Paper Reviewed

Sánchez-de León, Y., Wise, D.H., Lugo-Pérez, J., Norby, R.J., James, S.W. and Gonzalez-Meler, M.A. 2018. Endogeic earthwork densities increase in response to higher fine-root production in a forest exposed to elevated CO 2 . Soil Biology and Biochemistry 122: 31-38.

Noting that very few studies have examined the impact of elevated CO 2 concentrations on belowground macrobiota, Sánchez-de León et al. (2018) set out to investigate "the response of earthworms to increased leaf and root-litter inputs caused by increased atmospheric CO 2 exposure."

The work was conducted at the Oak Ridge National Environmental Research Park in Roane County, Tennessee, USA, in a sweetgum (Liquidambar styraciflua) plantation. Free-air CO 2 Enrichment (FACE) plots were established in the plantation in 1998, where for the following twelve growing seasons the CO 2 concentration was enriched to an average 547 ppm during daylight hours. Ambient CO 2 plots, in contrast, averaged 395 ppm.

Results of the analysis showed that both the number of earthworms and overall earthworm biomass was higher in the elevated CO 2 treatment than in the ambient CO 2 treatment (see Figure 1). It was also determined that the increase in the number of earthworms was "associated with higher net primary productivity" of the sweetgum trees, which responded positively to atmospheric CO 2 enrichment. In short, elevated CO 2 set in motion a process where it increased the growth of the sweetgum trees, particularly fine-root and leaf litter production, which stimulated belowground carbon and helped enhance the growth and activity of earthworms, which growth and activity further helped to promote and stabilize soil carbon via the formation of soil aggregates. Consequently, Sánchez-de León et al. say their results "suggest that earthworms can have a significant influence in promoting the carbon accrual observed at the ORNL FACE site through promoting physical protection in soil aggregates."

Thus we see yet another example how CO 2 emissions produced by the burning of fossil fuels are enhancing the natural world, in this case both plants and animals in a synergistic manner. And that is great news for the future.



Figure 1. Mean (± SE) earthworm numerical density (Panel A) and biomass (fresh weight; Panel B) in elevated and ambient CO 2 treatments across time. Source: Sánchez-de León et al. (2018).