Researchers studied Eleocharis mutata, a water plant, growing in soils that contained fresh crude oil or weathered crude oil. The experiment ran for 56 weeks in controlled wetland microcosms. The soil was pre‑treated to mimic natural wetland conditions.
When the soil received fresh oil at 30, 60 or 90 grams per kilogram, the plant showed a positive response. Its height increased, it produced more flower structures, and its total dry weight grew. These stimulatory effects were reflected in higher physiological index values greater than one.
In contrast, a larger amount of weathered oil at 126 grams per kilogram slowed the plant down, reducing its growth and reproductive output. At the same time, the plant helped six groups of soil microbes thrive, raising the overall microbial index. The