Level Terrace Enhances the Distribution of Soil Organic Carbon Along the Depth Gradient in Mixed Forests: Microbial Mechanisms and Carbon Fraction Dynamics on the Loess Plateau

Soil and water conservation engineering measures exert a significant impact on soil microbial characteristics, soil factors, and soil organic carbon. However, in the Loess Plateau region of northwestern China, the influence of site preparation measures on the variations in microbial characteristics, soil nutrient availability regulators, and soil organic carbon fractions with soil depth remains insufficiently understood—and this knowledge gap is crucial for enhancing SOC sequestration. The present study measured soil organic carbon (SOC) and its fractions, soil nutrient availability regulators, microbial biomass, and enzyme activities at different soil depths in level terraces (LT) and natural slopes (NS). It aimed to reveal the regulatory mechanisms underlying the variation of SOC with soil depth under different site preparation measures.
1. Soil organic carbon and its fractions
mineral-associated organic carbon (MAOC), particulate organic carbon (POC), soil organic carbon (SOC)
2. Soil nutrient availability regulatory factors
Soil bulk density (BD) , Soil water content (SWC) , Soil pH, Total nitrogen (TN) , Total phosphorus (TP) , dissolved organic carbon (DOC) , dissolved organic nitrogen (DON), Nitrate nitrogen (NO3⁻-N) , ammonium nitrogen (NH4⁺-N) , Available potassium (AK) , available phosphorus (AP)
3. Microbial biomass and extracellular enzymes
Microbial biomass carbon (MBC) , microbial biomass nitrogen (MBN) , Microbial biomass phosphorus (MBP) . The activities of soil β-glucosidase (BG), β-N-acetyl-glucosaminidase (NAG), leucine aminopeptidase (LAP), alkaline phosphatase (AlkP), and cellobiohydrolase (CBH) .