冻融期温带草地土壤呼吸和土壤异养呼吸的日变化特征及对水氮添加的响应

探讨冻融期土壤呼吸和土壤异养呼吸如何响应降雨变化和氮沉降增加，对于准确预估未来全球变化背景下陆地生态系统土壤碳动态有着重要意义。选择内蒙古温带典型草地开展增雨和氮沉降增加野外模拟实验，分析水氮变化条件下冻融期土壤呼吸及土壤异养呼吸的日变化特征。冻融期，土壤呼吸及土壤异养呼吸通量（CO₂排放速率）最大值出现在温度最高的午后或是土壤发生冻融后的早晨，最小值则出现在昼夜内温度最低的时间段。在秋季和春季两个昼夜观测日期内，水氮增加对呼吸通量的促进效应均不显著（P > 0.05），但却促使土壤呼吸累积通量分别增加了约145 mg m?2和70 mg m?2。由于异养呼吸在土壤呼吸中占比高（> 70.3%），因此，这两个观测时段内，水氮增加促使土壤异养呼吸日累积通量增加的值与土壤呼吸增加的值十分接近。呼吸通量与土壤水分、氮含量以及5 cm和10 cm地温的相关性不显著（P > 0.05），与气温和表层地温的相关性显著，且呈现显著的一元二次非线性拟合关系（P < 0.01），其中，气温可以解释呼吸通量日变化的53% ~ 84%。温度是控制呼吸通量日变化的主要因子，水氮添加在昼夜观测尺度上对土壤呼吸和土壤异养呼吸的日累积通量的促进效应不容忽视。

Diurnal Variation Characteristics of Soil Respiration and Heterotrophic Respiration in Freeze-thaw Period of Temperate Grassland and Its Response to Water and Nitrogen Addition

To investigate how soil respiration and heterotrophic respiration respond to rainfall changes and increased nitrogen deposition during the freeze-thaw period is important for accurate prediction of soil carbon dynamics in terrestrial ecosystems in the context of future global change. A field simulation experiment of increased rainfall (15% of multi-year average rainfall) and nitrogen deposition (25 kg ha?1yr?1) was conducted in a typical temperate grassland in Inner Mongolia to analyze the daily variations of soil respiration and heterotrophic respiration during the freeze-thaw period under changing water and nitrogen conditions . The maximum values of soil respiration and heterotrophic respiration flux (CO₂ emission rate) occurred in the afternoon when the temperature was highest or in the morning after the occurrence of soil freeze-thaw, and the minimum values occurred at night when the temperature was the lowest. The increase in respiration flux caused by water and nitrogen was not significant (P > 0.05), but the elevation in cumulative soil respiration fluxes induced by water and nitrogen were about 145 mg m?2 and 70 mg m?2 during the two diurnal observation dates in autumn and spring, respectively. Due to the high proportion of heterotrophic respiration in soil respiration (> 70.3%), the stimulation of daily cumulative flux of heterotrophic respiration induced by water and nitrogen in autumn and spring was close to that of soil respiration. The correlation between respiration flux and soil moisture, nitrogen nutrient content, and 5 cm and 10 cm ground temperature was not significant (P > 0.05); and the correlation between respiratory flux and air temperature and surface soil temperature was significant, showing a significant quadratic nonlinear fit (P < 0.01), where air temperature explained 53% to 84% of the daily variation of respiratory flux. Air temperature and 0 cm soil temperature were the main factors controlling the daily variations of respiration fluxes, and the positive effect of increased water and nitrogen on the daily cumulative fluxes of soil respiration and heterotrophic respiration should not be neglected.