Understanding Plant-Microbe Interactions for Phytoremediation of Petroleum-Polluted Soil

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.植物-微生物互作（Plant-microbe interactions）被认为是决定石油污染植物修复（phytoremediation）效率的关键过程，但目前对石油污染如何影响这类互作的认知仍相对匮乏。本研究采用微宇宙实验法（microcosm approach），以具备石油污染修复能力的芦苇（Phragmites australis）为研究对象，探究了石油污染对其植物生理生态性状、土壤养分及微生物活性的影响。总体而言，石油污染会抑制植物生长表现，且在植物生长早期的抑制效应尤为显著。石油污染主要通过降低污染土壤中植物可利用的无机氮含量，对有机态氮向无机态氮的净累积（即净氮矿化，net nitrogen mineralization, NNM）产生负面影响。但值得注意的是，石油污染土壤中检测到了大量溶解态有机氮（dissolved organic nitrogen, DON）。为弥补无机氮的初始不足，植物可借助高定殖率的丛枝菌根真菌（arbuscular mycorrhizal fungi）吸收部分溶解态有机氮以满足自身生长需求。此外，本研究通过实时聚合酶链反应（real-time polymerase chain reaction）技术，基于降解烃类细菌的分解代谢基因（即alkB（烷烃单加氧酶）、nah（萘双加氧酶）及tol（二甲苯单加氧酶）基因）定量分析了这类细菌的功能性状。靶标基因计数结果显示，不同降解烃类细菌在植物修复过程中呈现出各异的动态变化趋势，且在植物营养生长阶段检测到了更高丰度的alkB基因。由于石油不同组分的降解由不同类别的降解烃类细菌完成，因此植物对石油不同组分的修复能力可能随植物生命周期发生变化。鉴于在营养生长阶段检测到了更高丰度的携带alkB和tol基因的降解烃类细菌，该阶段的植物修复效果可能最佳。本研究的结果加深了我们对石油污染如何影响植物-微生物互作，以及这类互作在石油污染土壤植物修复中所发挥作用的认知。