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Phenotypic variation and germination behavior between two altitudinal populations of two varieties of Bidens pilosa in Taiwan

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(1)Taiwania 60(4):194‒202, 2015 DOI: 10.6165/tai.2015.60.194. Phenotypic Variation and Germination Behavior between Two Altitudinal Populations of Two Varieties of Bidens pilosa in Taiwan. Han-Ling Huang1, Ya-Lun Huang1, Tai-Chung Wu1 and Wen-Yuan Kao1,2* 1.Institute of Ecology and Evolutionary Biology, National Taiwan University, 1 Roosevelt Rd., Section 4, Taipei 106, Taiwan. 2.Department of Life Science, National Taiwan University, 1 Roosevelt Rd., Section 4, Taipei 106, Taiwan. * Corresponding author. Tel: +886-2-33662511; Email: wykao@ntu.edu.tw (Manuscript received 9 October 2015; accepted 10 December 2015) ABSTRACT: Bidens pilosa L. var. radiata, an invasive plant in Taiwan, is distributed into mountain area. In contrast to B. pilosa var. radiata, B. pilosa var. minor is a naturalized plant and distributed mainly in mid-altitude of the island. This study aims to (1) investigate phenotypic variations between low- and mid-altitudinal populations of these two varieties of B. pilosa, and (2) evaluate the causes, environmental effect or genetic differentiation, of the variations. Two populations, one from low-(500 m) and the other from mid- altitude (1300 or1600 m) along an elevation gradient in central Taiwan, of both varieties were selected for the study. We compared ecophysiological traits of field populations and of progeny of these populations cultivated in a common garden. For both varieties, mid-altitudinal populations had significantly higher chlorophyll and N contents, more positive δ13C values and larger seeds than low-altitudinal populations. However, most of the phenotypic variations between altitudinal populations disappeared in common garden-grown plants. The results suggested that these variations were phenotypic plasticity in response to changes in environmental factors associated with altitudes. Comparing between populations of the same variety, seeds of the var. minor collected from mid-altitudinal population germinated faster. In contrast, seeds of the var. radiata from mid-altitudinal populations germinated slower and required more days to germinate. Thus, seeds produced by the mid-altitudinal population of the var. radiata had inferior germination performance, which might reduce its competitive ability at mid-altitude. However, high degree of phenotypic plasticity would allow B. pilosa var. radiata to spread into mountain area. KEY WORDS: altitudinal variation, Bidens pilosa var. radiata, Bidens pilosa var. minor, ecophysiological traits, invasive plants, phenotypic plasticity, seed germination. INTRODUCTION Effects of biological invasion on biodiversity and ecosystem functions have been studied worldwide (Vilà et al., 2011). The results indicated that biological invasion is a key driver for the decline of biodiversity and the changes of ecosystem functioning (Vitousek et al., 1997; Mooney and Hobbs, 2000). Because of the harsher climatic condition and less human disturbance, biologists thought that mountains were less vulnerable to biological invasion than lowland ecosystems (Humphries et al., 1991; Millennium Ecosystem Assessment, 2003). Therefore, most of the studies on the impact of the invasive plants focused on lowland ecosystems. However, more and more surveys showed that mountain vegetation might not be so resilient to biotic invasion (Pauchard et al., 2009). Thus, it is necessary to evaluate the possibility and then prevent the dispersion of invasive plants from lowland into high altitude ecosystems. After been introduced into Taiwan in the late 20th century, Bidens pilosa L. var. radiata has spread and becomes one of the ten most notorious plants in lowland Taiwan during the last two decades (Chiang et al., 2003). Morphological, physiological, growth and reproductive traits of the invasive plant at lowland environment have been studied (Hsu and Kao, 2009; 194. Huang et al., 2012, Huang and Kao, 2014; Hsu and Kao, 2014). Further investigation found expanded distribution of B. pilosa var. radiata from lowland ecosystems into high elevation area (Huang, 2008). In Taiwan the percentage of endemic species increases with increasing altitude, consequently, a highly positive correlation between endemism and altitude was found (Hsieh, 2002). The occurrence of B. pilosa var. radiata in the mountain suggests that the invasive plant might be able to invade high elevation ecosystems, subsequently might reduce biodiversity and threaten the survival of endemic species of Taiwan. To reduce the risk of ecosystem disrupted by invasive species, research into high-elevation plant invasions is important for developing appropriate management policies. In addition, as Körner (2007) suggested that conducting this type of research could help us understanding factors that influence spread of plant species along steep environmental gradients. B. pilosa var. minor is another introduced variety of B. pilosa in Taiwan (Peng et al., 1998). In contrast to B. pilosa var. radiata, var. minor is a naturalized plant and currently distributed mainly in mid-altitude whereas relatively rare in lowland Taiwan (Authors’ obs.). To gain a better understanding in the traits making B. pilosa var. radiata invasive Taiwan, Hsu (2006) and Huang (2014) have studied ecophysiological, floral and.

