Soil CO2 and N2O emissions and microbial abundances altered by temperature rise and nitrogen addition in active-layer soils of permafrost peatland

Abstract

Changes in soil CO₂ and N₂O emissions due to climate change and nitrogen input will result in increased levels of atmospheric CO₂ and N₂O, thereby feeding back into Earth's climate. Understanding the responses of soil carbon and nitrogen emissions mediated by microbe from permafrost peatland to temperature rising is important for modeling the regional carbon and nitrogen balance. This study conducted a laboratory incubation experiment at 15 and 20°C to observe the impact of increasing temperature on soil CO₂ and N₂O emissions and soil microbial abundances in permafrost peatland. An NH₄NO₃ solution was added to soil at a concentration of 50 mg N kg^-1 to investigate the effect of nitrogen addition. The results indicated that elevated temperature, available nitrogen, and their combined effects significantly increased CO₂ and N₂O emissions in permafrost peatland. However, the temperature sensitivities of soil CO₂ and N₂O emissions were not affected by nitrogen addition. Warming significantly increased the abundances of methanogens, methanotrophs, and nirK-type denitrifiers, and the contents of soil dissolved organic carbon (DOC) and ammonia nitrogen, whereas nirS-type denitrifiers, β-1,4-glucosidase (βG), cellobiohydrolase (CBH), and acid phosphatase (AP) activities significantly decreased. Nitrogen addition significantly increased soil nirS-type denitrifiers abundances, β-1,4-N- acetylglucosaminidase (NAG) activities, and ammonia nitrogen and nitrate nitrogen contents, but significantly reduced bacterial, methanogen abundances, CBH, and AP activities. A rising temperature and nitrogen addition had synergistic effects on soil fungal and methanotroph abundances, NAG activities, and DOC and DON contents. Soil CO₂ emissions showed a significantly positive correlation with soil fungal abundances, NAG activities, and ammonia nitrogen and nitrate nitrogen contents. Soil N₂O emissions showed positive correlations with soil fungal, methanotroph, and nirK-type denitrifiers abundances, and DOC, ammonia nitrogen, and nitrate contents. These results demonstrate the importance of soil microbes, labile carbon, and nitrogen for regulating soil carbon and nitrogen emissions. The results of this study can assist simulating the effects of global climate change on carbon and nitrogen cycling in permafrost peatlands.

Keywords: boreal peatland; climate warming; enzyme activity; nitrogen availability; soil microbial abundance.

Figure 1

Effects of temperature rising and nitrogen addition on soil CO₂ (A) and N₂O (B) emissions in permafrost peatland. CK, control; NA, add 50 mg N kg⁻¹ soil.

Figure 2

Effects of temperature rising and nitrogen addition on soil total CO₂ (A) and N₂O (B) release and their temperature sensitivity (Q₁₀) (C) in permafrost peatland. CK, control; NA, add 50 mg N kg⁻¹ soil. Different lowercase letters in the figure indicate significant differences in the means between different treatments.

Figure 3

Effects of temperature rising and nitrogen addition on soil bacterial (A), fungal (B), mcrA (C), pmoA (D), nirK (E), and nirS (F) abundances in permafrost peatland. CK, control; NA, add 50 mg N kg⁻¹ soil.

Figure 4

Pearson’s correlation analysis of soil CO₂ and N₂O emissions, carbon and nitrogen contents, microbial abundances, and enzyme activities. βG, β-1,4-glucosidase; CBH, cellobiohydrolase; NAG, β-1,4-N-acetylglucosaminidase; AP, acid phosphatase; DOC, dissolved organic carbon; DON, dissolved organic nitrogen; NH₄⁺-N, ammonium nitrogen; NO₃^—N, nitrate nitrogen. * indicates significant p < 0.05; ** indicates significant p < 0.01.

Figure 5

Effects of temperature rising and nitrogen addition on soil enzyme activities in permafrost peatland. CK, control; NA, add 50 mg N kg⁻¹ soil. βG, β-1,4-glucosidase (A); CBH, cellobiohydrolase (B); NAG, β-1,4-N-acetylglucosaminidase (C); AP, acid phosphatase (D).

Figure 6

Effects of temperature rising and nitrogen addition on soil dissolved organic carbon (A), dissolved organic nitrogen (B), NH₄⁺-N (C), and NO₃⁻-N (D) contents in peatland. CK, control; NA, add 50 mg N kg⁻¹ soil; DOC, dissolved organic carbon; DON, dissolved organic nitrogen; NH₄⁺-N, ammonium nitrogen; NO₃^—N, nitrate nitrogen. Different lowercase letters in the figure indicate significant differences in the means between different treatments.