摘 要 ：根系呼吸是准确评估森林生态系统土壤碳收支的一个重要依据。基于LI-COR-6400-09土壤呼吸系统连续2a测定的3个生长阶段杨树人工林的根系呼吸数据，分析了根系呼吸的季节变化规律及树龄、土壤水热因子和细根生物量对它的影响。结果表明：3个不同树龄人工林的根系呼吸速率均呈明显的季节变化,最大值出现在夏初,最小值出现在秋末,基本上与表层土壤温度的季节变化相一致。根系呼吸的峰值早于土壤温度和细根生物量的峰值，说明林木根系的季节生长节律、地下碳分配模式都可能影响根系呼吸的季节变化。2年生人工林的根系呼吸速率最高，平均为3.78 μmol CO2 m-2 s-1，并随树龄增长呈下降趋势。3个树龄人工林根系呼吸占土壤呼吸的比例介于38.6%-58.0%之间，且2年生人工林最大。不同林龄之间根系呼吸的差异主要与根系的生长周转速率及代谢活性随生长阶段的变化有关。总的来说，表层土壤温度和细根生物量的协同作用可解释根系呼吸速率变化的76%。此外在评估一个轮伐期内的根系呼吸强度时，应考虑不同生长阶段对它的影响。
Abstract:Information about root respiration is essential for evaluating soil carbon cycling and sequestration in forest plantation ecosystems. Using LI-COR-6400-09 system, root respiration was determined in poplar plantations at three different developmental stages in Xinjiang. Based on the field observation in 2007 and 2008, the seasonal dynamics of root respiration and its main controlling factors including tree age, soil conditions and fine root biomass were analyzed. The results showed that root respiration rate of the plantations (aged from 2, 7 to 12) displayed similar seasonal patterns, with the maximum occurred in early summer and the minimum in autumn, closely followed the seasonal variation of soil temperature in the top layer. Furthermore, root respiration rate peaked earlier than soil temperature and fine root biomass in the growing season, which could imply that root seasonal phenology and belowground carbon allocation also played a role in variation of root respiration. The average root respiration in the 2-year-old stands was 3.78 μmol CO2 m-2 s-1, then declined with increasing plantation age. The contribution of root respiration to soil respiration varied from 38.6% to 58.0%, with the maximum occurred in the 2-year-old stands. The variability in root respiration with tree ages mainly resulted from the differents in root production, turnover and metabolism at these three stages. In sum, soil temperature and fine root biomass at top depth jointly explained 76% of variation in root respiration. Also, our results hightlight the importance of developmental stage in evaluating root respiration over a full rotation.