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Dingus, Abigail [1], Roslund, Marja I. [2], Brauner, Soren [3], Sinkkonen, Aki [4], Weidenhamer, Jeffrey [5].

Toxic soils impact size hierarchies and competitive outcome.

Plant growth responses to toxic metals in soil can be density-dependent, with reduced toxicity at higher plant densities. This effect is thought to result from the exudation of citrate and other metal-binding compounds, and a study was carried out to test this hypothesis with wild-type and citrate-deficient Arabidopsis thaliana. Arabidopsis plants were grown at densities of 1, 3, 5 and 7 plants per pot in soil treated with copper at concentrations of 1, 75, 125 and 175 micrograms copper per g soil (µg/g). Plants were harvested before bolting, two weeks after treatment application. Size hierarchies were impacted by both copper dose and plant density. For wild type plants, the coefficient of variation (CV) was 0.17 and 0.33 for control plants at densities of 3 and 7 plants per pot, respectively. For plants treated with 175 µg copper per g soil, the CV values at these densities were 0.75 and 1.36 respectively. In addition, for plants in the high-density pots, the average size of the largest plant per pot increased with copper dose. In controls, the average shoot dry mass of the largest plant was 15.5 mg, while for plants receiving 175 µg/g, the average size of the largest plant was 23.9 mg, and the largest individual plant was found in the 175 µg/g treatment. Soil analyses confirmed that copper, which was applied through watering the pots, was distributed heterogeneously in the soil. We hypothesize that plants with root systems that first penetrated less-toxic regions of soil grew larger under less stress and had a competitive advantage over smaller plants. Our findings suggest that toxic substances in soil can have counterintuitive impacts on plant communities, and that plant density, along with the concentration and distribution of pollutants in soil, can shape plant communities. In soils with a heterogenous distribution of contaminants, competition for non-toxic regions of soil may drive size hierarchies and thereby determine competitive outcomes. Heterogeneous distribution of anthropogenic contaminants such as heavy metals can readily be envisioned depending on how the contamination occurred; and heterogeneous distribution of naturally occurring allelopathic chemicals is also likely. In the field, observations of plots with larger individuals would not generally suggest that toxic substances in soil were determining both plant size and competitive outcomes, yet our data suggest that this may be the case. These results also underscore the importance of plant density when assessing the effects of toxic substances through ecotoxicological testing.

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1 - MIchigan State University, Plant, Soil and Microbial Sciences, East Lansing, MI, 48824, USA
2 - University of Helsinki, Faculty of Biological and Environmental Sciences, Helsinki, Finland
3 - Ashland University, Department Of Biology, 401 College Ave., Ashland, OH, 44805, United States
4 - Natural Resources Institute Finland , Helsinki, Finland
5 - Ashland University, Department of Chemistry, Ashland, OH, 44805, USA

Size hierarchies
Metal toxicity

Presentation Type: Oral Paper
Session: ECO5, Ecology: Stress
Location: /
Date: Thursday, July 22nd, 2021
Time: 1:00 PM(EDT)
Number: ECO5003
Abstract ID:125
Candidate for Awards:None

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