Nitrogen fertilization and rhizosphere processes regulate methane uptake in a nitrogen-limited forest

Area of Science:

• Environmental Science
• Soil Science
• Ecology

Background:

• Soil methane (CH4) uptake is vital for mitigating atmospheric CH4 concentrations.
• Nitrogen (N) addition and rhizosphere processes are known to influence soil CH4 uptake.
• The mediating role of rhizosphere activity in the response of soil CH4 uptake to N addition is not well understood.

Purpose of the Study:

• To quantitatively assess the rhizosphere contribution to soil CH4 uptake in a temperate larch plantation.
• To evaluate the effects of different N addition levels and durations on CH4 uptake.
• To understand how rhizosphere activity mediates CH4 uptake responses to N addition.

Main Methods:

• Conducted in-situ measurements of CH4 fluxes using collar methods.
• Applied varying levels of N addition (0, 20, and 50 kg N ha-1 yr-1) and assessed short-term and long-term effects.
• Performed a global meta-analysis to synthesize findings.

Main Results:

• High-level N addition (50 kg N ha-1 yr-1) significantly reduced soil CH4 uptake by 20.9%.
• Rhizosphere CH4 uptake decreased even under low-level N addition (20 kg N ha-1 yr-1) due to reduced rhizosphere activity.
• Meta-analysis confirmed N addition > 25 kg N ha-1 yr-1 suppressed CH4 uptake by increasing soil ammonium and nitrate.
• N addition duration did not significantly affect soil CH4 uptake.

Conclusions:

• Rhizosphere processes critically regulate soil CH4 uptake under N addition.
• Forest soils show differential responses to N addition levels, with higher levels suppressing CH4 uptake.
• Findings have implications for predicting forest soil CH4 sinks under future N deposition scenarios.