Phytotoxicity of natural soils using physiological and biochemical endpoints reveals confounding factors: can a weight of evidence tackle uncertainty?
Standard assays for phytotoxicity provide a reductionist view on the performance of plants under toxic stress. To address two of the most prominent issues in plant toxicity studies, our aims were (1) to assess how well physiological and biochemical parameters complement standard toxicological endpoints when testing natural soils and (2) to assess the suitability of three commonly used control soils as comparative references.
Material and methods
We compared the performance of Zea mays and Helianthus annuus in three control soils (artificial Organisation for Economic Co-operation and Development (OECD) soil, standard LUFA 2.2 soil, and turf-perlite) against three natural soils representing a gradient of contamination (from a deactivated uranium mine). Standard endpoints (emergence and biomass) were estimated, along with pigment content, photosynthetic parameters, cellular injury, and proline content.
Results and discussion
The toxicological profile of natural soils was highly dependent on the control soil used as reference; also, plant physiological performance was influenced by the soils’ properties. We discuss the need to interpret and combine multiple lines of evidence as a way to increase the degree of confidence one classifies soils based on their ecotoxicity, and this is where the integration of physiological and biochemical parameters bring added value.
When facing large variability in soil characteristics, it is best to collect and integrate as much information possible to strengthen conclusions about phytotoxicity of natural soils. Obviously, this refutes reductionist views and places the final conclusion in the hands of expert judgment.
KeywordsNatural and standard soils Physiological performance Plant bioassays Standard protocols
This work was supported by European Funds through COMPETE and by National Funds through the Portuguese Science Foundation (FCT) within project PEst-C/MAR/LA0017/2013 and UID/AMB/50017/2013. Maria Celeste Dias and Glória Pinto were supported by FCT by means of a post-doctoral grant (SFRH/BPD/100865/2014 and SFRH/BPD/101669/2014, respectively).
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