Phylloremediation of Air Pollutants: Exploiting the Potential of Plant Leaves and Leaf-Associated Microbes

Abstract

Air pollution is air contaminated by anthropogenic or naturally occurring substances in high concentrations for a prolonged time, resulting in adverse effects on human comfort and health as well as on ecosystems. Major air pollutants include particulate matters (PMs), ground-level ozone (O3), sulfur dioxide (SO2), nitrogen dioxides (NO2), and volatile organic compounds (VOCs). During the last three decades, air has become increasingly polluted in countries like China and India due to rapid economic growth accompanied by increased energy consumption. Various policies, regulations, and technologies have been brought together for remediation of air pollution, but the air still remains polluted. In this review, we direct attention to bioremediation of air pollutants by exploiting the potentials of plant leaves and leaf-associated microbes. The aerial surfaces of plants, particularly leaves, are estimated to sum up to 4 × 108 km2 on the earth and are also home for up to 1026 bacterial cells. Plant leaves are able to adsorb or absorb air pollutants, and habituated microbes on leaf surface and in leaves (endophytes) are reported to be able to biodegrade or transform pollutants into less or nontoxic molecules, but their potentials for air remediation has been largely unexplored. With advances in omics technologies, molecular mechanisms underlying plant leaves and leaf associated microbes in reduction of air pollutants will be deeply examined, which will provide theoretical bases for developing leaf-based remediation technologies or phylloremediation for mitigating pollutants in the air.

Evaluation of the Importance of Some East Asian Tree Species for Refinement of Air Quality by Estimating Air Pollution Tolerance Index, Anticipated Performance Index, and Air Pollutant Uptake

“…Previous studies of elevated air pollutants have demonstrated the genesis of an oxidative burst response as initial events in injury to plants by air pollutants, because plants must cope with the persistent levels of air pollution in natural or ecological contexts [32]. The uptake of ozone (O 3 ) through leaf stomata generates a range of ROS within the apoplast.…”

“…The functional changes result from a stress response mechanism that blocks their intracellular uptake during O 3 exposure. Plants can mitigate secondary damage from O 3 by using a stomatal pore-blocking strategy [32]. According to [43], a decrease in photosynthetic damage rate over time in leaves exposed to a constant rise in O 3 could be explained by a decrease in stomatal conductance.…”

“…As mentioned previously, air pollution mitigation potential by urban trees occurs mainly due to precipitation into leaf surfaces and/or stomata. Adsorption refers to the deposition of solid particulates in the atmosphere onto plant surfaces such as leaves or bark, and absorption indicates biofiltration by chemical reactions of plants with reactive air pollutants such as O 3 and SO 2 [32]. Air pollution reduction potential depends on physio-biochemical characteristics and antioxidative defense systems of plants [29,33,34], so it is necessary to improve air quality by selecting suitable species.…”

Dynamics of plant responses to combinations of air pollutants

“…; Wei et al . ). However, acute exposure to air pollutants typically results in clear symptoms that differ from leaf injury caused by bacterial pathogens or insect herbivores, such as the very distinct necrotic and chlorotic spots on leaves, either marginal or interveinal, which are usually red, brown or black, depending on the plant species (Taylor & Frost ; Slovik et al .…”

“…; Wei et al . ). Thus, biotechnological application of these systems will benefit from our increasing understanding of plant ecology and of the mechanisms behind plant–microbe interactions.…”