Tracing carbon flow through a sugar maple forest and its soil components: role of invasive earthworms

Aims We conducted a suite of tracer studies using the stable isotope C-13 to follow and quantify the flow of carbon from leaf litter and roots into soil components including aggregates and biota with and without invasive earthworms. Methods Ten-year-old saplings of sugar maple growing in the understory of a thinned northern hardwood forest were labeled with (CO2)-C-13. The C-13 labeled leaf litter was applied to forest plots with and without invasive earthworms (Lumbricidae) and traced for three years. We also traced the label from the trees through the roots and into soil components in the labeling chambers. Labeled fine roots and stem wood were incubated in a forest and the label was quantified over six years of decomposition. Results We were able to detect the litter tracer to 10 cm soil depth in plots without earthworms and to 20 cm with earthworms present, and earthworms promoted C incorporation into soil aggregates. The soil food web was much more enriched in the label from roots than from aboveground plant litter.. Rapid fine root decay was observed (k = 0.9 yr(-1)), and although labelled wood was almost completely decayed, little C-13 was recovered in soil (0.33%). Conclusion The approach was successful for quantifying transport and fate of tree carbon in forest soils and could be enhanced with careful quantification of gross assimilation.

Automated summary

The study successfully tracked and quantified the transport and fate of tree carbon in forest soils, finding that earthworms promoted C incorporation into soil aggregates and the soil food web was more enriched in label from roots than aboveground plant litter. Rapid fine root decay was observed (k = 0.9 yr(-1)), and although labeled wood was almost completely decayed, little C-13 was recovered in soil (0.33%).