(2) December 2015. Huang et al. : Phenotypic variation and germination of Bidens pilosa. life history traits of the plant. However, their studies focused on lowland populations. To our knowledge, characteristics of mid-altitude populations of both varieties have not been studied. Comparing changes in phenotype of populations at different altitudes between the invasive and naturalized varieties may help us evaluating which factors would favor or limit the invasive plant spread into high elevation. In this study, two populations, at low- and mid-altitudes (locations listed in Materials and Methods) along an elevation gradient in Central Taiwan, of B. pilosa var. radiata and B. pilosa var. minor, were selected. We measured ecophysiological traits of these populations in situ in three seasons. We also grew progeny of these populations in two seasons in a common garden at lowland and repeated the measurement of the ecophysiological traits. Finally, we compared germination response of seeds collected from these populations under two temperature regimes. The objectives of this study were: (1) to investigate variations in phenotype and germination behavior between low- and mid-altitude populations of these two varieties of B. pilosa, (2) to evaluate the causes, environmental effect or genetic differentiation, of the phenotypic variation between populations, and (3) to asses the risk of B. pilosa var. radiata invading mountain area in Taiwan.. MATERIALS AND METHODS Materials The two study plants belong to the species Bidens pilosa, a member of the Asteraceae family. B. pilosa var. radiata is an annual or perennial herb, while B. pilosa var. minor is an annual herb (Peng, 1998). The two varieties, sometimes growing sympatrically, can be distinguished by their ray florets, which are usually longer than 10 mm in var. radiata but shorter than 8 mm in var. minor. Field study site and measurements Populations of B. pilosa var. radiata at two altitudes (120°36′E, 23°26′N alt. 500 m and 120°41′E, 23°28′N alt.1300 m) and those of B. pilosa var. minor at two altitudes (120°36′E, 23°26′N alt. 500 m and 120°43′E, 23°24′N alt.1600 m) in Central Taiwan were selected for the investigation. Plants of the two varieties at the lowland site grew sympatrically. The mean monthly air temperature and mean monthly precipitation (Fig. 1) close to the study area in 2007 were provided by two weather stations, Chiayi (23°29′52′′E, 120°25′28′′ N, alt. 28 m) and Fanchihu (23°29′45′′E, 120°41′28′′N, alt. 1385 m), of Central Climate Bureau, Taiwan. Chlorophyll content of leaves from plants (n = 8) growing at each altitude were estimated with a chlorophyll meter (SPAD-502, Minolta Co., Japan).. Fig. 1. Mean monthly precipitation (bars) and air temperature (square) during the year of 2007. Data are from Chiayi (23°29′52′′E, 120°25′28′′N, alt. 28 m) (Low alt.) and Fan-Chi Lake (23°29′52′′E, 120°25′28′′N, alt. 1405 m) (Mid alt.) weather stations located at central Taiwan.. After the chlorophyll contents recorded, leaves were excised, leaf area was measured using a leaf area meter (LI-3100, Licor, Lincoln, NE, USA). The leaf was then dried at 60 °C for at least 48 h and its dry mass weighted with an electronic balance (Mettler AB104). Leaf mass per area (LMA= mg cm-2) was then calculated as leaf dry mass/leaf area. The leaf material was then ground and subsequently its nitrogen (N) content and stable carbon isotopes ratio (δ13C) were determined using continuous flow isotope mass spectrometry (CF-IRMS)consisting an elementary analyzer (FlashEA1112, ThermoFisher, Italy) connected to an isotopic ratio mass spectrometer (delta V, Finnigan, Germany). δ13C values were calculated as: δ13C (‰) = [(R sample /R standard ) -1] × 1000, where R is the corresponding ratio of δ13C: δ12C of a standard (PDB, R standard = 0.0112372) or the measured sample (R sample ) (Ehleringer and Osmond, 1989). To calculate the mean weight of a seed for an individual plant, total seeds of the individual plant were collected, counted and weighted. Seeds collected from 10 individual plants of each population in April and Dec. of 2007 were compared. Measurements of common garden-grown plants Seeds collected from populations at two altitudes were germinated in Petri dishes (diameter of 9 cm), followed by transplanting of the seedlings to the experimental farm of National Taiwan University, Taipei. Two transplants were conducted, one from spring to fall (Apr. to Oct. 2007) and the other from fall to spring (Oct. 2007 to May 2008). Measurements of ecophysiological traits, above mentioned, were taken in August 2007 and in March 2008, respectively, for both experiments. 195.

