Changes in the Size of the Active Microbial Pool Explain Short-Term Soil Respiratory Responses to Temperature and Moisture

Salazar, Augusto; Blagodatskaya, Еvgenia; Dukes, Jeffrey S.

doi:10.3389/fmicb.2016.00524

Cited by 41 publications

(34 citation statements)

References 70 publications

(133 reference statements)

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“…This emphasises that changes in total microbial biomass were not the key factor controlling the sign or magnitude of the microbial community response. As indicated above, analysis of only DNA provides no information on active members of the community and further work is required to determine if changes in active microbial biomass could be involved [55]. It has also been argued that thermal adaptation should be investigated in conditions where substrate availability is non-limiting (R mass , [17]), and substrate induced-respiration has been expressed per unit microbial biomass to test this.…”

Section: Discussionmentioning

confidence: 99%

The Role of Microbial Community Composition in Controlling Soil Respiration Responses to Temperature

et al. 2016

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Rising global temperatures may increase the rates of soil organic matter decomposition by heterotrophic microorganisms, potentially accelerating climate change further by releasing additional carbon dioxide (CO2) to the atmosphere. However, the possibility that microbial community responses to prolonged warming may modify the temperature sensitivity of soil respiration creates large uncertainty in the strength of this positive feedback. Both compensatory responses (decreasing temperature sensitivity of soil respiration in the long-term) and enhancing responses (increasing temperature sensitivity) have been reported, but the mechanisms underlying these responses are poorly understood. In this study, microbial biomass, community structure and the activities of dehydrogenase and β-glucosidase enzymes were determined for 18 soils that had previously demonstrated either no response or varying magnitude of enhancing or compensatory responses of temperature sensitivity of heterotrophic microbial respiration to prolonged cooling. The soil cooling approach, in contrast to warming experiments, discriminates between microbial community responses and the consequences of substrate depletion, by minimising changes in substrate availability. The initial microbial community composition, determined by molecular analysis of soils showing contrasting respiration responses to cooling, provided evidence that the magnitude of enhancing responses was partly related to microbial community composition. There was also evidence that higher relative abundance of saprophytic Basidiomycota may explain the compensatory response observed in one soil, but neither microbial biomass nor enzymatic capacity were significantly affected by cooling. Our findings emphasise the key importance of soil microbial community responses for feedbacks to global change, but also highlight important areas where our understanding remains limited.

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Section: Discussionmentioning

confidence: 99%

The Role of Microbial Community Composition in Controlling Soil Respiration Responses to Temperature

et al. 2016

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“…A high E a_m results in large changes of microbial biomass C with temperature. However, observations often show a negative but moderate effect of temperature on microbial biomass (Grisi et al, 1998;Salazar-Villegas et al, 2016).…”

Section: Temperature Effectsmentioning

confidence: 99%

Diffusion limitations and Michaelis–Menten kinetics as drivers of combined temperature and moisture effects on carbon fluxes of mineral soils

Moyano¹,

Vasilyeva

Menichetti

2018

Biogeosciences

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Abstract. CO 2 production in soils responds strongly to changes in temperature and moisture, but the magnitude of such responses at different timescales remains difficult to predict. Knowledge of the mechanisms leading to the often observed interactions in the effects of these drivers on soil CO 2 emissions is especially limited. Here we test the ability of different soil carbon models to simulate responses measured in soils incubated at a range of moisture levels and cycled through 5, 20, and 35 • C. We applied parameter optimization methods while modifying two structural components of models: (1) the reaction kinetics of decomposition and uptake and (2) the functions relating fluxes to soil moisture. We found that the observed interactive patterns were best simulated by a model using Michaelis-Menten decomposition kinetics combined with diffusion of dissolved carbon (C) and enzymes. In contrast, conventional empirical functions that scale decomposition rates directly were unable to properly simulate the main observed interactions. Our best model was able to explain 87 % of the variation in the data. Model simulations revealed a central role of MichaelisMenten kinetics as a driver of temperature sensitivity variations as well as a decoupling of decomposition and respiration C fluxes in the short and mid-term, with general sensitivities to temperature and moisture being more pronounced for respiration. Sensitivity to different model parameters was highest for those affecting diffusion limitations, followed by activation energies, the Michaelis-Menten constant, and carbon use efficiency. Testing against independent data strongly validated the model (R 2 = 0.99) and highlighted the importance of initial soil C pool conditions. Our results demonstrate the importance of model structure and the central role of diffusion and reaction kinetics for simulating and understanding complex dynamics in soil C.

