Humusica 1, article 8: Terrestrial humus systems and forms – Biological activity and soil aggregates, space-time dynamics

In: Applied Soil Ecology, 2017, 122, pp. 103-137. Litter biodegradation is a process of life. Organisms feed, reproduce, die and decompose. Decomposition is essential, and it is never complete. In addition, the elements generated by this process become new bricks for building more complex structures in a dynamically evolving environment. In this article, we show some pictures of the main actors in litter biodegradation. We also try to associate living organisms to the soil aggregates they generate, furnishing photographs of organisms and aggregates visible in the field even with a naked eye. The transformation of dead bodies, organs or cells and droppings in the soil ecosystem is influenced by biotic and abiotic factors and hence it must be considered as a dynamic, never ending, local evolution. Instead of focusing on specific data, we have tried to present the involved phenomena to a non-specialised public (naturalists, students, teachers, etc.) through the use of graphical schemes, indicating arrows, photographs, and drawings. In the end, readers will be aware that things are not as simple as expected, that static models cannot give a precise image of a reality in constant evolution. The article can be inspected as a photo album, read as a comic strip or used as a dictionary. The authors aim to illustrate rather than to explain the relationships between humus systems, climate and biodiversity.