Dominant Aggregate Binding Agent Dynamics of Quaternary Ancient Red Soils under Different Land Use Patterns

Abstract

The cementation mechanisms and processes of aggregate binding agents are important in understanding aggregate formation. However, the role of threshold values and the proportions of organic and inorganic binding agents in aggregate formation remain unclear. This research investigated the dominant aggregate binding agent dynamics in a sequence comprising buried ancient red soil unaffected by modern climate changes and human activities, alongside nearby exposed Quaternary ancient red soils subjected to different land use patterns influenced by these factors in northeastern China. By analyzing soil age, aggregate compositions, and organic/inorganic indicators of binding agents, including soil organic matter (SOM), free iron oxide (Fed), poorly crystalline iron oxide (Feo), crystalline iron oxide (Fed-Feo), and total clay particles (TCL), we determined the relative contributions of different binding agents using redundancy analysis (RDA). The results revealed that the buried ancient red soil did not contain dominant binding agents in the aggregate formation before 91.01 ka BP. Due to denudation, the buried ancient red soil was exposed at the surface and experienced the importation of soil organic matter, weathering of silicate-bound iron oxides, and crystallization of poorly crystalline iron oxides resulting from the effects of different land use patterns from 91.01 ka to the present. Under the influence of binding agent dynamics, dominant binding agents in the exposed Quaternary ancient red soils’ aggregate formation changed into SOM and Fed. When the C/(Fed-Feo) molar ratio was less than 2.13, Fed-Feo was the dominant aggregate binding agent. When the C/(Fed-Feo) molar ratio was greater than 2.13, SOM was the dominant aggregate binding agent. The results of this study improve our understanding of aggregate formation and the relationship between soil organic matter and iron oxides.

Different Land-Use Effects on Soil Aggregates and Aggregate-Associated Organic Carbon in Eastern Qinghai–Tibet Plateau

“…Through the analysis of PLR and VIP, the SOC in each soil layer and aggregate fraction could be predicted well by silt and sand particles (Figure 4, VIP values > 1). The reason might be that the weak microbial activity in the high-altitude area [12] led to the universally and significantly higher contribution rate of abiotic factors (represented by silt particles) to SOC within aggregate fractions than that of biological factors (represented by RDWD EE-GRSP, T-GRSP).…”

“…Land use/land cover change (LUCC) is the primary human activity driving soil structure and organic carbon storage change [9][10][11][12]. Due to low temperatures, drought and weak microbial activity from high altitude, the decomposition, stability and accumulation of SOC in alpine grassland are different from those in the grasslands of other climate types [13,14].…”

“…Due to low temperatures, weak microbial activity and long-time accumulation, the composition and storage of SOC and soil aggregate structure in alpine grassland differ remarkedly from those in a low-altitude area [11][12][13]. Despite substantial studies on the effects of land use change on soil aggregates and SOC with aggregate factions, few studies are focused on the contribution of land use change starting from alpine grassland to soil aggregates and aggregate-associated SOC, and the influencing mechanism is still unclear.…”