Objective To clarify the response of carbon and nitrogen content and CH4 emission to different soil moisture conditions and the additions of amino acid in the dark brown soil of temperate forests, this study analyzed the relationship between soil pH and nitrogen, CH4 emission rate and soil carbon and nitrogen content, to assist related research on water management, carbon and nitrogen transformation, and greenhouse gas emission in temperate forest dark brown soil.
Method In this study, an indoor soil incubation was conducted with 40%, 60%, and 90% of the soil water holding capacity (WHC). Additionally, the potential effects of adding two amino acids on soil carbon and nitrogen content and CH4 emissions were explored. The Pearson correlation analysis was used to analyze the correlation between soil carbon and nitrogen content, pH and methane emission rate.
Result (1) Amino acid addition increased soil dissolved organic carbon (DOC) content, and meanwhile significantly increased \textNH_4^ + -N content and CH4 emission rate. Leucine treatment increased the contents of DOC and \textNH_4^ + -N by 21.39%−45.10%, respectively, and the CH4 emission rate was 3.20 times higher than that of CK, methionine treatment increased the contents of DOC and \textNH_4^ + -N by 21.39%−72.71%, respectively. and the CH4 emission rate was 7.00 times higher than that of CK. (2) The influence of different amino acids on soil \textNO_3^ - -N content was different. Leucine treatment increased \textNO_3^ - -N content in soil by 8.41%, but its effect on nitrification in soil may have a lag, while methionine can significantly inhibit nitrification in soil, and \textNO_3^ - -N content was significantly reduced by 37.90%. (3) Different soil moisture conditions had significant effects on soil DOC, \textNH_4^ + -N, \textNO_3^ - -N and CH4 emission rates. 90% WHC increased DOC content by 11.95%−19.91%, \textNH_4^ + -N by 19.83%−35.46%, \textNO_3^ - -N by 10.05%−23.79%, and CH4 emission rate increased to 1.48−2.06 times of the other two water conditions. Under 60% WHC condition, \textNH_4^ + -N increased by 13.05%, \textNO_3^ - -N content increased by 24.62%. 60% WHC may be the optimum water content for nitrification in temperate dark brown soil. The 90% WHC condition was conducive to the accumulation of DOC, and had an obvious inhibitory effect on \textNO_3^ - -N production. (4) Soil pH was significantly positively correlated with \textNH_4^ + -N content, positively correlated with \textNO_3^ - -N content. The CH4 emission rate was significantly negatively correlated with \textNO_3^ - -N content and \textNH_4^ + -N content, and significantly positively correlated with DOC content.
Conclusion Addition of different types of amino acids plays different roles on the carbon and nitrogen content and CH4 emissions of dark brown soil in temperate forests. Within a certain range, the increase of soil moisture content is beneficial to soil \textNH_4^ + -N, \textNO_3^ - -N, DOC accumulation and CH4 emission, but high soil moisture content inhibits the production of \textNO_3^ - -N. Therefore, the role of amino acids and changes in moisture should be considered when studying carbon content, CH4 emissions and nitrogen transformation mechanisms in temperate forest dark brown soils.
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