Age matters: consequence of ageing on the fate of soil organic matter in earthworm casts

Mariana Märten1, Dr Cornelia  Rumpel2, Prof. Martin Kaupenjohann1, Dr Pascal Jouquet2, Dr Laure Soucemarianadin3, Hanane Aroui2, Dr Tien  Tran Minh4, Dr Nicolas Bottinelli2

1Institute of Ecology, Department of Soil Science, Technische Universität, Berlin, Germany, , , 2CNRS, Sorbonne Université, IRD, Institute of Ecology and Environmental Sciences (UMR iEES-Paris), Paris, France, , , 3Laboratoire de Géologie, PSL Research University, CNRS-ENS UMR8538, Paris, France, , , 4Department of Soil sciences, Soils and Fertilizers Research Institute (SFRI), Hanoi, Vietnam, ,

Earthworms are impacting the soils’ carbon cycle and particularly organic carbon dynamics. However, their effect on the stabilisation of soil organic matter (SOM) pools over time is unknown. We hypothesised that SOM properties in casts evolve during ageing to reach similar properties than those of the surrounding topsoil. The aim of this study was to assess the fate of SOM in surface casts produced by the anecic earthworm Amynthas khamy in comparison with control aggregates (0-10 cm depth) sampled in a tropical woodland in Northern Vietnam. Casts presenting five different ages were selected according to their humidity and degradation features. We determined physicochemical properties of bulk aggregates as well as their chemical composition by analytical pyrolysis (polysaccharides, lignin and N-compounds), Rock-eval pyrolysis (hydrogen-index) and medium reflectance infrared Fourier transform spectroscopy (humic-index). Moreover, we assessed the distribution of soil organic carbon in three density fractions (light fraction: FLF-C, occluded light fraction: OLF-C and heavy fraction: HF-C). Our results indicated that properties of casts were significantly different from control aggregates regardless their age. On average, casts showed higher OC (4.8 vs. 2.6%), polysaccharides (14.7 vs. 10.6%), lignin (1 vs. 0%), hydrogen-index (180 vs. 154), FLF-C, (0.2 vs. 0.1 %), OLF-C (0.5 vs. 0.1%), HF-C (4.1 vs. 2.4%) and a lower humic-index (22.5 vs. 34.2) than control aggregates. SOM properties of casts were stable during the first month after production and afterwards changed gradually, to reach after 6 months of ageing closer properties than control aggregates. In conclusion, our results indicated that SOM in casts contained chemically and thermally labile C regardless their age and higher amounts of mineral associated SOM, suggesting a high level of protection. This study highlights the need to take into account the age of casts when assessing the impact of earthworms on carbon storage.


Biography:

Cornelia Rumpel is a research director working for the French National Research Center (CNRS) at the Institute of Ecology and Environmental Sciences Paris. She studied forestry in Germany and Scotland and received a master diploma from the Ludwig-Maximilans University at Munich, Germany in 1994. Afterwards, she worked as a research scientist at the Brandenbourg University of Technology in Cottbus, Germany, where she obtained her PhD degree in natural sciences in 1999. she studied the origin and fate of terrestrial organic matter, aiming to understand the mechanisms controlling carbon sequestration in soils. Her studies concerned various spatial and temporal scales in different environments ranging from soils and sediments in mining areas to natural as well as managed ecosystems, including those affected by fire. Her work was carried out in temperate and tropical climates and the results of her research changed of a number of paradigms. She published >160 papers, which were cited more than 8000 times. In 2016 and 2017 she was listed as a highly cited researcher. She was nominated ambassador of the Technical University of Munich and has been the chair of the STC of the 4p1000 initiative since 2018.

SOIL ORGANIC MATTER

7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia

Australia

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