(3) Taiwania. Vol. 60, No. 4. Table 1. Results of P value from the two-way ANOVA (general linear model) assessing the effect of season, population (altitude) and the interactions of both on leaf mass per unit area (LAM), chlorophyll content (Chl), nitrogen content (N), stable carbon isotope ratio (δ13C) and seed weight of Bidens pilosa var. minor growing in field or in a common garden. NA: not available. Field growing plants. Variable. Garden cultivated plants. Season. Altitude. Season × Altitude. Season. Altitude. Season × Altitude. <0.01 0.13 <0.01 0.78 <0.01. 0.09 <0.01 <0.01 <0.01 <0.01. 0.06 0.38 0.13 0.02 0.01. <0.01 <0.01 <0.01 <0.01 NA. 0.24 <0.01 0.79 0.64 0.47. 0.87 0.39 0.35 0.26 NA. LMA Chl N δ13C Seed weight. Table 2. Mean weight of a seed (mg) (Mean ± SE, n = 10) collected from plants of B. pilosa var. minor and B. pilosa var. radiata growing in field at two altitudes and from their progeny grown in a common garden. B. pilosa var. minor 500 m field. Apr., 2007 Dec.,2007. B. pilosa var. radiata. 1600 m c*. 1.37±0.02. b. 1.46±0.02. c. 500 m b. 1.58±0.03. a. 1.79±0.03. 1300 m e. 1.16±0.02d. e. 1.15±0.02d. 0.95±0.02 0.92±0.02. garden Apr., 2008 1.39±0.06 1.47±0.03 1.33±0.11 1.11±0.07d * Means within the same raw followed by different letters are significantly different (LSMEAN, P < 0.05).. Measurements of germination behavior Seeds collected from field growing plants were placed on water-saturated filter paper in a Petri dish (diameter × height = 90 mm × 15 mm), with 25 seeds per Petri dish and 5 Petri dishes per species per treatment. These Petri dishes were then transferred to two growth chambers controlled at relative humidity of 70%, light/dark cycle of 12/12 h and PFD (photosynthetic photon photon flux density) of 100-150 μmol m-2 s-1 at light period and air temperature (light/dark period) of 30/25 and 18/13 °C, respectively, simulating summer and winter temperature in lowland (< 500 m) Taiwan. Seed germination was recorded every day for 14 days. Seeds were considered germinated when radicals could be observed by naked eyes. After 14 days of treatment, cumulative germination percentage, speed of germination and mean days to geminate were calculated following Hou et al. (2000). Cumulative germination percentage = seed germinated / 25 seeds sowed. d: days after germination (1-14), f d : number of seeds germinated on the d day, N: total number of seeds germinated on each Petri-dish within 14 days Statistical and data analysis Two ways analyses of variance (general linear model procedure of SAS, release 9.1, SAS Inst. Inc.) were used to determine differences in parameters 196. bc. cd. between populations and among seasons and the interaction.. RESULTS Phenotypic variation between altitudinal populations In B. pilosa var. minor, seasonal effect on LMA was detected, however, no significant difference was found in LMA between populations (Fig. 2a, Table 1). In contrast, significant differences were found in chlorophyll (Chl) and N contents (per leaf area), δ13C and seed weight between populations (Table 1). In general, plants at 1600 m had significantly higher Chl (ca. 5 μg cm-2 more, Fig. 2c) and N content (Fig. 2e), more positive δ13C values (ca. 1-1.5‰, Fig. 2g) and heavier mean dry weight of seeds (ca. 20%, Table 2) than those at 500 m. Similar to B. pilosa var. minor, pattern of differences in Chl (Fig. 2d) and N contents (Fig. 2f), δ13C values (Fig. 2h) and mean seed weight was found in B. pilosa var. radiata at two altitudes. In contrast to no difference in LMA between populations of B. pilosa var. minor (Table 1), B. pilosa var. radiata plants at 1300 m had significantly higher LMA (about 30%) than those at 500 m (Fig. 2b). Values of leaf δ13C (-32 to -29‰, Fig.2g, 2h) confirm that both varieties are C3 plants. Measurements of common garden-grown plants For both varieties the values of LMA, Chl and N content and δ13C showed significant difference between seasons (Table 1, Table 3). Populations of both varieties showed consistent, seasonal trends in these parameters (Fig. 3). Leaves of plants grown in summer had significantly less LMA, more Chl, higher N content.

