Corrected calculations for soil and ecosystem measurements of CO2 flux using the LI-COR 6200 portable photosynthesis system
Corrected calculations for soil and ecosystem measurements of CO2 flux using the LI-COR 6200 portable photosynthesis system
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DOI：
10.1007/s00442-002-0870-3
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发表时间：
2002-06-01
期刊：
影响因子：
2.7
通讯作者：
Durant, M
中科院分区：
文献类型：
--
作者：
Hooper, DU;Cardon, ZG;Durant, M
LI-COR 6200便携式光合作用测定仪(LI-6200)通常与大气室结合使用，用于测量小型植被生态系统(农业、冻土带、草原、森林林下植被等)的生态系统水平的二氧化碳通量。该方法的两个问题导致了对生态系统二氧化碳净同化率的人为低估计(或对生态系统呼吸的高估)。首先，LI-6200用来计算光合作用的公式的准确性取决于小室中恒定的水蒸气压力。当蒸散率很高时，大型生态系统室通常会违反这一假设。我们提供了纠正这个问题的方程，并允许重新计算Li-CoR通量。第二个问题是静止条件下的边界层形成问题，例如在夜间。由于接近地面的高浓度二氧化碳被箱式风扇混合在一起，导致生态系统净呼吸的值异常高。要使速率稳定下来，需要相当长的混合时间。随着生态学家试图了解全球变化可能如何影响整个生态系统的碳平衡，必须解决这两个技术问题才能获得准确的结果。
The LI-COR 6200 portable photosynthesis (LI-6200) is commonly used in combination with large chambers to measure ecosystem level CO2 flux in ecosystems with small-statured canopies (agriculture, tundra, grasslands, forest understory, etc.). Two problems with the methodology lead to artifactually low estimates of rates of net ecosystem assimilation of CO2 (or overestimates of ecosystem respiration). The first is that accuracy of the equations used by the LI-6200 to calculate photosynthesis depends on a constant vapor pressure in the chamber. This assumption is commonly violated with large ecosystem chambers when evapotranspiration rates are high. We provide equations that correct this problem and permit recalculation of the LI-COR fluxes. The second problem is that of boundary layer formation under still conditions, such as at night. As high concentrations of CO2 close to the ground surface become mixed by chamber fans, exceptionally high values of net ecosystem respiration result. Substantial mixing time is necessary for rates to stabilize. As ecologists attempt to understand how global change might affect whole-ecosystem carbon balance, both of these technical problems must be addressed to get accurate results.