Abstract
Secondary plant metabolites (SPMEs) play an important role in plant survival in the environment and serve to establish ecological relationships between plants and other organisms. Communication between plants and microorganisms via SPMEs contained in root exudates or derived from litter decomposition is an example of this phenomenon. In this review, the general aspects of rhizodeposition together with the significance of terpenes and phenolic compounds are discussed in detail. We focus specifically on the effect of SPMEs on microbial community structure and metabolic activity in environments contaminated by polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs). Furthermore, a section is devoted to a complex effect of plants and/or their metabolites contained in litter on bioremediation of contaminated sites. New insights are introduced from a study evaluating the effects of SPMEs derived during decomposition of grapefruit peel, lemon peel, and pears on bacterial communities and their ability to degrade PCBs in a long-term contaminated soil. The presented review supports the “secondary compound hypothesis” and demonstrates the potential of SPMEs for increasing the effectiveness of bioremediation processes.
Highlights
Plants as primary producers synthesize tremendous amounts of organic compounds while consuming carbon dioxide and light energy
low molecular weight (LMW) carbon-containing (LMW-C) components of the root exudates are hypothesized to be the reason for the primary response in rhizosphere microorganisms [14,57], resulting in a “priming effect” on the microbial community—the increase of microbial biomass and soil organic matter decomposition after the input of fresh organic matter [58]
Chemotaxis of beneficial microflora is important for disease suppression in some plants due to competitive colonization of plants by symbionts protecting the host plant from pathogenic bacterium. One example of this is the plant symbiont Pseudomonas fluorescens, which is attracted to citric and malic acid released by tomato (Lycopersicon esculentum L.) roots [88] and can protect the host plant from a pathogenic bacterium, Ralstonia solanacearum, which is attracted to its host by diverse amino and organic acids and different SPMEs [89]
Summary
Plants as primary producers synthesize tremendous amounts of organic compounds while consuming carbon dioxide and light energy. Several studies focusing on the effects of SPMEs on microbial diversity and activity towards pollutants have delivered supporting evidence, the introduction of metagenomics [24] and high-throughput sequencing techniques (for review see [25]) has opened up new possibilities for addressing this topic, which has not yet been fully exploited. Despite these advances, linking one specific molecule from exudates with its effect under complex environmental conditions and relationships still remains challenging. Further examination of communities in environments polluted by polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) is presented
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