模拟水位下降与刈割对高寒湿地土壤氨氧化与反硝化微生物的影响

湿地土壤是温室气体重要的源和汇,认识湿地生态系统氮循环过程有助于预测氮循环对未来气候变化的响应与反馈机制。为探讨硝化作用和反硝化作用对土壤水位变化和刈割的响应机制,依托于2013年在青藏高原东部若尔盖泥炭地南部湿地设置的野外实验,通过在样地周围挖掘不同深度的排水沟模拟水位下降,结合刈割处理,研究水位下降和刈割对泥炭地土壤氨氧化古菌(Ammonia-oxidizing archaea,AOA)、氨氧化细菌(Ammonia-oxidizing bacteria,AOB)和反硝化细菌(Denitrifying bacteria)丰度的影响。2014年7月取样分析结果表明:水位下降显著降低土壤含水量,水位下降与刈割均显著降低土壤呼吸;氨氧化及反硝化微生物功能基因丰度在各处理间无显著差异,但刈割及其与水位下降的交互作用显著影响AOA-amo A与AOB-amo A基因丰度比。刈割处理显著增加AOB-amo A基因相对丰度,但对AOA-amo A基因丰度无显著影响,揭示AOB可能在湿地土壤硝化过程中占主导地位。土壤nir S基因丰度显著高于nir K基因,表明nir S基因对水位下降及刈割的响应更为敏感。随着土壤水位的下降,刈割促进了由AOB主导的氨氧化过程,而反硝化微生物丰度的增加削减了氨氧化产物硝酸盐的积累,继而降低了土壤硝酸盐含量。

Effects of water table lowering and mowing on soil ammonia oxidizers and denitrifiers in alpine wetlands

Wetlands serve as the main sources and sinks of greenhouse gases. Understanding nitrogen cycling in wetlands would greatly help in the assessment of their response and feedback to global climate change. To investigate the effect of water table lowering and mowing on soil nitrification and denitrification in wetlands, a simulated water table lowering via digging drainage ditches at different depths and mowing experiment was set up in the Zoige peatland in the eastern Qinghai-Tibetan Plateau in 2013. The abundances of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and denitrifying groups were detected using a real-time PCR approach. Results based on the samples taken in July 2014 showed soil moisture decreased significantly with water table lowering. Both water table lowering and mowing significantly decreased soil heterotrophic respiration.The abundances of ammonia oxidizers and denitrifiers did not change under the treatments of water table lowering and mowing, whereas the ratio of abundance of AOA-amoA to AOB-amoA was significantly influenced by both mowing and interaction of mowing and water table lowering.Mowing significantly increased the relative abundance of the AOB-amoA gene but had no influence on that of the AOA-amoA gene, suggesting that the predominant role of AOB in ammonia oxidation.The abundance of nirS gene was higher than that of the nirK gene, indicating that the nirS gene was more sensitive to water table lowering and mowing. With the decline of water table, mowing promoted AOB-driven ammonia oxidation, while higher abundance of denitrifiers mitigated the accumulation of nitrate originated from ammonia oxidation, resulting in low soil nitrate content.