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| Titel |
Applicability and limitations of enzyme addition assays for the characterisation of soil organic phosphorus across a range of soil types |
| VerfasserIn |
Klaus Jarosch, Ashlea Doolette, Ronald Smernik, Emmanuel Frossard, Else K. Bünemann |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091025
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| Publikation (Nr.) |
 EGU/EGU2014-5290.pdf |
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| Zusammenfassung |
| Solution 31P NMR spectroscopy is a powerful tool for the characterisation and
quantification of organic P classes in soil. Potential limitations are due to costs, equipment
accessibility and the requirement of relatively large amounts of sample. A recent
alternative approach for the quantification of specific organic P classes is the use of
substrate-specific phosphohydrolase enzymes which cleave the inorganic orthophosphate
from the organic moiety. The released orthophosphate is detectable by colorimetry.
Conclusions about the hydrolysed class of organic P can be made based on the
comparison of inorganic P concentrations in enzymatically treated and untreated
samples.
The aim of this study was to test the applicability of enzyme addition assays for the
characterisation of organic P classes on a) NaOH-EDTA extracts, b) soil:water filtrates
(0.2 μm) and c) soil:water suspensions. The organic P classes in NaOH-EDTA
extracts were also determined by 31P NMR spectroscopy, enabling a comparison
between methods. Ten topsoil samples from four continents (five cambisols, two
ferralsols, two luvisols and one lixisol) with varying total P content (83 – 1,1560 mg
kg-1), pHH2O (4.2 – 8.0) and land management (grassland or cropped land) were
analysed. Four different classes of organic P were determined by the enzyme addition
assay: 1) monoester like-P (by an acid phosphatase known to hydrolyse simple
monoesters, pyrophosphate and ATP), 2) DNA-like P (by a nuclease in combination
with an acid phosphatase), 3) inositol phosphate-like P (by a phytase known to
hydrolyse all monoester like-P plus myo-inositol hexakisphosphate and scyllo-inositol
hexakisphosphate) and 4) enzyme stable-P (enzymatically not hydrolysed organic P
forms).
In the ten topsoil samples, NaOH-EDTA-extractable organic P ranged from 6 – 1,115 mg
P kg-1 soil. Of this, 33 – 92 % was enzyme labile, with inositol phosphate-like P being the
largest organic P class in most soils (15 – 51%), followed by monoester-like P (10 – 47%)
and DNA-like P (0 – 15%). The four soil organic P classes detected by either 31P NMR
spectroscopy or enzyme addition assays were well correlated with each other (R2 0.93 –
0.99). In soil:water filtrates, 0.1 – 4.1 mg enzyme-labile P kg-1 soil were detected, which
consisted mainly of inositol phosphate-like P. In some soils, a low absolute amount of
water-soluble organic P hindered a more detailed characterisation. In soil:water
suspensions, enzyme-labile organic P ranged from 4.3 – 12.6 mg P kg-1 soil. However,
the enzyme addition assay was only applicable on three soils, since in the other
soils i) added enzymes were partly inhibited in soil:water suspensions and ii) the
hydrolysis of organic P classes by soil intrinsic enzymes could not be accounted
for.
In conclusion, enzyme addition assays appear to be a promising approach for a rapid
determination of four main soil organic P classes in NaOH-EDTA extracts. Especially the
small amount of required sample size (< 1ml) and the relatively simple instrumentation
facilitate a rapid and cheap analysis on these extracts. Application of this method is also
possible on soil:water filtrates, but low amounts of organic P may hinder detailed
analysis.
Key words: soil organic phosphorus characterisation, enzyme addition assays, 31P NMR
spectroscopy, soil suspensions, soil filtrate |
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