Soil Carbon in the World: Ecosystem Services Linked to Soil Carbon in Forest and Agricultural Soils

Soil C can protect the environment from global changes. Indeed small relative changes in soil abundance content and composition can affect Earth ecosystem processes. Organic C loss from soil generally increases carbon dioxide emissions. On the other hand, the formation and conservation of soil organic C improves soil stability, primary production, C sequestration, waterholding capacity, biodiversity, nutrient cycles, and soil fertility, and therefore allows the maintaining of ecosystem services essential to human well being. OM can bind clay and silt components to form soil colloidal organomineral aggregates, which improve soil structure, facilitate water infiltration, help hold water, and protect organic C from mineralization. OM also provides cohesive strength to soil thus improving the resistance of soil to erosion. In addition, OM provides nutrients and physical protection for extracellular enzymes, thus sustaining the biochemical processes carried out by soil organisms and plant roots. The availability of C and nutrients in soil, and especially in the rhizosphere, strongly affects activity, biomass, and composition of microbial communities. Soil management can significantly affect the relative balance of these soil processes. When soils are converted to agriculture, C inputs from plants and activity and biomass of microbial communities decline with shifts in microbial diversity; in addition, cultivation breaks up existing soil aggregates, leaving C within aggregates more vulnerable to decomposition. The irrational land-use change and wrong management options are adverse to maintaining of ecosystem services, mainly resulting in soil C losses; however, suitable measures, such as the use of crop residues, animal manure, compost, and, sewage sludge, can increase soil C storage.Despite its importance, the size of the global soil organic C stock and its distribution in space and among land-use/land-cover classes is poorly known, hence possible carbon dioxide emissions result from soil due to changes in land use and land cover. Future research should address processes, such as formation, and conservation of soil OM sink, and the relative new findings should be integrated in decision support tools for policy makers and disseminated and adopted by land managers at various levels. A better understanding of soil organic C stocks and fluxes could allow soil scientists and ecologists to monitor soil status and to predict ecosystem behavior toward climate changes. Moreover, these findings will give a solid base to assist decision makers and land managers to choose the more sustainable land-use and management options. As recommended by Schmidt et al. (2011), new research should be addressed to: (1) study the processes driving SOM stabilization and destabilization; (2) develop new soil models representing the mechanisms driving soil response to global change; and (3) connect the different research communities that are involved in studying SOM cycles and terrestrial ecology. On the basis of the continuous and higher demand of ecosystem services arising from climate change and population increase, a rational and aware management of soil C will represent one of the key strategies to reach the UN sustainable development goals in a more effective way.