Assessment of the energy production potential from phytoremediation derived biomass

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Effects of soil sterilization and metal spiking in plant growth promoting rhizobacteria selection for phytotechnology purposes

Publication . Moreira, Helena; Pereira, Sofia I. A.; Marques, Ana P. G. C.; Rangel, António O. S. S.; Castro, Paula M. L.

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.

2019Journal article

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Selection of metal resistant plant growth promoting rhizobacteria for the growth and metal accumulation of energy maize in a mine soil — Effect of the inoculum size

Publication . Moreira, Helena; Pereira, Sofia I. A.; Marques, Ana P. G. C.; Rangel, António O. S. S.; Castro, Paula M. L.

Heavy metals, such as Cd and Zn, are spilled in soils by several anthropogenic sources, including mining activities. Their toxic effects can be minimized using plants especially when paired with plant growth promoting rhizobacteria (PGPR), under phytomanagement strategies. Several factors can contribute to the failure of rhizobacterial inoculation, such as bacteria selection and the inoculum size. In this work five metal resistant PGPR (Ralstonia eutropha 1C2, Chryseobacterium humi ECP37, Pseudomonas fluorescens S3X, Rhizobium radiobacter EC1B and Pseudomonas reactans EDP28) were investigated for their in vitro growth promoting traits and for their ability to induce growth of maize seedlings exposed to Zn and Cd. PGPR inoculum size (10 and 20 mL) and inoculation effectiveness was assessed in energy maize sowed in a mine soil. The results showed that some bacteria only exhibited or enhanced PGP traits when exposed to metals. The bacterial strains ECP37 and EDP28 were the most efficient in improving seedling growth with increasing metal concentrations, followed by S3X. When inoculated in energy maize grown in mine soil, these same strains also outperformed the others by increasing shoot biomass and elongation, metal accumulation, and by decreasing it in roots. The most evident effect of doubling the inoculum size was the increase in Cd accumulation, which was of 17% and 31% in roots and shoots, respectively. Other effects included a slight reduction in shoots' biomass (13%) and a general decrease in P tissue content. The results obtained suggest that PGPR selection prior to inoculation in the target soils should be primarily based in seedling growth promotion under metal exposure. Additionally, the size of the inoculum applied in the soil rhizosphere appears to be important in remediation processes and should be taken into account when planning phytomanagement strategies, especially when the biomass of plants is an important demand.

2016Journal article

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