(4) December 2015. Huang et al. : Phenotypic variation and germination of Bidens pilosa. Fig. 2. Leaf mass per area (LMA) (a, b), chlorophyll content (Chl) (c, d), nitrogen content (N) (e, f) and stable carbon isotope ratio (δ13C) (g, h) of leaves of Bidens pilosa var. minor (Bpm) (a, c, e, f) and B. pilosa var. radiata (Bpr) (b, d, f, h) growing in low-(open symbols) and mid-(closed symbols) altitudes in different month of 2007.. 197.

(5) Taiwania. Vol. 60, No. 4. Table 3. Results of P value from the two-way ANOVA assessing the effect of season, population (altitude) and the interactions of both on leaf mass per unit area (LAM), chlorophyll content (Chl), nitrogen content (N), stable carbon isotope ratio (δ13C) and seed weight of Bidens pilosa var. radiata growing in field or in a common garden. NA: not available. Variable LMA Chl N δ13C Seed weight. Field growing plants. Garden transplants. Season. Altitude. Season × Altitude. Season. Altitude. Season × Altitude. <0.01 <0.01 <0.01 0.25 0.54. <0.01 <0.01 <0.01 <0.01 <0.01. 0.08 0.08 0.08 0.09 0.80. <0.01 <0.01 0.01 0.02 NA. 0.61 0.79 0.08 0.42 0.15. 0.65 0.34 0.80 0.20 NA. but more negative δ13C values than those in spring. Consistently higher LMA, Chl and N content and more negative δ13C values was found in B. pilosa var. minor plants of 1600 m source population than those of 500 m source one (Fig. 3). However, among these parameters, significant difference was detected only in Chl content between populations (Table 1). In B. pilosa var. radiata, the phenotypic differences in LMA, Chl and N content between field populations growing at alt. of 500 and 1300m was not found in common garden grown plants (Table 3, Fig. 3). Seed germination behavior In comparison between seeds of the two altitudinal populations of B. pilosa var. minor germinated at the same temperature regime, similar cumulative germination percentage (ca. 97%) was found after 14 days of sowing, however, seeds collected from 1600 m population germinated faster and required significant less days to germinate (Fig. 4a, Table 4). Comparing at two temperature regimes, seeds produced by B. pilosa var. minor population at the same altitude showed no significant difference in cumulative germination percentage after 14 days of sowing (Table 4). However, seeds at 30/25 °C had faster germinated speed and required significantly less days to germinate than those at 18/13°C require (Table 4). In comparison between seeds of the two altitudinal populations of B. pilosa var. radiata germinated at 30/25°C, no significant difference was found in cumulative germination percentage (ca. 90%) after 14 days of sowing, but seeds of 500 m populations had significantly faster germination speed and required less days to germinate (Fig. 4b, Table 5). In comparisons of seeds between the two altitudinal populations germinated at 18/13°C, seeds produced by 500 m population had significantly higher germination percentage (ca. 20% more), faster germination speed and required less days to germinate (Fig. 4b, Table 5). In addition, significant difference in germination behavior was found between seeds of B. pilosa var. radiata collected from the same altitudinal population but grown at different temperature regimes, higher germination percentage, faster germination rate and less mean days to germinated at 30/25°C than at 18/13°C. 198. Note: Only a small population of about 10 individuals were found. In the Platanthera genus in Taiwan, the labella have sidelobes only found in three species: P. devolii, P. sonoharae and P. nantousylvatica. This species differs from the other two in having elliptic or oblong leaves, in contrast to linear ones. The specific epithet refers to the location where it was found.. DISCUSSION This study measured ecophysiological traits of plants of two varieties of B. pilosa growing in two different altitudes in natural condition and those of their progeny grown in a common garden. Results of the measurements not only provide information on the degree of phenotypic variation between the altitudinal populations but also provide opportunity to determine whether the variation is under environmental and/or genetic control. The