Phytoremediation of soil contaminated with weathered petroleum hydrocarbons by applying mineral fertilization, an anionic surfactant, or hydrocarbonoclastic bacteria.

This study evaluated the effect of the application of mineral fertilization (F), the anionic surfactant Triton X-100 (TX100), or the inoculation with a hydrocarbooclastic bacterial consortium (BCons) on the growth of Clitoria ternatea during the phytoremediation of a Gleysol contaminated with weathered petroleum hydrocarbons (39,000 mg kg-1 WPH) collected from La Venta, Tabasco (Mexico). The experiment consisted of a completely randomized design with seven treatments and four replications each under greenhouse conditions. The application of F (biostimulation) increased plant growth and biomass production; in contrast, TX100 only favored root biomass (11%) but significantly favored WPH degradation. Bioaugmentation with BCons did not show significant effects on plant growth. Nevertheless, the combination of biostimulation with bioaugmentation (BCons + F, BCons + TX100, and BCons + F+TX100) enhanced plant growth, hydrocarbonoclastic bacteria population, and WPH degradation when compared to treatments with the single application of bioaugmentation (BCons) or biostimulation (F).

Application of mineral fertilization and commercial surfactant favored root biomass and degradation of weathered petroleum hydrocarbons (WPH). The reintroduction of hydrocarbonoclastic and surfactant-producer bacteria did not enhance plant growth but significantly contributed on WPH degradation from a chronically contaminated soil.

Efecto de bacterias emulsificantes en la atenuación de la fitotoxicidad de suelos contaminados con petróleo intemperizado / Effect of emulsifying bacteria on phytotoxicity attenuation of soils contaminated with weathered petroleum hydrocarbons

Introducción: Las plantas y los microorganismos se han utilizado como bioindicadores de la toxicidad inducida por hidrocarburos presentes en los suelos. Objetivo: El presente trabajo evaluó la toxicidad de un Gleysol contaminado de origen con diferentes concentraciones de petróleo intemperizado, recolectado en la Venta Tabasco (México), en el crecimiento de Clitoria ternatea, y la atenuación de la fitotoxicidad con la inoculación de bacterias emulsificantes. Metodología: Se usaron suelos con 50 y 150 g HTPI kg-1, y un suelo testigo con 0.15 g HTPI kg-1 (origen biogénico), y la inoculación de seis bacterias emulsificantes y su combinación (consorcio). La fitotoxicidad de los HTPI se evaluó considerando la altura, la biomasa seca (radical, aérea y total), el área foliar, el área foliar específica, y la eficiencia del fotosistema II (EPSII), a los 30 días. Resultados: Los HTPI no afectaron la altura, pero el suelo con 50 g HTPI kg-1 redujo la biomasa seca radical y total, y el área foliar con respecto a las plantas en los suelos testigo y con 150 g HTPI kg-1. La cepa Sml (Stenotrophomonas maltophilia C10S1) incrementó significativamente la biomasa seca total; la cepa Ro (Raoultella ornithinolyticaC5S3) produjo mayor área foliar específica con respecto a plantas no inoculadas. En el suelo testigo, el consorcio bacteriano estimuló la altura; las cepas Sm (Serratia marcescens C11S1) y Sm2 (S. marcescens C7S3) mejoraron la altura y el área foliar específica con respecto a plantas no inoculadas, en el suelo con 50 g HTPI kg-1. En el suelo con 150 g HTPI kg-1, las cepas Spa (Stenotrophomonas pavanii C5S3F) y Cfr (Citrobacter freundii C4S3) incrementaron la biomasa seca radical y aérea, respectivamente. La EPSII no fue afectada por la contaminación de los suelos. Las bacterias emulsificantes redujeron la fitotoxicidad de HTPI, pero dependiendo de su contenido en los suelos. Conclusiones: El suelo con 50 g HTPI kg-1 mostró mayor toxicidad en el crecimiento de las plantas. La inoculación bacteriana favoreció el crecimiento, producción de biomasa, y área foliar en el suelo con 150 g HTPI kg-1. La EPSII no fue afectada por la presencia de HTPI en el suelo.

Introduction: Plants and microorganisms have been used as bioindicators to evaluate the toxicity of hydrocarbons in soils. Objective: This study evaluates the toxicity of a chronically-contaminated Gleysol with several concentrations of weathered petroleum hydrocarbons (WPH), collected from La Venta, Tabasco (Mexico), on the growth of Clitoria ternatea and the phytoxicity attenuation due to inoculation of emulsifying bacteria. Methods: Soils with 50 and 150 g WPH kg-1, and control soil with 0.15 g WPH kg-1 (biogenic origin) were utilized, as well as the inoculation of six emulsifying bacteria and their combination (consortium). The WPH-phytotoxicity was evaluated by considering plant height, dry biomass production (root, shoot, and total), leaf area, specific leaf area, and the efficiency of photosystem II (EPSII), after 30 days. Results: WPH did not affect plant height, but soil with 50 g WPH kg-1 diminished root and total dry weight, and leaf area, when compared to both control soil and soil with 150 g WPH kg-1. The strain Sml (Stenotrophomonas maltophilia C10S1) significantly increased shoot and total dry weight, while the strain Ro (Raoultella ornithinolytica C5S3) produced higher specific leaf area relative to uninoculated plants. In control soil, the bacterial consortium stimulated plant height. The strains Sm (Serratia marcescens C11S1)and Sm2 (S. marcescens C7S3) improved plant height and specific leaf area when compared to uninoculated plants in soil with 50 g WPH kg-1. In soil with 150 g WPH kg-1, strains Spa (Stenotrophomonas pavanii C5S3F)and Cfr (Citrobacter freundii C4S3)enhanced root and shoot dry weight, respectively. The EPSII was unaffected by soil contamination. Emulsifying bacteria reduced the phytotoxic effects of WP, but depending on the content of WPH in soils. Conclusions: Soil with 50 g WPH kg-1 showed the greatest phytotoxic effects on plant growth. Bacterial inoculation favored growth, biomass production and leaf area in soil with 150 g WPH kg-1. The EPSII was not affected by WPH in soils.