Biostimulants in action: enhancing nickel phytoextraction in Odontarrhena decipiens (Nyár.) grown in serpentine soil

Pablo Carril ¹, Gaia Regini ², Donatella Fibbi ³, Alessio Papini ⁴, Cristina Gonnelli ², Ilaria Colzi ²

Department of Biology, Università` degli Studi di Firenze, Via Micheli 1, Florence 50121, Italy ¹, Department of Biology, Università degli Studi di Firenze, Via Micheli 1, Florence 50121, Italy ², G.I.D.A. S.p.A, Via di Baciacavallo 36, 59100 Prato, Italy ³, Department of Plant Biology, Università degli Studi di Firenze, Via La Pira 4, Florence, Italy ⁴

Nickel is a highly-demanded metal in the industrial sector, primarily due to its role in the production of lithium-ion batteries, stainless steel and nickel alloys. However, conventional methods of Ni extraction often lead to soil erosion due to the overuse of both heavy machinery and harmful chemicals, posing serious threats to the environment. In this context, agromining, i.e. the use of plants to extract trace elements from contaminated soils and to recover them from the plant biomass, offers a promising solution for the recovery of Ni from contaminated substrates, such as soils, sediments, and even activated sludge from wastewater treatment plant. In particular, hyperaccumulators from the Odontarrhena genus are specialized plants growing on serpentine soils (highly rich in Ni levels) with a remarkable capacity to accumulate extraordinarily high levels of Ni in their aboveground tissues, making them ideal candidates for agromining applications. However, since Ni accumulation depends on several factors, especially high and fast plant biomass production and soil health, it is crucial to adopt effective and sustainable strategies to maximize phytoextraction efficiency with low ecological impact. In this context, organic amendments are well-known to improve soil structure, reduce soil erosion and supply essential nutrients. Hence, by enriching the soil with organic matter, these amendments not only could support the growth of hyperaccumulator plants, but also enhance their ability to extract metals from the soil while creating a healthier ecosystem that can sustain both plant growth and metal recovery over time. In the present study, we carried out a 60-day pot experiment to evaluate the efficacy of two biostimulants - spirulin, i.e. the dried biomass produced from the cyanobacterium Athrospira platensis, and wood distillate (WD), a by-product of the pyrolysis of plant biomass - on enhancing both plant growth and Ni accumulation in Odontarrhena decipiens (Nyár.). Plants were grown in serpentine soil and treated with varying concentrations of spirulin (0.1%, 0.5%, and 1% (m/v)) and wood distillate (0.1%, 0.2%, 0.3%, and 0.5% (v/v)), which were applied in three different forms: foliar spray, fertirrigation and a combination of both. Compared to non-treated plants, O. decipiens fertirrigated with spirulin at 1% and with WD at 0.5% exhibited a significant increase in both plant fresh weight (over 50% in both cases) and dry weight (50% and 38% increase, respectively), suggesting a key role for both biostimulants in increasing plant growth and overall biomass production. Regarding the Ni accumulation, application of 0.1% WD increased plant leaf Ni content by 45%, indicating that both WD-mediated biomass increase and Ni accumulation improvement were not directly correlated. On the other hand, application of 1% spirulin showed the highest leaf Ni accumulation, which increased significantly compared to non-treated plants, suggesting a dual role for this concentration in boosting both plant biomass and phytoextraction capacity. The present findings not only contribute to the understanding of agromining as a sustainable metal recovery approach, but also underscore the viability of incorporating biostimulants into agromining strategies to maximize metal recovery while potentially promoting ecological restoration of contaminated areas.

Main author career stage: Postdoc / Fellow

Contribution type: Talk

First choice session: 4. Structure, physiology, and development

Second choice session: 3. Biodiversity and global change