Soil respiration measurements along climate and black spruce productivity gradients in interior Alaska

Soil respiration measurements were made using an infrared gas analyzer (IRGA; EGM-4 gas analyzer, PP Systems, Haverhill, MA) with a dynamic soil respiration chamber (SRC-2, PP Systems). Respiration collars (18) were randomly located on three 20 x 20 m sampling grids (separate from WSOC collection) at each site. The respiration collars (10.2 cm diameter schedule 40 polyvinyl chloride) were inserted to a depth of 2.5 cm at least 1 week prior to initial measurements and were left in place for the duration of the experiment. Care was taken to ensure that the collars remained at the same depth throughout the measurement period. All vascular plants were removed from the collars prior to measuring. Measurements were made approximately bi-weekly at each site, from May through September in 2004 (n = 5 or 6). A portable thermometer was used to measure soil temperature at 10 cm below the surface concurrently with soil respiration measured at each collar. Changes in collar-specific air volumes (caused by changes in microtopography and the presence of moss) were measured directly through use of the ideal gas law by injecting 25 cm-3 of 3500 mg m-3 CO2 into the soil respiration chamber and measuring the subsequent dilution of CO2 concentration with the IRGA. All flux values have been adjusted for these collar specific volumes.

本研究采用红外气体分析仪（infrared gas analyzer, IRGA；EGM-4型气体分析仪，PP Systems公司，美国马萨诸塞州黑弗里尔市）搭配动态土壤呼吸室（SRC-2，PP Systems）开展土壤呼吸测定。共布设18个土壤呼吸环，在每个研究站点的3块20×20 m采样网格（与水溶性有机碳（WSOC）采样区域相互独立）中随机布设。所用呼吸环采用SCH 40型聚氯乙烯（polyvinyl chloride, PVC）制成，直径10.2 cm，于首次测定前至少1周插入土壤，插入深度为2.5 cm，并在整个实验周期内保持固定位置，全程确保呼吸环的插入深度无变化。每次测定前，需移除呼吸环内所有维管植物。2004年5月至9月期间，每个站点约每两周开展1次测定，共计获得5~6组有效数据（n=5或6）。测定时同步采用便携式温度计测定每个呼吸环对应位置的土壤表层10 cm处的土壤温度。针对各呼吸环因微地形变化及苔藓附着导致的专属气室体积变化，通过向土壤呼吸室内注入25 cm³浓度为3500 mg·m⁻³的CO₂，结合红外气体分析仪测定后续CO₂浓度的稀释情况，并利用理想气体定律直接计算得到体积变化量。所有土壤呼吸通量值均已根据各呼吸环对应的专属气室体积完成校正。