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The Ni biogeochemical cycle in a tropical agromining crop system

Abstract : Hyperaccumulation is a phenomenon that was only discovered 45 years ago, it has been the focused of very intensive research because of the unusual behaviour of metals in the ecosystem and also because it offers a vast potential for nature-based solutions. Describing the Ni biogeochemical cycle within the soil-hyperaccumulator plants ecosystem is necessary to elucidate the ecological role of hyperaccumulator plants in their natural environment, but also to understand their potential behaviour under tropical agromining systems. Agromining and exporting Ni rich-biomass will interrupt the cycle. It is therefore important to understand the mechanisms which govern the Ni biogeochemical cycle in both natural and agromining systems: What are the Ni cycles (internal and external) and their impact on the ecological functioning of tropical hyperaccumulator forest? How rapid are the Ni fluxes across the soil-plant compartments, and what is the turnover of Ni in a hyperaccumulator tropical system? How fast can a tropical Agromining crop deplete Ni in soil? How can we manage soil fertilisation for a sustainable tropical Ni agromining crop? Therefore, the objectives were: (i) to study the biogeochemical cycling of a natural forest of Phyllanthus rufuschaneyi in order to assess and evaluate the natural fluxes of Ni in the ecosystem; (ii) to manipulate such an ecosystem in order to perform a sensitivity test of the ecosystem for the following flux: litter return to the soil; (iii) to optimize the cropping system of P. rufuschaneyi for Ni agromining. Two parallel stands of P. rufuschaneyi were instrumented, monitored and compared over two years (2018 and 2019), (i) a natural secondary 100-m2 forest and (ii) a densely planted field in which litter returns to the soil were calibrated; from no return (export) to a doubling of the return.This study did not prove allelopathy of tropical hyperaccumulator plants, despite the extreme influence of Ni hyperaccumulators in building up available Ni stocks in topsoils. Nickel cycle was mainly driven by internal fluxes, i.e. degradation and recycling of the hyperaccumulator biomass. The percentage of Ni recycled by litterfall tended to decrease with increasing litter addition to the soil and was not influenced by coppicing, at least in the short term. Major nutrient (NPK) fertilisation did not affect Ni yield (i.e. 75kg Ni ha-1 yr-1) in the short term either, even if N fertilisation reduced Ni concentrations in leaves and plant biomass production. Nickel turnover should be taken into account when designing tropical agromining crops and natural secondary forests are a good surrogate to evaluate the long term impacts of agromining. Further study of the weathering processes would help to precise the contribution of bedrock and soil mineral horizons in the Ni and nutrient budgets of the system.
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Submitted on : Wednesday, October 6, 2021 - 9:41:12 AM
Last modification on : Thursday, July 7, 2022 - 9:32:20 AM

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Romane Tisserand. The Ni biogeochemical cycle in a tropical agromining crop system. Agricultural sciences. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0115⟩. ⟨tel-03367141⟩

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