Scholarly article on topic 'Plant-microbe Interactions to Improve Crude Oil Degradation'

Plant-microbe Interactions to Improve Crude Oil Degradation Academic research paper on "Agricultural biotechnology"

CC BY-NC-ND
0
0
Share paper
Academic journal
Energy Procedia
OECD Field of science
Keywords
{"microbial activity" / petroleum / "plant biomass" / rhizosphere}

Abstract of research paper on Agricultural biotechnology, author of scientific article — Xu Ying, Gao Dongmei, Liu Judong, Wang Zhenyu

Abstract Plant-microbe joint interactions have a great potential to deal with the total petroleum hydrocarbon (TPH) during the effective remediation process. After four months plant cultivation, significant decreases of TPH concentration were observed in the rhizospheres of Scorzonera mongolica Maxim., Atriplex centralasiatica, and Limonium bicolor. Larger shoot and root biomass stimulated microbial biodegradation of TPH efficiently, higher average well color development (AWCD) was observed in the rhizosphere of these three plants compared with the non-rhizosphere soil, which was strongly associated with the higher TPH degradation rate. The data gathered from this study provides important information for utilization of the local plants for plant-microbe joint remediation of the crude oil contaminated soil. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of RIUDS

Academic research paper on topic "Plant-microbe Interactions to Improve Crude Oil Degradation"

Energy

Procedía

IACEED2010

Plant-microbe Interactions to Improve Crude Oil Degradation

Xu Yinga, Gao Dongmeia, Liu Judongb, Wang Zhenyua*

aKey Laboratory of Marine Environment & Ecology, Ministry of Education, College of Environmental Science and Engineering,

Ocean University of China, Qingdao 266100, China bNortheast Institute of Geography and Agroecology, Chinese Academy of Sciences, Harbin 150081, China

Abstract

Plant-microbe joint interactions have a great potential to deal with the total petroleum hydrocarbon (TPH) during the effective remediation process. After four months plant cultivation, significant decreases of TPH concentration were observed in the rhizospheres of Scorzonera mongolica Maxim., Atriplex centralasiatica, and Limonium bicolor. Larger shoot and root biomass stimulated microbial biode gradation of TPH efficiently, higher average well color development (AWCD) was observed in the rhizosphere of these three plants compared with the non-rhizosphere soil, which was strongly associated with the higher TPH degradation rate. The data gathered from this study provides important information for utilization of the local plants for plant-microbe joint remediation of the crude oil contaminated soil.

© 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of RIUDS Keywords: microbial activity; petroleum; plant biomass; rhizosphere

1. Introduction

Large numbers of petroleum products released into the environment are posing an ever increasing risk of soil contamination. Petroleum hydrocarbons are a mixture of chemical substances, which are composed of aliphatic, aromatic, heterocyclic, and asphaltene/tar hydrocarbons [1]. Remediation of crude oil polluted soil is becoming a concerned problem in the environmental protection. Some previous studies dealing with the total petroleum hydrocarbon (TPH) in soil used indigenous soil microorganisms, while the removal of the pollutant is far from complete [2]. Thus, dig out a cost-effective technique to degrade the residual TPH is of vital important.

Rhizoremediation has been tentatively used for treating many types of organic pollutants through the plant-microbe joint interactions [1, 3]. Most of the successful researches were obtained by introduce of

* Corresponding author. Tel.: +86-532-66782092; fax: +86-532-66782092. E-mail address: wang0628@ouc.edu.cn.

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedia 5 (2011) 844-848

1876-6102 © 2011 Published by Elsevier Ltd. doi:10.1016/j.egypro.2011.03.149

traditional plant species or exogenous microorganisms [2, 4], only a few native plants were proved to be effective in degrading the crude oil. In order to enhance and stimulate indigenous bioremediation of local environment for the protection and sustainable development, some native dominated plant species were chosen in present study. In addition, plant biomass, microbial activity and number were also detected, to exploit the interactions between plant and rhizosphere microbe during rhizoremediation.

2. Materials and methods

2.1. Plant cultivation

Three local plants (Scorzonera mongolica Maxim., Atriplex centralasiatica, and Limonium bicolor.) were chosen to degrade the crude oil in the contaminated soil at an oil refinery land farm (Dongying city, Shandong province, China). Atriplex centralasiatica and Limonium bicolor started from seeds germinated, while Scorzonera mongolica Maxim. was transplanted with initial 4-cm long root. All plants were grown in the previously treated soil.

2.2. Sampling and analysis

Plants were harvested after 4 months. The rhizosphere soil samples were collected by shaking roots to remove the soil adhering to roots. Soil pH was using 10 g air-dried soil (1 mm) suspended in 25 mL 0.01 mo l L-1 CaCl2 solution using a pH meter. Water content was determined by drying at 105 °C for 8 h. The procedure utilized to extract soil TPH was modified form Gurska et al. [1]. One grams of soil sample was extracted 3 times in hexane by ultrasonication for 1 h each time. Then analysis was conducted with the method by Phillips et al. [3].

