Influencing factors of soil nitrous oxide emission during freeze-thaw cycles

doi:10.17521/cjpe.2021.0040

Abstract

Abstract:

Aims Enhanced duration, intensity, and frequency of freeze-thaw cycles owing to global climate change may significantly affect soil nitrous oxide (N₂O) emission. N₂O is an important greenhouse gas, but our current understanding of soil N₂O emission and its influencing factors during freeze-thaw cycles is still limited.

Methods Here, we adopted the meta-analysis method and collected 30 articles on the effects of freeze-thaw cycles on soil N₂O flux and cumulative emission from peer-reviewed journal articles. Our objectives were to explore the effects of freeze-thaw cycles on N₂O emissions in different ecosystems and to comprehensively explore the influencing factors from the perspectives of experimental settings, soil physical and chemical properties, and the patterns of freeze-thaw cycles.

Important findings Results showed that freeze-thaw cycles significantly increased N₂O instantaneous emission, cumulative emission, and nitrification by 72.34%, 143.25%, and 124.63%, respectively. Freeze-thaw cycles also increased denitrification by 162.56%. Conversely, freeze-thaw cycles significantly decreased microbial biomass nitrogen by 6.39%. The effect of freeze-thaw cycles on N₂O emission was significantly affected by the variations in soil microclimate and soil physical and chemical properties in different ecosystems. When the mean annual temperature (MAT) of a site exceeded 5 °C, freeze-thaw cycles could significantly enhance the N₂O flux by 104.13%, which was significantly higher than that the effect at sites with MAT between 0-5 °C (25.56%) or less than 0 °C (55.29%). When soil moisture was greater than 70%, the increase of soil N₂O flux caused by freeze-thaw cycles was 109.17%, which was significantly higher than that when soil moisture was between 50%-70% (65.67%) or less than 50% (20.37%). The higher soil clay and nutrient contents were, the greater the increase in N₂O emission caused by freeze-thaw cycles became. Freeze-thaw cycles could significantly increase soil N₂O flux by 91.21% in the presence of plants, which was higher than the effect in the absence of plants (54.43%). The impact of freeze-thaw cycles on N₂O emission could be enhanced by soil sieving. In addition, soils sampled during the freeze-thaw cycling period showed more responses to freeze-thaw cycles than soils sampled during other times. The response of cumulative N₂O emissions to freeze-thaw cycles was significantly improved by longer duration of thawing, higher intensity of freezing, and higher frequency of freeze-thaw cycles. When the freezing temperature was lower than -10 °C, freeze-thaw cycles could enhance soil N₂O flux by 100.73%, which was significantly higher than the effect when the freezing temperature was between -10- -5 °C (47.74%) or more than -5 °C (70.25%). The main reason was that higher intensity of freezing could promote the release of more nutrients from soil microorganisms and soil structure, thereby increasing the production and emission of N₂O. Overall, these results can help better understand the response of soil N₂O to freeze-thaw cycles and its influencing factors, and provide scientific data for accurately predicting the impact of global climate change on N₂O emission in the future.

Key words: freeze-thaw, nitrous oxide (N₂O), microbial biomass, global climate change, denitrification

GAO De-Cai, BAI E. Influencing factors of soil nitrous oxide emission during freeze-thaw cycles[J]. Chin J Plant Ecol, 2021, 45(9): 1006-1023.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2021.0040

https://www.plant-ecology.com/EN/Y2021/V45/I9/1006

Figures/Tables 8

Fig. 1 Effects of freeze-thaw cycles on soil nitrous oxide (N2O) flux, cumulative N2O emissions, microbial biomass nitrogen (MBN) content, nitrification, and denitrification rates. Error bars stand for 95% confidence intervals. Values next to the error bars represent the number of observations of the variable. Dashed line indicates that there is no effect.

Table 1 Experimental settings in the studies used in this meta-analysis

Fig. 2 The distribution of the freeze-thaw cycles experiments selected in this meta-analysis in the world. •, site.

Fig. 3 Effects of freeze-thaw cycles on soil nitrous oxide (N2O) flux and cumulative N2O emissions. The variables are categorized into different groups according to mean annual temperature, experimental method, ecosystem type, soil treatment, presence of plant, period of sampling soil, temperature of freezing, and soil moisture. Error bars stand for 95% confidence intervals. The values next to the error bars represent the number of observations of the variable. Dashed line indicates that there is no effect. FT represents the freeze-thaw period.

Fig. 4 Relationships between the effect size of freeze-thaw cycles on soil nitrous oxide (N2O) flux (ln R (N2O flux)) and mean annual precipitation (MAP)(A) and mean annual temperature (MAT)(B).

Fig. 5 Relationships between the effect size of freeze-thaw cycles on soil nitrous oxide (N2O) flux (ln R (N2O flux)) and basic physical and chemical characteristics of soils. Those with significant relationships were shown in this figure, but those with non-significant relationships were shown in Appendix I.

Fig. 6 Relationships between the effect size of freeze-thaw cycles on soil nitrous oxide (N2O) flux (ln R (N2O flux)) and the effect size of freeze-thaw cycle on denitrification rate (ln R (Denitrification))(A) and the effect size of freeze-thaw cycles on nitrification rate (ln R (Nitrification))(B).

Fig. 7 Relationships between the effect size of freeze-thaw cycles on soil nitrous oxide (N2O) flux (ln R (N2O flux))(A, B, C) and cumulative N2O emissions (ln R (Cumulative N2O emissions))(D, E, F) and the duration, temperature, and frequency of freeze-thaw cycles. Those with significant relationships were shown in this figure, but those with non-significant relationships were shown in Appendix II.

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