The effect of boreal forest composition on soil respiration is mediated through variations in soil temperature and C quality Jérôme Laganière a, b, c, * , David Paré a , Yves Bergeron b, c , Han Y.H. Chen d a Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre,1055 du P.E.P.S., P.O. Box 10380, Stn. Sainte-Foy, Québec, QC, Canada G1V 4C7 b Centre d’étude de la forêt, Université du Québec à Montréal, C.P. 8888, Succ. Centre-ville, Montréal, QC, Canada H3C 3P8 c NSERC-UQAT-UQAM Industrial Chair in Sustainable Forest Management, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l’Université, Rouyn-Noranda, QC, Canada J9X 4E5 d Faculty of Natural Resources Management, Lakehead University, 955 Oliver Road, Thunder Bay, ON, Canada P7B 5E1 article info Article history: Received 25 October 2011 Received in revised form 24 April 2012 Accepted 27 April 2012 Available online 12 May 2012 Keywords: Boreal forest Black spruce Trembling aspen Mixedwood Autotrophic and heterotrophic respiration Decomposition Litter quality Soil temperature Climate warming abstract Getting a better understanding of CO 2 efflux from forest soils is critical for increasing our comprehension of the global C cycle. We examined the influence of two common boreal tree species, either in pure stands (BS ¼ black spruce; TA ¼ trembling aspen) or in mixtures (MW ¼ BS þ TA mixedwood), on total (R S ), heterotrophic (R H ) and autotrophic soil respiration (R A ) and their relationship with soil temperature and moisture, distance to the nearest tree, labile and total soil organic C (SOC), and root content. Stand- specific soil respirationetemperature models were developed to estimate annual soil CO 2 efflux. Soil temperature was the main factor explaining R S and its components, followed by labile and total SOC. These three variables were significantly affected by forest composition, while no difference in soil moisture, distance to the nearest tree and root content was observed between stand types. A reciprocal forest floor transplant experiment showed that the influence of stand types on mineral soil temperature was due to a difference in light penetration rather than forest floor characteristics. Annual R S and R H were significantly greater in MW and TA than in BS, whereas annual R A was greater in BS and MW than in TA. Temperature sensitivity (Q 10 ) of both R S and R H was significantly higher in BS than in MW and TA, suggesting that CO 2 efflux from BS soils could be increased more under climate warming than that from the other stand types. Our results show evidence that boreal forest composition affects soil CO 2 efflux and that litter quality is not the only factor explaining the differences between stand types. The influence of forest composition on soil CO 2 efflux would be mediated through effects on soil temperature as well as on factors affecting the accumulation and the quality of SOC. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Boreal forest holds a major part of the global terrestrial carbon (C) and, unlike warmer ecosystems, boreal soils in general contain a much greater share of it than the vegetation (Lal, 2005). Soil respiration (R S ) is a major contributor to atmospheric CO 2 ; thus, it is important to quantify CO 2 efflux from forest soils and to understand how it is affected by forest management and climate change (Lorenz and Lal, 2010). Climate change can have direct effects on R S by bringing changes to the soil temperature regime and by affecting the importance and duration of the period during which the soil is above the freezing point (IPCC, 2007; Mellander et al., 2007). It can also have indirect effects by bringing changes to disturbance regimes that may have an impact on vegetation composition (Bond-Lamberty et al., 2007; Soja et al., 2007). R S is the sum of autotrophic respiration (R A ) produced by living roots and their associated rhizosphere (i.e. mycorrhizae and rhizosphere bacteria) and heterotrophic respiration (R H ) generated by microbial decomposition of soil organic matter. Because R A and R H are mediated by different organisms and involve different C sources and qualities as well as different processes (Kuzyakov, 2006; Subke et al., 2006; Epron, 2009), their response to changes in environmental conditions may differ. However, the contrasting results reported in a number of publications illustrate the lack of a mechanistic understanding of this process (Lin et al., 1999; Lavigne et al., 2003; Subke et al., 2006; Zhou et al., 2007; Schindlbacher et al., 2009; Wei et al., 2010). * Corresponding author. Present address. Department of Earth Sciences, Memo- rial University of Newfoundland, 300, Prince Philip Drive, St. John’s, NL, Canada A1B 3X5. Tel.: þ1 709 864 3454; fax: þ1 709 864 7437. E-mail address: jerome.laganiere@hotmail.com (J. Laganière). 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.2012.04.024 Soil Biology & Biochemistry 53 (2012) 18e27