Weed Science, 54:452–457. 2006
Effects of environmental factors on germination and emergence of Crofton weed (Eupatorium adenophorum) Ping Lu
Laboratory of Quantitative Vegetation Ecology, Institute of Botany, the Chinese Academy of Sciences, Nanxincun 20, Xiangshan, Haidian District, Beijing, 100093, People’s Republic of China and Graduate School of the Chinese Academy of Sciences, Beijing, 100039, People’s Republic of China
Weiguo Sang
Corresponding author. Laboratory of Quantitative Vegetation Ecology, Institute of Botany, the Chinese Academy of Sciences, Nanxincun 20, Xiangshan, Haidian District, Beijing, 100093, People’s Republic of China;
[email protected]
Keping Ma
Laboratory of Quantitative Vegetation Ecology, Institute of Botany, the Chinese Academy of Sciences, Nanxincun 20, Xiangshan, Haidian District, Beijing, 100093, People’s Republic of China
Laboratory and greenhouse studies were conducted to determine the effect of several environmental factors on seed germination and seedling emergence of Crofton weed. Seeds germinated over a range of 10–30 C, with optimum germination at 25 C. High temperature markedly restricted germination, with no germination occurring at 35 C. Crofton weed was moderately photoblastic, with 17% germination occurring in the dark. Crofton weed germinated in a narrow range of pH (5–7). Maximum germination (94%) was observed in distilled water at pH 5.7. Germination was totally inhibited at osmotic stress higher than 20.7 MPa. Germination was greater than 65% at less than 100 mM NaCl, with no germination at 300 mM NaCl. Maximum emergence occurred when seeds were planted on the soil surface. No seedlings emerged when seeds were planted 1.5 cm deep. These results suggest that the future range of Crofton weed in China will be restricted largely to the Yunnan-Guizhou Plateau, which includes major parts of Yunnan and Guizhou provinces, the southwestern part of Sichuan province, and the western part of Guangxi province. Crofton weed also tends to be a sporadic problem in other regions, where the climatic and edaphic conditions are suitable for the seed germination. Nomenclature:
Key words: Invasive weed, light, osmotic potential, pH, planting depth, salt stress, temperature.
Crofton weed native to Mexico and Costa Rica of Central America is a worldwide noxious invasive weed (Auld 1969a, 1969b; Qiang 1998; Papes and Peterson 2003; Lu and Ma 2004). It is a shrubby perennial with a woody root stock and numerous upright branching stems. It is shallow rooted, and usually 0.8–2.5 m in height (Zhou et al. 2004). It is a prolific seed producer (Auld and Martin 1975; Liu et al. 1989), and is characterized by the accumulation of longlived seed bank (Shen and Liu 2004), so it has great potential to increase in distribution and density. Since the invasion into China from the borders of Vietnam and Burma, the rate of spread has been faster than anticipated, particularly in the southern and southwestern parts of the country. Crofton weed now prevails in Yunnan province, and has expanded its distribution to the southwestern parts of Sichuan and Guizhou provinces, and the western part of Guangxi province. It also tends to be a sporadic problem in Chongqing City, Hubei, Tibet, and Taiwan provinces (Figure 1). It invades a variety of habitats including roadside, riverside, farmland, grassland, shrub, broad-leaf forest, and pine forest (Zhou et al. 2004; Yu et al. 2004). Crofton weed forms dense monospecific stands, displacing native species. According to investigation, only 3 yr after invading into natural pasture, the coverage of Crofton weed can reach 85–95% and reduce grass output by 70–80% (Zhou et al. 2004). As a result, it is considered a serious threat to local diversity and economics. Unfortunately, Crofton weed is extremely difficult to control or eradicate. Most control measures, including mechanical, manual, chemical, natural enemies, and biological control, have had limited success (Lu et al. 2005). Considerable effort is being put forward to find new and innovative methods for integrated management of Crofton weed, which 452
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Crofton weed (Eupatorium adenophorum ‘Spreng’).
should be based on a detailed understanding of weed biology and ecology. Germination is one of the most critical phases in plant development. Each plant species has a specific range of environmental requirements necessary for germination (Baskin and Baskin 1989). Environmental factors such as temperature, light, pH, and soil moisture are known to affect seed germination (Chachalis and Reddy 2000; Taylorson 1987). The burial depth of seed also affects germination and seedling emergence (Koger et al. 2004). Although Crofton weed has received considerable attention and research (Auld 1969a, 1969b, 1970; Auld and Martin 1975; Liu et al. 1989; Lu and Ma 2004, 2005; Shen and Liu 2004; Yu et al. 2005), information about Crofton weed germination is lacking. To date, no detailed study has specifically investigated the germination biology of this troublesome invasive weed. An understanding of germination and emergence of Crofton weed seeds would help to predict its potential spread into new areas and would be useful in developing effective control measures. The information may help explain why Crofton weed has successfully invaded such a large area of southwestern China. Therefore, the purpose of this research was to determine the effects of temperature, light, pH, water stress, salt stress, and planting depth on Crofton weed seed germination and seedling emergence.
