OOS 3-7 - The soil environment: Edaphic and climatic controls over root decomposition

Monday, August 3, 2009: 3:40 PM
Brazos, Albuquerque Convention Center
Roser Matamala, Argonne National Laboratory
Background/Question/Methods Soil organic matter (SOM) represents the largest reservoir of C in terrestrial ecosystems and climate change is expected to modify the C storage potential of soils. Root decomposition might represent the primary source of SOM in most ecosystems.  While the decomposition dynamics of aboveground materials have been extensible studied, root decomposition dynamics and the transfer of root-derived C to soils is still not well understood.  Recent studies showed that fine roots may represent a source of recalcitrant plant detritus that can contribute to an increase in the SOM pool. Moisture and temperature effects on litter decomposition have been widely study in controlled environments. However, there is a need to do more field root decomposition studies and separate the effects of climate and edaphic factors on root decomposition and transfer of root derived materials to soil to better define the transfer functions used in models. In this study we established root litter manipulations enriched with 14C at four sites covering the climatic extent of the eastern deciduous forest.  These sites cover a range of temperature and precipitation from 6.2 to 12.8 C and 750 to 1400 mm respectively and soil types. Enriched fine roots (<1 mm diameter) were obtained by excavating roots of Quercus, Acer and Liriodendron trees in a 14C enriched forest experiment (EBIS). A total of 240 root-bags were installed. The bags were filled with native soil and the roots substituted by the enriched (530 to 490‰ 14C) fine roots. The C, N concentration, lignin content, root mass and the root and soil 14C signature was followed with time. Soil moisture and temperature was also measured.
Results/Conclusions

Initial soils ranged from 0.5 to 4.8%C root mass was approximately 200 gdw m-2 at all sites. The soil light soil fraction had a 30% C at all sites. The enriched roots changed the C content of the original soil less than 10%. We estimated that a 10% transfer of root litter to mineral soil should change the 14C of the mineral soil from 15 to 74% depending on the initial 14C of the soil. We expect that root decomposition and C transfer will be slower in colder and/or drier environments and the rate of root derived materials to the mineral soil will be modified by the soil environment. This will allow us to calculate a root decomposition response function to climate by soil type.

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