| 1. |
- Ekblad, Alf, 1957-, et al.
(författare)
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Analysis of delta C-13 of CO2 distinguishes between microbial respiration of added C-4-sucrose and other soil respiration in a C-3-ecosystem
- 2000
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Ingår i: Plant and Soil. - 0032-079X .- 1573-5036. ; 219:1-2, s. 197-209
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Tidskriftsartikel (refereegranskat)abstract
- The main aim of this study was to test various hypotheses regarding the changes in δ13C of emitted CO2 that follow the addition of C4-sucrose to the soil of a C3-ecosystem. It forms part of an experimental series designed to assess whether or not the contributions from C3-respiration (root and microbial) and C4-respiration (microbial) to total soil respiration can be calculated from such changes. A series of five experiments, three on sieved (root-free) mor-layer material, and two in the field with intact mor-layer (and consequently with active roots), were performed. Both in the experiments on sieved mor-layer and the field experiments, we found a C4-sucrose-induced increase in C3-respiration that accounted for between 30% and 40% of the respiration increase 1 h after sucrose addition. When the course of C3-, C4- and total respiration was followed in sieved material over four days following addition of C4-sucrose, the initially increased respiration of C3-C was transient, passing within less than 24 h. In a separate pot experiment, neither ectomycorrhizal Pinus sylvestrisL. roots nor non-mycorrhizal roots of this species showed respiratory changes in response to exogenous sucrose. No shift in the δ13C of the evolved CO2 after adding C3-sucrose to sieved mor-layer material was found, confirming that the sucrose-induced increase in respiration of endogenous C was not an artefact of discrimination against 13C during respiration. Furthermore, we conclude that the C4-sucrose induced transient increase in C3-respiration is most likely the result of accelerated turnover of C in the microbial biomass. Thus, neither respiration of mycorrhizal roots, nor processes discriminating against δ13C were likely sources of error in the field. The estimated δ13C of evolved soil CO2 in three field experiments lay between −25.2‰ and −23.6‰. The study shows that we can distinguish between CO2 evolved from microbial mineralisation of added C4-sucrose, and CO2 evolved from endogenous carbon sources (roots and microbial respiration).
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| 2. |
- Ekblad, Alf, 1957-, et al.
(författare)
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C-13-discrimination during microbial respiration of added C-3-, C-4- and C-13-labelled sugars to a C-3-forest soil
- 2002
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 131:2, s. 245-249
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Tidskriftsartikel (refereegranskat)abstract
- We tested whether 13C-discrimination during microbial respiration, or during CO2 sampling in the field, can explain changes observed in the δ13C of emitted CO2 that follow the addition of C4-sucrose, as a microbial substrate, to the soil of a C3-ecosystem. We approached this problem by adding C3-glucose (δ13C=–23.4‰), C4-sucrose (–10.8‰) or 13C-labelled glucose (103.7‰) to the intact mor layer, the upper organic soil (–26.5‰, bulk soil organic matter), of a boreal Pinus sylvestris L. forest. If 13C-discrimination is significant, it should generate illusory differences in the calculated contributions from the added C and endogenous C3-C to total soil respiration, when C4-sucrose or 13C-labelled glucose is added. Further, if discrimination occurs, we should also be able to detect a shift in the δ13C of respired CO2 after the addition of C3-glucose. The addition of the three sugar solutions gave similar increases in soil respiration (up to a doubling 1 h after the additions), while the addition of water gave no increase in respiration. There was no change in δ13C of the emitted CO2 after additions of H2O or C3-glucose. In contrast, the addition of C4-sucrose and 13C-labelled glucose gave δ13C values of evolved CO2 that were 4.5‰ and 30.3‰ higher than the pre-sugar values, respectively. The calculated respiration rates of the added carbon sources, C4-C or 13C-labelled C, were very similar. Also, we found very similar sugar-induced increases in respiration of endogenous C3-C in the plots supplied with C4-sucrose and 13C-labelled glucose, accounting for about 50% of the total increase in respiration 1 h after addition. Our results confirm that any microbial 13C-discrimination during respiration is minor.
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| 3. |
- Ekblad, Alf, 1957-, et al.
(författare)
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Is growth of soil microorganisms in boreal forests limited by carbon or nitrogen availability?
