Our understanding of the relationship between the decomposition of soil organic matter (SOM) and soil temperature affects our predictions of the impact of climate change on soil-stored carbon. One current opinion is that the decomposition of soil labile carbon is sensitive to temperature variation whereas resistant components are insensitive. The resistant carbon or organic matter in mineral soil is then assumed to be unresponsive to global warming. But the global pattern and magnitude of the predicted future soil carbon stock will mainly rely on the temperature sensitivity of these resistant carbon pools. To investigate this sensitivity, we have incubated soils under changing temperature. Here we report that SOM decomposition or soil basal respiration rate was significantly affected by changes in SOM components associated with soil depth, sampling method and incubation time. We find, however, that the temperature sensitivity for SOM decomposition was not affected, suggesting that the temperature sensitivity for resistant organic matter pools does not differ significantly from that of labile pools, and that both types of SOM will therefore respond similarly to global warming.
"However, previous studies have shown inconsistent patterns of Q 10 values of soil respiration with soil depth. Increase (Lomander et al. 1998; Fierer et al. 2003; Jin et al. 2008; Karhu et al. 2010), decrease (Winkler et al. 1996; MacDonald et al. 1999; Gillabel et al. 2010), or no changes (Fang et al. 2005; Leifeld and Fuhrer 2005; Rey et al. 2008) in apparent Q 10 values with increasing soil depth have been observed in different studies. Much of the variation in the apparent temperature sensitivity of SOC decomposition may be related to the fact that labile substrate availability is often unaccounted for in these studies (Davidson and Janssens 2006; Gershenson et al. 2009; Conant et al. 2011). "
" Paul et al . , 1997 ; Schöning and Kögel - Knabner , 2006 ) . Little direct evidence has been provided showing that SOC stabilized under previous conditions will remain stable with changing conditions , such as with climate change , and some studies have shown that previously stable SOC may be rapidly mobilized to CO 2 ( Fontaine et al . , 2007 ; Fang et al . , 2005 ) ."
"The old organic C in soil has generated much interest because it represents the majority of SOC and the stability of this C is uncertain, in particular when faced with external perturbations, such as climate change or changes in land management (e.g. Fang et al., 2005; Reichstein et al., 2005; Davidson and Janssens, 2006; Hartley and Ineson, 2008). Although this C is treated as one or two homogenous pools in most C dynamics models, i.e. the old pool in ICBM (Andr en and K€ atterer, 1997), the slow and passive organic C in the Century model (Parton et al., 1987) or the humus and inert pools in the RothC model (Jenkinson and Rayner, 1977), it is likely that it is made up of a diverse range of organic compounds that are stabilised through a range of different mechanisms. "
[Show abstract][Hide abstract] ABSTRACT: Bare fallow soils that have been deprived of fresh carbon inputs for prolonged periods contain mostly old, stable organic carbon. In order to shed light on the nature of this carbon, the functional diversity profiles (MicroResp™, Biolog™ and enzyme activity spectra) of the microbial communities of long-term bare-fallow soils were analysed and compared with those of the microbial communities from their cultivated counterparts. It was assumed that the catabolic and enzymatic profiles would reflect the type of substrates available to the microbial communities. The catabolic profiles suggested that the microbial communities in the long-term bare-fallow soil were exposed to a less diverse range of substrates and that these substrates tended to be of simpler molecular forms. Both the catabolic and enzyme activity profiles suggest that the microbial communities from the long-term bare-fallow soils were less adapted to using polymers. These results do not fit with the traditional view of old, stable carbon being composed of complex, recalcitrant polymers. Microbial communities from the long-term bare fallow soils tended to preferentially use substrates with higher nominal oxidation states of carbon relative to the substrates used by the microbial communities from the cultivated soils. This suggests that the microbial communities from the long-term bare-fallow soils were better adapted to using readily oxidizable, although energetically less rewarding, substrates. Microbial communities appear to adapt to the deprivation of fresh organic matter by using substrates that require little investment, such as enzyme production.
Soil Biology and Biochemistry 06/2015; DOI:10.1016/j.soilbio.2015.05.018 · 3.93 Impact Factor
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