Introduction
The soil pollution
has been considered as the “hidden danger “and a major threat to agricultural
land and ecosystem across the continents (Rodríguez-Eugenio et
al. 2018). The soil
pollution is caused by petroleum derived products, industrial byproducts,
livestock agrochemicals and municipal waste (Cachada et al. 2018).
It does not degrade soil but also reduces crop yields as well as the production
of products which is unsafe for consumption by humans and livestock. These
pollutants cause significant harm to soil microflora, soil biodiversity and
destroying the beneficial microbial population (Hentati et
al. 2013; Mair et al. 2013; Baldan et al. 2015; Ramadass et
al. 2015). The
various plant species have differential tolerance levels to these organic
pollutants (Aisien et al. 2009),
because physiological processes of plants including photosynthetic efficiency,
nutrients uptake and water relations (Iwegbue et
al. 2007; Ibemesim 2010; Ambreen
et al. 2016),
photosystem II (PSII) (Li et al. 2010; Wang et
al. 2012; Agnello et al. 2016) and
chlorophyll contents (Li et al. 2008; Njoku et
al. 2009) are the ones which are the worst affected in response
to hydrocarbon contaminated soil.
The anthropogenic and mechanical error is responsible for the
pollution of terrestrial land with petroleum hydrocarbons. The petroleum
products spreading into different parts of the environment including soil and water
due to accidental spillage worldwide, however, the exact data of petroleum
hydrocarbons pollution is a hard task to present due to unintentional
contamination. In Pakistan, in July 2003 a Greek ship (Tasman Spirit) cracked
and resulting in 28,000 tons of crude oil accidentally polluted Karachi coastal
line area. In September 2009 one more incident of an accidental spill of 18
crude oil tankers occurred in Sindh, Pakistan as a result of crashing two
freight trains (Khan 2009). Another incident in Korangi Town Karachi, Pakistan
was that the residental of the area found oil in their houses, streets, and
shops because of destruction in the pipeline of Pak Arab Refinery Corporation
(PARCO) while working of underground construction by Sui Southern Gas Company
(Alam 2008). The big oil spillage incident of two NATO oil tankers having
60,000 liters of gasoline collapsed on Khojak Pass near Chaman, Pakistan.
Moreover, petroleum hydrocarbon contamination happened during the extraction of
crude oil at well places, and petroleum refinery industries. The industries of
petroleum refining in Pakistan are situated in Multan, Kot Adu, Qasaba Gujrat,
Rawalpindi, and Karachi are the origin of contamination of oily residues
sulphides, phenols, and hydrocarbons (NEPP 1999).
The extremely intricate and lethal petroleum
hydrocarbons contaminate the surroundings though, complicates elimination. The
conventional method (excavation, incineration, supercritical fluid
oxidation and encapsulation, thermal desorption) are used for the cleanup of
polluted sites (Peng et al. 2009; Khan
et al. 2014) whereas these pollutants are
necessary for immediate elimination and to constrain oil dispersal (Dixit et al. 2016). However, these
methods exhibited demerits including high cost because of fuel consumption and
less ecofriendly to environment and people (Kaimi
et al. 2006). The eradication of petroleum hydrocarbons from the
environs is done by an effective approach of phytoremediation (Pilon-Smits 2005; Afzal et al. 2012)
Bioaugmentation is a promising strategy that remediates or detoxifies petroleum hydrocarbons with
particular enzymatic characteristics by stimulating hydrocarbons microbial
decontamination (Yousaf et al. 2010;
Afzal et al. 2013; Sessitsch et al. 2013; Afzal et al. 2014;
Souza et al. 2014; Hou et al. 2015; Xun et al. 2015;
Fatima et al. 2016; Shahzad et al. 2016; Zhang et al.
2016; Ummara et al. 2020). Consequently, Plant and microbe are
used together for detoxification of recalcitrant hydrocarbon pollutants (Jabeen et al. 2016; Guo et al. 2017).
