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Soil Moisture Mediates the Effects of Heating, Roots, and Depth on Root Litter Decomposition
Published: December 27, 2017
Posted: June 22, 2018

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.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Margaret Torn
University of California, Berkeley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
mstorn@lbl.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).

Publications
Castanha, C., B. Zhu, C.E.H. Pries, K. Georgiou, and M.S. Torn. “The effects of heating, rhizosphere, and depth on root litter decomposition are mediated by soil moisture.” Biogeochemistry 137(1–2), 267–279 (2018). [DOI:10.1007/s10533-017-0418-6]

Topic Areas:

  • Research Area: Terrestrial Ecosystem Science

Division: SC-33.1 Earth and Environmental Sciences Division, BER

 

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