Megathyrsus maximus and Brachiaria decumbens improve soil characteristics and select promising rhizobacteria during rhizoremediation of petroleum hydrocarbons

Abstract

Brachiaria decumbens and Megathyrsus maximus are promising grass species for the phytoremediation of soils contaminated with petroleum hydrocarbons (PHC). However, little is known about their root-associated microbiome, which is crucial for PHC degradation and plant health. Here, 16s rRNA amplicon sequencing was implemented over one year to characterize the rhizosphere bacterial communities of these two plants when growing in soil contaminated with PHC. PHC concentration and soil physicochemical parameters were monitored to analyze their interplay with the microbiome. Overall, both plants significantly increased soil fertility parameters compared to the initial soil. Specifically, porosity increased from 30.2 to 51.8; available phosphorus (AP) from 0.10 to 7.68 mg/kg; and cation exchange capacity (CEC) from 1.82 to 6.23 meq/100 g. The diversity of bacterial communities was influenced by the plants and the rhizosphere community beta-diversity was more related with AP and pH changes than with PHC concentration. M. maximus treatment showed the fastest removal of PHC (on average 23.38% less PHC compared to initial levels) at 3 months and the genera Ohtaekwangia, Luteolibacter and Ellin6067 were significantly more abundant in M. maximus’ rhizosphere compared to the other plant and the control. Additionally, genera with known plant growth promotion characteristics and PHC degradation capacity were identified to be associated with the plants and these can be targeted in future studies to confirm their role and utility as biostimulants, allowing the optimization of phytoremediation with these grasses.