长期不同施氮量下微生物残体氮对土壤氮库稳定性和玉米氮素吸收的影响OA北大核心CSTPCD

In farmland ecosystems,the application of chemical nitrogen(N)fertilizers is a crucial management strategy to ensure stable and high grain yields while maintaining the stability of soil N pools.Soil microorganisms play a pivotal role in both N mineral-ization and immobilization,thereby actively contributing to N retention and supply,which directly affects N uptake and utilization by crops.This study was conducted in the wheat-maize rotation field of the Luancheng Agro-Ecosystem Experimental Station of the Chinese Academy of Sciences.This study relied on a 14-year long-term positioning experiment with different N application rates.Three typical treatments were selected for N application rates during the maize season:150 kg(N)·hm-2(N150),200 kg(N)·hm-2(N200),and 300 kg(N)·hm-2(N300).Micro-plots were used to apply 15N-labeled N fertilizer to investigate the distribution of"old N"from soil and"new N"from fertilizer within soil N pools and their impact on crop N uptake and utilization.At harvest,the maize yield,total N uptake by the aboveground parts,and N uptake from fertilizers were measured.The contents of total N(TN),microbial residue N(MRN),fixed ammonium(FN),mineral N(NH4+-N+NO3-N,MN),and other organic N(ON)in the 0-20 cm soil layer were analyzed,along with the interception of 15N by different N pools.Multivariate regression and path analyses were used to estab-lish the relationships between various N pool forms and maize N uptake.The results indicated that maize yield,N uptake,and soil TN content were the highest under the N200 treatment,favoring high crop yields and soil N pool cultivation.Fertilizer N uptake and residue were higher under the N300 treatment than under the N200 treatment,suggesting a stronger"priming effect"under the N300 treatment,which induces greater mineralization and loss of soil"old N".The stability of soil TN pool was poor under the N300 treat-ment,with a higher degree of turnover.Among the TN pools,MRN was dominant,with the N200 treatment being significantly high-er than N150 treatment,contributing more than 50％of the TN.Fungal residue N(FRN)was the main contributor to MRN accumula-tion.The ratio of FRN to bacterial residual N(BRN)was higher in the N200 treatment than in the N150 and N300 treatments,indicat-ing that optimal N application could significantly enhance the contribution of fungi to N accumulation,thereby improving the stabil-ity of the soil N pool.Insufficient N application(N150)or excessive N application(N300)increased the contribution of bacteria to N accumulation,which was not conducive to stabilizing the soil N pool.The MN and FN contents were significantly higher in the N300 treatment than in other treatments,suggesting that excessive fertilization predominantly enhanced the active N pool.In conclusion,optimal N application can optimize the soil N pool distribution,promote the sequestration of N into microbial residue pools,signifi-cantly enhance the N immobilization capacity of soil microorganisms,and foster the benign operation of soil N retention and supply.This ensures maize N uptake and yield.The study provides a scientific basis for guiding farmland fertility improvement and N ferti-lizer reduction in the North China Plain.