Abstract:

Studying the effects of exogenous carbon (C) and nitrogen (N) addition on soil N transformation and greenhouse gas emissions can provide a scientific basis for soil nutrient management and greenhouse gas emission reduction. An incubation experiment under the condition of 25 ℃ and 60% WHC was conducted to investigate the effects of exogenous C (glucose and acetate) and N (sulfate ammonium) addition on net N transformation rates and greenhouse gas emissions from black cropland soil. The results showed that the net N mineralization rate of the control treatment without N added was 0.03 mg·kg^-1·d^-1, the addition of N fertilizer alone inhibited the organic N mineralization, and the net N mineralization rate was decreased to -0.56 mg·kg^-1·d^-1, indicating the occurrence of N immobilization. However, net nitrification rate and N₂O emission rate were increased to 33.3 times and 4.69 times of the control treatment, respectively, but no significant effect on CO₂ emission was observed. In comparison with the treatment with N fertilizer added alone, combined addition of N fertilizer and glucose or acetate significantly decreased the contents of ammonium and nitrate in soil, and the effect of combined addition of N fertilizer and glucose on ammonium content was higher than that in the treatment with combined addition of N fertilizer and acetate. Combined addition of C and N decreased net N mineralization rate, and the net N mineralization rate in the treatment of combined addition of N fertilizer and glucose was -5.97 mg·kg^-1·d^-1, significantly lower than that in the treatment with combined addition of N fertilizer and acetate (-5.00 mg·kg^-1·d^-1). The net nitrification rate of the treatment of N fertilizer added alone was 10.66 mg·kg^-1·d^-1, combined addition of N fertilizer and glucose or acetate significantly decreased net nitrification rates to 7.28 mg·kg^-1·d^-1 and 8.27 mg·kg^-1·d^-1, respectively. Combined addition of C and N significantly promoted the emissions of N₂O and CO₂, the average N₂O emission rates in the treatments with N fertilizer combined with glucose and acetate (43.60 μg·kg^-1·d^-1, 30.17 μg·kg^-1·d^-1) were increased to 2.31 times and 1.60 times of that in the treatment with N fertilizer added alone (18.85 μg·kg^-1·d^-1), respectively, and the average CO₂ emission rates (75.25 mg·kg^-1·d^-1, 108.87 mg·kg^-1·d^-1) were increased to 3.63 times and 5.26 times of that in the treatment with N fertilizer added alone (20.69 mg·kg^-1·d^-1). Our results implied that combined addition of C and N could significantly reduce the contents of inorganic N in the soil and promote N immobilization, and the inhibition effect on nitrification could reduce the occurrence of denitrification and the risk of nitrate leaching. However, combined addition of C and N promoted greenhouse emissions from soil, so the ecological impact of active exogenous C addition on cropland needs to be comprehensively evaluated.

Key words: glucose, acetate, mineralization, nitrification, N₂O, CO₂

摘要：

研究外源碳氮施加对土壤氮素转化和温室气体排放的影响可为土壤养分管理、温室气体减排提供科学依据。以东北农田黑土为对象，采用室内培养试验，在25 ℃和60% WHC水分条件下研究外源碳（葡萄糖和乙酸）、氮（硫酸铵）施加对土壤净氮转化速率和温室气体排放的影响。结果表明，对照处理土壤净氮矿化速率为0.03 mg·kg^-1·d^-1，单施氮肥抑制了土壤有机氮的矿化，净氮矿化速率降为-0.56 mg·kg^-1·d^-1，表现为对氮素的固定，而净硝化速率和N₂O排放速率分别显著增加至对照处理的33.3倍和4.69倍，但对CO₂排放速率没有显著影响。与单施氮肥处理相比，氮肥配施葡萄糖或乙酸处理显著降低了土壤中铵态氮和硝态氮含量，氮肥配施葡萄糖对铵态氮的影响程度大于氮肥配施乙酸处理。碳氮配施使得净氮矿化速率进一步降低，氮肥配施葡萄糖处理的净氮矿化速率为-5.97 mg·kg^-1·d^-1，显著低于氮肥配施乙酸处理（-5.00 mg·kg^-1·d^-1）。单施氮肥处理的净硝化速率为10.66 mg·kg^-1·d^-1，氮肥配施葡萄糖和氮肥配施乙酸处理的净硝化速率分别降低至7.28 mg·kg^-1·d^-1和8.27 mg·kg^-1·d^-1。碳氮配施显著促进了N₂O和CO₂的排放，氮肥配施葡萄糖（43.60 μg·kg^-1·d^-1）和氮肥配施乙酸处理（30.17 μg·kg^-1·d^-1）的N₂O平均排放速率分别是单施氮肥处理（18.85 μg·kg^-1·d^-1）的2.31倍和1.60倍，CO₂平均排放速率（75.25、108.87 mg·kg^-1·d^-1）分别是单施氮肥处理（20.69 mg·kg^-1·d^-1）的3.63倍和5.26倍。由此表明，碳氮配施能够显著降低土壤中的无机氮含量，促进氮素的固定，对硝化作用的抑制效应降低了反硝化作用发生和硝态氮淋溶的风险。但是，碳氮配施促进了土壤中温室气体的排放，施加活性碳源对农田生态效应的影响还需综合评估。

关键词: 葡萄糖, 乙酸, 矿化, 硝化, 一氧化二氮（N₂O）, 二氧化碳（CO₂）