Original data-45-year long-term fertilization enhances soil organic carbon sequestration and soil aggregation

Exchangeable K+, Na+, Ca²⁺ and Mg²⁺ were determined. Air-dried undisturbed soil samples were sieved through a 2 mm mesh and placed on filter paper. Ultrathin sections (200 nm thick) were cut using an ultramicrotome and transferred onto a carbon-free, 200-mesh silica-coated copper grid.

SR-FTIR analysis was performed at the BL01B1 beamline, using a Thermo-Nicolet 6700 FTIR spectrometer coupled with a continuous-scan infrared microscope in reflection mode. Collected spectral data were processed. Subsequently, spectral curves representing the peak heights of Al-O (910 cm–1), Si-O-Si (1028 cm–1), aromatic C (1514 cm–1), and clay-OH (3621 cm–1) were generated.

Spectra were extracted from each discrete point (5 μm interval) and 2D-COS analysis. Results showed that SOC content and stock decreased with increasing soil depth, particularly in the 20-30 cm layer. M and MN significantly increased SOC across all soil layers.

Compared to CK, M and MN increased the proportion of soil macroaggregate (>0.25 mm) by 7.9%-18.4%, enhanced soil aggregate stability (MWD, increased by 53.3%-86.6%), and elevated intra-aggregate SOC contents. Partial least squares structural equation modeling (PLS-SEM) revealed the main driving pathways of SOC and MWD were “Fertilization-Ca2+ or Na+-MWD or Aggregates C-SOC” and “Fertilization-Ca2+ or Na+- Al-O or SOC or Clay-OH -MWD”.

Synchrotron radiation-based Fourier transform infrared spectroscopy (SR-FTIR) combined with two-dimensional correlation spectroscopy (2D-COS) analysis demonstrated that organic amendment enhances SOC sequestration by promoting the formation of clay-OH, Si-O-Si, and Al-O functional groups. The relative peak area ratios of clay-OH, Si-O-Si, and Al-O in organic amendment treatments were 0.43-2.03 times higher than those in CK.

In addition, soil functional groups exhibited high heterogeneity at microscale levels.