Bacterial
inoculation of Streptomyces sp. (Palaniyandi et
al. 2014) in tomato and Burkholderia
phytofirmans (Naveed et
al. 2014) in maize alleviated the stress condition and
subsequently enhanced biomass production. Under stress
condition, in Brassica juncea
inoculation (Trichoderma harzianum)
mitigated Na+ uptake whereas progressed nutrient up take,
acquisition of antioxidant and osmolytes (Ahmad et
al. 2015). The ACC deaminase activity and production
of indole acetic acid (IAA) were ameliorated by inoculation of Pseudomonas sp. and Acinetobacter sp. in barley and oats under stress condition (Chang et al. 2014). Plant growth
regulator directly enhanced by microbes including nitrogen fixation, Fe and Zn
sequestration, K and P solubilization, phytohormone and siderophore production (Almaghrabi et al. 2013; Meena et
al. 2017).
There
are evidences that various bacterial strains could be utilized to degrade PAHs.
Therefore, the research studies were undertaken to quantify the efficiency of
the isolated bacterial strains to degrade the hydrocarbons and to determine
their effects on maize crop. A vast polluted waste land is
lying around high ways which could be utilized to grow cereal crops after
degrading with bacterial strains. This research provides valuable understanding
concerning physiological and biochemical effects of diesel contaminated soil
and bacterial consortium on maize crop which could be used to subsistence the
bioremediation strategy.
Materials
and Methods
Experimental design
The pot-culture
experimental studies were undertaken at the Institute of Pure and Applied
Biology, Bahauddin Zakariya University, Multan-Pakistan. For two maize crop
seasons (October–November 2017 and March–April 2018). The treatments were
consisted of two maize varieties (MMRI -Yellow and Pearl- white) (b), four regimes
of diesel (0.0,1.5,2.5,3.5 g /kg soil) and (c) two bacterial strains
inoculation levels, (non-inoculated) and inoculated with Pseudomonas
aeruginosa BRRI54, Acinetobacter sp. ACRH80 and Acinetobacter sp.
BRSI56. The treatments were arranged in a three factor factorial
with completely randomized design and each treatment was repeated four times. The strains P. aeruginosa BRR154 and Acinetobacter
BRSI56 were isolated from the root and shoot of Brachiaria mutica, respectively, whereas Acinetobacter sp. strain
ACRH80 was isolated from the rhizosphere of Acacia
ampliceps (Fatima et al. 2015).
These bacteria were capable to degrade a range of hydrocarbons having alkane
hydroxylase gene (such as alkB) and exhibiting plant growth-promoting characteristics (phosphate
solubilization, siderophore production, and 1-aminocyclopropane-1-carboxylate
(ACC) deaminase activity) were previously
characterized and reported by Fatima et
al. (2015).
Seed inoculation
Bacterial strains were grown in LB broth at
30°C on a shaker (100 rpm). The LB broth medium
used for the culture of bacterial strains was harvest by centrifugation
at 10,000 rpm for 10 min. Further washed and
resuspended in sterilized normal saline solution (0.9% NaCl, w/v). Then seed
and soil inoculation were done by using bacterial suspension (Afzal et al. 2012; Ummara et
al. 2020). Before sowing, the seeds were
surface-sterilized in a 5% (v/v) NaOCl for 10 min, washed three times with
sterilized distilled water. After sterilizing, the seeds were dipped in the
prepared bacterial inoculum (108 cfu mL-1) for 2 h and numeration of
bacterial inoculants in the rhizosphere soil, shoot and root samples collected
at the time of harvest was checked and reported in latest study (Ummara et al. 2020). The pots
were arranged in a green house in a completely randomized block designed. The plastic pots were filled with 6 kg of
soil and contaminated with various levels of commercial disease. Five plants
were maintained in each pot by thinning at 7 days after germination.
Estimation of chlorophyll (Chl) content and chlorophyll
(Chl) fluorescence
The estimation of Chl a, b, total Chl,
carotenoids were carried out as previously described with certain modifications
(Aronoff 1946). Briefly, 0.2 g of the fresh leaf was
grinded in 80% acetone and absorbance was read at 663 nm, 645 nm, and 470 nm.
