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Rapid soil formation after glacial retreat shaped by spatial patterns of organic matter accrual in microaggregates
Author(s) -
Schweizer Steffen A.,
Hoeschen Carmen,
Schlüter Steffen,
KögelKnabner Ingrid,
Mueller Carsten W.
Publication year - 2018
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.14014
Subject(s) - glacial period , organic matter , soil organic matter , geology , physical geography , environmental science , soil science , earth science , soil water , geomorphology , geography , ecology , biology
Global change contributes to the retreat of glaciers at unprecedented rates. The deglaciation facilitates biogeochemical processes on glacial deposits with initiating soil formation as an important driver of evolving ecosystems. The underlying mechanisms of soil formation and the association of soil organic matter ( SOM ) with mineral particles remain unclear, although further insights are critical to understand carbon sequestration in soils. We investigated the microspatial arrangement of SOM coatings at intact soil microaggregate structures during various stages of ecosystem development from 15 to >700 years after deglaciation in the proglacial environment of the Damma glacier (Switzerland). The functionally important clay‐sized fraction (<2 μm) was separated into two density fractions with different amounts of organo‐mineral associations: light (1.6–2.2 g/cm 3 ) and heavy (>2.2 g/cm 3 ). To quantify how SOM extends across the surface of mineral particles (coverage) and whether SOM coatings are distributed in fragmented or connected patterns (connectivity), we developed an image analysis protocol based on nanoscale secondary ion mass spectrometry (Nano SIMS ). We classified SOM and mineral areas depending on the 16 O − , 12 C − , and 12 C 14 N − distributions. With increasing time after glacial retreat, the microspatial coverage and connectivity of SOM increased rapidly. The rapid soil formation led to a succession of patchy distributed to more connected SOM coatings on soil microaggregates. The maximum coverage of 55% at >700 years suggests direct evidence for SOM sequestration being decoupled from the mineral surface, as it was not completely masked by SOM and retained its functionality as an ion exchange site. The chemical composition of SOM coatings showed a rapid change toward a higher CN :C ratio already at 75 years after glacial retreat, which was associated with microbial succession patterns reflecting high N assimilation. Our results demonstrate that rapid SOM sequestration drives the microspatial succession of SOM coatings in soils, a process that can stabilize SOM for the long term.