Abstract
Ecological engineering of degraded ecosystems often manipulates plants, with positive outcomes for their restoration or ecosystem services production. The importance of soil biota for successional plant communities has prompted consideration of direct inoculation (active) or attraction (passive) of soil organisms as a relevant restoration strategy. However, few attempts have manipulated soil invertebrates as part of nature based solutions for ecosystem restoration, despite their major role in many soil ecological processes and in plant-soil feedback processes. In addition, while ecological restoration and ecological engineering approaches successfully incorporate plant traits, soil invertebrate traits remain underused. Exploiting the functional diversity of soil communities by adopting a trait-based approach could enhance restoration of soil chemical, biological and physical properties. Here, we conduct a narrative review and identify a set of soil invertebrate functional traits with great potential in ecosystem restoration. We focus on traits related to four main ecological functions that are often at the core of restoration plans: nutrient cycling and carbon cycling, pollutant detoxification, soil structure arrangement, and biological control agent by prey/pest regulation. This paper further proposes guidelines for stakeholders that need to be addressed to successfully integrate soil organism traits into ecological engineering. Finally, we highlight main knowledge gaps and limitations currently impeding the use of soil invertebrate traits in ecological engineering, and identify avenues for future research. We especially bring out (i) that few studies still use soil invertebrates in restoration, so even fewer are based on traits, (ii) a lack of data about soil invertebrate species role in ecosystems, (iii) a lack of data about attributes from specific traits and groups in existing soil functional trait databases, (iv) the complex relationships between functions and traits and (v) that future studies are needed to demonstrate the benefits of such trait-based approaches compared to approaches relying on emblematic species.