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| Titel |
Do chemical gradients within soil aggregates reflect plant/soil interactions? |
| VerfasserIn |
Jaane Krüger, Till Hallas, Lena Kinsch, Simon Stahr, Jörg Prietzel, Friederike Lang |
| 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 |
250135733
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| Publikation (Nr.) |
 EGU/EGU2016-16632.pdf |
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| Zusammenfassung |
| As roots and hyphae often accumulate at the surface of soil aggregates, their formation and
turnover might be related to the bioavailability especially of immobile nutrients like
phosphorus. Several methods have been developed to obtain specific samples from aggregate
surfaces and aggregate cores and thus to investigate differences between aggregate shell and
core. However, these methods are often complex and time-consuming; therefore most
common methods of soil analysis neglect the distribution of nutrients within aggregates and
yield bulk soil concentrations.
We developed a new sequential aggregate peeling method to analyze the distribution of
different nutrients within soil aggregates (4–20 mm) from four forest sites (Germany)
differing in concentrations of easily available mineral P. Aggregates from three soil depths
(Ah, BwAh, Bw) were isolated, air-dried, and peeled with a sieving machine performing four
sieving levels with increasing sieving intensity. This procedure was repeated in quadruplicate,
and fractions of the same sample and sieving level were pooled. Carbon and N concentration,
citric acid-extractable PO4 and P, as well as total element concentrations (P, K, Mg,
Ca, Al, Fe) were analyzed. Additionally, synchrotron-based P K-edge XANES
spectroscopy was applied on selected samples to detect P speciation changes within the
aggregates.
The results reveal for most samples a significantly higher C and N concentration at the
surface compared to the interior of the aggregates. Carbon and N gradients get more
pronounced with increasing soil depth and decreasing P status of study sites. This might
be explained by lower aggregate turnover rates of subsoil horizons and intense
bioturbation on P-rich sites. This assumption is also confirmed by concentrations of
citric acid-extractable PO4 and P: gradients within aggregates are getting more
pronounced with increasing soil depth and decreasing P status. However, the direction of
these gradients is site-specific: On P-rich study sites the results reveal a significant
depletion of citric acid-extractable PO4 and P on aggregate surfaces in subsoil horizons,
while at the other study sites a slight enrichment at the aggregate surfaces could be
observed.
Total P concentrations show no distinct gradients within topsoil aggregates,
but a slight P enrichment at the surface of subsoil aggregates at the P-rich site.
A strong correlation with the total Al concentrations may indicate a P speciation
change within aggregates (e.g., due to acidification processes). These results were
also confirmed by P K-edge XANES spectra of aggregate core and shell samples
of the P-rich site: In the aggregate shells of topsoil as well as subsoil aggregates,
organic P forms are most dominant (82 and 80 %, respectively) than in the aggregate
interior (54 and 66%, respectively). Moreover, P in the shell seems to be completely
associated to Al, whereas some of the P in the aggregate interior is bound to Fe and/or
Ca.
Overall, our results show that plant/soil interactions impact on small-scale distribution
and bioavailability of nutrients by root uptake and root-induced aggregate engineering. |
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