Abstract:

Long-term and high-rate nitrogen (N) deposition has inputted a large amount of reactive N into terrestrial ecosystems, leading to increasingly serious soil acidification problems in some forest ecosystems. The increase of exchangeable aluminum (Al) ions in soil caused by soil acidification directly threatens plant growth and ecosystem security. In order to explore the response of bamboo forest soil Al fractions to long-term N deposition, a ten-year simulated N deposition experiment was conducted in a Pleioblastus amarus plantation since October 2007. Four N treatments were set up, i.e., control (N 0 g∙m^-2∙a^-1), low N (N 5 g∙m^-2∙a^-1), medium N (N 15 g∙m^-2∙a^-1) and high N (N 30 g∙m^-2∙a^-1). After 10 years of continuous N addition, 0?10 cm rhizospheric and bulk soil samples were collected in July 2017 to determine the soil pH and Al fractions. The results showed that simulated N deposition significantly reduced the pH of rhizospheric soil, and high N treatment significantly reduced the pH of bulk soil. In the control treatment plots, the pH of the rhizosphere was 0.56 units higher than that of bulk soil. Simulated N deposition significantly increased exchangeable Al content in the rhizospheric soil, but did not affect the contents of carbonate Al, Iron-manganese Oxides Al, Organically bound Al and residual Al. However, simulated N deposition had no significant effect on the contents of all Al fractions in bulk soil. Correlation analysis results showed that the pH of rhizospheric and bulk soil was significantly negatively correlated with exchangeable Al content, and the pH of rhizosphere soil was also negatively correlated with organically bound Al content. However, there were no significant correlations between pH and the contents of other Al fractions. This study indicates that soil acidification caused by long-term N deposition activates the exchangeable Al in the soil, and the root system of P. amarus may suffer from Al toxicity, which is potentially harmful to the health of the bamboo forest ecosystem.

Key words: nitrogen deposition, soil acidification, rhizosphere, aluminum fractions

摘要：

长期高速率的氮（N）沉降将大量的活性N输入到陆地生态系统,使得部分森林生态系统的土壤酸化问题日益严重。酸化导致的土壤中交换性铝（Al）的增加直接威胁着植物生长和生态系统安全。为探索长期不同N沉降情形下竹林土壤Al组分的响应,于2007年10月在苦竹（Pleioblastus amarus）林中建立模拟N沉降样地,分别设置对照（CK,N 0 g∙m^-2∙a^-1）、低N（LN,N 5 g∙m^-2∙a^-1）、中N（MN,N 15 g∙m^-2∙a^-1）和高N（HN,N 30 g∙m^-2∙a^-1）4个处理,每个处理设置3个重复。在连续10 a的N添加处理后,于2017年7月采集0—10 cm根际与非根际土壤样品并测定土壤pH和土壤Al组分。结果表明,模拟N沉降显著降低了根际土壤pH,HN处理显著降低了非根际土壤pH。在对照处理下,根际土壤pH比非根际大0.56个单位。模拟N沉降对根际交换态Al组分含量有显著的影响,对碳酸态Al、有机络合态Al、铁锰氧化态Al和残留态Al组分含量无显著影响;模拟N沉降对非根际土壤的各个Al组分含量无显著影响。相关性分析结果表明根际土壤与非根际土壤的pH均与交换态Al组分含量呈极显著的负相关关系,根际土壤pH与有机络合态Al组分含量呈显著的负相关关系,与其余Al组分含量无显著相关性。研究结果表明长期N沉降导致的土壤酸化使得土壤交换态Al显著增加,苦竹根系或将遭受到Al毒害,对竹林生态系统健康存在潜在危害。

关键词: N沉降, 土壤酸化, 根际, Al组分