Mrs Charlotte Vedère2, Dr Laure Vieublé1, Mrs Valérie Pouteau2, Dr Cyril Girardin2, Prof. Claire Chenu1
1Ecosys – Agroparistech, Thiverval Grignon, France, 2Ecosys – INRA, Thiverval Grignon, France
Soils are spatially heterogeneous environments at different scales and this heterogeneity still very little taken-into-account in the study and prediction of soil organic matter dynamics. The incorporation of plant residues in soils leads to hot spots of microbial activity and biogeochemical cycling at the fine scale.
The objectives of this study were to determine: (i) the spatio-temporal evolution of microorganisms and their activity after the incorporation of fresh plant residues in soils, and (ii) how this evolution was affected by soil moisture, given the importance of soil moisture in regulating decomposition and (iii) what were the specific contributions of bacteria and fungi.
The experimental set-up was based on incubated soil microcosms with addition of a central layer of 13C labelled maize residues at different soil moistures (pF 1.5, 2.5 and 3.5). Total and residue derived 13C mineralization were monitored; the microcosms were destructively sampled at four dates, fractionated into soil layers with increasing distance from the residue layer and we quantified residue-derived carbon in these layers and determined microbial community abundance, structure and contribution to the biodegradation of residues with PLFA and SIP-PLFA.
We observed that the mineralization of the residues decreased with soil moisture but that the extent of the detritusphere (defined the zone in which residue derived C was present and microorganisms had been stimulated) increased with soil moisture. Soil moisture also affected the microbial community structure, and in particular the fungal and bacterial contributions to decomposition.
Professor of Soil Science at AgroParisTech