Contribution of aboveground litter, belowground litter, and rhizosphere respiration to total soil CO2 efflux in an old growth coniferous forest

Abstract

In an old growth coniferous forest located in the central Cascade Mountains, Oregon, we added or removed aboveground litter and terminated live root activity by trenching to determine sources of soil respiration. Annual soil efflux from control plots ranged from 727 g C m À2 year À1 in 2002 to 841 g C m À2 year À1 in 2003. We used aboveground litter inputs (149.6 g C m À2 year À1 ) and differences in soil CO 2 effluxes among treatment plots to calculate contributions to total soil efflux by roots and associated rhizosphere organisms and by heterotrophic decomposition of organic matter derived from aboveground and belowground litter. On average, root and rhizospheric respiration (R r ) contributed 23%, aboveground litter decomposition contributed 19%, and belowground litter decomposition contributed 58% to total soil CO 2 efflux, respectively. These values fall within the range of values reported elsewhere, although our estimate of belowground litter contribution is higher than many published estimates, which we argue is a reflection of the high degree of mycorrhizal association and low nutrient status of this ecosystem. Additionally, we found that measured fluxes from plots with doubled needle litter led to an additional 186 g C m À2 year À1 beyond that expected based on the amount of additional carbon added; this represents a priming effect of 187%, or a 34% increase in the total carbon flux from the plots. This finding has strong implications for soil C storage, showing that it is inaccurate to assume that increases in net primary productivity will translate simply and directly into additional belowground storage.

Alterations in forest detritus inputs influence soil carbon concentration and soil respiration in a Central-European deciduous forest

“…Moreover, the annual mean temperature at Síkfőkút is higher than that at the US DIRT sites. Even with significantly lower precipitation, litter fall at Síkfőkút (2754 kg C ha -1 yr -1 ) is 31% greater than at Bousson (2100 kg C ha -1 yr -1 , (Bowden et al, 1993)), 459% greater than at Andrews (600 kg C ha -1 yr 1 , (Sulzman et al, 2005)) and 26% greater than at Harvard Forest (2190 kg C ha -1 yr -1 , (Savage and Davidson, 2001)). These conditions, with lower precipitation and higher temperatures, create conditions that will hinder decomposition, and thus reduce soil CO 2 production.…”

“…A priming effect (Kuzyakov, 2010) was observed at the at the H.J. Andrews DIRT site (Sulzman et al, 2005;Crow et al, 2009) and may have reduced SOC early in the experiment; priming in concert with elevated rates of soil respiration would explain the lack of SOC increase with long-term doubled litter inputs. At Síkfőkút, soil respiration was not increased in DL or DW plots, but the upper soil layer of DL treatments showed significantly higher carbon concentrations than CO treatment.…”

“…These differences between the American and Hungarian DIRT sites may be explained by climate factors that control decomposition. First, annual precipitation at Síkfőkút is much lower than that at the US DIRT sites (Andrews: 2370 mm yr -1 ; Harvard: 1120 mm yr -1 ; Bousson: 1050 mm yr -1 ), and rainfall is more seasonally distributed (Sulzman et al, 2005;Crow et al, 2009). Moreover, the annual mean temperature at Síkfőkút is higher than that at the US DIRT sites.…”

“…For example, after five years of doubled litter additions at the H.J. Andrews DIRT site (Oregon, USA) soil C concentrations were not increased (Crow et al, 2009), and even after two decades of doubled litter inputs, the Harvard Forest and Bousson sites did not display increases in soil C. At all of these sites, soil CO 2 production is elevated in response to litter additions (Bowden et al, 1993;Sulzman et al, 2005; unpublished data) thus reducing the amount of organic matter that might enter the soil C pool. A priming effect (Kuzyakov, 2010) was observed at the at the H.J.…”

“…In the No Roots plots (NR), plots were trenched thus incising the living roots, thereby removing inputs from root litter and root exudates. In the No Litter plots (NL), annual aboveground litter (leaves, small twigs) was excluded, in the No Inputs (NI) treatment, both aboveground litter and roots were excluded (Nadelhoffer et al, 2004;Sulzman et al, 2005;Fekete et al, 2012) (Table 1). The surface solar radiation was approximately the same in all treatments.…”