Agronomy Research Expertise in Montpellier and Languedoc-Roussillon (South of France)

Agronomy : crops and cropping systemse

Keywords :

Rhizosphere–a suitable scale for assessing the phytoavailability of trace elements?

2. Minimizing the impact of cropping on biogeochemical cycles

2. Minimizing the impact of cropping on biogeochemical cycles

In situ sampled (1.5-4 mm thick) durum wheat plant with soil attached to its roots, representing the rhizosphere. - © M.Bravin Plants are key constituents of agroecosystems,so it is essential to study soil-plant transfers (phytoavailability) of trace elements (TE) in contaminated agricultural soils. Some TE such as arsenic (As) can accumulate in plants, with a high subsequent risk of contaminating the food chain. Other TE like copper (Cu) are mainly phytotoxic and affect crop yields. Research teams are assessing these risks by focusing on the rhizosphere, i.e. a thin soil layer (a few hundreds of micrometres to a few millimetres thick) in contact with roots and whose physicochemical properties are highly affected by root activities. Rhizospheres can be studied in situ by collecting soil attached to roots, but experimental laboratory tests, such as the RHIZOtest, which is based on the physical separation of soil and roots, can be used for a more in-depth analysis of the impacts of rhizosphere processes on TE phytoavailability.

In Southeast Asia, the high availability of As derived from irrigation water in flooded rice field soils boosts the risk of high As phytoavailability. However, in these soil reducing conditions, rice favours the formation of a matrix of iron oxyhydroxides on the surface of roots, which tend to sequester As in the rhizosphere and reduce its phytoavailability. In Languedoc-Roussillon region (France), studies on rhizosphere processes are also helping to gain insight into the development of Cu phytotoxicity in durum wheat in some former vineyard soils. In very acidic soils, plants reduce Cu phytoavailability by highly alkalizing its rhizosphere. Conversely, in calcareous soils, root exudates released by the plant into its rhizosphere exacerbate Cu phytoavailability, thus promoting its phytotoxicity. These two examples highlight the importance of conducting studies focused on rhizosphere processes to assess TE phytoavailability.

Contact(s) :
Matthieu Bravin, matthieu.bravin@cirad.fr
Emmanuel Doelsch, doelsch@cirad.fr
Philippe Hinsinger, hinsinger@supagro.inra.fr

Publication date : 30/05/2010

Reference(s)

Michaud AM, Bravin MN, Galleguillos M et Hinsinger P 2007 Copper uptake and phytotoxicity as assessed in situ for durum wheat (Triticum turgidum durum L.) cultivated in copper-contaminated, former vineyard soils. Plant Soil, 298, 99-111.
DOI link/ publisher web site

Bravin MN, Michaud AM, Larabi B et Hinsinger P 2010 RHIZOtest: A plant-based biotest to account for rhizosphere processes when assessing copper bioavailability. Environ. Pollut., 158, 3330-3337.

DOI link/ publisher web site

More illustrations

RHIZOtest, laboratory test set up to assess the impact of rhizosphere processes on the phytoavailability of trace metals.- ©M. Bravin




 


 
 

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