Materials and Methods Crofton weed seeds were collected from Chuxiong, China (258019N, 1018329E), on May 2, 2005. The seeds were dried for 7 d at room temperature, and then stored in paper
FIGURE 1. The present invasive distribution of Crofton weed in China. The data for distribution of Crofton weed in China were collected from herbarium records and survey. Herbarium records were collected from Institute of Botany, the Chinese Academy of Sciences; Kunming Institute of Botany, Chinese Academy of Sciences; Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences; Guizhou Institute of Biology; Sichuan Institute of Biology; Guangxi Institute of Botany; Guangxi Institute of Traditional Chinese Medicine; National Taiwan University; Taiwan Institute of Traditional Chinese Medicine; and Southwest state of Guizhou Forest Research Institute.
bags at room temperature (20 6 5 C) for 2 wk until the experiment started.
General Information Fifty seeds were placed on two sheets of filter paper in 9cm petri dishes. The filter paper was moistened initially with 4 ml of distilled water or test solution. If necessary, 1–3 ml of the appropriate solution was added to maintain adequate moisture. All dishes were sealed with Parafilm1 to reduce loss of water. They were placed in the growth chamber with diurnal 10-h light/14-h dark regime; the light period had a photon irradiance rate 250 mmol m22 s21. A preliminary study indicated that maximum germination of Crofton weed seeds occurred at approximately 25 C. Therefore, all germination experiments, excluding those measuring the effects of temperature, were conducted at 25 C. Germinated seed (seed were considered germinated when the radicle had emerged 1 mm) were counted and removed daily for a period of 35 d. No further germination was observed at 42 d after the start of any experiment.
Effect of Temperature Crofton weed seeds were placed in petri dishes and incubated at constant temperatures of 5, 10, 15, 20, 25, 30, 35, and 40 C to evaluate the response to a wide range of germination temperatures.
Effect of Light Petri dishes were covered with double layers of aluminum foil to ensure no light penetration, or left uncovered to allow continuous light exposure (250 mmol m22 s21 PPFD) to determine the effect of light on germination. Dishes assigned to dark treatments remained unopened until the final day of the experiment. The experiment was set in a dark room with a safe green light.
Effect of pH Crofton weed seeds were exposed to buffer solutions of pH 4–9. Distilled water (pH 5.7) was used as a control. For buffered pH solutions of 4.0, 4.5, 5.0, 5.5, and 6.0, a 0.1 M potassium hydrogen phthalate was used (Clark and Lubs 1916). For buffered pH solutions of 6.5 and 7.0, 0.1 M sodium hydrogen phthalate was used. For buffered solutions of 7.5, 8.0, 8.5, and 9.0, 0.2 M boric acid solution and 0.05 M borax solution were used (Li et al. 2000). Final adjustments of each buffer were made using 0.1 M HCl or 0.1 M NaOH.
Effect of Water Stress Crofton weed seeds were moistened with solutions of PEG 6000 with known water potentials. The PEG solutions were prepared according to the equations of Michel and Kaufmann (1973). The water potentials were set to 0, 20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8, 20.9, and Lu et al.: Crofton weed germination
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FIGURE 2. Effect of constant temperature (A), pH (B), NaCl concentration (C) and osmotic potential (D) on germination of Crofton weed seeds. Vertical bars represent standard errors of the means.
21.0 MPa. Germination of seeds and the level of PEG so-
lutions were assessed daily. Once a reduction in the level of PEG solution was detected, all filter papers and solutions were replaced with PEG solutions prepared on the day of replacement.
Effect of Salt Stress Salt effects on germination were studied with the use of solutions of 0, 50, 100, 150, 200, 250, and 300 mM sodium chloride.
ducted each experiment twice and pooled the data for analysis, because there was no significant experiment-by-treatment interaction. Regression analysis was used to determine the effect of salt stress and water stress on seed germination. One-way ANOVA was used to assess the effect of planting depth on emergence. Significant differences among treatments were identified with the use of Duncan’s multiplerange test (P , 0.05). Data met all normality conditions; therefore, data transformation was not required.
Results and Discussion
Effect of Planting Depth
Temperature
Seeds were planted in sand-peat medium (90% sand and 10% peat moss, v/v) in plastic pots (19-cm diam by 16-cm depth) at depths of 0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 cm below the soil surface. Greenhouse temperatures were 30 6 3 C during the day and 20 6 5 C during the night, and natural 12- to 13-h photoperiods (200–700 mmol m22 s21 PPFD) were used. Pots were watered throughout the study as needed to maintain adequate moisture. Seedlings were considered to have emerged when cotyledons were visible. Emergence counts were recorded daily and removed daily for a period of 35 d. No further germination was observed at 42 d after the start of any experiment.
