Abstract:
Nutrient availability is a key factor determining the growth and competitive dominance of
alien invasive plants. Variation for plastic response among introduced populations may provide the
potential for invasive plants to evolve greater plasticity and promote their invasions. Understanding
how nutrient availability affects the growth and competitive ability of invasive plants, as well as
whether there is variation for plastic response among introduced populations will help to predict the
invasion risk of alien plants. Bidens frondosa, which originated in North America, has been reported
in most provinces in China in recent years. In order to explore the potential of B. frondosa to become
invasive, we tested the growth and competitive response of B. frondosa by planting four introduced
populations of B. frondosa alone and together with the native congener B. biternata under three
nutrient levels. The results were as follows: (1) When grown alone under high nutrient, B. frondosa
had significantly higher values for plant height, branch number and total biomass compared with
those grown at low nutrient. The reproductive ratios of all the populations at low nutrient were
significantly greater than that at high nutrient except for the population Jiangsu. When grown in
competition with B. biternata, the competitive response of the plant height, branch number, total
biomass and reproductive biomass of the invasive populations of B. frondosa under high nutrient were significantly lower than that under low nutrient, indicating that this invasive weed was
suppressed less under high nutrient compared with that under low nutrient conditions. (2) Under all
nutrient conditions, the populations Guangxi and Jiangxi significantly grew higher and had a greater
total biomass than the population Hebei. The population Guangxi had the highest number of
branches among the four populations when grown at low, medium and high nutrients (12 �0.86,
16.83�.95 and 21.83�.14, respectively). The reproduction ratios of population Hebei grown at
low and high nutrients [(47.33 �3.29)% and (25.74 �2.82)%, respectively] were significantly
greater than those of population Guangxi when grown under comparable conditions [(30.92 �1.78)% and (19.77 �1.22)%, respectively]. In addition, the competitive response of total biomass
were significantly greater for the population Hebei (-0.51�.04) than for the population Guangxi
(-0.35�.06) under medium nutrient condition. The competitive response of reproductive biomass
of population Hebei (-0.46 �0.03) was also significantly greater than that of population Guangxi
(-0.28 �0.07) under medium nutrient. Our results show that nutrient addition can enhance the
growth and competitive ability of B. frondosa. Moreover, there are variations in the growth and
competitive response among the introduced populations. Therefore, increased nutrient and gene flow
may enhance the potential risks of invasion by B. frondosa.
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