- 2002
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Ingår i: Plant and Soil. - 0032-079X .- 1573-5036. ; 242:1, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- To study whether the biomass of soil microorganisms in a boreal Pinus sylvestris-Vaccinium vitis-idaea forest was limited by the availability of carbon or nitrogen, we applied sucrose from sugar cane, a C4 plant, to the organic mor-layer of the C3–C dominated soil. We can distinguish between microbial mineralization of the added sucrose and respiration of endogenous carbon (root and microbial) by using the C4-sucrose as a tracer, exploiting the difference in natural abundance of 13C between the added C4-sucrose (δ13C −10.8‰) and the endogenous C3–carbon (δ13C −26.6 ‰). In addition to sucrose, NH4Cl (340 kg N ha−1) was added factorially to the mor-layer. We followed the microbial activity for nine days after the treatments, by in situ sampling of CO2 evolved from the soil and mass spectrometric analyses of δ13C in the CO2. We found that microbial biomass was limited by the availability of carbon, rather than nitrogen availability, since there was a 50% increase in soil respiration in situ between 1 h and 5 days after adding the sucrose. However, no further increase was observed unless nitrogen was also added. Analyses of the δ13C ratios of the evolved CO2 showed that increases in respiration observed between 1 h and 9 days after the additions could be accounted for by an increase in mineralization of the added C4–C.
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| 4. |
- Ekblad, Alf, 1957-, et al.
(författare)
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Natural abundance of C-13 in CO2 respired from forest soils reveals speed of link between tree photosynthesis and root respiration
- 2001
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 127:3, s. 305-308
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Tidskriftsartikel (refereegranskat)abstract
- Soil respiration from a boreal mixed coniferous forest showed large seasonal variation in natural abundance of 13C, ranging from –21.6‰ to –26.5‰. We tested if weather conditions could explain this variation in δ13C of respired CO2, and found that the air relative humidity 1–4 days before the days of CO2 sampling best explained the variation. This suggested that high δ13C values were caused by effects of air humidity on isotope fractionation during photosynthesis and that it took 1–4 days for the C from canopy photosynthesis of 20–25 m trees to become available for root/rhizosphere respiration. We calculated that these new photoassimilates could account for at least 65% of total soil respiration.
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| 5. |
- Franklin, Oskar, et al.
(författare)
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Pine forest floor carbon accumulation in response to N and PK additions : Bomb C-14 modelling and respiration studies
- 2003
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 6:7, s. 644-658
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Tidskriftsartikel (refereegranskat)abstract
- The addition of nitrogen via deposition alters the carbon balance of temperate forest ecosystems by affecting both production and decomposition rates. The effects of 20 years of nitrogen (N) and phosphorus and potassium (PK) additions were studied in a 40-year-old pine stand in northern Sweden. Carbon fluxes of the forest floor were reconstructed using a combination of data on soil 14C, tree growth, and litter decomposition. N-only additions caused an increase in needle litterfall, whereas both N and PK additions reduced long-term decomposition rates. Soil respiration measurements showed a 40% reduction in soil respiration for treated compared to control plots. The average age of forest floor carbon was 17 years. Predictions of future soil carbon storage indicate an increase of around 100% in the next 100 years for the N plots and 200% for the NPK plots. As much as 70% of the increase in soil carbon was attributed to the decreased decomposition rate, whereas only 20% was attributable to increased litter production. A reduction in decomposition was observed at a rate of N addition of 30 kg C ha−1 y−1, which is not an uncommon rate of N deposition in central Europe. A model based on the continuous-quality decomposition theory was applied to interpret decomposer and substrate parameters. The most likely explanations for the decreased decomposition rate were a fertilizer-induced increase in decomposer efficiency (production-to-assimilation ratio), a more rapid rate of decrease in litter quality, and a decrease in decomposer basic growth rate.
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| 6. |
- Lundberg, Peter, 1958-, et al.