The plants were divided into shoots and roots. The biomass was gained after dried for 24 h by oven. Root parameters were obtained through WinRhizo image analysis software (Epson Scanning and WinRHIZO Pro. 2005).

2.3. Microbial activity and number

The capability of microbe to utilize carbon sources was assessed using the Biolog reader (Hayward, USA). Cell suspensions were prepared by extracting the soil samples with sterile NaCl solution, and a 150- ^ L suspension of 10-3 dilution was added to the Biolog ECO plates. Then the absorbance data were read at 590 nm at 0, 24, 48, 72, 96, 120, 144 and 168 h. The average well color development (AWCD) calculated as described by Sun et al. [5] was used to express the overall metabolic activity.

The number of TPH-degrading microorganism was determined by the most probable number (MPN) method adapt from Kirk et al. [4].

2.4. Statistical analysis

The results presented in the tables and figures were arithmetic means of three replicates. Statistical analyses were conducted using SPSS. The significance of the various parameters was tested by one-way analysis of variance (ANOVA) using the LSD test.

3. Results and discussion

3.1. Total petroleum hydrocarbon (TPH) removal

Fig. 1a shows the concentrations of TPH in soil after 4-month experimental period. The concentrations of TPH decreased significantly in all plant rhizospheres. It was found that the TPH concentration was reduced from 2578 mg kg-1 to 444, 422 and 329 mg kg-1 in the rhizosphere of Atriplex centralasiatica, Scorzonera mongolica Maxim. and Limonium bicolor, respectively, while there was no significant difference among them. However, the concentration of TPH in the bulk soil (non-rhizosphere) was still high (1539 mg kg-1).

It could be easily concluded that the contribution of plant rhizosphere effects was very high. Favorable conditions for crude oil degradation were created using proper local plant selection. During this 4-month trial experiment, TPH concentration in the soil declined to a safety level (< 500 mg kg-1). Successful remediation of crude oil could be induced by the joint action of plant and microbe in the rhizosphere.

3.2. Plant biomass

Shoot and root biomass of the plant were measured and depicted (Fig. 1b). Accordingly, it was indicated that Atriplex centralasiatica had the largest root system compared with other two plant species. The fast development of plant was easy to harvest and appeared a good endurance to petroleum contaminates, which could be recommended for the further phytoremediation.

10 m -a

£ 5 ^

A. centralasiaticaS.mongolica L. bicolor non-rhizp. Plant species

70 60 50 40 30 20 10

A. centralasiatica S.mongolica L. bicolor Plant species

0.20 g S

0.15 2

0.10 £

0.05 ^ 0.00

Fig. 1. (a): Total petroleum hydrocarbon (TPH) concentration in the rhizosphere of the three plants. TPH concentration values are means ± standard deviations of triplicate determinations. Left axis corresponds to the TPH concentration in rhizosphere/non-rhizosphere soil, right axis corresponds to the TPH degradation rate per day; (b): Biomass of the plant shoot and new root. Biomass values are means ± standard deviations of triplicate determinations. Symbols stand for shoot biomass and new root biomass respectively. Left axis corresponds to the shoot biomass, right axis corresponds to the new root biomass.

3.3. Microbial metabolic activity and number

The kinetic curves of AWCD varied significantly for different plant treatments. The AWCD value was the highest in the rhizosphere of Atriplex centralasiatica, the lowest in the adherent bulk soil (non-rhizosphere), and the middle in the rhizosphere of Limonium bicolor and Scorzonera mongolica Maxim. (Fig. 2a). The AWCD values represented the metabolic activity of soil microbe in using carbon sources, which suggested that the microbial metabolic activity as well as their intensity were greatly enhanced by root exudates [5]. Higher concentration of TPH in the non-rhizosphere (Fig. 1a) soil had significant

effects on the community composition and microbial activities [6], which subsequently led to lower TPH degradation rate (Fig. 1a).

According to the regression analyses between the number of degrader and TPH concentration showed in Fig. 2b, with the growth of bacterial population during the plant cultivation, the TPH concentration decreased gradually. That meant the larger number of TPH-degrading microorganisms in the rhizosphere soil probably did a good contribution to the higher rhizospheric degradation rate compared to the non-rhizosphere soil.

