Soil Moisture Mediates the Effects of Heating, Roots, and Depth on Root Litter Decomposition

In moisture-limited ecosystems, warming may retard, rather than stimulate, microbial decomposition of soil organic carbon.

The Science

To explore the effects of soil depth, warming (+4°C), and roots on the breakdown and decomposition of plant inputs, the research team from Lawrence Berkeley National Laboratory (LBNL) followed the fate of isotopically labeled root litter in a Mediterranean grassland ecosystem. The team (1) manipulated soil temperature, presence of plants, and depth of inputs; (2) monitored resulting soil temperature and moisture; and (3) measured litter remaining after one and two growing seasons.

The Impact

In this Mediterranean grassland, the season, depth, heating, and rhizosphere all influenced soil moisture, in turn, overwhelmingly explaining root litter decomposition. In moisture-limited ecosystems such as this one, warming may retard, rather than stimulate, microbial decomposition of soil organic carbon.

Summary

In a Northern California grassland, plots were subjected to three environmental treatments (heating, control, and plant removal), with 13C-labeled root litter buried in either the A horizon (shallow) or B horizon (deep). At the end of each growing season, the 13C remaining in the soil was recovered. In the first growing season, decomposition occurred faster in the B than in the A horizon, the latter having greater moisture limitation. Subsequently, there was almost no further decomposition in the B horizon. After two growing seasons, less than 20% of the added root litter carbon remained in the A or B horizons of all environmental treatments. Heating did not stimulate decomposition, likely because it exacerbated the moisture limitation. However, while plots without plants dried down more slowly than plots with plants, their decomposition rate was not significantly greater, possibly due to the lack of priming by root exudates.

Principal Investigator

Margaret Torn
Lawrence Berkeley National Laboratory, University of California, Berkeley
mstorn@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research was supported by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under Award Number DE-AC02-05CH11231, and the National Natural Science Foundation of China (#31622013).

References

Castanha, C., B. Zhu, C. E. H. Pries, and K. Georgiou, et al. "The effects of heating, rhizosphere, and depth on root litter decomposition are mediated by soil moisture". Biogeochemistry 137 (1–2), 267–279  (2018). http://dx.doi.org/10.1007/s10533-017-0418-6.