Effects Of Nitrogen-rich Biochar On Soil Iron Dynamics And Carbon Release In Paddy Field Of Fuzhou Plain

China’s rice production makes an important contribution to world food security,but at the same time,China’s paddy field carbon emissions play an important role in the global greenhouse effect.In the special field management mode of paddy soil in its special flooding-discharging mode,the frequency of soil dry-wet alternately changes,which makes the redox process frequent,which leads to a series of changes in soil environment.Iron is one of the most active elements in the soil,and its continuous transformation process affects the decomposition and transformation of soil organic carbon in paddy fields.Therefore,exploring the relationship between iron dynamics and carbon release and its control measures are of great significance for adjusting rice paddy management measures and improving the ecological benefits of paddy fields.The study taken the Wufeng Comprehensive Experimental Station of Fujian Rice Research Institute as the research site discuss the effects of different nitrogen-rice biochar application rates on soil iron dynamics and carbon release in paddy field.Following were the main research results:（1）The contents of Fe（II）in the early paddy field control group,4 t/hm² and 8t/hm² nitrogen-rich biochar treatment group were 1.79±0.13,2.13±0.12 and 2.37±0.12mg/g,respectively.The contents of Fe（II）in the late paddy field control group,4 t/hm²and 8 t/hm² nitrogen-rich biochar treatment group were 2.71±0.26,4.11±0.49 and 3.86±0.40 mg/g,respectively.The results showed that different nitrogen-rich biochars significantly promoted the Fe（II）content in paddy soil,during the early stage of rice transplanting（water flooding period）,and the difference was significant（p<0.05）.The effects of different nitrogen-rich biochar treatments on Fe（III）and total iron content were not significant differences.（2）At the genus level,among the different treatments of paddy field soil iron-reducing bacteria community structure composition,the 4 t/hm² and 8 t/hm²nitrogen-rich biochar treatment groups all reduced the adundance of Bacillus and increased the adundance of Thiobacillus in early and late paddy.At the genus level,among the different treatments of rice field soil iron oxide bacteria community structure composition,the 4 t/hm² and 8 t/hm² nitrogen-rich biochar treatment groups increased the adundance of Thiobacillus and Thermomonas,and decreased the adundance of Geobacter and Sideroxydans in early and late rice.There was a positive correlation between Anaeromyxobacter,Geothermobacter and Desulfovibrio and soil Fe（II）content in iron-reducing bacteria.Pseudogulbenkiania,Pseudomonas and Fe（III）content showed negative correlation in iron oxidizing bacteria.（3）The averaged CO₂ emissions of the soil in control group,4 t/hm² and 8 t/hm²nitrogen-rich biochar treatment groups were 204.16±46.10,288.23±47.89 and 319.69±9.51 mg·m^-2·h^-1 in the early paddy field,respectively.The averaged CO₂ emissions of the soil in control group,4 t/hm²,and 8 t/hm² nitrogen-rich biochar treatment groups were270.48±15.81,311.56±21.45 and 396.65±30.13 mg·m^-2·h^-1 in the late paddy,respectively.The application of nitrogen-rich biochar promoted the averaged CO₂emission of early and late paddy soil,and increased with the application amount of nitrogen-rich biochar.（4）The averaged CH₄ emissions of the control group,4 t/hm² and 8 t/hm²nitrogen-rich biochar treatment groups were 0.51±0.19,0.37±0.11 and 0.41±0.12,mg·m^-2·h^-1 in the early paddy soil,respectively.The averaged CH₄ emission of the control group,4 t/hm² and 8 t/hm² nitrogen-rich biochar treatment groups were 1.19±0.10,2.80±0.10 and 1.78±0.24 mg·m^-2·h^-1 in the late paddy soil,respectively.It indicated that the different application amount of nitrogen-rich biochar reduced the averaged CH₄ emission of the early rice soil,and promoted the averaged CH₄ emission of soil in late rice soil.（5）The mean values of DOC of the control group,4 t/hm²,and 8 t/hm² nitrogen-rich biochar treatment groups were 64.04±5.78,74.04±2.49 and 86.42±3.53 mg/kg in the early paddy soil,respectively.The averaged DOC contents of the control group,4t/hm²and 8t/hm² nitrogen-rich biochar treatment groups were 52.41±4.13,68.58±3.73 and82.43±3.20 mg/kg in the late paddy soil,respectively.The 4 t/hm² and 8 t/hm²nitrogen-rich biochar treatment groups in early and late paddy field significantly increased soil DOC contents（p<0.05）.（6）There was a significantly positive correlation among soil Fe（II）content and cumulative release of soil CO₂,CH₄ and total gaseous C（p<0.01）.There was a significantly negative correlation among the Fe（III）content and the cumulative release of CO₂,CH₄ and total gaseous C（p<0.01）.