Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, UK.
Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
Glob Chang Biol. 2017 Oct;23(10):4420-4429. doi: 10.1111/gcb.13752. Epub 2017 Jun 2.
Rising levels of atmospheric CO frequently stimulate plant inputs to soil, but the consequences of these changes for soil carbon (C) dynamics are poorly understood. Plant-derived inputs can accumulate in the soil and become part of the soil C pool ("new soil C"), or accelerate losses of pre-existing ("old") soil C. The dynamics of the new and old pools will likely differ and alter the long-term fate of soil C, but these separate pools, which can be distinguished through isotopic labeling, have not been considered in past syntheses. Using meta-analysis, we found that while elevated CO (ranging from 550 to 800 parts per million by volume) stimulates the accumulation of new soil C in the short term (<1 year), these effects do not persist in the longer term (1-4 years). Elevated CO does not affect the decomposition or the size of the old soil C pool over either temporal scale. Our results are inconsistent with predictions of conventional soil C models and suggest that elevated CO might increase turnover rates of new soil C. Because increased turnover rates of new soil C limit the potential for additional soil C sequestration, the capacity of land ecosystems to slow the rise in atmospheric CO concentrations may be smaller than previously assumed.
大气中 CO 浓度的升高通常会刺激植物向土壤输入物质，但人们对这些变化对土壤碳（C）动态的影响知之甚少。植物来源的输入物质可以在土壤中积累，并成为土壤 C 库的一部分（“新土壤 C”），或者加速已有（“旧”）土壤 C 的损失。新旧两个库的动态特征可能不同，从而改变土壤 C 的长期命运，但这些可以通过同位素示踪加以区分的独立库，在过去的综合研究中并未得到考虑。通过荟萃分析，我们发现，尽管大气 CO 浓度升高（体积分数为 550 至 800 ppm）在短期内（<1 年）会刺激新土壤 C 的积累，但这些影响在较长时间内（1-4 年）并不持久。在这两个时间尺度上，大气 CO 升高都不会影响旧土壤 C 库的分解或大小。我们的研究结果与传统土壤 C 模型的预测不一致，这表明大气 CO 升高可能会增加新土壤 C 的周转速率。由于新土壤 C 的周转速率增加限制了土壤 C 进一步固定的潜力，陆地生态系统减缓大气 CO 浓度上升的能力可能比之前认为的要小。
