Rhizosphere and growth responses of Eleocharis mutata in soils affected by fresh and weathered crude oil contamination: hormesis effects, rhizobacterial stimulation and phytoremediation potential.

Petroleum hydrocarbons released into tropical wetlands affect plant development and rhizosphere microbial activity, highlighting the need for ecological remediation strategies. This study evaluated the effects of fresh crude oil (CO; 30, 60, and 90 g kg-¹) and weathered crude oil (WCO; 126 g kg-¹) on the growth, reproduction, rhizobacterial activity, and total petroleum hydrocarbon (TPH) removal associated with Eleocharis mutata (E. mutata) under phytoremediation (PHY) and natural attenuation (NA) during a 56-week experiment in controlled wetland microcosm conditions. CO concentrations induced stimulatory physiological responses, reflected in physiological index values (PI > 1.0), including increased plant height, reproductive structures, and biomass production. In contrast, WCO exposure caused inhibitory responses (PI < 1.0), reducing plant growth and reproduction. PHY stimulated six rhizobacterial groups and increased the total bacteriological index (TBI) compared with NA at week 56. Although PHY and NA showed similar overall TPH removal, PHY promoted a modest increase in hydrocarbon removal under 60, 90 g kg-¹ CO and 126 g kg-¹ WCO conditions. These findings highlight the ecological resilience of E. mutata and support its potential role in PHY of hydrocarbon-contaminated tropical wetlands.