Understanding plant-microbe interactions for phytoremediation of petroleum-polluted soil.

Ming Nie,Jiakuan Chen,Lifen Jiang,Yijing Wang,Bo Li,Changming Fang,Ming Xiao,Jiayi Yu,Ji Yang,Alfredo Herrera-Estrella

doi:10.1371/journal.pone.0017961

Abstract

Plant-microbe interactions are considered to be important processes determining the efficiency of phytoremediation of petroleum pollution, however relatively little is known about how these interactions are influenced by petroleum pollution. In this experimental study using a microcosm approach, we examined how plant ecophysiological traits, soil nutrients and microbial activities were influenced by petroleum pollution in Phragmites australis, a phytoremediating species. Generally, petroleum pollution reduced plant performance, especially at early stages of plant growth. Petroleum had negative effects on the net accumulation of inorganic nitrogen from its organic forms (net nitrogen mineralization (NNM)) most likely by decreasing the inorganic nitrogen available to the plants in petroleum-polluted soils. However, abundant dissolved organic nitrogen (DON) was found in petroleum-polluted soil. In order to overcome initial deficiency of inorganic nitrogen, plants by dint of high colonization of arbuscular mycorrhizal fungi might absorb some DON for their growth in petroleum-polluted soils. In addition, through using a real-time polymerase chain reaction method, we quantified hydrocarbon-degrading bacterial traits based on their catabolic genes (i.e. alkB (alkane monooxygenase), nah (naphthalene dioxygenase) and tol (xylene monooxygenase) genes). This enumeration of target genes suggests that different hydrocarbon-degrading bacteria experienced different dynamic changes during phytoremediation and a greater abundance of alkB was detected during vegetative growth stages. Because phytoremediation of different components of petroleum is performed by different hydrocarbon-degrading bacteria, plants’ ability of phytoremediating different components might therefore vary during the plant life cycle. Phytoremediation might be most effective during the vegetative growth stages as greater abundances of hydrocarbon-degrading bacteria containing alkB and tol genes were observed at these stages. The information provided by this study enhances our understanding of the effects of petroleum pollution on plant-microbe interactions and the roles of these interactions in the phytoremediation of petroleum-polluted soil.

Highlights

Phytoremediation is the use of plants and their associated microbes for environmental cleanup [1]
Total carbon concentration (TC) of roots significantly decreased with increasing petroleum concentration, and total nitrogen concentration (TN) of leaves was positively correlated with petroleum concentration
In contrast to the earlier vegetative growth, total carbon concentration (TC) of roots significantly increased with increasing petroleum concentration and TN of rhizomes and roots was positively correlated with petroleum concentration

Summary

Introduction

Phytoremediation is the use of plants and their associated microbes for environmental cleanup [1]. The efficiency of phytoremediation depends mostly on the establishment of robust plant-microbe interactions [5]. Plants, through their ‘rhizosphere effects’, support hydrocarbon-degrading microbes that assist in phytoremediation in the root zone [6,7]. Petroleum hydrocarbons are known to be harmful to plant growth and development, and to microbial processes [9,10,11,12]. This is because petroleum hydrocarbons negatively affect photosynthesis and reduce nutrient assimilation and biomass accumulation [9,10]. Petroleum pollution intensifies competition between plants and microbes for nutrients during phytoremediation [5,14]

Methods

Results

Conclusion