two varieties showed differential response in leaf mass per area (LMA) to altitudinal variation (Fig. 2a, 2b). Mid-altitude population of the var. radiata had significantly higher LMA than low-altitude population indicating that mid-altitude population had thicker and/or denser leaves than the low-altitude population. The difference in LMA between two altitudinal populations of the var. radiata was not found in common garden-grown plants, which suggested that the population variation in LMA was due to phenotypic plasticity and not from genetic differentiation. It has been found that lower temperature could reduce leaf expansion and result in thicker leaves (Woodward, 1979). The pattern of seasonal changes in LMA, low in summer and high in winter, found in field populations (Fig. 2) and in plants grown at the common garden (Fig. 3) suggest that high LMA found in the mid-altitude population of the var. radiata may be a consequence of the effect of lower temperatures. Seasonal effect on LMA was also found in common garden-grown populations of the var. minor (Fig. 3, Table 1). However, difference in LMA between field populations of var. minor was only detected in Dec. 2007 but not in other seasons. It is known that light and water availability, in addition to temperature, also affected LMA. It is possible that difference in other environmental factors between mid-and low altitude.

(6) December 2015. Huang et al. : Phenotypic variation and germination of Bidens pilosa. Fig. 3. Leaf mass per area (LMA) (a, b), chlorophyll content (Chl) (c, d), nitrogen content (N) (e, f) and stable carbon isotope ratio (δ13C) (g, h) of leaves of Bidens pilosa var. minor (Bpm) (a, c, e, f) and B. pilosa var. radiata (Bpr) (b, d, f, h) plants, origins of low-(open symbols) and mid-(closed symbols) altitudes, grown at a common garden from April to Oct. of 2007 and from Oct. to May of 2008, respectively. Data were taken in August 2007 and March 2008.. 199.

(7) Taiwania. Vol. 60, No. 4. Fig. 4. Cumulative germination percentage of Bidens pilosa var. minor (a) and B. pilosa var. radiata (b) seeds, collected from low- (500 m) and mid- (1600 m or 1300 m) altitudinal populations, under two temperature regimes, 30/25 (HT) and 18/13℃ (LT),for 14 days.. offset the temperature effect on LMA of the var. minor. C3 plants growing at higher altitudes might compensate partially for reduced partial pressure of CO 2 by increasing the concentrations of RuBp carboxylase per unit leaf area, thus leaf N concentrations per area have been found to increase with altitudes in both herbaceous and woody species (Morecroft and Woodward, 1996; Weih and Karlsson, 2001; van de Weg et al., 2009). In this study, we also found that mid-altitudinal populations of both varieties had significantly higher leaf N content per unit leaf area than the low- altitudinal populations (Fig. 2e, 2f). In addition, mid altitudinal populations also had higher Chl contents than at low- altitudinal populations (Fig. 2c, 2d). An increased in leaf nitrogen and chlorophyll contents suggested that mid-altitudinal populations had higher photosynthetic capacity than low-altitudinal populations. In the common garden experiment, progeny of mid-altitudinal population of var. minor, but not var. radiata, also had significantly higher Chl contents than those of low-altitude population (Fig. 3c, 3d). Accordingly, our results evidenced both genetic and environmental effects on Chl. contents of the var. minor but mainly environmental effects on that of the var. radiata. In vascular plants, increase leaf δ13C with elevation has been reported widely in interspecific and intraspecific comparison (Morecroft, Woodward and Marrs, 1992; Hultine and Marshall 2000; Qiang et al., 2003; Takahashi and Miyajima, 2008). In this study, for both varieties growing in field, mid-altitudinal populations also had more positive δ13C (Fig. 2g, 2h), indicating a lower ratio of CO 2 partial pressure inside the leaf to that in the atmosphere and a higher ratio of carboxylation efficiency to stomatal conductance (Farquhar et al., 1982), than low 200. altitudinal populations. It has been found that the increase in leaf δ13C with elevation