Abstract: Praxelis clematidea is one of the nastiest invasive exotic weeds in southern China and poses lots of serious threats to biodiversity, agricultural production and ecological security of native ecosystems. In order to explore impacts of P. clematidea invasion (with an invasion period of 4 to 5 years) on soil ecosystem, we investigated the changes of soil chemical and microbiological properties, including soil nutrient, soil microbial biomass, soil enzyme activity, and metabolic activity, carbon substrate utilization and function diversity of soil microbial community from invaded and native sites in Hainan Island using field plot experiments. The results showed that compared with the native bush sites, the contents of soil organic matter, total nitrogen, alkaline nitrogen and available potassium were significantly decreased while the content of total potassium was significantly increased in the P. clematidea invasion sites. However, there was no significant difference in the contents of total phosphorus and available phosphorus between the invaded and native sites. Soil microbial biomass carbon, nitrogen, and phosphorus, as well as the activities of soil urease, protease, invertase and hydrogen peroxidase in the invaded sites were significantly lower than those in the native bush sites, while the activity of soil cellulase was significantly increased by the P. clematidea invasion. Functional diversity of soil microbial community, calculated from the average well color development (AWCD) of 31 carbon sources in a Biolog EcoPlate, was significantly decreased by the P. clematidea invasion. Compared with the native bush sites, AWCD, microbial utilization efficiency of carbohydrates, carboxylic acids, McIntosh index (U), and  richness index (S) of soil microbial community were significantly decreased, while Pielou index (E) was significantly increased in the P. clematidea invasion sites. There was no significant difference in Shannon’s index (H) and Simpson’s dominance index (D_s) between the invaded and native sites. Our results suggested that P. clematidea invasion could consume enormous soil nutrients and cause soil degradation in the invaded region.

Key words: mini-UAV image, estimation of scale parameter, supervised classification, visible vegetation index, object-oriented image classification., aquatic vegetation