Minimizing artifacts and biases in chamber-based measurements of soil respiration
Minimizing artifacts and biases in chamber-based measurements of soil respiration
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DOI：
10.1016/s0168-1923(02)00100-4
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发表时间：
2002-12-02
影响因子：
6.2
通讯作者：
Navarro, R
中科院分区：
文献类型：
--
作者：
Davidson, EA;Savage, K;Navarro, R
土壤呼吸是陆地生态系统中最大和最重要的碳通量之一。虽然涡度协方差方法正被广泛用于测量夜间总生态系统呼吸，使用放置在土壤上的室是测量土壤和凋落物层内发生的呼吸的最直接的方法。几十年的基于腔室的测量经验已经揭示了这种方法的大部分潜在误差来源。本文的目的是审查最近表达的几个关注的不确定性室为基础的测量土壤CO2排放量，评估这些潜在的错误的方向和幅度，并解释程序，尽量减少这些错误和偏见。在大多数情况下，扩散梯度的干扰导致通量低估小于15%，并且可以通过曲线拟合部分校正和/或可以通过使用简短的测量周期来最小化。由空气循环设计中的流动限制引起的腔室的欠压或过压可能导致大的误差，但也可以通过适当尺寸的腔室通风口和不受限制的流动来避免。我们发现，使用我们的腔室设计，流量估计中的压差非常小（+/-0.1 Pa）和适度（类似于15%），不一致的误差。在有风的条件下观察到的压差稍大（+/-0.9 Pa），在这种条件下进行的基于室的测量的准确性需要更多的研究。空间和时间的异质性可以通过适当的腔室大小和数量以及采样频率来解决。例如，在热带森林和牧场中，使用直径为300 cm（2）的腔室进行的36次测量中，随机选择8次通量测量的平均值在98%的时间内处于全部平均值的25%以内，在70%的时间内处于全部平均值的10%以内。最后，基于室的测量与基于塔的测量的比较需要分析的变化范围内的声称的塔足迹，在豪兰，ME的森林，土壤呼吸速率不同的2个因素之间非常差的排水和排水良好的土壤，但这些差异大多是偶然取消时，空间外推超过声称的足迹600-2100米长。虽然必须仔细考虑所有这些潜在的测量误差和采样偏差来源，但适当设计和部署的气室提供了准确测量陆地生态系统土壤呼吸的可靠手段。(C)2002爱思唯尔科技有限公司。保留所有权利。
Soil respiration is one of the largest and most important fluxes of carbon in terrestrial ecosystems. While eddy covariance methods are becoming widely used to measure nighttime total ecosystem respiration, the use of chambers placed over the soil is the most direct way of measuring respiration occurring within the soil and litter layers. Several decades of experience with chamber-based measurements have revealed most of the potential sources of error with this methodology. The objectives of this paper are to review several recently expressed concerns about uncertainties of chamber-based measurements of CO2 emissions from soils, to evaluate the direction and magnitude of these potential errors, and explain procedures that minimize these errors and biases. Disturbance of diffusion gradients cause underestimate of fluxes by less than 15% in most cases, and can be partially corrected for with curve fitting and/or can be minimized by using brief measurement periods. Underpressurization or overpressurization of the chamber caused by flow restrictions in air circulating designs can cause large errors, but can also be avoided with properly sized chamber vents and unrestricted flows. We found very small pressure differentials (+/-0.1 Pa) and modest (similar to 15%), inconsistent errors in flux estimates using our chamber design. Somewhat larger pressure differentials (+/-0.9 Pa) were observed under windy conditions, and the accuracy of chamber-based measurements made under such conditions needs more research. Spatial and temporal heterogeneity can be addressed with appropriate chamber sizes and numbers and frequency of sampling. For example, means of eight randomly chosen flux measurements from a population of 36 measurements made with 300 cm(2) diameter chambers in tropical forests and pastures were within 25% of the full population mean 98% of the time and were within 10% of the full population mean 70% of the time. Finally, comparisons of chamber-based measurements with tower-based measurements require analysis of the scale of variation within the purported tower footprint, In a forest at Howland, ME, soil respiration rates differed by a factor of 2 between very poorly drained and well drained soils, but these differences were mostly fortuitously cancelled when spatially extrapolated over purported footprints of 600-2100 m length. While all of these potential sources of measurement error and sampling biases must be carefully considered, properly designed and deployed chambers provide a reliable means of accurately measuring soil respiration in terrestrial ecosystems. (C) 2002 Elsevier Science B.V. All rights reserved.