was associated with higher leaf mass per area (LMA) at lower temperatures (Körner et al., 1991; Vitousek et al., 1990; Cordell et al., 1999). Though mid-altitudinal population of var. radiata also had higher LMA than low-altitudinal population (Fig. 2b), however, no significant difference was found in LMA between the two populations of var. minor (except in Dec. 2007, Fig. 2a). The result suggests that the difference in δ13C between populations of var. minor was not resulted from their differences in LMA; other factors (probably N content) were involved. In contrast to field growing populations, no significant difference was found in δ13C of plants with different altitude origins grown in a common garden (Fig. 3e. 3f). Accordingly, environmental effect contributed to phenotypic variation in δ13C between the two-altitudinal populations of both varieties. Seed weight is a critical trait of a plant’s life history. In general, larger seeds can have a higher establishment success, as they provide more reserves for seedlings (Moles and Westoby, 2004). As favorable conditions for seed recruitment decrease in higher altitudes, selection might favor populations producing large seeds at higher altitudes. Indeed, increasing seed weight of the same species with increasing altitude has been reported (Lord, 1994; Ayana and Bekele, 2000). In consistent with these reports, our results also showed that in both varieties mid-altitudinal populations did produce heavier seeds than low-altitudinal populations (Table 2). However, in common garden experiment, no significant difference was found in seed weight between seeds produced by progeny from different altitudes. Accordingly, environmental effects caused phenotypic variation in seed weight between field populations. It was reported that in Aegilops ovata.

(8) December 2015. Huang et al. : Phenotypic variation and germination of Bidens pilosa. Table 4. Germination percentage, means days to germinate and the speed of germination (no. of seed germinate per day) of Bidens pilosa var. minor seeds, collected from two altitudinal (500 m and 1600 m) populations, after germination at two temperature regimes (30/25 and 18/13℃),for 14 days. Values are means ± standard errors (n = 5). Means within the same category followed by different letters were significantly different (LSMEAN, P < 0.05). Germination temperature Seed source Germination(%) Mean days to germinate Speed of germination. 500m 1600m 500m 1600m 500m 1600m. 30/25℃. 18/13℃. 97.6 ± 0.98 98.4 ± 1.60 3.6 ± 0.2c 1.7 ± 0.1d 8.2 ± 0.5b 16.7 ± 0.5a. 92.8 ± 2.90 98.4 ± 0.98 9.5 ± 0.4a 6.9 ± 0.3b 2.7 ± 0.2c 3.8 ± 0.1c. Table 5. Germination percentage, means days to germinate and the speed of germination (no. of seed germinate per day) of Bidens pilosa var. radiata seeds, collected from two altitudinal (500 m and 1600 m) populations, after germination at two temperature regimes, 30/25 and 18/13 ℃,for 14 days. Values are means ± standard errors (n = 5). Means within the same category followed by different letters were significantly different (LSMEAN, P < 0.05). Germination temperature Seed source Germination(%) Mean days to germinate Speed of germination. 500m 1600m 500m 1600m 500m 1600m. (Datta et al., 1972) and in Plantago lanceolata (Alexander and Wulff, 1985; Lacey, 1996) the seeds produced under lower temperatures were heavier than those developed at warmer conditions. Thus, the phenotypic variation in seed weight of B. pilosa varieties might be also caused by growth temperature. Seeds of both varieties did not show apparent dormancy, but their germination is sensitive to temperature (Fig. 4). Regardless of their origins, seeds of both varieties germinated significantly more rapidly at 30/25 than at 18/13°C. The result suggests that seeds of both varieties produced by mid-altitudinal populations were not more adapted to germinate at 18/13°C than those by low-altitudinal populations. Though seed germination of both varieties showed similar response to temperature, difference was detected in germination speed between populations of the same variety at the same temperature regime (Table 4). In var. radiata, seeds produced by the mid-altitudinal population germination slower, either at 30/25 or at 18/13°C, than those by low-altitudinal population. Similar results were reported in Chenopodium bonus-henricus L. (Dorne, 1981) and in Festuca novae-zelandiae (Lord, 1994), in which slower germination rates were observed with increasing seed size. A different result was detected in the var. minor, in which seeds collected from mid-altitudinal population were also heavier; however, they geminated faster than those from low-altitudinal population (Table 4). Variation in germination characteristics between seeds from. 30/25℃. 