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Second field campaign at Pierrelaye: Long-term phytomanagement at one of pHYBi’s trial sites

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Pierrelaye is one of pHYBi’s key phytoremediation trial sites, located in the north-west of Paris (Île-de-France). Throughout the project, partners from the Chrono-environnement Laboratory at the University of Louis Pasteur (Montbéliard) are conducting a series of field monitoring campaigns at this site. These activities help to establish an initial baseline and closely track how remediation processes evolve under real-world conditions.

The Pierrelaye case study: from contamination to a living laboratory for phytomanagement

From the late 19th century to the early 21st century, the Pierrelaye agricultural plain was used for the disposal of untreated domestic wastewater rich in organic matter and salts. This practice led to long-term soil contamination with trace elements such as lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd). Intensive market gardening (maraîchage) further accelerated soil degradation. Data from the BIOSYSMO project also revealed elevated levels of PAHs and pesticide residues, with concentrations reaching up to ten times those found in nearby non-irrigated reference soils.

 

Today, pHYBi builds on earlier phytomanagement efforts by working with existing poplar plantations established 15–20 years ago. These plantations provide a unique long-term setting and form the basis of a circular approach to restoring and valorising the site.
 

 

The project focuses on monitoring and optimising the existing system, including the valorisation of poplar biomass through lignocellulosic fractionation pathways in line with circular bioeconomy principles. At the same time, pHYBi investigates how long-term field conditions influence remediation processes and provides a platform for testing new poplar hybrids with improved performance under suboptimal soil conditions, benchmarked against controlled experiments.
 

The site also offers a valuable reservoir of soil microorganisms adapted to these challenging conditions. By studying soil–plant–microbe interactions, including endophytic fungi, using both culture-dependent and culture-independent approaches, pHYBi aims to better understand their role in poplar performance and resilience in marginal soils.   

 

Monitoring campaigns tracking soil evolution at Pierrelaye
 
Over the course of the project, three field monitoring campaigns are conducted at the Pierrelaye site to assess how soils and vegetation evolve under long-term phytomanagement conditions.
 
The first campaign, carried out last year, focused on the physicochemical characterisation of both topsoil and subsoil. While trace elements are typically concentrated in topsoil, the presence of 15–20-year-old poplar plantations raises an important question: what happens at depth when roots gradually explore and modify subsoil conditions over time? Subsoil compartments are still poorly understood, yet they may play a key role in long-term system functioning, both as a potential zone for trace element redistribution and as habitats for largely unexplored microbial communities.
 

This baseline survey, based on LUCAS sampling, included key soil properties (pH, texture, organic carbon, etc) as well as measurements of total and bioavailable trace elements, providing a robust reference for tracking future changes.

 

Recent activities: biological indicators and dedometric measurements 

During this year’s campaign, project partners Humberto Castillo-González and Michel Chalot, together with Nicolas Garneret (research assistant engineer) and Enguerrand Denoux (M1 Master’s student completing a 10-week internship within pHYBi), focused on screening for biological indicators and monitoring trees to better understand ongoing phytoremediation processes at the site. 

Soil samples were collected for microbial activity and community structure, including assessment of mycorrhizal colonization, providing insight into belowground biological functioning. At the same time,  dendrometric measurements were carried out using a laser-based device to characterize growth. Leaf, bark, and wood samples were also collected for chemical analyses, allowing the scientists to track trace-element uptake and accumulation within plant tissues. 

To support plantation-scale monitoring, drone imagery was acquired across the approximately 6-hectare plantation. However, the complexity of the canopy structure made data acquisition challenging, leading to further exploration of complementary remote sensing approaches.

 

What the latest monitoring reveals about fungi, poplars and soil recovery at Pierrelaye 

The latest monitoring campaign at the Pierrelaye site highlights how long-term phytomanagement, past land use, and current poplar plantations interact within a complex soil–plant system. 

  • The site is characterised by coarse, sandy, near-neutral soils, which strongly control water movement, nutrient availability, and trace element behaviour. 
  • One notable finding concerns the legacy of mycorrhizal inoculation carried out around 15 years ago. Ectomycorrhizal structures are visible on some poplar roots as white, star-like branching patterns. Are these the same fungal partners introduced 15 years ago, or new ones that have taken over in the meantime? That’s still under investigation. 
  • Among the several poplar varieties present at the plantation, Skado was selected within pHYBi for further focus and valorisation. One of its particular features is its high leaf turnover, which contributes to limiting spontaneous vegetation. Clear differences in vegetation structure are observed between planted and unmanaged areas. 
  • Phytotoxicity tests show that soils from historically managed plots support higher germination and improved root elongation compared to untreated soils. In parallel, bioavailable trace element concentrations are generally lower in managed areas, consistent with long-term changes in metal behaviour, including reduced mobility in soils and potential transfer into plant biomass 
  • Finally, poplar trees and their rhizosphere act as active microbial reservoirs, supporting diverse microbial communities. Metagenomic data further show that this biological activity extends into deeper soil layers, confirming that subsoil compartments are far from inert.