Photosynthetic efficiency parameters (Y(II), Fv/Fm, NPQ) were determined using
a Dual-PAM 100 (Heinz Walz, Effeltrich, Germany) subsequently maize was
adapted to the dark for 30 min, where YII (PSII quantum yield effectiveness),
Fv/Fm (maximum quantum yield of PSII after dark adaptation), NPQ (PSII
photo-inactivation and constitutive heat dissipation).
Estimation of total soluble proteins and
total free amino acid (TPS and TAA)
TPS was quantified by using bovine serum
albumin (BSA) as a standard procedure with some modification (Bradford 1976). 0.2 g of fresh leaf tissue was
homogenized in phosphate buffer (pH 7.8, 4 mL) and centrifuged at 10,000×g. TAA
content was quantified by using the following protocol (Hamilton et al. 1943). The quantification was done by treating
the sample with 2% ninhydrin (1 mL) and 10% pyridine (1 mL). The absorbance was
taken at 570 nm and leucine as used as a standard.
Estimation of Na+ and K+
For the estimation of Na+ and K+
ions, dry sample (leaf and root, 0.1 g) was digested in 2 mL of sulfuric-
peroxide digestion mixture (Wang and Zhao 1995).
Then deionized water was used to maintain the volume (50 mL) of each sample.
The estimation of Na+ and K+ ion analysis was done by
using a flame photometer.
Gas exchange attributes
For the measurement of leaf gas exchange
attributes comprising, A, E, A/E, gs, and
Ci using an open system Ci-340
portable photosynthesis system (CID, USA). The measurements were made from
10:00 am to 14:00 pm with the subsequent amendments: leaf surface area 6.3 cm2,
ambient CO 2 concentration 385μmol mol−1, temperature of
leaf chamber fluctuating from 40 to 43°C, leaf chamber volume gas flow rate (v)
1068 mL min−1, leaf chamber molar gas flow rate (U) 1052 μmols−1,
ambient pressure (P) 100.09 kPa and PAR (Q leaf) at leaf surface maximum up to
874 μmol m−2 s−1.
Statistical analysis
SPSS software package (SPSS In., USA.) and
Excel (Microsoft, U.S.A.) was used to perform statistical analyses. Duncan’s
multiple range tests were applied for the analysis of variance and LSD between
means of data.
Results
Chlorophyll constituents
The quantum of chlorophyll constituents
i-e., ‘a’, ‘b’, total chlorophyll and carotenoids contents were degraded
significantly (p<0.001) with each increment of diesel oil stress in both
verities viz., “MMRI Yellow” and “Pearl White” of maize crop (Table 1).
However, the values of chlorophyll pigments were significantly increased in
maize plants grown when the soil was inoculated with bacterial strains as
compared to the non-inoculated growth medium. The contents of chl. ‘a’, ‘b’,
total chlorophyll and carotenoids were increased by quantum of 32.3%, 59.8%,
40.9%, 31.9%, respectively in var. MMRI Yellow grown on inoculated growth
medium over the non –inoculated soil condition. On the other hand, var. Pearl
White grown on inoculated growth medium contained lower values of chl, a, b,
total chlorophyll, and carotenoids by an amount of 27.6%; 56.5%; 36.8%; 9.8%,
respectively compared to non-inoculated soil environment.
Chlorophyll fluorescence attributes (Y (II),
Fv/Fm, NPQ)
The values of attribute Y(II) were reduced
significantly (P<0.001) in crop plants on growth medium contaminated with
3.5gkg-1 diesel oil (Fig. 1A). However, the content of Fv/Fm was
substantially increased in maize crop growing on inoculated soil medium (Fig.
1B). The var. MMRI Yellow maintained higher content of Fv/Fm by 6.67% compared
to Var. Pearl White, having an amount of 5.77% under inoculated growth medium
as compared to non-inoculated soil environment. Furthermore, the values of NPQ
were enhanced significantly (P<0.001) by growing crop plants on growth
medium inoculated with bacterial Table 1: Influence of
varying diesel regimes on chlorophyll contents of Zea mays L. cultivated for 4 weeks with and without bioaugmentation
of Pseudomonas aeruginosa BRRI54, Acinetobacter sp.