(författare)
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C-13 NMR spectroscopy studies of forest soil microbial activity : glucose uptake and fatty acid biosynthesis
- 2001
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Ingår i: Soil Biology and Biochemistry. - 0038-0717 .- 1879-3428. ; 33:4-5, s. 621-632
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Tidskriftsartikel (refereegranskat)abstract
- The intimate association of soil microorganisms with the soil matrix complicates analysis of their metabolism, since thorough separation of intact cells from the matrix is very difficult using standard protocols. Thus, in the study reported here, in situ glucose decomposition and metabolism in humus from a coniferous forest soil was monitored and evaluated using ‘solution state’ 13C NMR, which can be used in a non-invasive manner. [U-13C] glucose was added at a concentration of 1.73 mmol C g−1 dry organic matter, which is known to allow maximal substrate induced respiration (SIR), and the microbial metabolism of the added C was followed over a period of 28 days. The data showed that ∼50% of the added glucose was consumed within three days, coinciding with the appearance of label in CH3, –CH2– and –CH=CH– groups, and in glycerol-carbons, suggesting that olefinic triacylglycerols were being formed, probably located in oil droplets. During days two to three, around 40% of the consumed glucose C was allocated into solid state components, about 40% was respired and about 20% was found as triglycerols. The triacylglycerol signal reached a maximum after 13 days, but subsequently declined by 60%, as the triacylglycerols were apparently consumed, by day 28 of the incubation. Our results indicate there was an initial formation of structural microbial C (solid state carbon) followed by formation of storage lipid C, which subsequently decreased, probably because it was used to provide the organisms with energy when the external energy source (i.e. the glucose) was depleted. The formation of unsaturated triacylglycerols, typical storage metabolites of eucaryotes, suggests that fungi were the most active organisms in the glucose degradation.
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| 7. |
- Nyberg, Gert, et al.
(författare)
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Respiration from C-3 plant green manure added to a C-4 plant carbon dominated soil
- 2000
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Ingår i: Plant and Soil. - 0032-079X .- 1573-5036. ; 218:1-2, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- Application of tree leaves (C3 plants) on maize (Zea mays L.) (C4 plant) fields is an agroforestry management technology to restore or maintain soil fertility. The rate at which the tree leaves decompose is crucial for the nutrient supply to the crop. We studied the in situ decomposition of Sesbania sesban (L.) Merr. leaves or C3 sugar for 4 – 8 days after application to a maize field in Kenya. By using the difference of around 10‰ in natural abundance of 13C between the endogenous soil C (mainly C4) and the applied C (C3), we could calculate the contributions of the two C sources to soil respiration. The δ13C value of the basal respiration was from –15.9 to –16.7‰. The microbial response to the additions of leaves and sugar to this tropical soil was immediate. Application of sesbania leaves gave an initial peak in respiration rates that lasted from one to less than 6 days, after which it levelled off and remained about 2 – 3 times higher (230–270 mg C m-2 h-1) than the control respiration rates throughout the rest of the experiment (5 – 8 days). In the sugar treatment, there was no initial peak in respiration rate. The respiration rate was 170 mg C m-2 h-1 after 4 days. At the end of the experiments, after 4–8 days, as much as 14–17% of the added C had been respired and about 60% of the total respiration was from the added sesbania leaves or C3 sugar. This non-destructive method allows repeated measurements of the actual rate of C mineralisation and facilitates decomposition studies with high temporal resolution in the field.
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| 8. |
- Nyberg, Gert, et al.
(författare)
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Short-term patterns of carbon and nitrogen mineralisation in a fallow field amended with green manures from agroforestry trees
- 2002
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 36:1, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- The mineralisation of green manure from agroforestry trees was monitored with the objective to compare the temporal dynamics of mineralisation of litter from different species. Green manures from five agroforestry tree species were used on a fallow field during the long rainy season of 1997 (March–August) and from two species in the following short rainy season (September–January) in western Kenya. Different methods, i.e. measurements of isotopic ratios of C in respired CO2 and of soil organic matter (SOM) fractions, soil inorganic N and mass loss from litterbags, were used in the field to study decomposition and C and N mineralisation. Soil respiration, with the separation of added C from old soil C by using the isotopic ratio of 13C/12C in the respired CO2, correlated well with extractable NH4 + in the soil. Mineralisation was high and very rapid from residues of Sesbania sesban of high quality [e.g. low ratio of (polyphenol+lignin)/N] and low and slow from low quality residues of Grevillea robusta. Ten days after application, 37% and 8% of the added C had been respired from Sesbania and Grevillea, respectively. Apparently, as much as 70–90% of the added C was respired in 40 days from high quality green manure. Weight losses of around 80%, from high quality residues in litterbags, also indicate substantial C losses and that a build-up of SOM is unlikely. For immediate effects on soil fertility, application of high quality green manure may, however, be a viable management option. To achieve synchrony with crop demand, caution is needed in management as large amounts of N are mineralised within a few days after application.
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