In the rhizosphere, some microbes could secrete biosurfactant to facilitate the desorption of organic pollutants and increase their bioavailabilities, which accelerated the degradation of TPH [7]. Furthermore, some groups of bacteria within the rhizosphere could also exert beneficial effects on plant growth by producing phytohormones, solubilization of minerals and other compounds [8]. These microbes was termed plant growth-pro mo ting rhizobacteria, and several studies were conducted recently. In return, plant exudates helped stimulate the survival and action of microbe, which led to much more efficient degradation of contaminants. The plant roots could also help bacteria to spread through soil and penetrate deeper soil layers through the dissimilar root morphologies [4]. Plant-microbe interactions should be exploited to deal with the persistent organic pollutants in conatminated soil.

Time ^ MPN /kg-1 soil

Fig. 2. (a): Average well color development (AWCD) in BIOLOG ECOplates for the microbial community in the rhizosphere. AWCD values are means ± standard deviations of triplicate determinations. Symbols stand for Non-rhizosphere (A), Scorzonera mongolica Maxim. (A), Limonium bicolor fH), and Atriplex centralasiatica respectively; (b): Relationships between Most-probable-number (MPN) of hydrocarbon degrading microorganisms and total petroleum hydrocarbon (TPH) concentration. Regression equation, line of best fit and R2 were shown.

3.4. SoilpH

After 4 months of planting, compared with the bulk soil (7.90), the pH in the rhizosphere of Atriplex centralasiatica, Scorzonera mongolica Maxim. and Limonium bicolor decreased significantly to 7.65, 7.70 and 7.77, respectively (Table 1). The changes in the pH of the rhizospheres were due to several reasons: the addition of nitrogen, the root executes (organic acids) and microbe metabolites. In general, decreased soil pH value tended to favor the uptake of P, which in turn improved plant growth and yield higher degradation rate of TPH (Fig. 1a). Specifically, in present study site, as most of the soil was heavily alkaline, so that a little acidification trend of the soil usually did a greater deal for the better soil quality.

T able 1. pH of the soil in the rhizosphere and non-rhizosphere

Plant Non-rhizosphere Atriplex centralasiatica Limonium bicolor Scorzonera mongolica Maxim.

pH 7.90±0.02a 7.65±0.04c 7.77±0.05b 7.70±0.04bc

a-c: In the table, values followed by different letters indicate significant differences at p < 0.05 level by LSD test.

4. Conclusion

Over the four-month study period, the concentration of TPH decreased significantly in all plant rhizospheres. The local plants with the rhizospheric microbes can be considered as a potential joint plant-microbe remediation system to degrade the crude oil in contaminated soils. Studies focused on this not only can lead to a better understanding of plant-microbe interactions in contaminated environment but can also help in finding healthy, economic, suitable and effective strategies to enhance the adaptation of rhizoremediation to an ecological niche.

Acknowledgements

The authors are thankful and acknowledge the support under Foundation for Key Program of the Education Ministry, China (No. 308016).

References

[1] Gurska J, Wang W, Gerhard KE, Khalid AM, Isherwood DM, Huang XD, et al. Three year field test of a plant growth promoting rhizobacteria enhanced phytoremediation system at a land farm for treatment of hydrocarbon waste. Environmental Science & Technology, 2009, 43(12): 4472-4479.

[2] Tahhan RA, Ammari TG, Goussous SJ, Al-Shdaifat HI. Enhancing the biodegradation of total petroleum hydrocarbons in oily sludge by a modified bioaugmentation strategy. International Biodeterioration & Biodegradation, 2010, doi:10.1016/j.ibiod.2010.09.007.

[3] Phillips LA, Greer CW, Farrell RE, Germida JJ. Field-scale assessment of weathered hydrocarbon degradation by mixed and single plant treatments. Applied Soil Ecology, 2009, 42(1): 9-17.

[4] Kirk JL, Klironomos JN, Lee H, Trevors JT. The effects of perennial ryegrass and alfalfa on microbial abundance and diversity in petroleum contaminated soil. Environmental Pollution, 2005, 133(3):455-465.

[5] Sun T, Cang L, Wang Q, Zhou D, Cheng J, Xu H. Roles of abiotic losses, microbes, plant roots, and root exudates on phytoremediation of PAHs in a barren soil. Journal of Hazardous Materials, 2010,176(1-3): 919-925.

[6] Shi W, Bischoff M, Turco R, Konopka A Microbial catabolic diversity in soils contaminated with hydrocarbons and heavy metals. Environmental Science & Technology, 2005, 39(7): 1974-1979.

[7] Lai C, Huang YC, Wei Y, Chang J. Biosurfactant-enhanced removal of total petroleum hydrocarbons from contaminated soil. Journal of Hazardous Materials, 2009, 167(1-3): 609-614.

[8] Chauhan A, Oakeshott JG, Jain RK. Bacterial metabolism of polycyclic aromatic hydrocarbons: strategies for bioremediation. Indian Journal of Microbiology, 2008, 48(1): 95-113.