Response of Poplar and Associated Fungal Endophytic Communities to a PAH Contamination Gradient

Abstract

Microbial populations associated to poplar are well described in non-contaminated and metal-contaminated environments but more poorly in the context of polycyclic aromatic hydrocarbon (PAH) contamination. This study aimed to understand how a gradient of phenanthrene (PHE) contamination affects poplar growth and the fungal microbiome in both soil and plant endosphere (roots, stems and leaves). Plant growth and fitness parameters indicated that the growth of Populus canadensis was impaired when PHE concentration increased above 400 mg kg−1. Values of alpha-diversity indicators of fungal diversity and richness were not affected by the PHE gradient. The PHE contamination had a stronger impact on the fungal community composition in the soil and root compartments compared to that of the aboveground organs. Most of the indicator species whose relative abundance was correlated with PHE contamination decreased along the gradient indicating a toxic effect of PHE on these fungal OTUs (Operational Taxonomic Units). However, the relative abundance of some OTUs such as Cadophora, Alternaria and Aspergillus, potentially linked to PHE degradation or being plant-beneficial taxa, increased along the gradient. Finally, this study allowed a deeper understanding of the dual response of plant and fungal communities in the case of a soil PAH contamination gradient leading to new perspectives on fungal assisted phytoremediation.

Taxonomic and functional responses of soil and root bacterial communities associated with poplar exposed to a contamination gradient of phenanthrene

“…We showed in a previous study on the same samples (Gréau et al 2022) that fungal endophytic community structure was impacted in the roots. Therefore, different responses of fungal and bacterial endophytes to the phenanthrene contamination seem to occur.…”

“…We hypothesised that soil microbial community and functions would be impacted by the contamination and since soil microbial communities are the first reservoir of endophytic communities (Gaiero et al 2013;Pascale et al 2020), it would lead to a community shift in roots as shown in the literature with petroleum, hydrocarbon or metal stresses (Tardif et al 2016;Iffis, St-Arnaud and Hijri 2017;Lumactud and Fulthorpe 2018;Syranidou et al 2018). In a previous study using the same experimental design (Gréau et al 2022), we showed that poplar absorbed PHE in its tissues, at concentrations proportional to initial soil concentrations (see also Supplementary Table S2) and that fungal community structure of both soil and roots shifted due to increasing PHE concentrations. We thus explored the response of the bacterial community in term of taxonomic and functional diversity.…”

“…For each PHE concentration, four replicates were used (one plant per replicate), representing a total of 32 microcosms. Soil was watered to 100% of its water retention capacity (WRC) for the first three days and maintained at 70% WRC using tap water for the four weeks of plant growth in a chamber with controlled temperature, humidity and light conditions (Gréau et al 2022).…”

“…After four weeks of growth (time determined from preliminary experiment to have still PHE present in soils with the higher initial spiking), the plants were removed from the pots and the rhizospheric soil was recovered by slightly shaking the roots and using a small brush. Plant biomass parameters measured are displayed in Supplementary Table S2 and more detailed information are presented in Gréau et al (2022). Rhizospheric soil was stored at -80°C until DNA extraction and enzymatic analyses.…”

“…Some studies reported that the presence of plants could enhance the potential of PAH-biodegradation by soil microbial communities (Günther et al 1998;Binet, Portal and Leyval 2000). Recent data have shown that PAHs were taken up and translocated to plants (Sun et al 2014;Liao et al 2016;Gréau et al 2022), but their effects on plant endophytic populations in terms of diversity and activity are still not well documented. Poplar has been extensively studied and used in the context of phytoremediation due to an important root surface and high tolerance to a wide range of pollutants (Guerra et al 2011).…”