ARTICLE Winter effect on soil microorganisms under different tillage and phosphorus management practices in eastern Canada Yichao Shi, Roger Lalande, Chantal Hamel, and Noura Ziadi Abstract: Determining how soil microorganisms respond to crop management systems during winter could further our understanding of soil phosphorus (P) transformations. This study assessed the effects of tillage (moldboard plowing or no-till) and P fertilization (0, 17.5, or 35 kg P·ha −1 ) on soil microbial biomass, enzymatic activity, and microbial community structure in winter, in a long-term (18 years) corn (Zea mays L.) and soybean (Glycine max L.) rotation established in 1992 in the province of Quebec, Canada. Soil samples were collected at 2 depths (0–10 and 10–20 cm) in February 2010 and 2011 after the soybean and the corn growing seasons, respectively. Winter conditions increased the amounts of soil microbial biomasses but reduced the overall enzymatic activity of the soil, as compared with fall levels after corn. P fertilization had a quadratic effect on the amounts of total, bacterial, arbuscular mycorrhizal fungi phospholipid fatty acid markers after corn but not after soybean. The soil microbial community following the soybean and the corn crops in winter had a different structure. These findings suggest that winter conditions and crop-year could be important factors affecting the characteristics of the soil microbial community under different tillage and mineral P fertilization. Key words: winter, soil microbial biomass, community structure, tillage, P fertilization. Résumé : La réponse des micro-organismes terricoles aux systèmes de gestion des cultures pendant l’hiver permettrait de parfaire nos connaissances concernant les transformations subies par le phosphore (P) du sol. La présente étude a évalué l’impact du travail du sol (labour en planche ou sans-labour) et de la fertilisation au P (0, 17,5 ou 35 kg P·ha –1 ) sur la biomasse microbienne, son activité enzymatique et la structure de sa communauté microbienne d’un sol hivernal, dans le contexte d’une rotation a ` long terme (18 ans) de maïs (Zea mays L.) et de soya (Glycine max L.) mise en place en 1992 dans la province de Québec, Canada. On a prélevé des échantillons de sol a ` 2 profondeurs (0–10 et 10–20 cm) en février 2010 et 2011 après la saison du soya et du maïs, respectivement. Les conditions hivernales ont haussé la quantité de biomasse microbienne dans le sol, mais en ont diminué l’activité enzymatique générale, comparativement aux niveaux d’automne après la saison du maïs. La fertili- sation au phosphore a eu un impact d’ordre quadratique sur les quantités de marqueurs d’acides gras phospholipidiques totaux, bactériens et de champignons mycorhiziens arbusculaires après la saison du maïs mais pas après celle du soya. La communauté bactérienne du sol suivant les récoltes de soya et de maïs présentait une structure différente. Ces constata- tions portent a ` croire que les conditions hivernales et la rotation des cultures seraient des facteurs importants influençant les propriétés de la communauté microbienne du sol en conjonction avec les différents modes de labour et la fertilisation au P minéral. [Traduit par la Rédaction] Mots-clés : hiver, biomasse microbienne du sol, structure microbienne, travail du sol, fertilisation au P. Introduction The soil microbiota is a major driver of soil formation, nutrient cycling, and organic matter turnover (Sparling 1985; Jenkinson 1988) and is essential for long-term sustainability of agricultural systems (Wardle et al. 1999). Soil microorganisms respond to vary- ing climatic conditions, soil moisture contents, porosities, and particularly, soil organic matter levels, all of which are inter- related and influenced by soil management (Bardgett et al. 1999; Spedding et al. 2004; Hamel et al. 2006). Strong seasonal dynamics shape the ecosystems in cool temperate and high-latitude regions, where growing seasons are short, winters are cold, and soils re- main frozen for months, limiting nutrient decomposition and turnover (Giblin et al. 1991; Jonasson 1992). However, many eco- logical processes can persist owing to the presence of liquid water in the soil at temperatures near or below freezing (Brooks et al. 2011). In the winter, an insulating layer of snow can keep soil temper- atures warm enough to support a wide range of biotic activities, such as microbial respiration (Campbell et al. 2005; Monson et al. 2006). If the temperature drops below 0 °C, shifts in microbial substrate use occur (Schimel and Mikan 2005) and may be accom- panied by shifts in microbial communities and soil respiration (Lipson et al. 2002; Schmidt and Lipson 2004; Sjursen et al. 2005; Haei et al. 2011). Temperature changes could also induce very specific changes in the composition of soil microbial membranes owing to the phenotypic plasticity of microorganisms (Russell and Fukunaga 1990). All this evidence supports the idea that winter processes can contribute substantially to annual nutrient budgets and should be included in ecological studies (van Bochove et al. 1996). The studies of soil microorganisms in winter could lead to a better understanding of how the soil microbial community and activity respond to soil management systems. Received 10 December 2014. Revision received 19 January 2015. Accepted 31 January 2015. Y. Shi, R. Lalande, and N. Ziadi. Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Boulevard, Québec, QC G1V 2J3, Canada. C. Hamel. Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada, 1 Airport Road, Swift Current, SK S9H 3X2, Canada. Corresponding author: Chantal Hamel (e-mail: chantal.hamel@agr.gc.ca). Pagination not final (cite DOI) / Pagination provisoire (citer le DOI) 1 Can. J. Microbiol. 61: 1–12 (2015) dx.doi.org/10.1139/cjm-2014-0821 Published at www.nrcresearchpress.com/cjm on 11 February 2015. Can. J. Microbiol. Downloaded from www.nrcresearchpress.com by Agriculture and Agri-food Canada on 03/18/15 For personal use only.