Abstract
Plant surfaces are known as an important sink for various air pollutants, including particulate matter and its associated potentially toxic elements (PTE). Moreover, leaves surface or phylloplane is a habitat that harbors diverse bacterial communities (epiphytic). However, little is known about their possible functions during phytoremediation of air pollutants like PTE. The study of leaf epiphytic bacteria of plants colonizing mine residues (MR) containing PTE is thus a key to understand and exploit plant–epiphytic bacteria interactions for air phytoremediation purposes. In this research, we aimed (i) to characterize the functions of epiphytic bacteria isolated from the phylloplane of Brickellia veronicifolia, Flaveria trinervia, Gnaphalium sp., and Allionia choisyi growing spontaneously on multi-PTE contaminated MR and (ii) to compare these against the same plant species in a non-polluted control site (NC). Concentrations (mg kg-1) of PTE on MR leaf surfaces of A. choisyi reached up to 232 for Pb, 13 for Cd, 2,728 for As, 52 for Sb, 123 for Cu in F. trinervia, and 269 for Zn in Gnaphalium sp. In the four plant species, the amount of colony-forming units per cm2 was superior in MR leaves than in NC ones, being A. choisyi the plant species with the highest value. Moreover, the proportion of isolates tolerant to PTE (Zn, Cu, Cd, and Sb), UV light, and drought was higher in MR leaves than in those in NC. Strain BA15, isolated from MR B. veronicifolia, tolerated 150 mg Zn L-1, 30 mg Sb L-1, 25 mg Cu L-1; 80 mg Pb L-1, and was able to grow after 12 h of continuous exposition to UV light and 8 weeks of drought. Plant growth promotion related traits [N fixation, indole acetic acid (IAA) production, and phosphate solubilization] of bacterial isolates varied among plant species isolates and between MR and NC sampling condition. The studied epiphytic isolates possess functions interesting for phytoremediation of air pollutants. The results of this research may contribute to the development of novel and more efficient inoculants for microbe-assisted phytoremediation applied to improve air quality in areas exposed to the dispersion of metal mine tailings.
Highlights
The atmospheric dispersion of different pollutants has become a concern due to the consequences caused in the public health and the environment
According to analysis of similarities (ANOSIM), this grouping was significant (Figure 5). These results showed that the leaf characteristics of B. veronicifolia, Gnaphalium sp., and A. choisyi are different when coming from mine residues (MR) or non-polluted control site (NC)
The cultivable epiphytic bacterial from the phylloplane of four plant species identified as phytobarriers (B. veronicifolia, F. trinervia, Gnaphalium sp., and A. choisyi) and that naturally colonize MR was studied
Summary
The atmospheric dispersion of different pollutants has become a concern due to the consequences caused in the public health and the environment. Toxic elements (PTE) associated with solid particles are among these pollutants. PTE can be dispersed in the environment through the action of wind (aerial dispersion of solid particles) or water (runoffs and percolation) (González and González-Chávez, 2006; Cidu, 2011; García-Lorenzo et al, 2012). In arid and semi-arid regions, the restrictive environmental conditions limit the development of a plant cover; MR remain exposed to the action of environment promoting dispersion of particles containing PTE (Mendez and Maier, 2008). The role of the pioneer plants colonizing MR in the reduction of atmospheric dispersion of PTE associated with solid particles was documented and named as phytobarrier (Sánchez-López et al, 2015a)
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