Biological Responses of Tomato and Okra to Oil-Contaminated Soils in Southern Iraq
DOI:
https://doi.org/10.64354/7yw71076Keywords:
petroleum hydrocarbons; phytotoxicity; seed germination; root architecture; chlorophyll fluorescence; rhizosphere microbiome; bioindicator crops; Southern IraqAbstract
Oil fields, pipelines, refineries, and contaminated drainage networks, have led to increasing levels of petroleum contamination in cultivated soils of Southern Iraq, and are a growing threat to agricultural productivity. The study was conducted in a controlled randomized complete block pot experiment with four contamination levels ( control, low, moderate and high) of total petroleum hydrocarbon (TPH) (48, 5,082, 14,819, and 30,050 mg kg-1) each replicated five times for tomato (Solanum lycopersicum) and okra ( Abelmoschus esculentus). After 45 days of growth, germination behaviour, root architecture, leaf anatomy, photosynthetic pigments and chlorophyll-a fluorescence, gas exchange and rhizosphere microbial activity were measured. The germination percentage, seedling vigour, total root length, root biomass, palisade and spongy mesophyll thickness, the chlorophyll content, the maximum photosynthetic efficiency (Fv/Fm), and the net photosynthetic rate (NP) of the two species decreased significantly (p < 0.001) when TPH was increased, and stomatal density increased and root-to-shoot ratio shifted under stress. Total culturable bacteria and dehydrogenase activity decreased at high contamination levels, while, the hydrocarbon-degrading bacteria were highly enriched in the rhizosphere of contaminated plants. In almost every character observed, tomato was more sensitive than okra which was the relatively tolerant crop. Principal component analysis and correlation analysis was used to verify the correlation between soil TPH, plant physiological decline and microbial degradation response, and it was found that the three were highly correlated. The results offer a comprehensive phytotoxicity framework suitable for crop safety considerations, monitoring of soils in the vicinity of oil polluted areas and for rhizoremediation design.
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