祁连山中部亚高山草地土壤呼吸及其组分研究

Research of the soil respiration and its components in subalpine grassland in the middle section of the Qilian Mountains

草地碳通量组分的区分及其与环境因子的关系是了解生态系统碳循环的重要环节.于2013年6-8月在祁连山中部亚高山草地开展了土壤呼吸及其组分研究,利用根去除法区分根系自养呼吸和土壤微生物异养呼吸.采用LI-8100土壤碳通量系统测定生态系统呼吸、土壤呼吸及土壤微生物呼吸速率,同时测定10 cm处土壤温度和5 cm处土壤湿度.分析呼吸速率和环境因子的昼夜变化动态,自养呼吸和异养呼吸速率占土壤呼吸速率的比例,呼吸速率与土壤温湿度及与生物量的关系.结果表明:生态系统呼吸、土壤呼吸和土壤微生物呼吸速率的日变化趋势均呈单峰型曲线,具体表现为生态系统呼吸(11.07μmol·m^(-2)·s^(-1))>土壤呼吸(6.31μmol·m^(-2)·s^(-1))>异养呼吸(4.92μmol·m^(-2)·s^(-1))>自养呼吸(1.39μmol·m^(-2)·s^(-1));自养和异养呼吸速率分别占土壤呼吸速率的22.03%和77.97%;呼吸速率与10 cm处土壤温度呈指数相关,Q10值排序为:土壤微生物呼吸(Q10=3.74)>土壤呼吸(Q10=2.76)>生态系统呼吸(Q10=2.49),呼吸速率与5 cm处土壤湿度呈显著线性负相关关系,双因素模型明显提高了呼吸速率与温湿度的相关性,能够分别解释土壤微生物呼吸,土壤呼吸和生态系统呼吸速率变异的89%,79%和62%;地上生物量和呼吸速率之间存在显著线性正相关关系,地下生物量与呼吸速率之间呈二次回归关系(P=0.01),未刈割草地呼吸速率大于刈割草地土壤呼吸速率,刈割一年的土壤呼吸速率大于刈割两年的土壤呼吸速率.

Partitioning carbon flux is a very important step in understanding ecosystem- level carbon cycling.Studies of the processes and mechanisms of different components of carbon flux will help to promote greenhouse gases mitigation,carbon sequestration and storage and climate change adaptation. The objectives of this study were to analyze the hourly variations of the soil respiration,ecosystem rates and environmental factors,to determine the relative contributions of the autotrophic and the heterotrophic respiration to the soil respiration,to compare the day and night soil respiration rate,to evaluate the impact of soil temperature and moisture,underground and aboveground biomass on the soil respiration rate. The study area is located in the middle section of the Qilian Mountains. By investigation and monitoring with Li- 8100 soil carbon flux system,the soil respiration and the ecosystem respiration were measured from June to August in 2013 and 2015. At the same time,soil temperature at 10 cm depth and moisture at the 5 cm depth below surface were measured. Relations of the respiration rate with soil temperature and moisture were determined by fitting both into an exponential model and a two- factor model. The results show that in the growing season,the subalpine grassland respiration rate had obvious daily changes in the form of a single-peaked curve for the four components（the ecosystem respiration（Re）,the soil respiration（Rs）,the autotrophic respiration（Ra）and the heterotrophic respiration（Rh））. The rank of the respiration rates was：Re（11.07 μmol·m^-2·s^-1） 〉Rs（6.31 μmol·m^-2·s^-1） 〉Rh（4.92 μmol·m^-2·s^-1） 〉Ra（1.39 μmol·m^-2·s^-1）. The contribution rate of the autotrophic respiration and the heterotrophic respiration to soil respiration estimated in the growing season were 22.03% and 77.97%,respectively. The daily respiration（71% of the total）was more than the night respiration（29% of the total）. The ecosystem respiration,soil respiration and heterotrophic respiration were exponentially related to the temperature of soil at 10 cm depth. The Q10 values of the ecosystem respiration,the soil respiration,and the heterotrophic respiration were calculated based on the soil temperature,which were 2.49,2.76,and 3.74,respectively. The respiration rates of the three components had a significantly negative linear relationship with the soil moisture. Considering soil temperature and soil moisture,the relationship between the respiration rate and the two factors was better fitted using a two-factor model,which was able to explain 89%,79% and 62% variation in the heterotrophic respiration,the soil respiration and the ecosystem respiration,respectively. There were a significant positive linear correlation between aboveground biomass and soil respiration and a quadratic regression correlation between soil respiration and underground biomass（P=0.01）. From the viewpoint of cutting grass treatment,the rank of soil respiration rates was：never cutting year one cutting year two cutting years.