Allelopathy And Analysis Of Components Of Root Exudates From Xanthium Strumarium, X. Sibiricum And Bidens Biternata Grown In Different CO₂ Concentrations

Invasion of alien plant species have exerted dramatical impacts on society, economy and ecological environment in the invaded ranges, and become one of the key research topics in ecology. Allelopathy has played an important role in the invasion of exotic invasive plants. X. strumarium is one of the devastating alien invasive plants with strong allelopathy in Liaoning province. To explore the relationships between allelopathy and the invasiveness of X. strumarium, and the effects of elevated atmospheric CO2 on its allelopathic effects, this study identify differences of the allelochemical composition and the effects of root exudates on seed germination between X. strumarium and its co-occurring native plants (X. sibiricum and B. biternata) under ambient and elevated doubly CO2. The results showed that:1. The results of GC-MS showed that under ambient CO2 treatments, the numbers of chemical compounds of root exudates in X. strumarium, X. sibiricum and B. biternata were 15,19 and 25 respectively, while under elevated CO2 treatments, the numbers were 19,21 and 26 respectively. Those chemicals mainly were esters, aldehydes, hydrocarbons, thiazoles, amines and other compounds with, the Dibutyl phthalate and Diisooctyl phthalate having been confirmed with allelochemical activities. Consistent with the magnitude of allelochemical effects of root exudates, there were more kinds of chemicals under elevated CO2 with the same plant species.2. The biological experiment results.of allelochemical effects of root exudates showed that, in both the ambient and elevated CO2, root exudates of all the three species could inhibit seed germination and seedling growth of 4 plant species while such effects varied among species. The inhibition effects increased with the increasing concentrations of root exudates. The allelopathy was stronger for each of the three plant species under higher CO2 concentrations. More importantly, allelochemical effects of root exudates of invasive X. trumarium was stronger than the two co-occurring native plants growed in the same CO2 concentrations. These results indicated that the invasive species X. trumarium had higher concentration of allelochemicals in root exudates than the two native plants (X. sibiricum and B.biternata), and that the higher allelochemicals concentration of X. trumarium contributed to its higher invasiveness through inhibition on co-occurring natives. The magnitude the increased allelochemical effects by elevated CO2 concentration was higher in X. trumarium than that in the native plants.