01 Aug Paper In Geoderma
Title:¨Effects of soil sterilization and metal spiking in plant growth promoting rhizobacteria selection for phytotechnology purposes¨ Partners involved: UCP-CRP Publication data: Helena Moreira, Sofia I.A. Pereira, Ana P.G.C. Marques, António O.S.S. Rangel, Paula M.L. Castro (2018)
Abstract: The contamination of the soil with heavy metals (e.g. Zn) is a serious and crosscutting issue worldwide. Phytotechnologies can minimize the negative impact of this problem using plants and microorganisms in soil rehabilitation. However, the efficiency of proper plant-microbe combinations is usually assessed using spiked and/or sterilized soils, which do not mimic the conditions in situ, and therefore can lead to outcomes that will not be observed under field situations.
This study aimed to quantify the effect of soil origin and sterilization on the performance of the two plant growth promoting rhizobacteria (PGPR), Ralstonia eutropha 1C2 and Chryseobacterium humi ECP37, for promoting the growth and metal accumulation of maize plants. A two-experiment approach was applied: the PGPR were inoculated in maize plants growing in (i) sterilized soils spiked with Zn (0, 100, 500 and 1000 mg Zn kg−1); and in (ii) a field-contaminated soil, under sterilized and non-sterilized conditions (599 mg Zn kg−1). Biomass and Zn accumulation in the root and shoot, and Zn bioavailability in soils were determined. Additionally, lipid peroxidation, activity of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were assessed in the shoots of plants grown in the field-contaminated soil, as well as the composition of the rhizospheric bacterial community.
Zn in the soils negatively affected maize growth, and its effect was strongest in the field-contaminated soil. Overall, PGPR attenuated the negative effects of Zn by improving plant growth, although less pronounced in non-sterilized soils. Sterilization significantly reduced soil Zn availability and affected its’ accumulation in plant tissues. Bioinoculants performance was also different in sterilized soil, i.e., bacteria had no effect in the accumulation of Zn but tended to increase the biomass of maize plants. Despite the higher Zn accumulation in shoot tissues, lipid peroxidation was lower whereas antioxidant enzymes were enhanced in non-sterilized soils, suggesting that plant antioxidant system functioned properly. PGPR tended to decrease the diversity of the rhizospheric community.
This study highlights that while inoculation with PGPR is effective in increasing Zn bioavailability in soil, accumulation in the plant and maize growth in Zn-contaminated soils, the extent of their effect can be different depending on whether the soil is field-contaminated or metal spiked, and on whether is sterilized prior contaminated. Consequently, the effect of bacterial inoculants assessed exclusively in metal spiked soil and/or sterilized soil may be overestimated, and potentially not transferable to field conditions.