BRSI56, Acinetobacter sp. ACRH80
|
Varieties |
Treatment |
Hydrocarbon Concentration (g kg-¹ soil) |
Chlorophyll a |
Chlorophyll b |
Total Chlorophyll |
Carotenoids |
|
MMR1 yellow |
Bacterial Consortium |
0 |
0.51 ±0.00a |
0.28 ±0.00a |
0.80 ±0.01a |
0.37 ±0.00a |
|
1.5 |
0.33±0.01b |
0.17 ±0.02b |
0.51±0.02b |
0.25 ±0.01b |
||
|
2.5 |
0.31±0.00c |
0.15
±0.01bc |
0.46 ±0.01b |
0.20 ±0.01c |
||
|
3.5 |
0.28±0.00c |
0.11 ±0.01c |
0.40 ±0.01c |
0.18 ±0.01c |
||
|
Without Bacterial consortium |
0 |
0.38 ±0.00a |
0.17 ±0.01a |
0.57 ±0.01a |
0.28 ±0.01a |
|
|
1.5 |
0.31 ±0.00b |
0.13 ±0.02b |
0.43 ±0.00b |
0.19±0.01b |
||
|
2.5 |
0.25 ±0.01c |
0.12 ±0.00b |
0.38 ±0.03b |
0.16 ±0.01c |
||
|
3.5 |
0.17 ±0.00d |
0.10 ±0.00b |
0.28 ±0.00c |
0.14 ±0.01c |
||
|
Pearl White |
Bacterial Consortium |
0 |
0.45 ±0.01a |
0.25 ±0.00a |
0.71 ±0.01a |
0.30 ±0.00a |
|
1.5 |
0.32 ±0.00b |
0.14 ±0.00b |
0.46 ±0.01b |
0.21 ±0.01b |
||
|
2.5 |
0.29 ±0.00c |
0.13 ±0.01b |
0.43 ±0.01c |
0.19 ±0.01b |
||
|
3.5 |
0.27±0.00d |
0.11 ±0.01c |
0.38±0.01d |
0.16 ±0.01c |
||
|
Without Bacterial consortium |
0 |
0.35 ±0.01a |
0.16 ±0.00a |
0.52 ±0.01a |
0.27±0.01a |
|
|
1.5 |
0.28 ±0.00b |
0.12 ±0.01b |
0.40 ±0.01b |
0.18 ±0.01b |
||
|
2.5 |
0.22 ±0.00c |
0.10 ±0.01bc |
0.32 ±0.01c |
0.15 ±0.01c |
||
|
|
|
3.5 |
0.15 ±0.00d |
0.09±0.01c |
0.25 ±0.01d |
0.14 ±0.01c |
Values express in terms of means of four replicates ±
SE. According to Duncan’s multiple range test, dissimilar letter representing
means are significant statistically (P < 0.05)
consortium. Under the inoculated growth
medium, var. MMRI-Yellow contained lower value of NPQ by 2.92%, contrarily to
var. Pearl White having higher value of 4.2% as compared to non-inoculated
growth condition (Fig 1C).
Gas exchange attributes
The data of the net CO2
assimilation rate (A) was differed
significantly (P<0.001) in response to various diesel regimes, inoculating
growth medium with bacterial strains and crop varieties. The values of A decreased substantially in crop plants
with increasing levels of hydrocarbons. The crop treated with 3.5 g kg-1
diesel oil maintained minimal amount of net Photosynthetic rate (Fig. 2A). In
concurrence with increasing levels of hydrocarbons, to the tune of 3.5 g kg-1
diesel oil, the transpiration rate (E)
was reduced to the where minimums levels (Fig. 2B). However, its values were
appreciably enhanced in crop grown on bacterial consortium inoculated soil. The
growth medium contaminated with diesel oil caused significant (p<0.001)
reduction in water-use-efficiency (A/E).
