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| Titel |
Organic phosphorus mineralisation in a temperate grassland soil under
elevated atmospheric carbon dioxide concentrations |
| VerfasserIn |
Klaus A. Jarosch, Louise Andresen, André D. Gorenflo, Christoph Müller, Emmanuel Frossard, Else K. Bünemann |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128082
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| Publikation (Nr.) |
 EGU/EGU2016-8031.pdf |
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| Zusammenfassung |
| Background: Phosphorus (P) is an essential nutrient for all biota and significant proportions
of P in soil are present in organic form. Increased atmospheric concentrations of carbon
dioxide ([CO2]) have been shown to influence plant P uptake traits, resulting in
plant-mediated changes in soil P pools. However, little is known on the effect of elevated
[CO2] on organic P mineralisation rates in soil.
Study design & hypotheses: A 33P isotopic dilution experiment was performed with soils
of the 17-year-old Giessen free air carbon dioxide enrichment (GiFACE) – trial. At the
GiFACE, three plots are treated with 20 % elevated [CO2] while three control plots receive
ambient air. We hypothesised that i) the observed positive effect of elevated [CO2]
on plant growth translates into differences in soil organic P mineralisation rates
between treated and untreated plots, resulting in ii) differences in soil organic P
pools.
Methods: Fresh soil (0-8 cm) was sampled from each plot, labelled with a carrier free 33P
solution and incubated for 36 days at 19˚ C in the dark. On six time points, inorganic P and
33P in soil filtrates, soil microorganisms (by liquid fumigation) and resin extractable P were
quantified. The baseline of 33P isotopic dilution was assessed from a short term
batch experiment and extrapolated for 36 days. Gross organic P mineralisation rates
were determined as the difference between isotopic dilution in the incubated soils
(physicochemical + biological processes) minus extrapolated values (physicochemical
processes only). Additionally, enzyme addition assays on alkaline soil extracts were
performed to quantify different soil organic P classes, using enzymes with a known substrate
specificity.
Results & Discussion: Gross organic P mineralisation rates were high during the first
three days (5.5 – 34.3 mg P kg−1 d−1), possibly due to the soil disturbance at labelling soils
with 33P. However, gross organic P mineralisation decreased rapidly to rates between 0.7 and
4.2 mg P kg−1 d−1. Net organic P mineralisation during this phase was quantified by
subtracting microbial P immobilisation and ranged between 0.3 and 3.4 mg P kg−1 d−1. We
did not detect a significant effect of elevated [CO2] on soil organic P transformation rates,
however, relatively high P fertilisation since the start of the GiFACE-trial (equal to 5.6 g P
m−2) may have masked subtle changes in mineralisation rates. Significantly higher
concentrations of phytate-like P were found in plots treated with elevated [CO2]. We
assume that increased plant biomass production under elevated [CO2] caused the
formation of more inositol-hexakisphosphate (phytate), a P storage compound in
plants.
Conclusions & Outlook: Elevated [CO2] had no clear effect on soil organic P
mineralisation rates, but soil organic P classes were clearly affected. Organic P
transformation rates will also be verified with a recently developed numerical model. |
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