Effects Of Nighttime Warming On CH₄ And N₂O Reduction Processes In Silicon-fertilized Paddy Fields

Methane(CH₄)and nitrous oxide(N₂O)are two greenhouse gases second only to CO₂,and rice fields are one of the main sources of CH₄ and N₂O emissions from terrestrial ecosystems.Rice is the main food crop in my country.Rice fields account for 27%of the total cultivated land in China,and are an important source and sink of greenhouse gases.Under the background of global warming,it is of great significance to explore the process of CH₄oxidation and N₂O reduction in paddy soil and to reveal the law of greenhouse gas consumption in paddy fields.In this experiment,aerobic and anaerobic culture experiments were carried out on rice fields with normal temperature+no silicon fertilizer(CK),night warming treatment(NW),silicon fertilizer treatment(Si),and night warming+silicon fertilizer(NW+Si).Changes of aerobic CH₄ oxidation,anaerobic CH₄ oxidation rate and N₂O reduction rate in paddy fields,revealing their response characteristics to three exogenous nitrogen forms(NH₄⁺,NO₃^-,Urea),and exploring the contribution of CH₄ oxidation to soil organic carbon accumulation,to analyze the N conversion potential of N₂O reduction,and to identify the possible effects of N₂O on anaerobic CH₄ oxidation.The main conclusions are as follows:(1)There were significant differences in the aerobic CH₄ oxidation process among the four paddy soils.Among them,in the rhizosphere soil,the rate of aerobic CH₄ in the four rice fields was 7.48?10.85?g·g^-1soil·d^-1,the oxidation rate of Si rice field was the fastest,and the NW rice field was the slowest.The net increase of ¹³C-SOC was 8.92?13.58?mol·g^-1soil,among them,the net increase of silicon rice paddy field is the largest.Indicating that the nighttime warming inhibited the aerobic CH₄ process in the rhizosphere,but the application of silicon fertilizer greatly promoted the process,and the application of silicon promoted the assimilation of ¹³CH₄ into the soil Organic carbon,which improves the carbon sequestration efficiency of the aerobic CH₄ oxidation process.In the non-rhizosphere soil,the aerobic CH₄ oxidation rate was 16.11?16.48?g·g^-1soil·d^-1,and the net increment of ¹³C-SOC was 11.59?13.21?mol·g^-1soil,which were generally higher than those in the rhizosphere soil.The effects of exogenous N application on the aerobic CH₄ oxidation process in the four paddy soils were different.Among them,in the non-rhizosphere soil,under the condition of adding NH₄⁺-N,NO₃^--N,and urea in NW+Si paddy field,the aerobic oxidation rate of CH₄ was significantly higher than other paddy fields,respectively 23.34?41.20%,54.73?225.66%and 18.65?64.91%.And after the addition of three forms of N,the abundance and net increment of ¹³C-SOC in Si paddy field and NW+Si paddy field(rhizosphere soil and non-rhizosphere soil)were higher than those of the other two types of silicon-free paddy fields,indicating that under the condition of nitrogen application,Si application significantly promoted the carbon assimilation efficiency of aerobic CH₄ oxidation in paddy fields.(2)During the anaerobic CH₄ oxidation process in the four paddy fields,the anaerobic oxidation rate of CH₄ between the rhizosphere soils was 4.11?6.33 nmol CO₂·g^-1soil·d^-1,which was CK paddy field>NW+Si paddy field>NW paddy field>Si paddy field;The non-rhizosphere intersoil rate was 6.23?8.97 nmol CO₂·g^-1soil·d^-1,which was CK paddy field>NW+Si paddy field>Si paddy field>NW paddy field,indicating that warming and silicon application inhibited the rate of CH₄ anaerobic oxidation.The anaerobic CH₄ rates of the non-rhizosphere soils of the four paddy fields were generally higher than those of the rhizosphere soils.The abundance of ¹³C-SOC in the four rice fields was higher than the natural abundance.The net increment of¹³C-SOC in the rhizosphere soil was Si rice field>NW rice field>CK rice field>NW+Si rice field,and the non-rhizosphere soil was CK Rice field>NW rice field>NW+Si rice field>Si rice field.Except for the rhizosphere Si paddy soil,the net increase of ¹³C-CO₂/(net increase of ¹³C-SOC+net increase of ¹³C-CO₂)was higher than 50%in other paddy fields,indicating that most of ¹³CH₄ was reacted to ¹³CO₂ after anaerobic oxidation,but the application of silicon Facilitates soil carbon fixation.After applying different forms of exogenous N,the effects on the anaerobic oxidation of CH₄ were not consistent.In the rhizosphere soil,after adding NH₄⁺-N and NO₃^--N,the anaerobic CH₄ rate of NW paddy field,NW+Si paddy field,Si paddy field was higher than that of CK paddy field by 18.69?106.80%and 124.99?161.80%,respectively.After adding urea,the anaerobic CH₄ oxidation rate in NW paddy field and Si paddy field was higher than that in CK paddy field by 1.12%and 22.26%,respectively,indicating that under the condition of nitrogen application,both warming and silicon application promoted the anaerobic oxidation of CH₄ in the rhizosphere of paddy field.In the non-rhizosphere soil,the anaerobic oxidation rate of CH₄ in the silicon-fertilized paddy field after applying three different forms of N was lower than that in the CK paddy field,indicating that N input inhibited the CH₄ anaerobic oxidation process of the non-rhizosphere soil in the silicon-fertilized paddy field.(3)The reduction rates of N₂O in the rhizosphere soil of the NW paddy field and Si paddy field were higher than those of the CK paddy field,36.17%and 17.73%higher,respectively,while the reduction rates of the four non-rhizosphere soils were 12.84?17.49?g·g^-1soil·d^-1,there was no significant difference among the four rice fields.Under the condition of applying different forms of exogenous N,the N₂O reduction rate of NW+Si paddy field,Si paddy rhizosphere and non-rhizosphere soil is basically higher than that of NW paddy field,and the promotion effect of urea is the most obvious in non-rhizosphere soil.It was found that the reduction rate was closely related to the DOC content of paddy soil under the long-term warming/silicon application treatment.(4)Compared with the addition of CH₄,the addition of CH₄+N₂O significantly increased the rate of anaerobic CH₄ in the four paddy fields,in which the increase of rhizosphere soil was37.86?109.90%,and that of non-rhizosphere soil was 0.27?102.52%.Under the addition of CH₄+N₂O,the net increments of ¹³C-SOC in the rhizosphere and non-rhizosphere soils of the four paddy fields were higher than those under the condition of only CH₄,indicating that N₂O also promoted the anaerobic oxidation of CH₄ in paddy soils Rate and ¹³C-SOC assimilation.Under CH₄+N₂O treatment,the net increment of ¹³C-SOC in Si paddy field and NW+Si paddy field(rhizosphere and non-rhizosphere soil)was higher than that in non-silicon paddy soil,indicating that the application of silicon promoted soil carbon assimilation in the process of CH4 oxidation in paddy soil.