XANES and Pyrolysis-FIMS Evidence of Organic Matter Composition in a Hummocky Landscape

Abstract

The quantity and quality of soil organic N and C are strongly influenced by variations in landscape position and management practices such as cultivation. In this study, we used synchrotron-based C and N AT-edge x-ray absorption near-edge structure (XANES) spectroscopy coupled with pyrolysis-field ionization mass spectrometry (Py-FIMS) to explore C and N chemistry among soils obtained from dilferent landscape positions along a hummocky transect and from locations under different management practices. A distinct landscape pattern in soil organic matter (SOM) functionality was observed, but only a small effect of management (cultivated vs. uncultivated) was detected. We observed that both carbohydrates and low-molecular-weight aromatics. which are usualiy considered readily degradable, were apparently stabilized in divergent (i.e.. water-shedding) slope positions, while lipids and high-molecular-weight lignins were enriched in depressional areas. We posit that tillage incorporation was probably responsible for the enrichment of older, microbially altered carbohydrates and lignins at divergent positions. Using novel application of nonmetric multidimensional scaling ordination to XANES data, we observed more heterocydic N compounds in cultivated vs. uncultivated soils. The XANES data also showed the presence of unique, oxidized N-bonded aromatics, which predominated at calcareous divergent slope positions. These types of organic N compounds are rarely reported in the literature except for samples obtained in acidic or anaerobic environments. This study provides analytical evidence that C and N ^-edge XANES and Py-FIMS differentiate SOM composition at the molecular level from soils obtained from diverse topographic positions and management regimes in a hummocky prairie landscape. Results provide complementary evidence that SOM comprises more stabilized compounds at divergent slope positions and more active compounds at depressional positions.

The Composition and Stability of Clay-Associated Organic Matter along a Soil Profile

“…The decreasing abundance of sterols with soil depth is due to the lower input of plant materials, since sterols originating from octacosanol/nonacosanol at, m/z 392/406 ( Figure 3) [55,56], are of a plant origin. The relative proportions of alkylaromatics in the summit soil are comparable to those reported for the well-drained cultivated soils by Py-FIMS analysis [57,58]. The thermal stability of alkylaromatics showed no variation with soil depth and, thus, the greater proportion of alkylaromatics in subsoils is not due to the increased protection with soil depth.…”

Manipulation of rhizosphere organisms to enhance glomalin production and C sequestration: Pitfalls and promises

“…Despite strong differences observed between soil organic matter components in whole soil samples using XANES and Py-FIMS (Gillespie et al 2011b), no patterns of differences were found between GRSP extracted from different soils. This implies that GRSP is either uniform across soils or that the extraction method favors the production/extraction of similar substances.…”

“…Glomalin-related soil protein was obtained using the citrate extraction and autoclaving method and soils from a landscapescale study described elsewhere (Gillespie et al 2011b). We demonstrated that XANES and Py-FIMS were useful for describing the bulk GRSP mixture as well as the composition of the non-proteinaceous materials (Gillespie et al 2011a).…”

Long term effects of reduced fertilizer rates on millet yields and soil properties in the West-African Sahel

“…Carbohydrates are a preferentially degraded carbon form, and are released from decomposing polysaccharides. Carbohydrate content tends to decrease as decomposition proceeds (Kögel-Knabner 2000; Gillespie et al 2011). One study of temperate soils found that carbohydrates were lower in depleted soil where fertilizer was not applied, due to lower plant inputs and greater turnover of those inputs (Kiem et al 2000).…”