18/13℃. 91.2 ± 4.1a 89.6 ± 4.1a 4.4 ± 0.3d 6.5 ± 0.3c 7.0 ± 0.5a 4.0 ± 0.3b. 72.8 ± 3.2b 53.6 ± 3.0c 8.4 ± 0.2b 10.3 ± 0.4a 2.6 ± 0.2c 1.4 ± 0.1d. different environments may be due to heritable differences (ecotypic differentiation) and/or phenotypic difference resulting from differences in the environment experienced by maternal parent during seed maturation (maternal environment effect). Numerous studies have shown maternal effect on seed germinability (Alexander and Wulff, 1985; Gutterman, 2000; Figueroa et al., 2010). Ecotypic differentiation in seed germination was also reported (Meyer and Pendleton, 2005; Shin and Kim, 2013). Results of current study cannot distinguish the extent of these two factors contributing to the behavior of seed germination in these two varieties. Whatever the causes of the phenomenon, the result suggest that the var. minor is more adapted to mid-altitude than the var. radiata in term of their germination behavior. Though the spread of B. pilosa var. radiata into higher elevation might be potentially limited by its germination behavior, however, it is known that the plant is capable of vegetative reproduction (Hsu, 2006; Huang 2008) which might compensate for its inferiority in seed germination behavior at higher elevations. In conclusion, results of this study highlights high levels of phenotypic variability for leaf functional traits between two altitudinal populations of both varieties of B. pilosa. However, most of the variations, except Chl content of the var. minor, found between field populations of the same variety disappeared in common garden-grown plants. The results suggested that these variations were phenotypic plasticity in response to changes in 201.

(9) Taiwania. environmental factors associated with altitudes. Seeds of the var. radiata had inferior germination performance than those of the var. minor at lower temperature, which might reduce the competitive ability of the var. radiata at mid-altitude. However, high degree of phenotypic plasticity in combination with its ability of vegetative reproduction (Hsu and Kao, 2014) might contribute to the expansion of B. pilosa var. radiata into mountain area.. ACKNOWLEDGEMENTS This study was partly supported by a grant from the National Science Council of Taiwan, R.O.C. (NSC 100-2621-B-002-004).. LITERATURE CITED Alexander, H.M. and R. D. Wulff. 1985. Experimental ecological genetics in Plantago. X. The effects of maternal temperature on seed and seedling characters in P. lanceolata. J. Ecol. 73: 271–282. Ayana, A. and E. Bekele. 2000. Geographical patterns of morphological variation in Sorghum (Sorghum bicolor (L.) Moehch) germplasm from Ethiopia and Eritrea: quantitative characters. 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Fig. 1. Mean monthly precipitation (bars) and air temperature  (square) during the year of 2007
Table 1. Results of P value from the two-way ANOVA (general linear model) assessing the effect of season, population (altitude)  and the interactions of both on leaf mass per unit area (LAM), chlorophyll content (Chl), nitrogen content (N), stable carbon i
Fig. 2. Leaf mass per area (LMA) (a, b), chlorophyll content (Chl) (c, d), nitrogen content (N) (e, f) and stable carbon isotope  ratio (δ 13 C) (g, h) of leaves of Bidens pilosa var
Table 3. Results of P value from the two-way ANOVA assessing the effect of season, population (altitude) and the interactions of  both on leaf mass per unit area (LAM), chlorophyll content (Chl), nitrogen content (N), stable carbon isotope ratio (δ 13 C) a
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