Effects Of Birnessite On Nitrous Oxide Emission Of Two Paddy Soil

Nitrous oxide（N₂O）is a greenhouse with the third highest greehouse effect after carbon dioxide（CO₂）and methane（CH₄）.Its warming potential is about 298 times that of CO₂,which can raise global temperatures and destroy the ozone layer.The N₂O emitted by agricultural production accounts for 41.7%of the N₂O produced by human activities.Among them,the large amount of nitrogen fertilizer application and low utilization rate in the rice ecosystem can produce a large amount of N₂O.China is one of the countries with the largest rice cultivation area in the world,and rice cultivation area accounts for about28%of the world.Paddy soil contains more manganese oxide,and its redox state can change with the frequent changes of soil redox conditions during rice planting.Manganese can participate in the soil nitrogen cycle process under aerobic and anaerobic conditions,and promote the production of N₂O or reduce N₂O to nitrogen（N₂）,thus affecting N₂O emissions from paddy soil.At present,there are few studies on the effects of manganese oxides on the N₂O emission rate,emissions,emission pathways and microorganisms of paddy soil.Therefore,in this study,the soil treated with birnessite was used to explore the N₂O emission rate of different manganese contents in the soil through microcosmic incubation.Acetylene and different types of nitrogen sources were added to distinguish the effects of manganese on soil nitrification and denitrification,and the mechanisms of soil N₂O emissions under the influence of manganese were clarified,which provided a theoretical basis for formulating production management measures and reducing N₂O emissions in rice growing areas.The main results are as follows:（1）Birnessite increased the N₂O emission rate,cumulative emission and p H of red paddy soil,reduces soil nitrification potential,net mineralization rate and dissolove organic carbon（DOC）content,while it reduced the N₂O emission rate,emission volume and p H,and increased the soil nitrification potential,net mineralization rate and water-soluble organic carbon content in yellow brown paddy soil.Compared to CK,the cumulative N₂O emissions from the red paddy soil at 0.1%treatment increased from407.0μg kg^-1 to 1595.7μg kg^-1,and the cumulative N₂O emissions from the yellow brown paddy soil at 0.1%treatment was 1521.9μg kg^-1 to 1375.7μg kg^-1.（2）The most abundant relative bacteria are Proteobacteria,Acidobacteria and Green Campylobacter and the genus with the highest relative abundance are Candidatus＿Udaeobacter,Gemmatimonas,Ramlibacter in the red and yellow brown paddy soils,respectivily.The richness of microbial species in red paddy soil was higher than that in yellow-brown soil without birnessite,but the uniformity of microbial species was lower than that in yellow brown paddy soil.The Chao1 index and Shannon index of red paddy soil were 4684 and 9.073,and the Chao1 index and Shannon index of yellow brown paddy soil were 3654 and 9.778,respectively.Birnessite increased the microbial species richness of yellow brown paddy soil,but decreased its microbial species uniformity,so that the microbial species richness and uniformity of yellow brown paddy soil was higher than that after adding birnessite in red paddy soil.Compare to CK,the Chao1 index of the yellow brown paddy soil was increased from 3654 to 5245 with adding 0.1%birnessite,and the Shannon index decreased from 9.778 to 9.474 with adding 0.1%birnessite.The microbial species and abundances of red paddy soil and yellow brown paddy soil were significantly different（Anosim,P=0.001,R=0.934）,and the species and abundance of microorganisms in the control treatment and the birnessite treatment showed significant differences in red paddy soil and yellow brown paddy soil,respectively.（3）Birnessite increased the cumulative N₂O emissions from denitrification and decreased the cumulative N₂O emissions from nitrification from yellow brown paddy soil.After adding KNO₃,the N₂O emissions increased from 858μg kg^-1 treated with control to1612μg kg^-1 treated with 0.1%birnessite.After adding NH₄NO₃,the cumulative N₂O emissions were reduced from 1330μg kg^-1 treated with control to 1030μg kg^-1 treated with 0.1%birnessite.Birnessite reduced the contribution of denitrification to N₂O emissions from the treatment with KNO₃,from 60%of control treatment to 45%of 0.1%birnessite treatment,and increased the contribution of denitrification to N₂O emissions with NH₄NO₃ treatment,from the control treatment 48%increased to 55%of 0.1%birnessite.（4）The N₂O emissions and p H of yellow brown paddy soil at 100%water holding capacity（WHC）were higher than 60%WHC,the cumulative N₂O emissions were two orders of magnitude higher than when the soil water content is 60%WHC.Birnessite reduced the N₂O emissions,soil nitrification potential and net mineralization rate at 60%WHC under different water content conditions,but increased the soil net mineralization rate at 100%WHC.In summary,the suppression of N₂O emissions by birnessite in yellow brown paddy soil is mainly due to the suppression of nitrification,and the biochemical coupling process of birnessite and nitrification and denitrification was affected due to the suppression of nitrification,thereby reducing N₂O emissions.The inhibitory effect of birnessite on soil nitrification microorganisms gradually weakened during long-term cultivation,and the activity of microorganisms was restored to a certain extent.