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“…Three replicate samples were then adjusted to each of the moisture levels 1,3,7,9,11,13,15,17,19,21,25 % by weight by adding water or air drying. These 20 values range from air-dry to saturation, with saturation reached at 25 %.…”

Section: Observational Datamentioning

confidence: 99%

“…A high Ea_m results in large changes of microbial biomass C with temperature. However, observations often show a negative but moderate effect of temperature on microbial biomass (Grisi et al, 1998;Salazar-Villegas et al, 2016).…”

Section: Temperature Effectsmentioning

confidence: 99%

“…(Allison et al, 2010;Li et al, 2014) VU_ref 0.092 h -1 0.35 Reference rate of carbon uptake (Allison et al, 2010;Li et al, 2014) th 0.063 m 3 m -3 0 Moisture threshold for diffusion (Manzoni and Katul, 2014) Non-calibrated parameters Tref 293 °K -Reference temperature -Ea_m 10 kJ 4.6 Activation energy for rmd_ref (Grisi et al, 1998;Salazar-Villegas et al, 2016) Ea_e 10 kJ 2.2 Activation energy for rmr_ref (Grisi et al, 1998;Salazar-Villegas et al, 2016) …”

Section: Competing Interestsmentioning

confidence: 99%

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Diffusion based modelling of temperature and moisture interactive effects on carbon fluxes of mineral soils

Moyano

Vasilyeva

Menichetti

2018

Preprint

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Abstract. While CO2 production in soils strongly responds to changes in temperature and moisture, the magnitude of such responses at different time scales remains difficult to predict. In particular, little is known of the mechanisms leading to interactions in the effects of these drivers on soil CO2 emissions, even though such observations are common. Here we compare a number of modelling approaches to test which underlying mechanisms best simulate the interactive responses measured in soils incubated under combined levels of temperature and moisture. We found that two model components were critical for reproducing the observed interactive patterns: 1. Michaelis-Menten reaction kinetics, which strongly improved the model fit when applied to decomposition reactions, and 2. diffusion of dissolved C and enzymes. The latter replaces conventional empirical functions as a mechanism relating moisture content with C fluxes. Indeed, empirical functions failed to capture the main observed interactions. After model calibration we were able to explain 84&#8201;% of the variation in the data. Model simulations resulted in a decoupling of decomposition and respiration C fluxes in the short and mid-term, with interaction effects and general sensitivities to temperature and moisture being more pronounced for respiration. Sensitivity to different model parameters was highest for those affecting diffusion limitations, followed by activation energies, the Michaelis-Menten constant, and carbon use efficiency. Model validation resulted in a high fit against independent data (R2&#8201;=&#8201;0.99). The same underlying model parameters resulted here in different apparent temperature sensitivities compared to the calibration step, demonstrating a strong effects of initial soil conditions. With these results we could demonstrate the importance of model structure and the central role of diffusion and reaction kinetics for simulating complex soil C dynamics related to temperature and moisture interactions. Future studies should further validate this mechanistic approach and extend its use to a larger range of soils.

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Changes in the Size of the Active Microbial Pool Explain Short-Term Soil Respiratory Responses to Temperature and Moisture

Cited by 41 publications

References 70 publications

The Role of Microbial Community Composition in Controlling Soil Respiration Responses to Temperature

The Role of Microbial Community Composition in Controlling Soil Respiration Responses to Temperature

Diffusion limitations and Michaelis–Menten kinetics as drivers of combined temperature and moisture effects on carbon fluxes of mineral soils

Diffusion based modelling of temperature and moisture interactive effects on carbon fluxes of mineral soils

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