The greatest reduction of A/E was
recorded in crop grown on soil containing 1.5 g kg-1 diesel oil,
while, its values were found to be improved by growing both crop varieties on
soil contaminated with 3.5 g kg-1 diesel stress (Fig. 2C). The
occurrence of have relative rate of Transpiration due to inoculation of growth
medium with bacterial consortium resulted in changing stomatal conductance
under diesel polluted stress environment. The values of stomatal conductance (gs) and sub-stomatal CO2 (Ci) concentration were increased
significantly in maize plants grown on growth medium inoculated with bacterial
consortium as compared to non-inoculated growing conditions. However, values of
these attributes were found in decreasing order with increasing concentration
of diesel oil in growth medium (Fig 2D and E).
Assimilation of Ionic Constituents by Leaves and Roots
Tissue
The application of diesel oil in root growing medium caused increase in
assimilation of Na+ ion by shoot and root organs of both maize
varieties compared to non-hydrocarbon stress conditions. However, inoculation
of growth medium with bacterial consortium cause substantial reduction in the
uptake of Na+ ion compared to non-inoculated growing condition. The
maize varieties responded differently in the absorption of Na+
growing under inoculated growing medium. In proportion to total amount of Na+,
its absorption was decreased by var. MMRI Yellow and Pearl White to the tune of
13.08% and 11.31% respectively, in inoculated crop over the non-inoculated
growth condition (Fig. 3C and D).
Successive increase in the
levels of diesel stress caused sequential reduction in uptake of K+
ion by shoot and root organs in both maize varieties. The uptake of K+ ion
was substantially improved by growing crop on growth medium inoculated with
bacterial consortium. Var. “MMRI Yellow” assimilated higher amount of K+ ion
by 30.46% as compared to 29.73% by var. “Pearl White” once (Fig. 3A
and B).
Total soluble
protein and total free amino acid contents
Addition of various concentration of diesel
oil resulted in enhancement of total soluble proteins in root and shoot tissues
of both varieties. The greater quantity of total soluble protein content were
recorded in crop stressed at 3.5 g kg-1 as compared to non-polluted
soil. Moreover, crop grown on soil enriched with bacterial consortium maintain
higher amount total soluble protein in comparison with non-inoculated growing
environment (Fig. 4A, B). The values of total free amino acids were increased
substantially in crop grown on diesel contaminated growth medium. Moreover, its
value were also enhanced in root and shoot tissue of crop planted on soil
inoculated with bacterial consortium. The maximum amount of total free amino
acids were recorded in crop grown on soil contaminated with 3.5 g kg-1
as compared to other growth medium added with 1.5 and 2.5 g kg-1
diesel stress (Fig. 4C and D).
Discussion
The sustainability of chlorophyll
constituents, gas exchange and pattern of uptake of ions were studied under
hydrocarbon stress environment in maize crop. The findings of regarding
physiological processes revealed that both maize varieties exhibited
significantly greater production of quantum yield (Fv/Fm, photosystem II
efficiency [Y(II)], high uptake of K+ ions and CO2
assimilation rate, total free amino acid, and total soluble proteins; while
lessening non-photochemical quenching (NPQ), and transpiration rate, in
response to inoculation of growth medium with bacterial strains. The plants
growing on inoculated medium showed greater tolerance to hydrocarbon treated
soil compared to un-inoculated environments.
The
present investigation illustrated that inoculation of growth medium with
bacterial strains produce beneficial effects in the environment of
photosynthetic pigments, Fv/Fm and photosystem II efficiency in plants under
hydrocarbon stress. Ambreen et al. (2016) also reported same result in
corn plant under crude oil stress. Another investigate supported our result by
Agnello et al. (2016) in which Medicago
sativa grown in diesel and heavy metal (Cu, Pb and Zn) contaminated soil
and bioaugmentation with Pseudomonas
aeruginosa showed better result of quantum yield of photosystem II (Fv/Fm)
in inoculated group as compare to non-inoculated group.
