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Invasion by the exotic herb Ambrosia artemisiifolia L. has become a serious agricultural and environmental problem and of increasing research interest as the species continues its southward spread into subtropical regions of China. To better understand the possible physiological and morphological adaptations of A. artemisiifolia in this region, we conducted a greenhouse experiment using seedlings of A. artemisiifolia and a comparative native species, Urena lobata L. (Caesar’s weed), which is an erect annual shrub in the Malvaceae that commonly co-occurs with A. artemisiifolia in open, disturbed habitats in southern China. Seedlings of both plants were grown under four irradiance regimes (10%, 30%, 55%, and 100% irradiance) from 14 May to 13 July 2010. Ambrosia artemisiifolia showed significantly higher total biomass, total leaf area, specific leaf area, relative growth rate, and net assimilation rate but lower leaf mass fraction than U. lobata at the 30%–100% irradiance levels. With decreasing irradiance, A. artemisiifolia significantly increased biomass allocation to stems and decreased allocation to roots. Meanwhile, A. artemisiifolia exhibited higher light-saturated photosynthetic rates and light saturation points with wide variances except at the 10% irradiance treatment. These findings suggest that A. artemisiifolia has generally higher irradiance plasticity for traits pertaining to biomass partitioning, growth, and plant structure than U. lobata. The ability of A. artemisiifolia to tolerate high shade conditions while maintaining high growth rates at elevated irradiance levels may afford it a competitive advantage and may help explain its recent colonization and spread in southern China.

Successful establishment of invasive plant species may exert important effects on soil organisms and processes. To investigate the response of the soil meso-and micro-fauna community to Ambrosia artemisiifolia L. invasion and its age of colonization, samples were collected from three different depths in sites with and without the presence of A. artemisiifolia during the period of

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The exotic Chromolaena odorata is one of the most destructive invasive plant species in South China, and hence an efficient and sustainable control method is urgent. One method, replacement control, which eliminates harmful plants by introducing another competitive plant, is being used increasingly for controlling invasive plants. To test the potential of Pennisetum hydridum to control C. odorata, a series of polyculture experiments with different proportions of the two species was conducted. Competitive indices, plant morphological and physiological traits, and soil nutrient contents were measured to test the impacts of P. hydridum on C. odorata. The presence of P. hydridum significantly suppressed growth of C. odorata, and P. hydridum was not sensitive to the presence of C. odorata. Moreover, increased root/shoot ratios of P. hydridum enhanced its underground competitive ability, and competition between the two species resulted in remarkable reductions of soil nutrient contents which would further decrease the competitiveness of the invasive C. odorata. In summary, our results suggest that P. hydridum is a prospective candidate to control C. odorata.