University Honors

Invasive species are a serious and urgent problem worldwide. In California, the impact of invasive species on the ecological environment, economy, and human society has already caused significant losses. Among the methods discussed for controlling invasive species, the ìHomeland Securityî hypothesis suggests that the effect of inhibiting invasive species can be achieved through the allelopathy of local plants. Here, I selected the native plant Encelia farinosa from southern California and the invasive species Brassica tournefortii as a study system to test the feasibility of using the allelopathic effects of the native plant to control the invasive species. Encelia farinosa, or brittlebush, is a shrub that is distributed in the desert areas of the southwestern United States and northern Mexico. In earlier studies, it was identified that the leaves of brittlebush contain toxic plant compounds, namely 3-acetyl-6-methoxybenzaldehyde. Although this compound has been determined to inhibit plant growth, the extent to which these chemicals affect neighboring plants on an ecological scale remains undetermined. To confirm whether E. farinosa has allelopathic effects on B. tournefortii and whether it remains effective in the ecological environment, I conducted a germination experiment under laboratory conditions and an observational field study. The germination experiment confirmed that under laboratory conditions, the minimum concentration of the leaf extract of E. farinosa was only 2% w/v sufficient to inhibit the germination of the majority of B. tournefortii seeds. Subsequently, the observational field study confirmed that the abundance of B. tournefortii increased as the distance from E. farinosa increased. These results confirm that the leaf extract of E. farinosa has a strong inhibitory effect on B. tournefortii, and it seems that this pattern also holds true for their distribution in the wild. However, allelopathy is not necessarily the explanation. More tests are needed to prove that E. farinosa can control invasive species under natural conditions.