Dataset for: Differential responses to fertilization and competition among invasive, non-invasive alien and native Bidens species
Kim, Eunsuk (2021), Dataset for: Differential responses to fertilization and competition among invasive, non-invasive alien and native Bidens species, Dryad, Dataset, https://doi.org/10.5061/dryad.0rxwdbrz3
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.
2.1. Study species and seed sources
We examined two alien (B. frondosa, B. pilosa) and one native Bidens species (B. bipinnata), Asteraceae. All three species are herbaceous erect weedy species that inhabit disturbed areas or the periphery of rice fields in Korea. The achenes of B. bipinnata and B. pilosa are oblong-shaped with three to four barbed awns, but that of B. frondosa 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 B. bipinnata and B. frondosa were collected from natural populations in Pocheon-si (37° 46’ 20.057” N, 127° 9’ 56.314’’ E), and B. pilosa 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.
2.2. Experimental design
Achenes of Bidens 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 Bidens species to the center of pots containing Festuca arundinacea (tall fescue). F. arundinacea was chosen as a competing species because it has been widely used to recover anthropogenically disturbed areas in Korea. Before transplantation, 1 g of F. arundinacea 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.
2.3. Trait measurement
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. Bidens 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 B. bipinnata achenes, 290 B. frondosa achenes, and 140 B. Pilosa achenes.
Korea National Arboretum, Award: Project No. KNA1-2-26, 16-4
Gwangju Institute of Science and Technology, Award: GIST Research Institute (GRI) grant