Abstract
ABSTRACT Chromium contamination in soils affects plant growth and this metal can accumulate in plants tissues. In addition, Cr can affect soil microbial biomass and activity. On the other hand, plant growth-promoting rhizobacteria (PGPR) can protect plants against metals and, at the same time, promote plant growth and could alleviate adverse effects on microbial biomass. This study evaluated five PGPR on maize growth, Cr accumulation and soil microbial biomass in a Cr-contaminated soil. Five PGPR (LCC04, LCC41, LCC69, LCC81 and IPA403), isolated from soil under permanent application of composted tannery sludge and contaminated with Cr, were inoculated in maize plants grown in soils with (+Cr) and without (–Cr) Cr. In Cr-contaminated soil, LCC41 promoted the highest growth of maize, while LCC04 contributed with the highest N accumulation. The shoots of maize accumulated less Cr with LCC81, while LCC41 contributed to the highest Cr accumulation in roots. The translocation of Cr was highest with IPA403, while LCC81 contributed to reduce Cr translocation. In conclusion, LCC41 and LCC81 could be effective as PGPR inoculants to promote plant growth and reduce Cr accumulation in maize, respectively, in Cr contaminated soil.
Highlights
The accumulation of metals in soils has been an important environmental issue, since these elements are not naturally degraded, persist in the ecosystem and are translocated to different parts of plants (Ogundiran and Osibanjo 2009)
Five plant growth-promoting rhizobacteria (PGPR) (LCC04, LCC41, LCC69, LCC81 and IPA403), isolated from soil under permanent application of composted tannery sludge and contaminated with Cr, were inoculated in maize plants grown in soils with (+Cr) and without (–Cr) Cr
The PGPR showed no significant effects with respect to RDW, compared to the control, in noncontaminated soils; LCC41 showed a greater RDW than LCC81 (Fig. 1b)
Summary
The accumulation of metals in soils has been an important environmental issue, since these elements are not naturally degraded, persist in the ecosystem and are translocated to different parts of plants (Ogundiran and Osibanjo 2009). Chromium (Cr) shows high accumulation in soils, especially on those with a history of application of Cr-contaminated sludge, such as tannery sludge (Araújo et al 2013, 2018). Some studies have found different microbes that showed tolerance to high Cr concentration (Miranda et al 2018, 2019), including plant growth-promoting rhizobacteria (PGPR) (Rocha et al 2019). Some PGPR have been recognized to be tolerant to metal-contaminated soils, since they present different strategies to withstand these elements (Hao et al 2014; Ojuederie and Babalola 2017). Some strategies include the secretion of enzymes and bioactive metabolites that could protect plants against metals and, at the same time, promoting plant growth (Hao et al 2014). PGPR produce and release enzymes and exopolysaccharide (EPS) that can assist in metal detoxification and, indirectly, improve plant growth (Lal et al 2018)
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