Forest litter and carbon cycling

Ecosystems and the goods and services they generate for the human society are critical to the Earth’s life support system. Forest ecosystems, in particular, provide many functions and services to Human society. They participates to provisioning and regulation ecosystem services. Indeed, they are a source of wood production, they represent an important part of carbon storage, and they protect soils against erosion. Moreover, they are important sinks of plant and soil biodiversity.

Roughly, 90% of global terrestrial plant production enters the soil dead organic matter pool. This organic matter is fragmented by fauna, and/or decomposed by microorgansims. A part of this organic matter is then humified and forms humus (=organic superficial soil layers), which can represent a great part of carbon sequestration. Besides humification, leaf litter decomposition converts dead organic matter into CO2 and inorganic nutrients (=mineralisation) available for plants. This process is directly involved in the carbon budget dynamics of ecosystems, determining the role of sink vs source of carbon in soils.

Litter decomposition is mainly a biological process involving soil microorganisms (bacteria, fungi) and fauna (micro-, meso- and macro-fauna). This process depends on three factors:

(i) environmental conditions as temperature, precipitation;

(ii) litter chemical quality such as nutrients content (e.g. nitrogen) but also structural compounds (e.g. lignin) and specialized metabolites (e.g. phenolics or terpenoids which are known to be defense compounds against herbivory or environmental stresses);

(iii) biodiversity, biomass and activity of soil organisms.

Leaf litter decomposition is then a process relying ecosystem structure and functioning, and is a good predictive tool to evaluate the impact of global change on ecosystem functioning.

See also: Soil fauna