The Impact of Soil-Plant Interactions on Soil Organic Carbon Sequestration across spatial scales

Soil-plant interactions are critical drivers of carbon (C) cycling in terrestrial ecosystems, influencing processes from microscale rhizosphere activity to ecosystem-scale dynamics. These interactions shape ecosystem functioning, biogeochemical cycles, and soil organic carbon (SOC) sequestration. However, bridging the gap between fine-scale processes and large-scale patterns remains a key challenge in soil science.

Here, a concept is presented that compiles a number of studies and data across various spatial scales to identify mechanisms governing biogeochemical fluxes and C pools, with a focus on linking soil organic matter pools and vegetation properties under varying environmental conditions and disturbance regimes. The key research questions include: (1) how rhizosphere C inputs (e.g., exudation and rhizodeposition) affect SOC cycling, (2) which environmental factors regulate the incorporation and sequestration of phytogenic C sources (e.g., litter decomposition, particulate organic matter, dissolved organic C), and (3) which of these processes dominate along large-scale climatic gradients.

Initial findings revealed a close tie of soil respiration to microbial carbon use efficiency in rhizosphere hotspots, directly affecting pedon-scale SOC sequestration. At the ecosystem scale, direct vegetation effects were overprinted by their interaction with geomorphological gradients, controlling SOC stabilization through aggregate occlusion and mineral association. However, ecosystem SOC dynamics exhibited substantial local variance, likely driven by complex variable interactions and small-scale rhizosphere processes. Furthermore, vegetation zones remained a dominant control of plant- and microbial-derived organic matter contributions to SOC pools across large climatic gradients.

This suggests that microscale rhizosphere processes can significantly influence large-scale C budgets. However, their functioning relies on large-scale dynamics in land management, landscape modification, and environmental gradients reshaping dominant SOC storage mechanisms. These interactions become more complex on larger spatial scales, and further research is essential to fully understand and quantify their implications.