ORIGINAL PAPER Christian P. Andersen Æ Ivan Nikolov Æ Petia Nikolova Rainer Matyssek Æ Karl-Heinz Ha¨berle Estimating ‘‘autotrophic’’ belowground respiration in spruce and beech forests: decreases following girdling Received: 5 January 2005 / Accepted: 27 June 2005 / Published online: 1 October 2005 Ó Springer-Verlag 2005 Abstract Seasonal fluxes of CO 2 from soil and the con- tribution of autotrophic (root + mycorrhizal) to total soil respiration (SR) were estimated for a mixed stand of European beech (Fagus sylvatica) and Norway spruce (Picea abies) in Central Europe. Mature trees of each species were girdled in August 2002 to eliminate carbo- hydrate allocation to roots. SR was measured at dis- tances of 0.5, 1.0, and 1.5/2.0 m from the bole of each tree at 1–2 weeks intervals throughout the fall of 2002 and monthly during the spring and summer of 2003. The contribution of roots and mycorrhizae to total SR was estimated by the decrease in SR compared to ungirdled control trees to account for seasonal patterns evident in controls. SR decreased with soil temperature in the fall 2002 and increased again in 2003 as soil warmed. During most of the study period, SR was strongly related to soil temperature. During the dry summer of 2003, however, SR appeared to be uncoupled from temperature and was strongly related to soil water content (SWC). Mean rates of SR in beech and spruce control plots as well as root densities did not show a clear pattern with distance from the bole. SR decreased to levels below controls in beech within a few days after girdling, whereas spruce did not show a significant decrease until October 2002, 6 weeks after girdling. In both beech and spruce, decreased SR in response to girdling was greatest closest to the bole, possibly reflecting increased mycorrhizal activity close to the bole. Autotrophic respiration was estimated in beech to be as much as 50% of the total SR in the stand. The contribution of autotrophic respiration was less certain for spruce, although close to the bole, the autotrophic fraction may contribute to total SR as much as in beech. The large fraction of autotrophic respiration in total SR requires better understanding of tree level stresses that affect carbon allocation below ground. Keywords Fagus sylvatica Æ Picea abies Æ Autotrophic (root + mycorrhizal) respiration Æ Soil respiration Æ Soil temperature Æ Drought Æ CO 2 flux Æ Girdling Introduction Efflux of CO 2 from soils can account for over 70% of the respiration in some ecosystems (Raich and Schlesinger 1992). Law et al. (1999) estimated that 76% of the CO 2 lost from a ponderosa pine (Pinus ponderosa) ecosystem was derived from soil respiration (SR). Respiration from soils is comprised of both plant-derived ‘‘autotrophic’’ respiration from roots and mycorrhizae, and ‘‘hetero- trophic’’ respiration from free-living soil bacteria, fungi, and fauna (Nguyen 2003; Hanson et al. 2000; Whipps 1990). To understand the role of environmental factors on ecosystem carbon flux, it is important to clarify the seasonal course of SR, and how it is partitioned among autotrophic and heterotrophic components. Widen and Majdi (2001) found that the contribution of roots to total SR in a coniferous forest varies seasonally and was greater in the spring than the fall. Elevated temperature, limiting or supra-optimal soil water availability, nutrient limitations, and air pollution have all been shown to alter carbon allocation in trees, often resulting in a change in autotrophic, and hence total SR (Andersen 2003; Vose and Ryan 2002; Scagel and Andersen 1997; Edwards 1991). Understanding the contribution of roots/mycorrhizae (autotrophs) and decomposers (het- erotrophs), i.e., the two major biotic compartments in belowground respiration, to total SR will promote the reliability of models on forest productivity and atmo- spheric impact on ecosystem carbon flux (Vose and Ryan 2002; Epron et al. 2001; Ryan et al. 1996). Communicated by Hans Pretzsch C. P. Andersen Western Ecology Division, Office of Research and Development, United States Environmental Protection Agency, 200 SW 35th St., Corvallis, OR, 97333 USA I. Nikolov Æ P. Nikolova Æ R. Matyssek Æ K.-H. Ha¨berle (&) Ecophysiology of Plants, Technische Universita¨t Mu¨nchen, Am Hochanger 13, 85354 Freising, Germany E-mail: haeberle@wzw.tum.de Eur J Forest Res (2005) 124: 155–163 DOI 10.1007/s10342-005-0072-8