Research on the Threshold of Aluminum Toxicity and the Alleviation Effects of Exogenous Calcium, Phosphorus, and Nitrogen on the Growth of Chinese Fir Seedlings under Aluminum Stress

Abstract

Chinese fir (Cunninghamia Lanceolata Lamb, Hook) is generally considered a superior timber in southern China and other areas in the world. In the past few decades, aluminum (Al) toxicity has become one of biggest stress factors in the production and growth of Chinese fir, although this species prefers an acidic environment. To date, the selection of indicator species for Al toxicity remains critical in the field, and Al toxicity has not been successfully treated by artificially controlling Chinese fir plantations. To assess the Al toxicity risk, the height of the dominant tree, the concentration of calcium (Ca²⁺)/Al³⁺ in soil solution, and the concentration of Ca²⁺ / [Ca²⁺ + iron (Fe³⁺) + Al³⁺] in litter leached organic acids were introduced. The results indicated that eight plots had suffered Al toxicity. The threshold of Al toxicity was 37.53 mg kg⁻¹ in soil or 1.39 mmol L⁻¹ in soil solution, a pH of 4.15, a Ca²⁺ / (Ca²⁺ + Fe³⁺ + Al³⁺) molar ratio of 0.487, and a Ca²⁺/Al³⁺ molar ratio of 1.599. The positive effects of exogenous nutrition (Ca, phosphorus [P], and nitrogen [N]) on the growth of Cunninghamia lanceolata seedlings was also studied in pot experiments based on results in the field. The cation nutrition can lead to detoxification, and the exogenous nutrition thresholds were Ca²⁺/ Al³⁺ ≥ 2.8, phosphorus (P)/ Al³⁺ ≥ 4.4, ammonium (NH₄ ⁻)–nitrogen (N) / Al³⁺ ≥ 4.5. The data presented in this study are very helpful for the understanding of the degree of Al toxicity and have notable significance for the management of Chinese fir plantations.

Keywords:

• Aluminum toxicity
• calcium
• Chinese fir
• detoxification
• exogenous nutrition
• nitrogen
• phosphorus

Acknowledgments

We thank Baijing Wen for help in the field and Professor Zhang and Professor Liu for their helpful comments. We are also grateful to the Provincial Key Laboratory of Forestry Ecology at the Sichuan Agricultural University, Sichuan, China, for laboratory measurements. We also thank the anonymous reviewers for their constructive comments on the manuscript. This research was jointly funded by the National Key Technologies Research and Development Program of China (No. 2006BAC01A11) and the dual support program for Excellent Talents at the Sichuan Agriculture University (No. 00370501).