Comparing the effects of soil fauna on litter decomposition and organic matter turnover in sustainably and conventionally managed olive orchards

Soils and crops in Mediterranean agrosystems are vulnerable to climate change and environmental stresses, and they will be more and more in the next future. In this scenario, soil organic matter (SOM) plays a crucial role and its level is principally determined by the continuous physical and chemical action of soil fauna. While the importance of microorganisms in fruit agrosystems has been extensively and recently highlighted, the role of soil fauna - and particularly of macrofauna - to ecosystem services has been often overlooked. On this basis, the aim of this study was to characterize and compare C/N dynamics and other soil physicochemical parameters, soil macrofauna abundance, bioturbation and litter/SOM decomposition indices in a Mediterranean olive (Olea europaea L.) orchard subjected to two different soil management systems (namely sustainable, Smng, and conventional, Cmng) for 18 years. The adoption of the Smng system significantly increased almost three times the abundance of earthworms and two times that of other soil macrofauna. Bioturbation due to soil fauna and roots was significantly higher in the Smng system, and this caused a significantly faster SOM decomposition measured both in 90-day incubated local litter bags (decomposition constant = 0.092 and 0.072 in the Smng and Cmng system, respectively) and in tea bags (decomposition rate constant = 0.018 and 0.010 in the Smng and Cmng system, respectively). Soil C and N dynamics were also affected by different soil management. The results highlighted that the soil chemical quality of the Smng system is the result of the higher abundance and activity of soil fauna, in terms of enhanced litter decomposition and bioturbation. From the general analysis of the data obtained, it emerged that the role of soil fauna should be seriously taken into account in land management strategies not exclusively oriented to fruit yield and quality, but also to soil fertility restoration.