Spatial Variation of Soil Aggregate Stability and Its Multifactorial Driving Mechanism in Mollisol Region: Insights from Latitude, Topography and Plow Layer
Description
This study’s research hypothesis focuses on the effects of latitude, topography, and plow layer on Mollisol aggregate stability in Northeast China: latitude, topographic factors (slope gradient/aspect/position/elevation), and soil depth (0–20 cm top plow, 20–40 cm lower plow, 40–60 cm plow pan) jointly regulate aggregate stability by affecting soil properties, nutrients, and SOC fractions; higher latitude (mid-to-cold-temperate) correlates with higher stability (MWD/GMD/SSI), topographic factors have weaker effects; key controlling factors differ by layer (POC/clay in plow layer/plow pan, MOC for SSI in all layers); soil properties (pH, BD, particle composition) and nutrients (TN/TP/TK) vary with latitude, indirectly regulating stability via SOC fractions. Data were collected from five hilly regions (JT, LS, BX, HL, NJ) covering a mid-to-cold-temperate latitudinal gradient, with 3 slopes/location and 3 sample points/slope (upper/middle/lower), sampling 3 soil layers. On-site, slope aspect/gradient/elevation were recorded; ~1 kg undisturbed/fresh samples per layer were collected, air-dried, ground, sieved for tests. Ring knife samples measured BD and field water-holding capacity. Laboratory methods: BD (ring knife), mechanical composition (pipette), pH (potentiometric), TN (semi-micro Kjeldahl), TP (molybdenum-antimony colorimetry after HClO₄-H₂SO₄ digestion), TK (flame photometry after NaOH fusion), MWD/GMD (wet sieving), SSI (aggregate composition), SOC fractionation (wet sieving: 10 g soil + 100 mL 5 g L⁻¹ sodium hexametaphosphate, shaken, sieved, fractions >250 μm (cPOC), 53–250 μm (fPOC), MOC by difference). All samples were tested in triplicate; data (site characteristics, soil indices, aggregate stability) were presented as mean ± standard deviation (P < 0.05). Significant findings: pH, BD, silt, cPOC, TK decreased with latitude; fPOC, MOC, TN, TP, macroaggregate (>2 mm), clay, MWD/GMD/SSI increased; topographic factors correlated with silt, clay, cPOC, pH. db-RDA/VPA showed latitude (53.04%) was dominant driver, topographic factors (11.05%) weaker. PLS-SEM showed fPOC dominated plow layer MWD, cPOC/clay dominated plow pan MWD; MOC controlled SSI in all layers. Data were interpreted via descriptive statistics, Pearson correlation, db-RDA/VPA/PLS-SEM, and mechanism analysis. When using data, check triplicate reliability, select indicators by objectives, and analyze factors comprehensively, supporting Mollisol structure research and soil conservation.
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Steps to reproduce
In each of the five locations, three typical slopes were selected, with three sample points per slope based on position (upper, middle, lower). After removing surface debris, soil profiles were dug, and ~1 kg undisturbed soil samples were collected from 0–20 cm, 20–40 cm, and 40–60 cm layers using rigid plastic containers. These samples were taken to the laboratory, gently separated along natural seams into ~1 cm diameter pieces, with stones and plant residues removed. Slope aspect, gradient, and elevation of each site were recorded, and samples were air-dried in a cool, ventilated area for soil aggregate determination. Meanwhile, ~1 kg fresh soil samples were collected from each layer, sealed, and after removing stones and roots in the laboratory, air-dried, ground, and sieved for organic carbon fractions and physicochemical property determination. Ring knife samples were collected from each profile layer to measure bulk density (BD), field water-holding capacity, and other physical indicators. Collected soil samples were naturally air-dried, stones, debris, and roots removed, thoroughly mixed, ground, and sieved through 2 mm and 0.149 mm screens: 2 mm-passed samples for pH and mechanical composition analysis, 0.149 mm-passed samples for organic matter, total nitrogen (TN), total phosphorus (TP), and total potassium (TK) determination. BD was measured via ring knife method, mechanical composition via pipette method, pH via potentiometric method, TN via semi-micro Kjeldahl method, TP via molybdenum-antimony colorimetric method after HClO₄-H₂SO₄ digestion, and TK via flame photometry after NaOH fusion. Soil organic carbon fractionation used the wet sieving method: 10 g air-dried, 2 mm-sieved soil was placed in a 100 mL Erlenmeyer flask, mixed with 100 mL 5 g L⁻¹ sodium hexametaphosphate, hand-shaken for 10–15 min, then shaken on a reciprocating shaker (18°C, 150 rpm min⁻¹) for 16 h. The dispersed solution was poured through 250 μm and 53 μm nested sieves, repeatedly washed with distilled water until filtrate was clear. Sieved fractions were separated into >250 μm (cPOC) and 53–250 μm (fPOC), with MOC calculated by difference. Each fraction was dried at 60°C, weighed to calculate its percentage in total soil, then ground to pass 0.149 mm sieve; total organic carbon content was analyzed via heated potassium dichromate volumetric method. Detailed protocols are available from the corresponding author for replication.