Influence of initial soil carbon content on the stabilization of new carbon: a 2-year lab incubation study

The hotly debated concept of carbon (C) saturation in mineral soils not only affects our understanding of soil organic matter (SOC) dynamics but also holds critical implications for negative emissions strategies. Many recent studies have indicated that soil’s capacity to store and stabilize C in mineral form depends on the initial SOC content, i.e., the soil C saturation deficit. According to these studies, low-C soils are suggested to have a higher potential for SOC storage compared to high-C soils. In light of these considerations, our hypothesis presents a different viewpoint, suggesting that initial C content in soils mainly affects the absolute loss of old carbon (following first-order kinetics), while it will not significantly impact the soil’s ability to stabilize new C. To investigate this experimentally, we selected soils from the first German Agricultural Soil Inventory with varying C contents (0.7–14.5%) and three different soil textures (light to heavy). These soils were then incubated in air-tight glass jars, where the same amount of ¹³C labeled litter was added, along with an unamended control of each sample. After two years, soils were dried and physically fractionated into mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) using a size-cutoff of 20µm to find and δ¹³C as well as total SOC was measured. Here, we will present the first results from this lab incubation experiment, providing further systematic insights into whether the amount of initial carbon content or the ‘saturation C’ deficit truly affects the SOC dynamics with varying amounts of C contents in it.