| 1. |
- Andresen, Louise C., 1974, et al.
(författare)
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Nitrogen dynamics after two years of elevated CO2 in phosphorus limited Eucalyptus woodland
- 2020
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 150, s. 297-312
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Tidskriftsartikel (refereegranskat)abstract
- It is uncertain how the predicted further rise of atmospheric carbon dioxide (CO2) concentration will affect plant nutrient availability in the future through indirect effects on the gross rates of nitrogen (N) mineralization (production of ammonium) and depolymerization (production of free amino acids) in soil. The response of soil nutrient availability to increasing atmospheric CO2 is particularly important for nutrient poor ecosystems. Within a FACE (Free-Air Carbon dioxide Enrichment) experiment in a native, nutrient poor Eucalyptus woodland (EucFACE) with low soil organic matter (≤ 3%), our results suggested there was no shortage of N. Despite this, microbial N use efficiency was high (c. 90%). The free amino acid (FAA) pool had a fast turnover time (4 h) compared to that of ammonium (NH4+) which was 11 h. Both NH4-N and FAA-N were important N pools; however, protein depolymerization rate was three times faster than gross N mineralization rates, indicating that organic N is directly important in the internal ecosystem N cycle. Hence, the depolymerization was the major provider of plant available N, while the gross N mineralization rate was the constraining factor for inorganic N. After two years of elevated CO2, no major effects on the pools and rates of the soil N cycle were found in spring (November) or at the end of summer (March). The limited response of N pools or N transformation rates to elevated CO2 suggest that N availability was not the limiting factor behind the lack of plant growth response to elevated CO2, previously observed at the site.
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| 2. |
- Jiang, Mingkai, et al.
(författare)
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The fate of carbon in a mature forest under carbon dioxide enrichment
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 580:7802, s. 227-231
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1–5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3–5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7–10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear4,5,7–11. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests.
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| 3. |
- Pihlblad, Johanna, et al.
(författare)
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Stochiometric control of SOM and plant derived soil C pools dynamics under elevated CO2
- 2021
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Ingår i: EGU General Assembly 2021. - : EGU21-General Assembly.
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Konferensbidrag (refereegranskat)abstract
- Elevated carbon dioxide in the atmosphere (eCO2) has been found to influence soil C by altering the belowground balance between the decomposition of existing soil organic matter (SOM) and the accumulation of plant-derived C inputs. Even small changes in this balance can have a potentially large effect on future climate. The relative availability of soil nutrients, particularly N and P, are crucial mediators of both decomposition and new C accumulation, but both these two processes are rarely assessed simultaneously. We asked if the effect of eCO2 on soil C decomposition was mediated by soil N and P availability, and if the effect of CO2 and soil N and P availability on soil C decomposition was dependent on C pools (existing SOM C, newly added C). We grew Eucalyptus grandis and a C3 grass (Microlaena stipoides) from seed in an experimentally manipulated atmosphere with altered δ13C signature of CO2, which allowed the separation of plant derived C, from the existing SOM C. Then we manipulated N and P relative abundance via nutrient additions. We evaluated how the existing SOM and the new plant-derived C pool, and their respiration responded to eCO2 conditions and nutrient treatments. SOM respiration significantly increased in the eucalypts when N was added but was not affected by CO2. In the grass the SOM respiration increased with eCO2 and added N and SOM respiration per unit of SOM-derived microbial was significantly higher in both the added P and added N+P nutrient treatments. The rhizosphere priming of SOM was suppressed in both the added P and added N+P nutrient treatments. The heterotrophic respiration of plant-derived C was contingent on nutrient availability rather than eCO2 and differed by species. The grass-derived respiration was significantly higher than the eucalypt and was higher in both added P and added N+P nutrient treatments. Thus, nutrient stoichiometry had similar effects on SOM and plant derived C, but e CO2 only affected SOM and only for the Eucalyptus. This study shows how species differences have large effects on rhizosphere C cycling responses to eCO2 and stoichiometric conditions.
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