Similar response of labile and resistant soil organic matter pools to changes in temperature.
ABSTRACT 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.
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- "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. "
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 · 4.41 Impact Factor
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- "Moreover, soil decomposer organisms produce various types of enzymes and their activity is often constrained by substrate availability (Swift et al., 1979; Brussaard et al., 1997). Not surprisingly, empirical demonstration of the CQT hypothesis has led to inconclusive evidence (Liski et al., 1999; Fang et al., 2005; Leifeld and Fuhrer, 2005; Rey and Jarvis, 2006; Conant et al., 2008; Conen et al., 2008; Lef evre et al., 2014), though some apparent contradictions appear resolved (Sierra, 2012). A general pattern that follows the CQT hypothesis emerged with a recent continentwide study by Craine et al. (2010). "
ABSTRACT: Changes in the carbon (C) balance of boreal forest ecosystems may impact the global C cycle and climate. The degree to which antecedent temperature regime and mineral protection of soil organic matter (OM) influence the temperature response of boreal soil C pools remains unknown, however. To investigate these phenomena on time scales relevant to anthropogenic climate change, we quantified the temperature response of four soil C pools (L, F and H organic horizons and B mineral horizon) within soil profiles collected from replicated sites representing two regions along a climate transect (“regional warming”) during a 480-day incubation at 5 and 15°C (“experimental warming”). We hypothesized that 1) warmer region soils would exhibit reduced bioreactivity, a measure of C lability assessed via cumulative soil C mineralization, relative to colder region soils, paralleling a decrease in bioreactivity with depth in both regions, and 2) temperature sensitivity of C mineralization (denoted as Q10) would increase with decreasing bioreactivity congruent with the “C quality-temperature” (CQT) hypothesis, with a smaller effect in mineral soil where physico-chemical protection likely occurs. Cumulative C mineralization decreased from surface L to deeper horizons and from the cold to warm region for organic F and H horizons only. This decrease in soil bioreactivity with depth was paralleled by an increase in Q10 with depth as expected, except in mineral soil where Q10 was similar to or lower relative to the overlying organic layer. The lower bioreactivity in F and H horizons of the warm relative to the cold region was not, however, associated with a greater Q10. A warmer regional climate in these otherwise similar forests thus resulted in reduced bioreactivity of isolated soil C pools without increasing the temperature sensitivity of soil C mineralization. This suggests that assumptions about temperature sensitivity of C mineralization based on the propensity for isolated organic C pools to undergo mineralization may not be valid in some organic-rich, boreal forest soils.Soil Biology and Biochemistry 05/2015; 84:177-188. DOI:10.1016/j.soilbio.2015.02.025 · 4.41 Impact Factor
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- "This result also implies that the soot C pool sequestered in soils from the Qinghai Lake catchment and the larger Q-T Plateau may be relatively insensitive to increasing temperatures. Our results seem to be in conflict with those from some incubation and modelling studies (Fang et al., 2005) that showed no difference in temperature sensitivity between young and old or labile and recalcitrant carbon species. "
ABSTRACT: Black carbon (BC), composed of char and soot, is an important component of soil organic carbon (SOC), and these materials are potentially important for the global carbon cycle and global climate. A thermal-optical reflectance method was used to determine the spatial patterns of SOC, BC, char and soot in nine soil types collected from 152 sites in the Qinghai Lake catchment. All of the analytes showed large spatial variability: SOC, BC and char were most abundant in bog soils and least abundant in aeolian soils, while soot concentrations in alpine frost desert and in aeolian soils were about half of those in the other soils. The average BC concentration in the 0–20-cm soil layers was 1.3 g kg−1, and BC amounted to 5.6% of the SOC. Char, SOC and BC all decreased with soil depth, but soot showed little variation. The proportions of BC to SOC and char to BC showed contrasting trends in four soil profiles; the former increased and the latter decreased with depth. The quantity of SOC sequestered in topsoils of the catchment area was estimated to be 191 Tg; BC accounted for approximately 4.8% of this, and char made up approximately 85% of the total BC stock. The burning of animal dung for domestic cooking apparently was an important source of soil BC: combustion of other biofuels and fossil fuels was the other main source.European Journal of Soil Science 03/2015; 66(3). DOI:10.1111/ejss.12236 · 2.39 Impact Factor