Mapping field-scale spatial patterns of size and activity of the denitrifier community Laurent Philippot, 1,2 * Jiri C ˇ uhel, 3 Nicolas P.A. Saby, 4 Dominique Chèneby, 1,2 Alicia Chron ˇ áková, 3 David Bru, 1,2 Dominique Arrouays, 4 Fabrice Martin-Laurent 1,2 and Miloslav Šimek 3 1 INRA, UMR 1229, F-21000 Dijon, France. 2 University of Burgundy, UMR 1229, F-21000 Dijon, France. 3 Biology Centre, Institute of Soil Biology and University of South Bohemia – Faculty of Science, Na Sádkách 7, 370 05 C ˇ eské Budìjovice, Czech Republic. 4 INRA, Centre de Recherche d’Orléans, US 1106, INFOSOL Unit, BP 20619 Ardon – 45166, Olivet Cedex, France. Summary There is ample evidence that microbial processes can exhibit large variations in activity on a field scale. However, very little is known about the spatial distri- bution of the microbial communities mediating these processes. Here we used geostatistical modelling to explore spatial patterns of size and activity of the denitrifying community, a functional guild involved in N-cycling, in a grassland field subjected to different cattle grazing regimes. We observed a non-random distribution pattern of the size of the denitrifier com- munity estimated by quantification of the denitrifica- tion genes copy numbers with a macro-scale spatial dependence (6–16 m) and mapped the distribution of this functional guild in the field. The spatial patterns of soil properties, which were strongly affected by presence of cattle, imposed significant control on potential denitrification activity, potential N 2O produc- tion and relative abundance of some denitrification genes but not on the size of the denitrifier community. Absolute abundance of most denitrification genes was not correlated with the distribution patterns of potential denitrification activity or potential N2O pro- duction. However, the relative abundance of bacteria possessing the nosZ gene encoding the N2O reduc- tase in the total bacterial community was a strong predictor of the N2O/(N2 + N2O) ratio, which provides evidence for a relationship between bacterial commu- nity composition based on the relative abundance of denitrifiers in the total bacterial community and eco- system processes. More generally, the presented geostatistical approach allows integrated mapping of microbial communities, and hence can facilitate our understanding of relationships between the ecology of microbial communities and microbial processes along environmental gradients. Introduction Although most microbial processes are known to exhibit large variations at a field scale with areas of high activity (Parkin, 1993), it is not clear whether the microbial com- munities mediating these processes also exhibit spatial distribution patterns. Detecting patterns in microbial com- munity distribution would not only provide an insight into the underlying driving mechanisms but also facilitate our understanding of the relationships between the ecology of microbial communities and the microbial processes measured. Investigation of the distribution of microorganisms in space is recent (Martiny et al., 2006), even though micro- organisms are essential actors in ecosystem functioning. Therefore, little is known regarding the spatial organiza- tion and spatial dependence of microorganisms (Grund- mann and Debouzie, 2000; Nunan et al., 2002; Ritz et al., 2004; Fierer and Jackson, 2006). Thus, analysis of DNA from soil samples collected at a variety of separation distances ranging from 2.5 cm to 11 m revealed spatial autocorrelation of the bacterial community structure at scales ranging from 30 cm to more than 6 m, depending on the sampling extent considered (Franklin and Mills, 2003). Similarly, Ritz and colleagues (2004) reported metre scale spatial dependence of microbial properties in upland grassland. At a larger scale, analysis of bacterial community structure across North and South America by Fierer and Jackson (2006) revealed that it was largely independent of geographic distance and was controlled primarily by edaphic factors such as pH. Most previous studies investigating the spatial distribution of microor- ganisms have focused on the total bacterial community and functional communities have been neglected. However, McGill and colleagues (2006) proposed that a functional-traits-on gradients approach would be more Received 20 February, 2008; accepted 16 December, 2008. *For correspondence. E-mail Laurent.Philippot@dijon.inra.fr; Tel. (+33) 3 80 69 33 46; Fax (+33) 3 80 69 32 24. Environmental Microbiology (2009) 11(6), 1518–1526 doi:10.1111/j.1462-2920.2009.01879.x Journal compilation © 2009 Society for Applied Microbiology and Blackwell Publishing Ltd No claim to original French government works