1. Fine roots are a key component of carbon and nutrient dynamics in forest ecosystems. Rising atmospheric [CO₂] (eCO₂) is likely to alter the production and activity of fine roots, with important consequences for forest carbon storage. Yet empirical evidence of the role of eCO₂ in driving root dynamics is limited, particularly for grassy woodlands, an ecosystem type of global importance.
2. We sampled fine roots across seasons over a 2‐year period to examine the effects of eCO₂ on their biomass, production, turnover and functional traits in a native mature grassy Eucalyptus woodland in eastern Australia (EucFACE).
3. Fine root biomass, production and turnover varied greatly through time, increasing as soil water content declined. Despite a lack of consistent effects of eCO₂ on fine root biomass, production or turnover across the 2‐year sampling period, we found enhanced production pulses under eCO₂ between 10‐ and 30‐cm soil depth. In addition, eCO₂ led to greater carbon and phosphorus concentrations in fine roots and increased root diameter, but no detectable effects on other morphological traits.
4. Synthesis. We found minor quantitative effects of eCO₂ on fine root biomass dynamics that were largely driven by temporal variations in soil water availability. Our results suggest that in this mature grassy woodland, and perhaps also in other similar forested ecosystem types, eCO₂ effects are small and transient. This also implies a limited ability of these systems to mitigate climate change through below‐ground mechanisms.

中文翻译：

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在大气CO2浓度升高的情况下，水分的利用可驱动桉树林地的优良根系动态

1. 细根是森林生态系统中碳和养分动态的关键组成部分。大气中[CO ₂ ]（eCO ₂）的升高可能会改变细根的产生和活性，对森林碳储量产生重要影响。然而，有关eCO ₂在驱动根系动态中作用的经验证据有限，尤其是对于草木林地而言，这是一种具有全球重要性的生态系统类型。
2. 我们在2年的整个季节中取样了细根，以研究eCO ₂对澳大利亚东部天然成熟的草木桉树林地（EucFACE）的生物量，产量，周转率和功能性状的影响。
3. 细根生物量，产量和周转量随时间变化很大，随着土壤含水量的减少而增加。尽管在整个2年的采样期内，eCO ₂对细根生物量，产量或周转率缺乏一致的影响，但我们发现在eCO ₂下10到30厘米土壤深度下的生产脉动增强。此外，eCO ₂导致细根中的碳和磷浓度更高，并且根直径增加，但对其他形态性状没有可检测的影响。
4. 综合。我们发现eCO ₂对细根生物量动态的定量影响较小，这在很大程度上是由土壤水分有效性的时间变化驱动的。我们的结果表明，在这个成熟的草木林地中，以及在其他类似的森林生态系统类型中，eCO _2的影响很小且是短暂的。这也意味着这些系统通过地下机制缓解气候变化的能力有限。