Background and aims

Plants take up and use silicon (Si) as a beneficial nutrient for growth or survival, which can affect terrestrial Si biogeochemistry and its links with the carbon cycle. While nitrogen (N) deposition can impact many processes in terrestrial ecosystems (soil biogeochemical processes, plant productivity, etc.), how it affects plant Si cycling in subtropical forests remains unknown.

Methods

We performed a field experiment in a subtropical forest to explore the effects of nine − years of canopy and understory N addition at three rates (0, 25 and 50 kg N ha⁻¹ yr⁻¹) on Si biogeochemical cycling. We quantified different soil Si pools, and phytolith concentrations in the vegetation.

Results

In topsoil, soil pH decreased in all N − addition treatments. In CN50 and UN50, concentrations of CaCl₂ − Si (mobile Si) and NaOH − Si (amorphous Si) increased and decreased, respectively. H₂O₂ − Si (fragile phytoliths associated with SOM) concentrations increased following N addition. The rates of carboxylate exudation were significantly enhanced, especially under high − rate N addition. Leaf phytolith concentrations significantly increased in all N − addition treatments, except CN25. Concentrations of CaCl₂ − Si were negatively correlated with those of NaOH − Si and positively correlated with those of H₂O₂ − Si in topsoil. Rhizosheath organic acids, soil pH and CaCl₂ − Si were dominant factors affecting leaf phytoliths.

Conclusions

Nitrogen addition decreased soil pH, increased the soil H₂O₂ − Si pool, and stimulated carboxylate release of fine roots which, together, enhanced Si availability and plant phytolith accumulation. Our results show that atmospheric N deposition affects Si dynamics in plant-soil systems in subtropical forests.

中文翻译：

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大气氮沉降：对亚热带森林硅动态有何影响？

 背景和目标

植物吸收并使用硅 (Si) 作为生长或生存的有益营养物质，这会影响陆地硅生物地球化学及其与碳循环的联系。虽然氮（N）沉降会影响陆地生态系统的许多过程（土壤生物地球化学过程、植物生产力等），但它如何影响亚热带森林中的植物硅循环仍然未知。

 方法

我们在亚热带森林中进行了一项田间实验，以探索九年的冠层和林下氮添加量（0、25和50 kg N ha ^-1 yr ^-1 ）对硅生物地球化学循环的影响。我们量化了不同的土壤硅库和植被中的植硅体浓度。

 结果

在表土中，所有施氮处理中土壤 pH 值均下降。在CN50和UN50中，CaCl ₂ - Si（流动Si）和NaOH - Si（非晶Si）的浓度分别增加和减少。添加 N 后，H ₂ O ₂ − Si（与 SOM 相关的脆弱植硅体）浓度增加。羧酸盐渗出率显着提高，尤其是在高氮添加率下。除 CN25 外，所有 N - 添加处理中叶片植硅体浓度均显着增加。表土中CaCl ₂ - Si 浓度与NaOH - Si 浓度呈负相关，与表土中H ₂ O ₂ - Si 浓度呈正相关。根鞘有机酸、土壤pH和CaCl ₂ - Si是影响叶片植硅体的主导因素。

 结论

添加氮降低了土壤pH值，增加了土壤H ₂ O ₂ - Si库，并刺激了细根的羧酸盐释放，这些共同增强了Si的有效性和植物植硅体的积累。我们的结果表明，大气氮沉降影响亚热带森林植物-土壤系统中的硅动态。