Lucie Caron defended her thesis on 10 December 2024 on the ENSAIA site.
Her work focuses on the development of soil fauna engineering, through the prism of the functional traits of soil fauna, to rehabilitate degraded urban soils.
Abstract
This thesis explores the role of functional traits of soil organisms, particularly macroinvertebrates, in the refunctionalization of moderately degraded urban soils. Urban soils are often affected by compaction, biodiversity loss, and reduced fertility. Pedofauna engineering—which refers to the use of soil organisms for the restoration, rehabilitation, or renaturation of degraded environments—presents a valuable opportunity to restore these soils.
An original cognitive model was developed to link specific soil degradations (compaction and low fertility) to the functions that need restoration. This model connects these functions to key ecological processes, such as the creation of macroporosity, the fragmentation of organic matter, and the release of nutrients. These processes are closely linked to the functional traits and specific attributes of soil fauna involved.
Laboratory experiments in mesocosms and field trials were conducted to assess how assemblages of organisms (Porcellio scaber, Oniscus asellus, Lumbricus terrestris, Eisenia fetida, Glomeris marginata, and Tachypodoiulus niger), selected for their specific functional traits and attributes, contribute to the restoration of two critical functions: the maintenance of the water cycle and the recycling of organic matter into nutrients.
The results demonstrate that these organisms play a significant role in several processes related to these functions. For example, Lumbricus terrestris showed a remarkable ability to create deep burrows, promoting the creation of macroporosity and enhancing water infiltration in lightly to moderately compacted soils. Meanwhile, Glomeris marginata proved highly effective in fragmenting organic matter, particularly in leaf-litter-enriched soils, while Porcellio scaber performed similarly well in compost-enriched soils. These findings highlight the importance of combining species with complementary functional traits to maximize their impact on ecological processes.
The study also emphasizes that the addition of appropriate organic matter is crucial to support the activity of introduced organisms and enhance soil refunctionalization. The inoculation of organisms in field conditions (Porcellio scaber), combined with the proper supply of organic matter (leaf litter and domestic compost), proved to be a key driver for accelerating the improvement of fertility in an urban garden soil.
Sérigne Ndiawar Ly defended his thesis on Monday 16 December 2024 at 2 pm in the Cuenot amphitheatre, ENSAIA.
The subject was ‘Biomolecular and ecophysiological perspectives for the selection and improvement of Bornmuellera emarginata for nickel phytomining applications’.
Abstract
"Biomolecular and Ecophysiological Insights for Breeding Bornmuellera emarginata in Nickel Phytomining Applications".
Agromining is an economical and sustainable method to recover metals from naturally metal-rich soils by cultivating hyperaccumulator plants. However, these plants are still in their wild state and lack key traits, such as high biomass, necessary for efficient agromining. This study aimed to explore Bornmuellera emarginata as a candidate for Ni agromining, utilizing large-scale phenotyping and transcriptomics to provide a novel and mechanistic understanding of nickel hyperaccumulation. The primary objective was to gain insights into the physiological and molecular mechanisms responsible for nickel hyperaccumulation in B. emarginata and to explore how this knowledge could be applied to future breeding programs. Our research revealed significant phenotypic variability in biomass and Ni accumulation within and between populations of B. emarginata across its natural range. Notably, a genotype from the Pefki (PF) population produced a yield of 145 mg Ni per plant, which is remarkable for plants grown in pots. In our physiological assays, we highlighted the high tolerance of B. emarginata to Ni exposure, with no significant adverse effects observed even at high Ni concentrations (100 µM, which is higher than typical soil levels), although a mild osmotic stress was noted. Ni accumulation was reduced in the presence of Zn at equimolar concentrations, confirming that Ni uptake is mediated by a transporter belonging to the ZIP family. Comparative transcriptomics with a closely related non-accumulator species (Alyssoides utriculata) revealed specific processes that allow B. emarginata to avoid Ni toxicity. We found an overrepresentation of processes related to cellular detoxification, metal ion transport, and monoatomic ion transport under Ni exposure in B. emarginata compared to the non-accumulator. Genes associated with iron homeostasis, which are typically involved in Ni accumulation, were expressed at higher levels in B. emarginata. The RNA-seq comparison identified ten potential candidate genes, with AtNEET and AtHMP12 emerging as the most promising for their crucial roles in Ni hypertolerance and hyperaccumulation. This study not only advances our understanding of the mechanisms behind nickel hyperaccumulation but also provides a foundation for breeding programs aimed at improving the efficiency of Ni agromining using B. emarginata.
Key words: nickel hyperaccumulators, B. emarginata, Agromining, transcriptomic, physiology, plant breeding
