Are pseudo-sands internal soil biophysical reactors?

Most biogeochemical models commonly obtain their soil input from pedotransfer functions based on soil texture and other crude but widely available soil data. However, soil texture based on single grain size distribution neglects the impact of actual soil structures in the field. Consequently, scientific efforts are being made to correct for this systematic bias in predicting soil functioning. Pronounced discrepancies between field measurements and model predictions occur for tropical soils: overestimated N2O emissions is a prominent example of this mismatch. A well-known characteristic of tropical soils, potentially responsible for the systematic error, are stable aggregates called pseudo-sands. In the field they are perceived as sand, but in the lab measured as clay and silt. The simple assumption that pseudo-sands act just like sands in the field seems to work satisfactorily for certain hydrological predictions, so models were easily adjusted to it. However, here we pursue the hypothesis that, biogeochemically, pseudo-sands do not act like sands. Due to their high internal surface and rough structure, pseudo-sands, unlike sands, provide a wide variety of ecological niches for a diverse community of microorganisms to establish. We will present first evidence for pseudo-sands to act more like a biophysical reactor than just another grain of sand. The long-term goal is to develop a transfer function related to the properties of pseudo-sands that will lead to improved models for tropical soils.