The
chlorophyll synthesis was greater affected at a high concentration of
hydrocarbon, while it was a little at the lower concentrations. The quantum of
chl ‘a’ and chl ‘b’ content were not damaged to a greater proportion in maize
plants in bacterial inoculated group. The degeneration of photosynthetic
pigments might be affected due to membrane permeability and disturbance in the
chloroplast. The results of our study showed that toxicity caused by
hydrocarbon resulted in the diminishing of chloroplast function, which led to
damage to the chlorophyll contents. However, these damaging effects were
mitigated by inoculation with bacterial strains of hydrocarbon contaminated
soil. The hydrocarbon stress caused significant damaging effect to the
chlorophyll contents evidenced by Agnello et al. 2016 and Ambreen et al. 2016. However, Oryza sativa grown in
phenanthrene and pyrene contaminated soil badly affects photosynthetic
efficieny by causing disintegeration of chlorophyll contents but bacterial
inoculation (Acinetobacteria sp.) mitigated effects of phenanthrene and pyrene in rice
plant also reported by Li et al. 2008.
Results
of our investigation showed that stomatal conductance and sub-stomatal CO2
concentration of both maize varieties were improved due to bacterial
inoculation. Moreover, transpiration rate (E)
of both varieties were enhanced in inoculated group as compare to
non-inoculated group. The leaves of hydrocarbon stressed maize varieties
exhibited higher water use efficiency (WUE) as compare to control. Iwegbue et al.
(2007) reported that the photosynthetic processes were inhibited,
because of a reduction in net CO2 assimilation rate, transpiration
rate, sub stomatal CO2 concentration and coupled with high ambient
CO2 concentration. However, stomatal closure produces little effect
on the process of photosynthesis. During the process, the light energy is
captured by photosynthetic pigment to produce an excited state and contaminated
stress was a marker to demonstrate a sign of plant photosynthetic efficiency (Qian et al. 2014). Whereas,
other abiotic and biotic stresses also cause to reduce photosynthetic pigments
and photosynthetic efficiency in plants (Wen et
al. 2016; Li et al. 2018).
%20530-538_files/image002.png)
Fig. 1: Influence of
varying diesel regimes on chlorophyll fluorescence attributes (Y (II), Fv/Fm,
NPQ) of Zea mays L. Cultivated for 3
weeks with and without bioaugmentation of Pseudomonas aeruginosa
BRRI54, Acinetobacter sp. BRSI56, Acinetobacter sp. ACRH80.
(-) and (+) signs indicate that without inoculum and with inoculum
The
results of our study documented carotenoids severely damaged by hydrocarbon
stress in maize varieties grow in diesel contaminated soil. Ibemesim 2010 reported that sour grass grown in crude oil contaminated soil badly affects
photosynthetic efficieny by causing disintegeration of chlorophyll contents.Carotenoids
act as antioxidants as scavenge to free radicals, mitigating destruction of
cells and avoiding damage to chlorophyll membrane when stressful conditions (Czerpak et al. 2006). Thereby, the
quantum of chlorophyll content, biosynthesis of photosynthetic pigments,
mineralization of mineral nutrients and essential metabolites were substantially
affected by toxicity caused by hydrocarbons (Ibemesim
2010).
Our
study showed that the inoculation of growth medium with bacterial strains
resulted in reduced uptake of Na+ ions by leaves and roots of maize
plants. The reduction in absorption of Na+ led to the improvement in
plant growth and development by enhancing tolerance in the
plant system. However, our investigation revealed that the uptake of K+
ion was also accelerated with simultaneously suppressing the uptake
of Na+ ion under inoculated conditions. The previous investigation
by Ahmad et al. 2015 reported the similar
results that bacterial inoculation (Trichoderma harzianum) alleviated the abiotic
stress in Brassica
junce. Zhuang et al. (2007) revealed that inoculation of plant growth
promoting bacteria enhanced the process mineralization and providing better
condition for growth and development of the plant by reducing the effects of
stressful environment. The inoculation of growth medium induces
mineralization of minerals nutrients and creating a favourable environment for
greater absorption of nutrients by plant roots (Meena et
al. 2017).
%20530-538_files/image004.png)
Fig. 2: Influence of
varying diesel regimes on gas exchange attributes (A, B, C, D, E) of Zea mays L. cultivated for 6 weeks with
and without bioaugmentation of Pseudomonas
aeruginosa BRRI54, Acinetobacter sp.
