Feedback interactions between needle litter decomposition and rhizosphere activity

Abstract

The aim of our study was to identify interactions between the decomposition of aboveground litter and rhizosphere activity. The experimental approach combined the placement of labelled litter (delta13C=-37.9 per thousand ) with forest girdling in a 35-year-old Norway spruce stand, resulting in four different treatment combinations: GL (girdled, litter), GNL (girdled, no litter), NGL (not girdled, litter), and NGNL (not girdled, no litter). Monthly sampling of soil CO2 efflux and delta13C of soil respired CO2 between May and October 2002 allowed the partitioning of the flux into that derived from the labelled litter, and that derived from native soil organic matter and roots. The effect of forest girdling on soil CO2 efflux was detectable from June (girdling took place in April), and resulted in GNL fluxes to be about 50% of NGNL fluxes by late August. The presence of litter resulted in significantly increased fluxes for the first 2 months of the experiment, with significantly greater litter derived fluxes from non-girdled plots and a significant interaction between girdling and litter treatments over the same period. For NGL collars, the additional efflux was found to originate only in part from litter decomposition, but also from the decay of native soil organic matter. In GL collars, this priming effect was not significant, indicating an active role of the rhizosphere in soil priming. The results therefore indicate mutual positive feedbacks between litter decomposition and rhizosphere activity. Soil biological analysis (microbial and fungal biomass) of the organic layers indicated greatest activity below NGL collars, and we suppose that this increase indicates the mechanism of mutual positive feedback between rhizosphere activity and litter decomposition. However, elimination of fresh C input from both above- and belowground (GNL) also resulted in greater fungal abundance than for the NGNL treatment, indicating likely changes in fungal community structure (i.e. a shift from symbiotic to saprotrophic species abundance).

Towards a representation of priming on soil carbon decomposition in the global land biosphere model ORCHIDEE (version 1.9.5.2)

“…Priming is almost ubiquitously observed in ecosystem studies where organic matter inputs are altered in laboratory incubations (reviewed by Blagodatskaya and Kuzyakov, 2008) or directly on the field (Boone et al, 1998;Borken and Muhs, 2002;Chemidlin-Prévost-Bouré et al, 2010;Subke et al, 2004;Sulzman et al, 2005;Xiao et al, 2015). Priming can occasionally be negative but most commonly has a stimulative effect on the decomposition of organic matter that decomposes.…”

“…A second evaluation of the ORCHIDEE-PRIM model was performed at ecosystem scale against observations of four litter manipulation experiments (Boone et al, 1998;Chemidlin-Prévost-Bouré et al, 2010;Subke et al, 2004;Sulzman et al, 2005) and one compost amendment experiment (Borken and Muhs, 2002). In the litter experiments, two treatments and a control are generally performed.…”

Soil carbon dioxide efflux in pure and mixed stands of oak and beech

“…Among others, Boone et al [6] reported a higher Q 10 for rhizosphere respiration (4.6) than for soil respiration excluding roots (2.5); however, the higher Q 10 for rhizosphere respiration most likely results from the multiplicative effects of several processes: enzyme activity, root growth and photosynthate production. On another hand, Subke et al [42] showed that rhizosphere activity increases litter respiration, possibly by simulating microbial activity through the addition of easily accessible carbon (soil priming).…”

Disruption of root carbon transport into forest humus stimulates fungal opportunists at the expense of mycorrhizal fungi

“…Previous long-term studies of the effects of root disruption (Siira-Pietikäinen et al, 2001;Brant et al, 2006) or tree girdling (Högberg and Högberg, 2002;Subke et al, 2004) have all found marked decreases in fungal biomass, because of detrimental effects on mycorrhizal taxa (Yarwood et al, 2009). Physical disturbance of the microbial community in boreal forest soils also frequently results in release of NH 4 þ (Yavitt and Fahey, 1984;Siira-Pietikäinen et al, 2001;Lavoie and Bradley, 2003;Piirainen et al, 2007), and elevated NH 4 þ levels have also been observed in association with repeated freeze-thaw cycles (Sulkava and Huhta, 2003) and clear-cutting (Carmosini et al, 2003;Lapointe et al, 2005).…”