Molecular mechanisms of water table lowering and nitrogen deposition in affecting greenhouse gas emissions from a Tibetan alpine wetland

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• 作者：Hao Wang ; Lingfei Yu ; Zhenhua Zhang ; Wei Liu ; Litong Chen ; Guangmin Cao ; Haowei Yue ; Jizhong Zhou ; Yunfeng Yang ; Yanhong Tang and Jin-Sheng He
• 刊名：Global Change Biology
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：23
• 期：2
• 页码：815-829
• 全文大小：1009K
• ISSN：1365-2486

文摘

Rapid climate change and intensified human activities have resulted in water table lowering (WTL) and enhanced nitrogen (N) deposition in Tibetan alpine wetlands. These changes may alter the magnitude and direction of greenhouse gas (GHG) emissions, affecting the climate impact of these fragile ecosystems. We conducted a mesocosm experiment combined with a metagenomics approach (GeoChip 5.0) to elucidate the effects of WTL (−20 cm relative to control) and N deposition (30 kg N ha⁻¹ yr⁻¹) on carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes as well as the underlying mechanisms. Our results showed that WTL reduced CH₄ emissions by 57.4% averaged over three growing seasons compared with no-WTL plots, but had no significant effect on net CO₂ uptake or N₂O flux. N deposition increased net CO₂ uptake by 25.2% in comparison with no-N deposition plots and turned the mesocosms from N₂O sinks to N₂O sources, but had little influence on CH₄ emissions. The interactions between WTL and N deposition were not detected in all GHG emissions. As a result, WTL and N deposition both reduced the global warming potential (GWP) of growing season GHG budgets on a 100-year time horizon, but via different mechanisms. WTL reduced GWP from 337.3 to −480.1 g CO₂-eq m⁻² mostly because of decreased CH₄ emissions, while N deposition reduced GWP from 21.0 to −163.8 g CO₂-eq m⁻², mainly owing to increased net CO₂ uptake. GeoChip analysis revealed that decreased CH₄ production potential, rather than increased CH₄ oxidation potential, may lead to the reduction in net CH₄ emissions, and decreased nitrification potential and increased denitrification potential affected N₂O fluxes under WTL conditions. Our study highlights the importance of microbial mechanisms in regulating ecosystem-scale GHG responses to environmental changes.