Soil CO2 efflux in a beech forest: comparison of two closed dynamic systems
Soil CO2 efflux in a beech forest: comparison of two closed dynamic systems
复制标题
山毛榉林土壤二氧化碳流出：两个封闭动态系统的比较
DOI：
10.1023/a:1004737909168
复制
发表时间：
1999
期刊：
影响因子：
4.9
通讯作者：
E. Dufrene
中科院分区：
文献类型：
--
作者：
V. Dantec;D. Epron;E. Dufrene
本研究的目的是了解为什么两个封闭的动态系统具有非常相似的设计给了很大的差异，土壤CO2排放测量（PP系统和LI-COR）。无论是在现场（森林山毛榉林）和在实验室中，PP系统给出了更高的估计土壤CO2排放比LI-COR系统（范围从30%到50%）。土壤呼吸室内的风速差异（SRC-1室内为0.9 m s−1，LI-6000-09室内为0.4 m s−1）可能是两个系统之间差异的原因。呼吸室内过量的空气运动被认为会破坏森林地面上方的高层流边界层。这将促进积聚在上层土壤中的CO2排放到室内，并促进土壤中的CO2朝向呼吸室的横向扩散。两个系统之间的差异减少（i）通过降低SRC-1内的风扇速度，（ii）通过增加呼吸室外土壤表面的风速，或（iii）通过使用人工土壤设计，土壤孔隙中没有高CO2浓度。我们表明，风速是土壤CO2扩散的一个重要组成部分，必须考虑到测量土壤CO2排放时，即使在非常细的质地土壤，如粉壤土。保持室内风速低于0.4 m s-1可以实现正确的测量，因为低风速条件下森林树冠下占主导地位。然而，通过将室内的风速调节为代表在地板表面同时记录的风速的速度，将获得更精确的测量。
The aim of this study was to understand why two closed dynamic systems with a very similar design gave large differences in soil CO2 efflux measurements (PP systems and LI-COR). Both in the field (forest beech stand) and in the laboratory, the PPsystems gave higher estimations of soil CO2 efflux than the LI-COR system (ranging from 30% to 50%). The difference in wind speed occurring within the soil respiration chambers (0.9 m s−1 within the SRC-1 and 0.4 m s−1 within the LI-6000-09 chambers) may account for the discrepancy between the two systems. An excessive air movement inside the respiration chamber is thought to disrupt the high laminar boundary layer over the forest floor. This would promote an exhaust of the CO2 accumulated into the upper soil layers into the chamber and a lateral diffusion of CO2 in the soil towards the respiration chamber. The discrepancy between the two systems was reduced (i) by decreasing fan speed within the SRC-1, (ii) by increasing wind speed over the soil surface outside the respiration chamber, or (iii) by using an artificial soil design without high CO2 concentration in soil pores. We show that wind speed is an important component of soil CO2 diffusion which must be taken into account when measuring soil CO2 efflux, even on very fine textured soil like silt-loam soil. Proper measurement can be achieved by maintaining wind speed inside the chamber below 0.4 m s−1 since low wind speed conditions predominate under forest canopies. However, more accurate measurements will be obtained by regulating wind speeds within the chamber at a velocity representative of the wind speed recorded simultaneously at the floor surface.