Abstract
The remediation of contaminated sites using plant-based techniques has gained increasing attention in recent decades. However, information on the effects of contaminant imbibition on seed viability and germination rates are often lacking in the literature. To this end, our research investigated, by means of an event-time model, the effect of diesel fuel imbibition on the seed viability and germination rate of Medicago sativa, a plant species with great potential for remediation of organic contaminants. The event-time model provided an accurate and biologically relevant method for analysing germination data. Our results reveal that the direct imbibition of diesel fuel by M. sativa seeds for ≤48 h, or their exposure to soil diesel fuel concentrations of 0–10 g/kg diesel fuel, affects their germination rates, as shown by increasing t50 values from 90.6 (±2.78) to 114.2 (±2.67) hours, without significantly affecting seed viability. On the other hand, diesel fuel imbibition of longer duration, or the exposure of M. sativa seeds to ≥20 g/kg diesel fuel-contaminated soils, leads to no further effect on time to seed emergence. Instead, these conditions compromise seed viability, resulting in a decrease in the proportion of germinated seeds from 0.91 (±0.03) in 10 g/kg diesel fuel contaminated soil to 0.84 (±0.04) and 0.70 (±0.05) in 20 and 30 g/kg diesel fuel-contaminated soils, respectively. The fact that low concentrations of diesel fuel and 0–48 h of direct imbibition delayed seed emergence without adversely affecting the percentage of viable seeds suggests that this inhibitory effect on germination at low diesel fuel exposure could be attributed more to physical constraints rather than biological damage on the seeds. The models used in this study provide an accurate and biologically relevant method for the analyses of germination data. This is vital since expensive germination experiments, be it in the field of toxicology or agriculture, deserve to be accurately analysed.
Highlights
There is a growing body of evidence that plant roots, in conjunction with their associated microbial communities, offer an effective treatment strategy for in situ remediation of contaminated soils [1,2].Under a variety of environmental conditions, vegetation has been shown to enhance microbial degradation rates of organic chemical residues in soils [3]
The aim of the present study is to bridge this gap by examining the effect of exposure to diesel fuel on the seed viability and germination rate of Medicago sativa, a plant with great reclamation potential for soils contaminated with petroleum hydrocarbons [9,10,11,12,13,14]
When compared to nonlinear regression models, the event-time model provided the best fit for the germination data
Summary
There is a growing body of evidence that plant roots, in conjunction with their associated microbial communities, offer an effective treatment strategy for in situ remediation of contaminated soils [1,2]. Under a variety of environmental conditions, vegetation has been shown to enhance microbial degradation rates of organic chemical residues in soils [3]. Plant-based remediation (phytoremediation) is not a new concept. Plants 2020, 9, 1062 used for the treatment of some types of wastewater. Current research focuses on expanding phytoremediation to address contaminated soils and atmospheric pollutants [4]. These techniques provide environmentally friendly and cost-efficient advantages over excavation and off-site treatments of contaminated soils
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