Abstract

Phosphorus (P) deficiency in soil affects plant growth and primary production. Accelerated nitrogen (N) deposition can cause ecological carbon:nitrogen:phosphorus (C:N:P) stoichiometry imbalance and increase the degree of relative P deficiency in the soil. However, it remains unclear how N deposition affects P uptake and C:N:P stoichiometry in coniferous timber forests, and whether P addition diminishes the effect of N-induced P limitation on plant growth. From January 2017 to April 2018, we investigated the effects of nine different N and P addition treatments on 10-year old trees of Chinese fir, Cunninghamia lanceolata (Lamb.) Hook. Our results demonstrated that N and P additions at a high concentration could improve the photosynthetic capacity in Chinese fir by increasing the chlorophyll content and stimulating the photosynthesis activity. The C:N:P stoichiometry varied with the season under different N and P addition treatments, indicating that N addition at a moderate concentration could diminish the effect of the P limitation on the growth of Chinese fir. The soluble sugar content in the leaves displayed more stable seasonal variations, compared with those of starch. However, the non-structural carbohydrate (NSC) content in the leaves did not vary with the season under both P and N addition treatment. The data suggested that N and P combination treatment at moderate concentrations promoted carbon assimilation by accelerating the photosynthetic rate. Thus, our results provide new insights into the adaptation mechanisms of coniferous timber forest ecosystems to the effects of N deposition under P deficiency and can help to estimate the ecological effects of environmental changes linked to human management practices.

Highlights

  • Phosphorus (P) is an essential macronutrient for plant growth and development that plays an important role in photosynthesis, energy storage and transfer, and the development of new tissue [1].Plants acquire P from the soil through the roots

  • The C:N:P stoichiometry varied with the season under different N and P addition treatments, indicating that N addition at a moderate concentration could diminish the effect of the P limitation on the growth of Chinese fir

  • Our results suggested that N + P combination treatment at a high concentration can enhance the photosynthetic capacity in Chinese fir by increasing the chlorophyll content and photosynthesis activity

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Summary

Introduction

Phosphorus (P) is an essential macronutrient for plant growth and development that plays an important role in photosynthesis, energy storage and transfer, and the development of new tissue [1].Plants acquire P from the soil through the roots. P is often highly concentrated in the soil, it readily forms insoluble compounds with free iron (Fe) or aluminum (Al) oxides, which cannot be absorbed by the roots. This process reduces P availability, which impairs plant growth and primary production in most terrestrial ecosystems [2]. Especially fossil fuel combustion and fertilizer use, have resulted in increasing atmospheric N deposition. The global N input is estimated to increase from the historical level of 34 Tg N·yr−1 in 1860 to 200 Tg N·yr−1 in 2050 [3]. In southern China, the amount of N deposition has Forests 2019, 10, 1068; doi:10.3390/f10121068 www.mdpi.com/journal/forests

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