ELSEVIER Available online at www.sciencedirect.com '%' ScienceDirect Forest Ecology and Management 255 (2008) 2577-2588 Forest Ecology and Management www.elsevier.com/locate/foreco Linking tree biodiversity to belowground process in a young tropical plantation: Impacts on soil C0 2 flux Meaghan Murphy a *, Teri Balser b , Nina Buchmann c , Volker Hahn c , Catherine Potvin d ' e a Department of Geography, McGill University, 805 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6 Department of Soil Science, University of Wisconsin, 1525 Observatory Drive, Madison, WI53706, USA c Institute of Plant Sciences, ETH Zurich, LFW, C56, 8092 Zurich, Switzerland Smithsonian Tropical Research Institute, Panama, Panama "Department of Biology, McGill University, 1205 Dr. Penfield, Montreal H3A-1B1, Quebec, Canada Received 4 June 2007; received in revised form 2 January 2008; accepted 9 January 2008 Abstract This study examined the effect of tree species identity and diversity on soil respiration in a 3-year-old tropical tree biodiversity plantation in Central Panama. We hypothesized that tree pairs in mixed-species plots would have higher soil respiration rates than those in monoculture plots as a result of increased primary productivity and complementarity leading to greater root and microbial biomass and soil respiration. In addition to soil respiration, we measured potential controls including root, tree, and microbial biomass, soil moisture, surface temperature, bulk density. Over the courseof the wet season, soil respiration decreased from the June highs (7.2 ± 3.5 (Jtmol C02/(m s~ ) toalowof 2.3 ± 1.9 |xmol C02/(m s~ )in the last 2 weeks of October. The lowest rates of soil respiration were at the peak of the dry season (1.0 ± 0.7 jjtmol CO;/(m^ s -1 )). Contrary to our hypothesis, soil respiration was 19-31% higher in monoculture than in pairs and plots with higher diversity in the dry and rainy seasons. Although tree biomass was significantly higher in pairs and plots with higher diversity, there were no significant differences in either root or microbial biomass between monoculture and two-species pairs. Path analyses allow the comparison of different pathways relating soil respiration to either biotic or abiotic controls factors. The path linking crown volume to soil temperature then respiration has the highest correlation, with a value of 0.560, suggesting that canopy controls on soil climate may drive soil respiration. © 2008 Elsevier B.V. All rights reserved. Keywords: Biodiversity; Carbon cycling; Ecosystem function; Soil respiration; Tropics 1. Introduction Covering 40% of the world's land area, tropical systems house more than half of the terrestrial biomass and one third of soil carbon (C) while harboring as much as 65% of all species on earth (Buchmann et al., 2004; Lambertini, 2000). The tropics thus play a central role in the global C cycle (Knorr, 2000; Rayner et al., 2005). In particular, where there are high rates of land-use change, both biodiversity and terrestrial C reserves are decreasing. Until recently rising extinction rates and global climatic change have been studied separately but there is growing recognition of the potential feedbacks between these environmental perturbations (Chapin et al., 2000; Potvin et al., 2005; Sala et al., 2000; Thomas et al., 2004; Walther, * Corresponding author. Tel.: +1 514 398 4111; fax: +1 514 398 7437. E-mail address: mtmurphy_2000@yahoo.com (M. Murphy). 0378-1127/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2008.01.034 2003). Despite the importance of tropical systems most research integrating biodiversity and C cycling research has focused on temperate ecosystems neglecting the tropics (Raich and Schlesinger, 1992; Schimel et al., 2001). The most current figures indicate that tropical land-use change has resulted in emission of CC_ on the order of +1 to 2 Gt C year - in the last decade (Houghton, 2005) and approximately 136 ± 55 Gt C year -1 in terrestrial systems globally since the onset of the industrial revolution (Houghton, 1999). This amounts to roughly 20% of global greenhouse gas emissions (GHG). As a result of land-use changes including deforestation, biomass burning, plowing, and wetland drainage, terrestrial soils have historically released an estimated 40 Gt soil organic carbon, primarily via soil respiration (Houghton, 1999). Almost 10% of atmospheric CO2 passes through soils each year (Raich and Potter, 1995). In terrestrial systems, soil respiration, the combined CC_ efflux of microbial and roots respiration from soils, release 50-75 Gt C year - to the