The effects of phytochemicals on soil microbial communities

Abstract

The aims of this dissertation are to check and monitor how the species of Eucalyptus, Mediterranean thyme and Lavender leaves affect the microbial activity present in soil. There has been little to no research done on the effect of phytochemicals on soil microbial activity in Maltese soil, in fact there are no studies specifically on phytochemicals. Studies concerning indigenous plants which contain phytochemicals, such as the Mediterranean thyme. Eucalyptus and Mediterranean thyme residues were mixed with soil, these had a negative effect on the activity of arginase enzyme .The effect on urease activity was different from that of arginase, since when the treatments were mixed with urea amended soil, NH4+ concentration was higher in every treatment when compared to the untreated soil control, indicating an increase in urease activity. The respiration rate of the treated soils and grass positive control, were all high compared to the untreated soil, indicating that the degradation of organic matter was still happening throughout the incubations and thus the differences between the treatments with respect to arginase and urease was not due to lack of available carbon. These results show that different enzymes are affected differently by the compounds found in the leaves of these plants. Urease did not get negatively affected by the essential oils released from these plants, such as Eucalyptus. In contrast, arginase is negatively affected by the leaves since the rate, especially in the Eucalyptus treated soil was less than the control; moreover, the activity in the Mediterranean thyme treated soil was close to the untreated control.