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- Fanin, Nicolas
(författare)
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Aboveground litter quality is a better predictor than belowground microbial communities when estimating carbon mineralization along a land-use gradient
- 2016
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 94, s. 48-60
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Tidskriftsartikel (refereegranskat)abstract
- Because of the vegetation cover and anthropogenic disturbances, land-use management strongly influences soil heterotrophic decomposers. Yet, little is known about whether contrasting microbial communities originating from different ecosystems are functionally similar, and only a few studies have disentangled the direct and indirect effects of resource quality on both microbial communities and carbon mineralization rates. To assess the relative importance of aboveground litter quality and belowground microbial communities on litter decomposition, we conducted a reciprocal transplant experiment under controlled conditions using four litters (Triticum aestivum, Fagus sylvatica, Festuca arundinacea and Robinia pseudoacacia) and four soils (culture, plantation, grassland and forest) originating from a land-use gradient. We followed the kinetics of carbon mineralization over 21 dates spanning a 202-day period to assess the variability of responses generated by the plant soil interactions. Furthermore, at four time points (at 0, 27, 97 and 202 days), the mass loss rates for the main sugars within the cell wall, the microbial biomass (fumigation-extraction), the microbial community structure via phospholipid fatty acid (PLFA), and the activities of four carbon-related hydrolytic enzymes were investigated to assess the functional significance of microbial communities. Our results demonstrated that the importance of soil types and heterotrophic decomposers on carbon mineralization rates was minor (1.2% of the variance explained) compared with the predominant role of litter quality. The structure of the microbial communities responded strongly to both long-term land-use changes and short-term litter additions; specifically, (i) higher proportions of fungi were observed in natural ecosystems compared with agro-systems, and (ii) an opportunistic subset of the bacterial community was stimulated after litter additions. Even if the land-use management and litter quality can shape the microbial community structure in a foreseeable way, we found an important degree of plasticity in the responses of contrasting decomposer communities. In particular, the enzymatic efficiency (defined as the amount of enzyme produced by unit of carbon mineralized) differed among, litters but not among soil types, suggesting that the threshold between carbon allocation to growth and acquisition depended more on the 'resource-use strategies' of the soil microorganisms than on the community structure. The recalcitrant litters stimulated 'efficient' communities characterized by low enzymatic activities, microbial biomass and respiration rates at the opposite of labile litters that stimulated 'wasteful' communities characterized by higher activities and metabolic quotient (defined as the amount of carbon respired by unit of biomass). In addition to the direct effects of litter quality, the path analysis reinforced our conclusion that the functional traits of microorganisms via their enzymatic activities are more relevant than their identity for predicting carbon mineralization. Thus, although multiple and coordinated responses of soil microbes can improve our understanding of carbon fluxes, shifts in the plant community composition caused by land-use conversion will have a stronger impact on predictions of carbon mineralization than short-term changes in the microbial community composition. (C) 2015 Elsevier Ltd. All rights reserved.
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| 2. |
- Fanin, Nicolas
(författare)
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Eco-enzymatic stoichiometry and enzymatic vectors reveal differential C, N, P dynamics in decaying litter along a land-use gradient
- 2016
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 129, s. 21-36
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate carbon (C), nitrogen (N), and phosphorus (P) dynamics during the decomposition process, we investigated the temporal variability of extracellular enzymatic activities (EEA) associated with C, N, and P acquisition in microbial communities from different land uses. We hypothesized that EEA ratios would reveal different primary resource requirements with respect to microbial demand, depending on soil properties, litter type and the relative proportion of bacteria:fungi in the microbial community. To test this hypothesis, we implemented an experiment using four litters (Triticum aestivum, Fagus sylvatica, Festuca arundinacea and Robinia pseudoacacia) in four soils (cropland, plantation, prairie and forest) located in close proximity to one another on the same parent material. Analyses of EEA showed that overall N requirement increased relative to P during litter decay, but C requirement increased more rapidly than either N or P in most of these ecosystems. Soil type was the main factor controlling N versus P requirement whereas litter type was the primary driver of C versus nutrient requirement. Shifts in EEA were related to changes in metabolic quotient (C respired per unit biomass) but there was no evidence that the relative proportion of fungi:bacteria drove changes in EEA. We concluded that the use of EEA as a proxy of microbial resource demand improved our understanding of temporal shifts in resource requirements to microbial communities, their associated respiration efficiency and dynamics of C and nutrients among different ecosystems.
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| 3. |
- Fanin, Nicolas
(författare)
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Functional breadth and home-field advantage generate functional differences among soil microbial decomposers
- 2016
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97, s. 1023-1037
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Tidskriftsartikel (refereegranskat)abstract
- In addition to the effect of litter quality (LQ) on decomposition, increasing evidence is demonstrating that carbon mineralization can be influenced by the past resource history, mainly through following two processes: (1) decomposer communities from recalcitrant litter environments may have a wider functional ability to decompose a wide range of litter species than those originating from richer environments, i.e., the functional breadth (FB) hypothesis; and/or (2) decomposer communities may be specialized towards the litter they most frequently encounter, i.e., the home-field advantage (HFA) hypothesis. Nevertheless, the functional dissimilarities among contrasting microbial communities, which are generated by the FB and the HFA, have rarely been simultaneously quantified in the same experiment, and their relative contributions over time have never been assessed. To test these hypotheses, we conducted a reciprocal transplant decomposition experiment under controlled conditions using litter and soil originating from four ecosystems along a land-use gradient (forest, plantation, grassland, and cropland) and one additional treatment using C-13-labelled flax litter allowing us to assess the priming effect (PE) in each ecosystem. We found substantial effects of LQ on carbon mineralization (more than two-thirds of the explained variance), whereas the contribution of the soil type was fairly low (less than one-tenth), suggesting that the contrasting soil microbial communities play only a minor role in regulating decomposition rates. Although the results on PE showed that we overestimated litter-derived CO2 fluxes, litter-microbe interactions contributed significantly to the unexplained variance observed in carbon mineralization models. The magnitudes of FB and HFA were relatively similar, but the directions of these mechanisms were sometimes opposite depending on the litter and soil types. FB and HFA estimates calculated on parietal sugar mass loss were positively correlated with those calculated on enzymatic activity, confirming the idea that the interaction between litter quality and microbial community structure may modify the trajectory of carbon mineralization via enzymatic synthesis. We conclude that although litter quality was the predominant factor controlling litter mineralization, the local microbial communities and interactions with their substrates can explain a small (<5%) but noticeable portion of carbon fluxes.
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