that incorrect harvesting patterns may effectively deprive the forest ecosystem of valuable nutrients that would ordinarily have been returned to the soil.

Highlights

Nutrients are essential for plant growth [1] such that a shortage can significantly limit plant growth and ecosystem productivity
Total N concentrations decreased with increasing soil depth in all Chinese fir plantations, and were at their lowest and the highest in the 20and 30-year-old plots, respectively (Figure 2A)
Concentrations of N in 30-year-old plots were significantly higher in the 0–10, 10–20, and 20–40 cm soil layers than the other two soil layers (40–60 and 60–80 cm)

Summary

Introduction

Nutrients are essential for plant growth [1] such that a shortage can significantly limit plant growth and ecosystem productivity. At the individual plant level, nutrients are absorbed in inorganic form by roots through a series of physiological and biochemical reactions (e.g., assimilation, transportation, aging, recycling, remobilization) [2,3], and are used for building the plant body and driving metabolic processes [4]. At the forest ecosystem level, the plants absorb nutrients from the soil and transform them into important compounds (e.g., protein, nucleic acids, hormones) used for growth and development. Some compounds are retained in vegetation as biomass, while others are returned to the soil as leaf (including branches) and root litter where they further decompose and are converted to nutrients in the soil, which are absorbed by other vegetation [3,5]. The recycling of nutrients in individual plants and in forest ecosystems ensures the balance of nutrients in the ecosystem. A former study suggested overstory trees and understory plants have different nutrient acquisition patterns and nutrient-use efficiencies, but there were significant correlations between the concentrations of carbon (C), nitrogen (N), and phosphorus (P) in soils and plants in the different aged Robinia pseudoacacia forests on the Loess Plateau, China [6]

Methods

Results

Discussion

Conclusion