Perspectives of the Fritz‐Scheffer Awardee 2021: Profile‐ to ecosystem‐scale perspectives on soil organic matter formation as demonstrated by woody debris in forest dynamics

Soil organic matter (SOM) forms along a continuum from individual particles, pores, and aggregates to litter–soil profiles and larger ecosystems such as forests. However, forest management of SOM stocks and the carbon therein requires knowledge on which processes and factors at which scales determine SOM formation from forest biomass. As evident from woody debris at the profile scale, SOM forms through additions, transformations, translocations, and removals of litter by soil organisms and environmental components. Yet SOM stocks only increase if litter additions‐to‐removals are out of steady state or enter a new steady state that ignores older litter. Both happen through disturbance and self‐selecting feedback processes in ecosystems consisting of autotrophs, heterotrophs, and their physical environment. One such positive feedback process is litter‐SOM transformation by heterotrophs that releases nutrients that promote plant productivity and thus litter input. Stocks of litter‐SOM, heterotrophs, nutrients, and plants thus exhibit Lotka–Volterra dynamics (i.e., predator–prey interactions) and only increase when attractor states (i.e., steady series or sets of states) change due to disturbance. Evidence of evolving feedback processes and disturbance in SOM would help identify limits, potentials, and precariousness of ecosystems in light of global change, but remains to be found.