Introduction

Carbon (C) is key element of any ecosystem. It has multiple forms (gaseous, mineral, organic) across wide spatial (from micro- to global) and time scales. C plays functional role in all spheres of earth (land and soil "litho- and pedo-", living organisms "bio-", air "atmo-", water "hydro-"). Current learning toolbox is mainly covering topics of C pools, forms, dynamics and related processes in soil-plant system. Principle is to handle topics from simple overview in to the deep details in specific sub-topics.

Carbon pool is a reservoir of carbon in defined part of earth system. In terrestrial ecosystem above- and belowground biomass, litter, dead wood and soil organic carbon are forming carbon pool. Carbon stock is a quantity of carbon mass within a specified space in pool at a specified time.

Flux is a transfer of carbon from one pool/stock to another. In many pools C can be quite dynamic. Autotrophs (mainly higher plants) capture carbon from atmosphere in the form of CO2 relatively rapidly through photosynthesis. When plants die, organic matter will be decomposed by heterotrophic organisms and C is transferred back to air. Part of organic matter will stored in various phases of decomposition in soil for longer period. Depending on balance between sequestration (capture and storage) and release of C, terrestrial pools can act as sink or source of C. Global soil organic carbon stocks (ca 1500 billion tons) are estimated to be triple compared to biosphere and double compared to atmosphere C reserves. Thus, sustainable land use and soil management has gained more highlight also in the context of global climate change.

Carbon is key element of soil organic matter (SOM). Carbon and organic matter cycling are not only global issues but are determining many ecological processes and functions in local level. Almost all C capture or release processes in plant-soil system are happening cell or molecular level and have biochemical and/or microbial nature. Organic matter is main soil quality indicator and linked to many soil functions and bioeconomy sectors.