Precipitation changes regulate the annual methane uptake in a temperate desert steppe.

Area of Science:

• Environmental Science
• Soil Science
• Biogeochemistry

Background:

• Desert soils play a crucial role in the global methane (CH4) budget as significant atmospheric CH4 sinks.
• Understanding how CH4 fluxes in desert-steppe ecosystems respond to precipitation variability is essential for accurate climate modeling.

Purpose of the Study:

• To investigate the impact of altered precipitation regimes on CH4 uptake in Inner Mongolian desert-steppe soils.
• To identify the key mechanisms driving CH4 flux responses to precipitation changes in this ecosystem.

Main Methods:

• A two-year in situ controlled experiment was conducted to manipulate precipitation levels.
• CH4 fluxes were monitored, and soil properties, including water-filled pore space (WFPS), microbial gene abundance (pmoA), soil porosity, plant biomass, and nutrient content, were analyzed.
• Structural equation modeling was employed to determine the relationships between variables and CH4 uptake.

Main Results:

• The studied desert steppe acted as a substantial CH4 sink, with an annual uptake of 2.93 kg C ha-1.
• Decreased precipitation significantly reduced CH4 uptake, particularly during spring and summer, while increased precipitation showed a non-significant positive trend.
• CH4 uptake was most sensitive to precipitation reduction, with optimal uptake occurring at moderate WFPS (not exceeding 32%); extreme WFPS levels inhibited uptake.
• The copy number of the pmoA gene was the most critical factor directly influencing CH4 uptake, while soil moisture indirectly affected uptake through soil porosity, plant biomass, and nitrate availability.

Conclusions:

• Precipitation is a key regulator of CH4 sink strength in desert-steppe ecosystems.
• Methane uptake is primarily controlled by methane-oxidizing bacteria (carrying the pmoA gene) and water-filled pore space.
• Reduced precipitation poses a significant threat to the CH4 sink capacity of these arid environments, highlighting the vulnerability of these ecosystems to climate change.