DOI: 10.5061/dryad.0rxwdbrz3
title: Dataset for: Differential responses to fertilization and competition among invasive, non-invasive alien and native Bidens species

description: Comparative studies of invasive, non-invasive alien, and native congenic
 plant species can identify plant traits that drive invasiveness. In
 particular, functional traits associated with rapid growth rate and high
 fecundity likely facilitate invasive success. As such traits often exhibit
 high phenotypic plasticity, characterizing plastic responses to
 anthropogenic environmental changes such as eutrophication and disturbance
 is important for predicting the invasive success of alien plant species in
 the future. Here, we compared trait expression and phenotypic plasticity
 at the species level among invasive, non-invasive alien, and native Bidens
 species. Plants were grown under nutrient addition and competition
 treatments, and their functional, morphological, and seed traits were
 examined. Invasive B. frondosa exhibited higher phenotypic plasticity in
 most measured traits than did the alien non-invasive B. pilosa or native
 B. bipinnata. However, differential plastic responses to environmental
 treatments rarely altered the rank of trait values among the three Bidens
 species, except for the number of inflorescences. The achene size of B.
 frondosa was larger, but its pappus length was shorter than that of B.
 pilosa. Two species demonstrated opposite plastic responses of pappus
 length to fertilization. These results suggest that the plasticity of
 functional traits does not significantly contribute to the invasive
 success of B. frondosa. The dispersal efficiency of B. frondosa is
 expected to be lower than that of B. pilosa, suggesting that long-distance
 dispersal is likely not a critical factor in determining invasive success.
description: <b>2.1.
 Study species and seed sources</b>           We examined two alien
 (<i>B. frondosa</i>, <i>B. pilosa</i>) and one
 native <i>Bidens</i> species (<i>B.
 bipinnata</i>), Asteraceae. All three species are herbaceous erect
 weedy species that inhabit disturbed areas or the periphery of rice fields
 in Korea. The achenes of <i>B. bipinnata</i> and <i>B.
 pilosa</i> are oblong-shaped with three to four barbed awns, but
 that of <i>B. frondosa</i> is obovate-shaped with two awns.
 The achenes used in this study were obtained from the seed stock center in
 the Korean National Arboretum. According to the information of the seed
 stock center, achenes of <i>B. bipinnata</i> and <i>B.
 frondosa</i> were collected from natural populations in Pocheon-si
 (37° 46’ 20.057” N, 127° 9’ 56.314’’ E), and <i>B. pilosa</i>
 were collected in Seogwipo-si, Korea (33° 14’ 43.062’’ N, 126° 24’ 40.24’’
 E) in 2014. Since we used field-collected achenes for this study, maternal
 effects might influence the results. However, our primary objective is
 comparing trait expressions between species, and maternal effects likely
 have limited effects on the species-level comparisons. <b>2.2.
 Experimental design</b>           Achenes of
 <i>Bidens</i> species were sterilized using 0.5% sodium
 hypochlorite for 10 min, carefully scarified twice with a razor blade, and
 maintained in Petri dishes with wet filter paper in June 2016. After cold
 treatment at 4 °C for two weeks, achenes were allowed to germinate in a
 customized walk-in chamber under a 12-hour light/dark photoperiod at 23
 °C. Individual seedlings were planted in flats containing commercial soil
 medium (ShinSung Mineral Co. LTD., Kyunggi-do, Korea) and grown under the
 same conditions present during germination. After one month of growth,
 plants were transplanted into plastic pots (21.5 cm × 21.4 cm × 15.5 cm)
 filled with 50% commercial saprolite and 50% soil medium on August 25,
 2016. The plants were maintained in a common garden at the Gwangju
 Institute of Science and Technology (35°13′28.47″ N, 126°50′36.81″ E).
 According to the Korean Meteorological Administration, the temperature
 during the 2016 summer season was the second hottest since 1973, and
 precipitation was around half of the ten-year average. To prevent
 transplant shock and the abrupt death of plants, plants were watered every
 other day for one month.              To evaluate the effects of
 competition and fertilization, we employed a full factorial design with
 four treatment combinations. As a competition treatment, we transplanted
 one individual seedling of each <i>Bidens </i>species to the
 center of pots containing <i>Festuca arundinacea</i> (tall
 fescue). <i>F. arundinacea</i> was chosen as a competing
 species because it has been widely used to recover anthropogenically
 disturbed areas in Korea. Before transplantation, 1 g of <i>F.
 arundinacea</i> seeds was sowed in each pot following the
 distributor’s recommendations and grown for one and a half months in the
 common garden. To simulate the high nutrient content of soil in
 agricultural areas, half of the pots in each competition treatment
 received 1 g of slow-release fertilizer pellets (Osmocote Plus N:P:K 13 –
 13 – 13+ 2MgO + trace element, Everris International B.V., Geldermalsen,
 NL) following the manufacturer’s instructions. Pots containing plants were
 randomly positioned using a completely randomized design. Thirty
 individuals of each plant species were used for each of the four
 treatments, resulting in a total of 360 plants. We harvested half of the
 plants to measure plant growth and functional traits six weeks after the
 treatment application. The remaining plants were grown until they
 completed reproduction to measure fecundity and achene traits.
 <b>2.3.
 Trait measurement</b>           After six weeks of treatment, we
 collected whole plants, washed their roots to remove all soil, and dried
 them in a dry oven (Hanbaek, Co. LTD., Kyunggi-do, Korea) at 65 °C for
 three days to weigh their dry mass. The R/S ratio was calculated as the
 dry mass of the root divided by the aboveground biomass. Before
 harvesting, we took one fully expanded leaf from each plant and scanned it
 to measure the leaf area (Digimizer software ver. 4.6.1; MedCalc Software
 bvda, Ostend, Belgium). Leaves were dried at 65 °C for three days, and the
 SLA was calculated as the leaf area divided by the dry mass. We estimated
 the leaf chlorophyll content using a SPAD-520 plus chlorophyll meter
 (Spectrum Technologies, IL, USA). The SPAD values exponentially correlate
 with the chlorophyll content.              We counted the number of
 inflorescences as a proxy of fecundity, because many fruits fell onto the
 ground during the experiment. <i>Bidens</i> species produce
 morphologically distinctive achenes at the center and periphery of the
 capitulum (Brändel, 2004). Disk achenes tend to be larger and disperse
 more readily than ray achenes (Rocha, 1996). We randomly selected more
 than two achenes from the central area of the capitulum of each plant
 individual and photographed them using a stereomicroscope. Images were
 analyzed using Digimizer software to measure the length of the pappi and
 the cross-sectional areas of the achenes. Achenes with broken pappi were
 excluded from the image analysis, and morphological characteristics were
 analyzed for a total of 250 <i>B. bipinnata</i> achenes, 290
 <i>B. frondosa</i> achenes, and 140 <i>B.
 Pilosa</i> achenes.