Plant and fertiliser effects on rhizodegradation of crude oil in two soils with different nutrient status

Abstract

Soils and sediments polluted with crude oil are of major environmental concern on various contaminated sites. Outdoors pot experiments were conducted to test the phytodegradation potential of common reed (Phragmites australis) and poplar (Populus nigra × maximowiczii) in fertilised and non-fertilised control treatments. Two topsoils (E, G) of different texture were mixed with crude oil. Soil analysis included hydrocarbon (HC) measurements, detection of labile phosphorus and mineralised nitrogen as well as dehydrogenase activity. Increased HC degradation by native soil biota was clearly related to higher P availability in soil G and to fertilisation in soil E. Except of the non-fertilised common reed treatment, plants did not enhance crude oil degradation. We found even inhibited degradation of high molecular weight HC in the presence of plants together with declining labile phosphorous concentrations due to planting on soil E. Native soil biota were able to use the whole range of crude oil compounds (C 10 to C 60 ) as a carbon source in the presence of sufficient nutrient concentrations in soil. This study is the first to show that reduced HC degradation in the higher molecular weight crude oil fraction (C 20 to C 40 ) is likely to be a consequence of decreased phosphorus availability for microorganisms in the plant rhizosphere.

Effect of N and P fertilisation and aeration on biodegradation of crude oil in aged hydrocarbon contaminated soils

“…Before use, the soils were passed through a 2-mm stainless steel mesh. Due to the sieving, initial HC concentrations of soils E and G were higher compared to the values at the end of the experiment presented in Unterbrunner et al (2007), where non-sieved soils E and G including the skeleton fraction were used. Extractable N, P and K were determined one month before starting the first incubation experiment.…”

“…The experimental soils E and G (Ap horizon of Haplic Chernozems) described in Unterbrunner et al (2007) were obtained from unplanted control pots of a rhizodegradation experiment. The soils had been spiked with crude oil two years before starting the incubation experiments described here (E: 16.4 g/kg; G: 13.3 g/kg).…”

“…Unfertilised Unterbrunner et al (2007); **soil GF is identical with soil G but was freshly spiked controls and selected fertiliser treatments (N3, P3, N3 + P3) were incubated with and without agitation (i.e., manual mixing for one minute three times per week using a glass stirrer). Hydrocarbon extraction and analysis.…”

“…Although it has been shown that the establishment of plants and/or the application of fertiliser can enhance crude oil degradation in soil, plants and degrader-microorganisms may compete for nutrients in soils (Unterbrunner et al 2007). In order to overcome potential competition for nutrients and/or to overcome nutrient deficiencies, the application of fertilisers may result in enhanced degradation rates of crude oil.…”

“…Repeated aeration of the contaminated soil may further increase the biodegradation of HC. To test these two hypotheses, we have taken the untreated (i.e., without plants) hydrocarbon-contaminated control soils of the study of Unterbrunner et al (2007) and investigated the effects of fertilisation with N and P and of agitation on the degradation of crude oil in two incubation experiments.…”