EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

The promotion of decomposition of root-derived biomass by warming is depth dependent in a temperate forest 

Binyan Sun1, Cyrill Zosso1,3, Guido Wiesenberg1, Margaret Torn2, and Michael Schmidt1
Binyan Sun et al.
  • 1University of Zurich, Department of Geography, Zurich, Switzerland
  • 2Lawrence Berkeley National Laboratory, Berkeley, the United States
  • 3Agroscope, Zurich, Switzerland

IPCC climate scenarios (RCP 8.5) suggest 4°C warming until 2100, which could accelerate soil carbon loss, greenhouse gas release, and further promote global warming. Despite low carbon concentrations, subsoils (> 30 cm) store more than half of the total global soil organic carbon stocks. However, it remains largely unknown, how deep soil carbon will respond to warming and how root-derived carbon as a potential recalcitrant part of soil carbon could contribute to carbon stabilization in subsoils. After three years of root-litter incubation, we aim to i) quantify decomposition of root-litter at different depths in a +4°C warming field experiment, ii) assess whether specific plant polymers will degrade differently in warmed and control plots, iii) identify decomposition products of plant biomass remaining.

In a field experiment in a temperate forest (Blodgett Forest, Sierra Nevada, CA, USA), 13C labelled root-litter was incubated at three soil depths (10-14, 45-49, 85-89 cm) in soil cores for one and three years. For bulk soil, we measured carbon and nitrogen concentrations, and δ13C isotope composition. For individual molecular analysis, we quantified and determined the δ13C isotope composition of microbial biomarkers (PLFA), and plant-derived biomarkers (mainly suberin monomers released after base hydrolysis). We also explored suberin monomers as biomarkers for root-derived biomass (here ω-hydroxy fatty acids).

We observed the following:
i) In the plots without additional labelled root-litter, warming led to heavier suberin biomarker δ 13C values compared with control plots, especially in the topsoils. This indicates a more advanced degradation due to warming.
ii) In plots with added labelled root-litter, bulk soil δ13C values become heavier with soil depth. For individual suberin markers, we find less excess 13C with warming especially in topsoils, indicating more advanced decomposition in topsoils with warming. This advanced decomposition was not found in subsoils.

We conclude that the decomposition of root organic matter is depth dependent, and warming promotes the loss of suberin in topsoils, which contradicts the present assumption of suberin as a slowly degrading part of plant-derived organic matter.

How to cite: Sun, B., Zosso, C., Wiesenberg, G., Torn, M., and Schmidt, M.: The promotion of decomposition of root-derived biomass by warming is depth dependent in a temperate forest , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7743,, 2023.