Diurnal variation of soil basal respiration and CO2 emission from a typical paddy soil after rice harvest under long-term different fertilizations

Soil respiration(SR) and the CO2 evolution is the dominant pathway of rapid exchange of soil-air carbon flux between terrestrial ecosystem and atmosphere,and hence impacts on atmospheric CO2 concentration change.Here the authors report a study on soil basal respiration and CO2 flux under long term different fertilization treatments during non-rice growing season from a typical paddy soil in Taihu Lake Region,China.Diurnal dynamics of CO2 flux from was monitored every 3 hours in four continuous 2 days early November and the CO2 flux was measured using closed chamber method and CO2 determined by GC spectroscopy using FID and Porapak Q column.The results showed that soil respiration CO2 flux ranged from CO2-C 12.2 to 25.2 mg/(m2h) and the total daily flux ranged from CO2-C 327.2 to 607.1 mg/(m2d),being smaller than the reported values for forest and grassland soils,and those from dry croplands.The daily flux under long-term single application of chemical fertilization alone increased by 55%85% compared to that under combined organic and chemical fertilization,meanwhile,the sensitivity of soil temperature response(5cm) was also markedly promoted.Correlation analysis revealed a significant(P0.05) correlation of CO2 flux with the microbial N,Cmic/Nmic,P availability respectively.Furthermore,a more prompt response of CO2 flux under long-term chemical fertilization alone was observed than that under combined fertilization though the flux was significantly closely related to temperature of air and of soil at 5cm depth.The smaller respiration and CO2 flux supported our former findings of C significant sequestration trend in China's paddy soils.However,our results indicated that the level of bio-available N and P accessible to microbial community notably influence soil respiration and hence,the CO2 evolution from the paddy soil.Long-term chemical fertilization alone in paddy not only enhanced the total soil basal respiration rate and the CO2 flux but its sensitivity to soil warming also.Thus,combined organic and chemical fertilization in paddy should be pursued as a practical mean for reducing CO2 flux from paddy fields.The variation of soil respiration and CO2 flux intensity under long-term different fertilization implicated a possible change of soil microbial community with higher the respiration activity,which deserves further study.