Reclamation of moderately degraded urban soils: creation of a cognitive model to link soil organisms’ functional traits to soil processes & functions

Human activities frequently cause soil degradation, altering its multifunctionality and therefore its capacity to provide ecosystem services. Urban soil degradation notably results in high bulk densities due to trampling and machine traffic, loss of biodiversity, and lack of organic matter. The anthropic and ecological functions of soils can then be dysfunctional.

One of the major pillars in maintaining the balance of these ecosystems are the living organisms that populate them. Through their diverse lifestyles, soil fauna plays an active role in soil functions at different scales, through the prism of their functional traits.

We would like to promote the development of “pedofauna engineering” as a tool for the ecological reclamation of moderately degraded urban soils.

A conceptual framework has been created, linking functional traits of interest to soil fauna in the water cycle regulation function. We considered two sub-functions (infiltration and retention of water) and four soil processes in relation to them (creation of porosity, bioturbation, aggregation and organic matter fragmentation). To assess the success of reclamation through functional traits, it also appears that residual activities (e.g. burrows, biogenic aggregates) of soil organisms could be considered as relevant indicators of the ecological processes.

In order to test these postulates, we have selected a list of functional traits and attributes of interest in relation to soil compaction. Three species of organisms carrying the traits of interest (Lumbricus terrestris anecic worm, Eisenia fetida epigeal worm and Porcelio scaber isopod) were introduced into cosmes with urban park soil, compacted at 1, 1.3 and 1.45 g cm^-3.

Our results demonstrate that soil organisms with their related functional traits and attributes "Strong capacity to dig burrows", "Strong capacity to move in the soil" and "Body length between 12 and 22 cm", led to the creation of macroporosity and enhance the infiltration of water into the soil.

This conceptual framework is a work in progress but can surely provide a deeper and better understanding of the who and how of soil fauna's involvement in soil multifunctionality.