Study on the Relationship Between Total Nitrogen and Nitrogen Functional Microorganisms in Soil Aggregates under Long-term Conservation Tillage
[Objective]Long-term tillage practices can significantly change the distribution of soil aggregates,microbial abundance and total nitrogen storage in farmland.However,whether there is a correlation between these properties remains unclear.This study aimed to reveal the relationship between total nitrogen content and nitrogen functional microorganisms within different particle sizes aggregates under long-term conservation tillage in dry farming areas of the Loess Plateau.[Method]Based on the 10-year(2009-2020)long-term tillage experiment(conventional tillage:plow tillage,PT;conservation tillage:chisel plow tillage,CPT and zero tillage,ZT),the effects of long-term conservation tillage on the distribution of total nitrogen and its relationship with the abundance of functional genes(amoA-AOA,amoA-AOB,nirS,nirK,nosZⅠ and nosZⅡ)within aggregates in dry farmland were studied.[Result]Long-term conservation tillage(CPT and ZT)significantly increased the mass percentage of mega-aggregates(>2 mm)and macro-aggregates(0.25-2 mm),while it decreased the mass percentage of micro-aggregates(<0.25 mm).Compared with PT,long-term CPT and ZT treatments significantly decreased the soil nitrogen mineralization rate,nitrification potential,and denitrification potential but increased the total nitrogen content in the 0-20 cm soil layer by 53.4%and 49.9%,respectively.The total nitrogen contribution rate of macro-aggregates of CPT and ZT treatments increased by 16.2%and 21.8%,respectively.Using qPCR technology,it was found that CPT and ZT significantly increased the abundance of bacteria,fungi and nitrogen functional genes(except amoA-AOB);and the abundance of fungi,nirS,and nosZⅠ in macroaggregates was significantly higher than that in microaggregates and macroaggregates,while the abundance of nosZⅡ gene showed the opposite trend.Mantel analysis showed that aggregate size,soil texture,mineral nitrogen content,sucrase activity,and urease activity were the key factors regulating the abundance of nitrogen-functional microorganisms within aggregates.Correlation analysis showed that the total nitrogen content in aggregate soil was positively correlated with MBN,DON,and the abundance of bacteria,fungi,amoA-AOB,and nosZⅡ genes,while negatively correlated with the abundance of nirS and nirK denitrification genes.[Conclusion]Long-term conservation tillage can increase soil total nitrogen storage mainly by increasing the contribution rate of nitrogen in macro-aggregates.As the abundance of bacteria,fungi,and nitrification process genes in macroaggregates increases,the abundance of nirS and nirK denitrifying microorganisms decreases,which improves the trend of the nitrogen cycle and significantly increases soil total nitrogen content.
Conservation tillageTotal nitrogen within aggregatesNitrogen functional microorganismDry farmland
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