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 in low-nutrient forested ecosystems is limited, particularly for grassy woodlands, an ecosystem type of global importance.

We sampled fine roots across seasons over a two-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).

Fine root biomass, production and turnover varied greatly through time, increasing as soil water content declined. Despite a lack of persistent effects of eCO₂ on fine root biomass, production or turnover across the two-year sampling period, we found enhanced production pulses under eCO₂ between 10-30 cm soil depth. These eCO₂-driven production pulses were associated with large changes in abiotic conditions. 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.

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 characterized by low phosphorus content in the soil, eCO₂ effects are small and transient. This suggests limited belowground fine root productivity responses to rising atmospheric CO₂ concentrations and, thus, perhaps also a limited ability of these systems to mitigate climate change through belowground mechanisms.

The methods used to collect the data are detailed in the article. Metadata and units for each variable are given in the dataset itself. 

Any missing values are time periods data was not collected.