Impact of Crude Oil on Functional Groups of Culturable Bacteria and Colonization of Symbiotic Microorganisms in the &lt;i&gt;Clitoria-Brachiaria&lt;/i&gt; Rhizosphere Grown in Mesocosms

Alejandro Alarcón,Rosalba Esquivel Cote,Ronald Ferrera-Cerrato,Juan José Almaraz Suarez,Ofelia Ferrera Rodriguez,Mariano García Díaz,Laura Verónica Hernández Cuevas

doi:10.15446/abc.v24n2.64771

Abstract

This research evaluated the changes on populations of culturable N-fixing free bacteria (NFFB) and P-solubilizing bacteria (PSB), as well as on the root nodulation by native rhizobia, the root colonization and spore number of arbuscular mycorrhizal fungi (AMF), in the rhizosphere of Clitoria ternatea and Brachiaria brizantha grown in mesocosms contaminated with crude oil (0, 3000, 6000, 9000, and 12000 mg kg-1), for 240 days. After 24 h of soil contamination, the highest populations of NFFB and PSB (5.5 and 4.9 LogUFC, respectively) were found in control, and the lowest populations were obtained at 12000 mg kg-1 (5.1 and 4.2 LogUFC, respectively). In contrast, at 60 and 240 days, the control showed lower populations of NFFB and PSB (5.4 and 4.8 LogUFC, respectively) than contaminated treatments. The highest number or root nodules in C. ternatea was quantified in control at 60 and 240 days (25 and 27 nodules, respectively) in comparison to those observed at the treatment with 12000 mg kg-1 (7 and 1 nodule, respectively). At 60 days, AMF colonization in both plant species, and the number of spores significantly decreased as the crude oil concentration increased; however, at 240 days, the highest number of AMF spores was recorded at treatments with 6000 and 12000 mg kg-1. The dry weight of both plant species significantly decreased as crude oil concentrations increased. Although C. ternatea was more susceptible to the toxic effects of crude oil, this plant species showed greater content of total chlorophyll than B. brizantha.

Highlights

Plant rhizosphere harbors several microbial groups whose physiological activity significantly influences soil fertility, quality, and health properties (De Ridder-Duine et al, 2005; Sanon et al, 2009; Nie et al, 2011), and stimulates the proliferation and abundance of microorganisms able to detoxify or degrade soil contaminants (Sanon et al, 2009; Sun et al, 2015)
The present study evaluated the effects of crude oil contaminated soil on the culture-dependent population of rhizosphere microorganisms, whose physiological activity is related to the incorporation of atmospheric nitrogen, the solubilization of inorganic phosphates in the soil, and the promotion of growth of two plant species established in mesocosms under greenhouse conditions
At 240 days, the nitrogen-fixing free-living bacteria (NFFLB) population was significantly higher in treatments with 9000 and 12000 mg kg-1 than the control (Fig. 1a), while the P-solubilizing bacteria (PSB) population was similar among treatments (Fig. 1b)

Summary

Introduction

Plant rhizosphere harbors several microbial groups whose physiological activity significantly influences soil fertility, quality, and health properties (De Ridder-Duine et al, 2005; Sanon et al, 2009; Nie et al, 2011), and stimulates the proliferation and abundance of microorganisms able to detoxify or degrade soil contaminants (Sanon et al, 2009; Sun et al, 2015). Arbuscular mycorrhizal fungi (AMF) are obligated biotrophic symbionts that colonize cortical cells of roots of most of the extant terrestrial plants, and enhance plant nutrition and growth, as well as plant adaptation against stressful soil conditions, water deficiency, contamination, or pathogens (Linderman, 2000; Jeffries et al, 2003; Liu et al, 2004; HernándezOrtega et al, 2012) These fungi have important effects during the phytoremediation of soils contaminated with petroleum hydrocarbons (Cabello, 2001) by enhancing plant adaptation, growth, nutrition or by stimulating the proliferation of petroleum-degrading microorganisms in the rhizosphere (Joner and Leyval, 2003; Alarcón et al, 2008; Hernández-Ortega et al, 2012). The later benefits highlight the crucial role of rhizosphere microorganisms by improving physical and chemical properties in the surrounding edaphic environment (Zhang et al, 2006; Bento et al, 2012)

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