BRSI56, Acinetobacter sp. ACRH80. (-) and (+) signs indicate that
without inoculum and with inoculum
%20530-538_files/image006.png)
Fig. 3: Influence of
varying diesel regimes on K+ (A and B) and Na+ (C and D)
uptake in the leaf and root tissues of Zea
mays L. Cultivated for 6 weeks with and without bioaugmentation of Pseudomonas aeruginosa BRRI54, Acinetobacter sp. BRSI56, Acinetobacter
sp. ACRH80. (-) and (+) signs indicate that without inoculum and with
inoculum
The
increased accumulation of total free soluble proteins and total free amino
acids play a significant role in the maintenance of physiological functions in
response to stressful conditions during the growth period (Ashraf and Harris 2004). The results of our
study also revealed that quantum of total free amino acids and total soluble
proteins also increased under stressful conditions of hydrocarbon present in
the rhizosphere in maize crop. Ambreen et al. 2016 also reported that maize plant grown in crude oil contaminated soil showed increased amount of total
soluble proteins and total free amino acid. Li et al. 2008 also reported that rice plant grown in polycyclic aromatic hydrocarbon contaminated soil
showed enhanced leveel of total soluble
proteins. The existence of a potential association between plants and
microbes is important in degrading hydrocarbon substances from the soil (Afzal et al. 2012).
%20530-538_files/image008.png)
Fig. 4: Influence of
varying diesel regimes on total free amino acids (A and B) and total soluble
protein (C and D) of Zea mays L.
cultivated for 4 weeks with and without bioaugmentation of Pseudomonas aeruginosa BRRI54, Acinetobacter sp.
BRSI56, Acinetobacter sp. ACRH80. (-) and (+) signs indicate that
without inoculum and with inoculum
The
bacterial degrade the complex structures of hydrocarbons and convert into
soluble forms. Thereby, the nutrients are made available and easily absorbed by
plant roots, restoring to improving tolerance to stress conditions (Muratova et al. 2012; Hou et
al. 2015; Gerhardt et al. 2017a; Gerhardt et
al. 2017b).
Moreover,
vegetation covers also provide the habit for microbes to burgeon their
population in the vicinity of roots in the rhizosphere (Susarla et al. 2002). The microbial populations in the
rhizosphere do not only degrade substances of hydrocarbons but also convert
other crop residues and farmyard manure into soluble substance. The products
work as biofertilizers, psychostimulants and creating a favorable environment
for better growth and development. The prevalence of a better rhizosphere
microenvironment for plant roots resort to a greater proliferation of microbial
activities (Braud et al. 2009; Hayat et
al. 2010).
Conclusion
A pot-culture study was undertaken to
quantify the association of bacterial consortium to degrade the diesel polluted
soil. The cereal maize (Zea mays L.) crop was used as test plant. The
findings of this research indicated that contamination of soil with PAHs impacted
negatively on the growth and development of maize crop. The maximum
concentration of 3.5 g kg-1 diesel oil proved to be more injurious
on various physiological and biochemical attributes. The negative effects of
polluted soil could be ameliorated by inoculation of growth medium with
bacterial consortium, viz. Pseudomonas
aeruginosa BRRI54, Acinetobacter
sp. ACRH80 and Acinetobacter sp. BRSI56. The soil inoculated with
bacterial strains caused improvement in photosynthetic machinery, assimilation
of K+ at the cost of Na+ ion by plant organs and osmotic
adjustment via accumulation of total proteins and amino acids.
The preliminary experimental evidence has shown that
inoculation of soil with various bacterial strains that hold good in the
different eco-edaphic environment could be best utilized to bring back
hydrocarbon polluted soil under plough for development agro-forestry sector.
The small farming households would be greatly benefited to bring their marginal
lands for cultivation of maize crop. The bacterial strains employed in this
study were isolated from the natural habitat. Therefore, these strains would
have an equal opportunity to survive in different farming system. The finding
of this study could be extrapolated under field condition. Moreover, the
research and endeavors could be strengthen to isolate more environment friendly
bacterial strains, that could be more efficient and greater capability to
survive for degradation of diesel polluted soil.
Authors Contributions
UU, SN, ZUZ and MA designed the experimental
setup and UU conducted the experiments. UU and SN wrote the manuscript. UU
analyzed the data. SN critically revised the manuscript to the current form.
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