Evaluating the effects of gross nitrogen mineralization, immobilization, and nitrification on nitrogen fertilizer availability in soil experimentally contaminated with diesel

Abstract

Sandy clay loam soil was contaminated with 5000 mg kg(-1) diesel, and amended with nitrogen (15.98 atom% (15)N) at 0, 250, 500, and 1000 mg kg(-1) to determine gross rates of nitrogen transformations during diesel biodegradation at varying soil water potentials. The observed water potential values were -0.20, -0.47, -0.85, and -1.50 MPa in the 0, 250, 500, and 1000 mg kg(-1) nitrogen treatments respectively. Highest microbial respiration occurred in the lowest nitrogen treatment suggesting an inhibitory osmotic effect from higher rates of nitrogen application. Microbial respiration rates of 185, 169, 131, and 116 mg O(2) kg(-1) soil day(-1) were observed in the 250, 500, control and 1000 mg kg(-1) nitrogen treatments, respectively. Gross nitrification was inversely related to water potential with rates of 0.2, 0.04, and 0.004 mg N kg(-1) soil day(-1) in the 250, 500, and 1000 mg kg(-1) nitrogen treatments, respectively. Reduction in water potential did not inhibit gross nitrogen immobilization or mineralization, with respective immobilization rates of 2.2, 1.8, and 1.8 mg N kg(-1) soil day(-1), and mineralization rates of 0.5, 0.3, and 0.3 mg N kg(-1) soil day(-1) in the 1000, 500, and 250 mg kg(-1) nitrogen treatments, respectively. Based on nitrogen transformation rates, the duration of fertilizer contribution to the inorganic nitrogen pool was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg kg(-1) nitrogen treatments, respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were considered losses of fertilizer with only gross mineralization of organic nitrogen contributing to the most active portion of the nitrogen pool.

Input of organic matter enhances degradation of weathered diesel fuel in sub-tropical sediments

“…Therefore, higher N:P ratios do not appear to limit biodegradation of moderately weather diesel. An increase in nitrate concentrations over time was observed which was expected, as similar to results reported in other hydrocarbon remediation studies (Walecka-Hutchison and Walworth, 2007;Mortazavi et al, 2013a). Nitrite concentrations on the other hand, after an initial spike at day 7 continuously decreased till the end of the experiment.…”

Understanding Plant-Microbe Interactions for Phytoremediation of Petroleum-Polluted Soil

“…Our data suggest that greater abundances of total bacteria and hydrocarbon-degrading bacteria revealed by real-time PCR were generally found in petroleum-polluted soils in comparison to unpolluted soils (Figure 3 and Table 3). Thus microbial immobilization that removes inorganic nitrogen by microbial uptake may intensify nitrogen limitations to the plants due to higher consumption rate of nitrogen by a large number of hydrocarbon-degrading microbes during phytoremediation [11], [28]. The results obtained through 15 N isotopic dilution technique also support the idea that the consumption rate of inorganic nitrogen is higher in petroleum-polluted soils than in unpolluted soils [29].…”

“…Therefore, nitrogen becomes the primary limiting nutrient for plant growth [11], [20]. Our results indicate that petroleum had consistently negative effects on NNM (Figure 1D and Table 1), which might reflect the decrease in the potential of microbes for supporting plant growth because NNM dominates inorganic nitrogen supply to the plants [26], [27].…”

“…Petroleum hydrocarbons often result in the degradation of plant-beneficial functions of microbes and high microbial consumption rate of nitrogen during phytoremediation [11], [19]. Therefore, nitrogen becomes the primary limiting nutrient for plant growth [11], [20].…”

“…This plant species is an excellent study organism owing to its potential of breaking down petroleum pollutants because of its well-developed roots, high biomass production, and stimulating effects for microbial degraders [6], [7], [14], [16], [17]. Due to the considerable impact of petroleum pollution on plants, soil properties, and microbes [11], [18]–[20], we hypothesized that petroleum pollution will negatively impact plant–microbe interactions.…”