Structural Variations in Soil Organic Matter with Different Soil Layers and Locations at Juniper Butte Range, Idaho.

Naturally occurring humic substances in soils hold promise as a factor favoring the restoration of native plants. We have characterized humic acids from the Juniper Butte Range (JBR) soils in Idaho, which may promote the establishment of slickspot peppergrass (Lepidium papilliferum) seedlings, using advanced solid-state NMR techniques. A series of soil humic acids from different soil layers through the soil profile, silt (0 - 2.5 cm), vesicular (2.5 - 3.5 cm), and clay (3.5 - 15 cm), as well as inside and outside of slickspots were investigated. The advanced solid-state NMR techniques used include spectral-editing such as ¹³C chemical-shift-anisotropy filtering and CH₂ selection to identify specific functional groups, two-dimensional ¹H-¹³C heteronuclear correlation NMR to detect the connectivities of different functional groups, and ¹H-¹³C recoupled long-range dipolar dephasing to selectively observe fused ring carbons. All the humic acids consist of four main structural components: aliphatic chains; peptides; sugar rings; and aromatic/olefinic carbons. Quantitative ¹³C NMR shows that with increasing depth the aromaticity increases. Samples from inside the slickspots have a lower aromaticity than those from outside the slickspots.