Temperature Sensitivity of Soil Carbon Decomposition and Feedbacks to Climate Change

Department of Biology, University of Antwerp, Antwerpen, Flanders, Belgium
Nature (Impact Factor: 41.46). 04/2006; 440(7081):165-73. DOI: 10.1038/nature04514
Source: PubMed


Significantly more carbon is stored in the world's soils--including peatlands, wetlands and permafrost--than is present in the atmosphere. Disagreement exists, however, regarding the effects of climate change on global soil carbon stocks. If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition, a positive feedback to climate change would occur. Conversely, if increases of plant-derived carbon inputs to soils exceed increases in decomposition, the feedback would be negative. Despite much research, a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition. Unravelling the feedback effect is particularly difficult, because the diverse soil organic compounds exhibit a wide range of kinetic properties, which determine the intrinsic temperature sensitivity of their decomposition. Moreover, several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed 'apparent' temperature sensitivity, and these constraints may, themselves, be sensitive to climate.

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Available from: Ivan A. Janssens, Jun 11, 2015
    • "Generally, livestock grazing may reduce Re by reducing aboveground biomass and litterfall (Wan and Luo, 2003; Cao et al., 2004; Kang et al., 2013) and/or enhance Re through increased soil temperature (Wei et al., 2012; Li et al., 2013b) and fertilization effects of grazer urine and dung on plant growth and microbial activity (Augustine et al., 2003; Bardgett and Wardle, 2003). The temperature sensitivity (Q 10 ) of Re may be also regulated by changes in carbon substrate availability (Yuste et al., 2004; Davidson et al., 2006; Gershenson et al., 2009), which would be subjected to increased livestock grazing pressures in grassland ecosystems. The net effect of grazing on Re should be attributed to the balance of negative and positive effects. "
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    ABSTRACT: Little is known about how livestock grazing could modify altitudinal trends in seasonal ecosystem respiration (Re) and its temperature sensitivity (Q10). We aim to test the hypotheses that the altitudinal grazing effect on growing-season Re is well correlated with the grazing-induced change of plant biomass, and grazing exclusion tends to reduce the Q10 of Re along altitudes. We conducted a 7-year altitudinal grazing exclusion experiment across lower and upper limits of alpine meadows (4400–5100 m) on the central Tibetan Plateau. Plant biomass, Re and related environmental factors were observed across fenced and grazed treatments at each of 6 altitudes during the growing seasons of 2012–2013. The stimulations of above- and belowground biomass due to grazing exclusion decreased with increasing altitude, which were positively correlated with the change of Re. The Q10 of seasonal Re generally increased with increasing altitude, but tended to decrease under grazing exclusion. Soil organic carbon did not have a direct effect on the altitudinal variation of Re. Our data supported the hypotheses, suggesting that plant biomass change could be served as an integrated indicator for spatiotemporal variations of Re. Grazing exclusion might be a promising measure to reduce the temperature sensitivity of Re.
    No preview · Article · Mar 2016 · Agricultural and Forest Meteorology
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    • "This variable is determined by the net primary production (NPP) from plants and the heterotrophic respiration (R het ). While NPP is controlled both by the canopy conductance (g s ) and by the stomatal demand for CO 2 (c i /c ratio), R het is known to be a function of soil temperature (Karhu et al., 2014; Davidson and Janssens, 2006). In that way, g s acts as a coupling point for the carbon cycle, the water, and the heat cycles previously described by H9 and H14 (see Fig. 1a). "
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    ABSTRACT: Land-surface models used in studies of the atmosphere and vegetation during droughts usually include an underlying parameterization that describes the response of plants to water stress. Here, we show that different formulations of this parameterization can lead to significant differences in the coupling strength (i.e. the magnitude of the carbon and water exchange) between the land surface and the atmospheric boundary layer (ABL). We use a numerical model that couples the daytime surface fluxes typical for low vegetation to the dynamics of a convective ABL, to systematically investigate a range of plant water-stress responses. We find that under dry soil conditions, changing from a sensitive to an insensitive vegetation response to water stress has the same impact on the land-atmosphere (L-A) coupling as a strong increase in soil moisture content. The insensitive vegetation allows stomata to remain open for transpiration (+150Wm-2 compared to the sensitive one), which cools the atmosphere (-3.5K) and limits the ABL growth (-500m). During the progressive development of a dry spell, the insensitive response will first dampen atmospheric heating because the vegetation continues to transpire a maximum of 4.6mmday-1 while soil moisture is available. In contrast, the more sensitive vegetation response reduces its transpiration by more than 1mmday-1 to prevent soil moisture depletion. But when soil moisture comes close to wilting point, the insensitive vegetation will suddenly close its stomata causing a switch to a L-A coupling regime dominated by sensible heat exchange. We find that in both cases, progressive soil moisture depletion contributes to further atmospheric warming up to 6K, reduced photosynthesis up to 89%, and CO2 enrichment up to 30ppm, but the full impact is strongly delayed for the insensitive vegetation. Then, when we analyze the impact of a deviation of the modeled large-scale boundary conditions (e.g. subsidence, cloud cover, free-troposphere lapse rates, etc.) from their true state during a drought, we find that the two coupled systems (with a sensitive or insensitive vegetation) respond much differently to the generated atmospheric warming, this due to the difference in the basic surface coupling regime (coupled vs. uncoupled). This is of importance for the simulation of heat waves and meteorological droughts, as well as carbon-climate projections, as we show the predictive skill of coupled models is tied to the underlying vegetation response to water stress.
    Full-text · Article · Feb 2016 · Agricultural and Forest Meteorology
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    • "R S is controlled by many factors. Soil temperature (ST) and soil moisture (SM) are the most notable abiotic factors associated with seasonal and inter-annual changes driving R S (Davidson et al., 1998; Wang et al., 2006). It is generally accepted that R S increases with increasing ST (Wang et al., 2010), and annual R S is closely related to average annual temperatures (Bahn et al., 2010). "
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    ABSTRACT: Moso bamboo forests represent an important forest type commonly found throughout subtropical China and are characterized by fast growing forests, and involves intensive management, such as reclamation, fertilization, and understory removal. However, effects of intensive management on soil respiration (RS) and net ecosystem production (NEP) remain unclear. In this study, RS was partitioned into root respiration (RR), litter respiration (RL), and soil organic matter derived respiration (RM) by litter removal and trenching approaches. One-year measurements of respiration rates, soil temperature, and soil moisture were conducted in an unmanaged and an intensively managed stand. Regardless of stand management, RS and source components increased exponentially with soil temperature and linearly with soil moisture. Temperature sensitivity (Q10) ranged from 1.6 to 2.5, with the highest value for RM, highlighting the importance of RM in regulating the response of RS to soil temperature change. Annual RS, RR, RL, and RM were 32.6, 10.7, 6.9, and 15.0t CO2 ha-1 a-1 for unmanaged stand, compared to 38.6, 12.5, 7.1, and 18.9t CO2 ha-1 a-1 for intensive managed stand, respectively, indicating that intensive management increased RS by RR and RM. Intensive management also increased NEP with 17.2t CO2 ha-1 a-1 for unmanaged stand and 20.4t CO2 ha-1 a-1 for intensive managed stand. This increase was mainly attributed to the increase in net primary production of bamboo forests under intensive management. However, the sustainability of intensive management needs further investigation due to the reduction of soil organic carbon content after intensive management. Forest management associated with the reduction in soil CO2 flux and increase in stand production should be developed for Moso bamboo forests.
    Full-text · Article · Feb 2016
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