Root development of Lolium perenne in diesel contaminated soil

Abstract: When studying phytoremediation, one of the most important aspects is root development, with its associated rhizosphere that improves hydrocarbon degradation. Plant performance of Lolium Perenne grown in diesel contaminated soil was studied in a rhizobox experiment where root development could be visually monitored. The effect of layer geometry, irrigation and textural heterogeneity on root development was investigated as well as the relationship between root length and diesel degradation. Adding a thin layer of clean soil on top of a contaminated layer allowed germination but all treatments showed severe stress symptoms, such as reduced shoot and root growth, in the presence of diesel and in response to water stress. The presence of a diesel contaminated layer at five cm depth allowed root development in the uncontaminated surface soil without roots penetrating the contamination. With a thinner layer of clean soil roots did penetrate the contaminated layer but showed reduced root development. Natural attenuation was responsible for most of the degradation with a variation between 78 % and 84 % for all treatments. Root length was positively correlated (r2 = 0.52) to diesel degradation but improved degradation was also dependent on spatial distribution of roots where to root presence inside the contaminated layer proved to be important. No diesel movement was found regardless of irrigation technique. When a layer of finer material of varying diesel concentration was imbedded in a coarser sand profile the roots were spreading in this layer regardless of diesel concentration emphasising the importance of optimal moisture and nutrient conditions. The importance of moisture was also shown in the treatments with sub-irrigation where the plants received too little water and died.