Invertebrate control of soil organic matter stability

The control of soil organic matter (SOM) stability by soil invertebrates is evaluated in terms of their impact on the inherent recalcitrance, accessib ility to microorganisms, and interaction with stabilizing substances of org anic compounds. Present knowledge on internal (ingestion and associated tra nsformations) and external (defecation, constructions) control mechanisms o f soil invertebrates is also reviewed. Soil animals contribute to the stabi lization and destabilization of SOM by simultaneously affecting chemical, p hysical, and microbial processes over several orders of magnitude. A very i mportant aspect of this is that invertebrates at higher trophic levels crea te feedback mechanisms that modify the spatio-temporal framework in which t he micro-food web affects SOM stability. Quantification of non-trophic and indirect effects is thus essential in order to understand the long-term eff ects of soil biota on SOM turnover. It is hypothesized that the activities of invertebrates which lead to an increase in SOM stability partly evolved as an adaptation to the need for increasing the suitability of their soil h abitat. Several gaps in knowledge are identified: food selection and associ ated changes in C pools, differential effects on SOM turnover, specific ass ociations with microorganisms, effects on dissolution and desorption reacti ons, humus-forming and humus-degrading processes in gut and faeces, and the modification of invertebrate effects by environmental variables. Future st udies must not be confined merely to a mechanistic analysis of invertebrate control of SOM stability, but also pay considerable attention to the funct ional and evolutionary aspects of animal diversity in soil. This alone will allow an integration of biological expertise in order to develop new strat egies of soil management which can be applied under a variety of environmen tal conditions.