CO2 flux estimates tend to overestimate ecosystem C sequestration at elevated CO2
CO2 flux estimates tend to overestimate ecosystem C sequestration at elevated CO2
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DOI：
10.1046/j.1365-2435.2000.t01-1-00456.x
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发表时间：
2000-10-01
影响因子：
5.2
通讯作者：
Leadley, PW
中科院分区：
文献类型：
--
作者：
Niklaus, PA;Stocker, R;Leadley, PW
1.瞬时叶片光合作用和基于陆地面积的净生态系统CO2交换(NEC)在CO2浓度升高时几乎普遍增加，至少在短期和强光条件下是这样。这增加了陆地生态系统为了应对二氧化碳升高而封存额外的碳的可能性，并假设这些额外的碳的一部分储存在土壤中。对生态系统碳封存进行实验量化的尝试是基于(1)生态系统二氧化碳交换测量；(2)碳同位素跟踪；和(3)直接碳储量测量。由于直接的碳储量测量对生态系统碳储量在预期范围内的增加不敏感，而且由于需要考虑新的和旧的土壤碳库，碳同位素跟踪在方法上是困难的，因此NEC测量被认为是一种更直接和公正的方法来估计在CO2.4升高时的生态系统净生产量和碳封存。在这里，我们提供了一个案例研究，在石灰质草原下的长期二氧化碳增加，我们证明了计算的碳平衡是极其敏感的系统性实验偏差在任何二氧化碳通量为基础的研究在二氧化碳浓度升高。敏感性分析表明，这些系统误差往往会导致在CO2.5升高时对生态系统碳增量的严重高估。碳同位素数据和来自同一研究的土壤碳和氮库的测量进一步证明，在二氧化碳浓度升高时，通过测量二氧化碳通量得出的碳平衡被高估了。基于这一证据，以及对二氧化碳浓度升高时碳固存的广泛关注，我们建议重新考虑在二氧化碳浓度升高的生态系统中测量NEC的适宜性，以此作为计算二氧化碳浓度升高时生态系统碳平衡的基础。
1. Instantaneous leaf photosynthesis and land area-based net ecosystem CO2 exchange (NEC) are almost universally increased at elevated CO2 concentrations, at least in the short term and under high light conditions. This raises the possibility that terrestrial ecosystems sequester extra C in response to elevated CO2, and it has been hypothesized that part of this extra C is stored in soils.2. Attempts to quantify ecosystem C sequestration experimentally are based on (i) ecosystem CO2 exchange measurements; (ii) C isotope tracking; and (iii) direct C stock measurements.3. Because direct C stock measurements are insensitive to increases in ecosystem C storage in the range expected, and C isotope tracking is methodologically difficult because of the need to account for new and old soil C pools, NEC measurements were considered to be a more direct and unbiased method to estimate net ecosystem production and C sequestration at elevated CO2.4. Here we present a case study in calcareous grassland under long-term CO2 enrichment in which we demonstrate that calculated C balances are extremely sensitive to systematic experimental biases inherent in any CO2 flux-based study at elevated CO2. A sensitivity analysis demonstrates that these systematic errors tend to result in severe overestimation of ecosystem C accretion under elevated CO2.5. Carbon isotope data and soil pool C and N measurements from the same study add to the evidence that the C balance derived from CO2 flux measurements at elevated CO2 is overestimated.6. Based on this evidence, and the wide attention given to C sequestration at elevated CO2, we suggest a critical reconsideration of the appropriateness of NEC measurement in CO2-enriched ecosystems as a basis for calculating ecosystem C balances at elevated CO2.