水稻土基底呼吸与CO2排放强度的日动态及长期不同施肥下的变化

土壤呼吸排放是陆地生态系统土气交换快速而活跃的途径之一,对大气CO2浓度的变化有显著的影响。本文对太湖地区一个代表性水稻土水稻收割后土壤基底呼吸CO2排放进行了昼夜观测和采样分析。结果表明,不同小区平均土壤呼吸与CO2排放速率在CO2-C.12.2～25.2.mg/(m2h)之间,日排放量在CO2-C.327.2～604.1mg/(m2d)之间,低于文献报道的森林和草地及旱作农田的土壤呼吸;与长期有机-无机配施处理相比,长期单施化肥CO2日排放量提高了55%～85%,并且显著提高了土壤呼吸对土壤(5.cm)温度的响应敏感性。相关分析表明,土壤呼吸CO2排放强度与土壤微生物N(Nmic)、微生物C∶N(Cmic/Nmic)和P的有效性有密切的关系;生物有效N和P的有效性显著地影响着土壤呼吸与CO2的生成和排放。本试验结果进一步支持了水稻土的固碳效应。但是,供试不同小区土壤呼吸排放强度的变异隐含着长期不同施肥处理可能使与高呼吸活性有关的微生物群落发生改变,有待于进一步研究。

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/(m²·h) and the total daily flux ranged from CO₂-C 327.2 to 607.1 mg/(m²·d),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(P<0.05) 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.