Consequences of agricultural management intensity for litter-inhabiting arthropods and their role in decomposition

Background/Question/Methods

The importance of arthropods for ecological services in managed ecosystems cannot be overstated, and their roles as pollinators, predators and parasitoids have been well documented.  Yet, our understanding of the roles that arthropods play in litter decomposition, and the functional importance of litter-inhabiting arthropods in agricultural systems remains uncertain.  This uncertainty is intensified by a poor understanding of the factors which regulate the size and composition of arthropod communities in decomposing litter.  Thus, there is great incentive for characterizing the responses of arthropod communities to agricultural management intensity and determining the functional importance of these responses.  A 730 day litter decomposition study was conducted to explore the impacts of soil management intensity and resource quality on litter-inhabiting arthropods during long-term decomposition.  Variation in litter mass loss and chemistry was also assessed to identify key links between arthropod communities and litter chemical transformations during litter decay. 

Results/Conclusions

Within five days of decomposition, total arthropod density reached roughly 200 individuals per gram of litter.  Arthropod densities varied considerably over time and were heavily influenced by management intensity and litter type.  In contrast to the typical response of soil-dwelling arthropods, arthropod densities in decomposing litter increased with management intensity.  The densities of many arthropod taxa also responded negatively to initial litter carbon-to-nitrogen ratio (C:N), and temporal variation in arthropod communities during decomposition corresponded with shifts in precipitation and litter chemistry.  Additionally, the importance of management intensity for structuring arthropod communities in litter varied by litter type.  For example, collembolan densities were sensitive to management intensity when colonizing grass litter (C:N – 18), but not corn litter (C:N – 60).  Thus, management intensity is an important factor structuring arthropod communities in decomposing litter, and temporal shifts in arthropod communities during decomposition result from interactions between management intensity, litter quality, and climate.  Relationships between arthropod densities, mass loss rates, and litter chemistry reveal that variation in arthropod communities can lead to significant physico-chemical shifts during decomposition which may have long-term consequences for soil organic matter formation and stability.