Linking microbial community to soil water-stable aggregation during crop residue decomposition C. Le Guillou a, b, c , D.A. Angers d , P.A. Maron e , P. Leterme a, b, c , S. Menasseri-Aubry a, b, c, * a INRA, UMR 1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France b Agrocampus Ouest, UMR 1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France c Université européenne de Bretagne, France d Agriculture et Agroalimentaire Canada, Centre de Recherche sur les Sols et les Grandes Cultures, 2560 Boulevard Hochelaga, Québec, Québec, Canada G1V 2J3 e INRA, UMR 1229 Microbiologie du Sol et de l’Environnement, F-21065 Dijon, France article info Article history: Received 21 December 2011 Received in revised form 7 March 2012 Accepted 9 March 2012 Available online 29 March 2012 Keywords: Bacteria Fungi Organic matter quality N Decomposition Aggregate stability abstract The dynamics of soil water-stable aggregation (WSA) following organic matter (OM) addition are controlled by microbial activity, which in turn is influenced by carbon substrate quality and mineral N availability. However, the role of microbial communities in determining WSA at different stages of OM decomposition remains largely unknown. This study aimed at evaluating the role of microbial communities in WSA during OM decomposition as affected by mineral N. In a 35-day incubation experiment, we studied the decomposition of two high-C/N crop residues (miscanthus, C/N ¼ 311.3; and wheat, C/N ¼ 125.6) applied at 4 g C kg 1 dry soil with or without mineral N addition (120 mg N kg 1 dry soil). Microbial characteristics were measured at day 0, 7, and 35 of the experiment, and related to previous results of WSA. Early increase in WSA (at 7 days) was related to an overall increase of the microbial biomass (MBC) with wheat residues showing higher values in MBC and WSA than miscanthus. In the intermediate stage of decomposition (from day 7 to 35), the dynamics of WSA were more asso- ciated with the dynamics of microbial polysaccharides and greatly influenced by mineral N addition. Mineral N addition resulted in a decrease or leveling off of WSA whereas it increased in its absence. We suggest that opportunistic bacterial populations stimulated by N addition may have consumed binding agents which decreased WSA or prevented its increase. To the contrary, microbial polysaccharide production was high when no mineral N was added which led to the higher WSA in the late stage of decomposition in this treatment. The late stage of decomposition was associated with a particular fungal community also influenced by the mineral N treatment. We suggest that WSA dynamics in the late stage of decomposition can be considered as a « narrow process 3 where the structure of the microbial community plays a greater role than during the initial stages. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Water-stable aggregation (WSA) is an important characteristic of soil functioning (Carter, 2002). It is a determinant factor of soil susceptibility to erosion (Le Bissonnais, 1996), soil’s ability to sustain plant germination and early growth (Angers and Caron, 1998) and is a mechanism of organic matter (OM) protection in soils (Balesdent et al., 2000). Among factors affecting WSA, soil organic matter is a major one (Tisdall and Oades, 1982) that can be managed through agricultural practices such as returning crop residue to soil (Lal, 2009). The effects of organic inputs on WSA are generally related to their decomposability (Abiven et al., 2009) such that easily decomposable residues have intense but transient effects on WSA whilst less decomposable residues have smaller but longer lasting effects on WSA. The role of microorganisms in WSA following crop residue addition has long been demonstrated (Martin and Waksman, 1940; Angers and Chenu, 1998). Addition of crop residue rapidly stimu- lates microbial growth and activity which generate transient binding agents mostly involving polysaccharides in the first few weeks (Tisdall and Oades, 1982). Fungi have often been shown to have a dominant role in WSA (e.g. Metzger et al., 1987; Denef et al., 2001) by producing polysaccharides (Chenu, 1989) but also * Corresponding author. INRA, UMR Sol Agro et hydrosystème Spatialisation, 65 Route de Saint-Brieuc, CS 84215-35042 Rennes Cedex, France. Tel.: þ33 2 23 48 54 73; fax: þ33 2 23 48 54 80. E-mail address: Safya.Menasseri@agrocampus-ouest.fr (S. Menasseri-Aubry). Contents lists available at SciVerse ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2012.03.009 Soil Biology & Biochemistry 50 (2012) 126e133