Effects of seasonal nitrogen addition on soil net nitrogen mineralization in typical temperate grasslands of Inner Mongolia,northern China
[Objective]This study aimed to explore the effects of seasonal nitrogen(N)addition on soil inorganic N pool and N mineralization rates in temperate steppe grasslands.It focused on revealing monthly dynamics,interannual variations,and environmental driving mechanisms to support understanding soil N cycling and its relationship with atmospheric N deposition.[Method]A field experiment was established with N addition applied in different seasons:autumn,winter,and the growing season.Inorganic N content and N mineralization rates were measured by top-cover PVC cylinders method to explore the effects of seasonal N addition on net N mineralization potential.[Result]Compared with control,N addition significantly increased inorganic N pools but declined over time.Compared with N addition in autumn and winter,N addition in growing season significantly increased inorganic N by 226.5%.The response of ammonium N,nitrate N and inorganic N to N addition in different seasons showed obvious seasonal pattern.Meanwhile,N addition in different seasons significantly increased the rate of N mineralization.At the end of growing season,net ammonification rate showed a trend of decreasing first and then increasing after N addition in growing season.N addition in growing season significantly increased net nitrification rate and net N mineralization rate at the end of growing season.N mineralization rate showed significantly monthly and interannual changes to N addition in different seasons.The response of mineralization rate to N addition in different seasons was mainly influenced by environmental factors.It was found that temperature had a negative effect on nitrification rate and net N mineralization rate,while precipitation had a positive effect.N addition in different seasons was main factor causing the difference of N mineralization rate.[Conclusion]Seasonal N addition significantly alter soil inorganic N pools and mineralization rates in temperate grasslands,showing notable seasonal and interannual patterns with experimental time.In conclusion,study of the effects of different seasonal N addition on soil N mineralization provides theoretical support for in-depth understanding of response rule and mechanism of soil N conversion process to atmospheric N deposition.It also helps to comprehensively evaluate the relationship between seasonal effects of atmospheric N deposition and soil N cycle.
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