Crofton weed seed germination increased from 43 to 93% between 10 and 25 C, and then declined to 0 at 35 C (Figure 2A). No germination occurred at a constant temperature of 5 and 35 C. Crofton weed seed germinated over a temperature range of 10–30 C, which could allow for germination throughout the spring and summer months in much of southwestern China. The optimum germination temperature occurs from March until October in Yunnan. The optimum germination temperature of 10–25 C occurs in early spring in Yunnan and may allow Crofton weed to germinate and begin growth early in the growing season, possibly before other species. This is of great importance in Yunnan, because many of the tropical and subtropical plants require relatively high temperatures to initiate growth. High temperature ($ 35 C) markedly inhibited germination, which indicates that Crofton weed seed can only germinate at relatively cool temperatures; consequently, spread of this
Statistical Analysis All experiments were conducted with the use of a completely randomized design with four replicates. We con454
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TABLE 1. Environmental factors of each province in China.
Province
Yunnana
Guizhoua Sichuana Guangxia Chongqinga Hubeia Tibeta Taiwana Ningxia Shanxi Fujian Zhejiang Gansu Heilongjiang Neimenggu Xinjiang Jilin Liaoning Hebei Beijing Tianjin Shaanxi Qinghai Shandong Henan Jiangsu Anhui Shanghai Hunan Jiangxi Guangdong Hainan
Annual mean temperature (8C)
14.8 14.8 7.9 19.8 15.1 14.8 20.8 13.9 7.6 7.7 17.4 15.7 5.2 1.3 3.5 4.9 4.3 7.6 9.0 10.0 12.2 10.1 22.1 12.7 14.0 14.8 15.2 15.9 16.2 17.2 20.7 23.7
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
4.1 1.7 7.0 1.8 2.6 2.2 5.3 8.6 1.4 2.9 1.7 1.3 4.3 2.8 4.1 6.9 1.3 1.3 4.1 2.2 0.6 2.3 3.7 0.9 1.4 0.6 0.9 0.2 1.2 1.2 1.6 0.9
Relative humidity (annual mean) (%)
73.6 79.9 68.2 78.9 79.2 76.5 48.6 84.7 54.9 58.9 81.8 79.3 53.1 67.9 54.3 48.2 65.8 62.5 59.4 56.6 61.4 64.6 49.6 66.8 70.1 75.8 75.7 78.5 80.3 79.4 79.5 82.5
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
5.4 1.5 10.0 1.3 2.6 2.4 10.3 4.2 4.8 2.6 1.8 1.2 10.6 4.3 11.1 7.7 4.9 4.7 3.8 1.2 1.1 6.9 9.5 2.8 3.5 2.9 2.2 0.9 1.1 1.4 1.4 1.5
Soil moisture (based on 150-mm water-holding capacity) (mm)
110.0 130.4 128.4 111.5 132.6 109.3 89.1 118.1 11.8 43.6 117.5 129.6 29.9 69.8 19.5 4.4 83.9 87.8 33.6 37.6 30.2 66.3 53.3 53.2 62.9 93.9 103.7 111.9 116.7 108.6 108.9 81.0
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
24.0 10.6 20.8 16.1 12.9 23.3 52.3 27.2 19.5 16.6 18.4 10.3 45.0 31.0 27.8 9.2 46.3 39.3 18.7 12.3 4.4 36.0 54.8 25.9 26.3 17.5 25.9 1.3 9.5 10.1 10.4 22.4
Soil pH
6.0 5.9 6.2 5.8 6.2 6.4 6.7 6.4 7.6 7.1 5.9 6.0 7.4 6.6 7.4 7.5 7.0 6.9 6.9 6.8 7.0 7.0 7.0 6.9 6.9 6.8 6.5 6.7 5.9 5.9 6.0 5.9
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
0.5 0.3 0.5 0.2 0.3 0.5 0.8 0.2 0.2 0.3 0.2 0.4 0.6 0.4 0.5 0.5 0.3 0.2 0.3 0.1 0.1 0.7 0.8 0.2 0.6 0.4 0.5 0.2 0.3 0.3 0.2 0.3
a Infested by Crofton weed. Annual mean temperature and relative humidity (1971–2000) from CERN (Chinese Ecosystem Research Network), soil pH and soil moisture from IGBP-DIS data set (http://www.sage.wisc.edu/atlas/).
weed may be restricted to temperate regions. The present study also suggested that the invasive capacity of Crofton weed might be impaired during the process of spread to southeastern China, which has a higher extreme high temperature range (35–40 C) than the invaded region (30 C) (annual means 1950–1990; from the China Meteorological Administration, www.digitalagri.cn). Zhao and Ma (1989) reported that Crofton weed (vegetative plants) could survive in a temperature range of (211.5–;35 C). So we predict that the future range of Crofton weed in China will be restricted largely to the Yunnan-Guizhou Plateau, which is located in southwestern China, including major parts of Yunnan and Guizhou provinces, the southwestern part of Sichuan province, and the western part of Guangxi province (Zhao and Chen 2001).
pH, Salt and Water Stress Crofton weed germinated in a narrow range of pH (5– 7), indicating that pH may be a limiting factor for germination in soils. Germination was greatest in distilled water (pH 5.7) followed by buffer solutions with pH 6 (Figure 2B). No germination of seed was observed at pH less than 5 or greater than 7. In contrast, seeds of redvine [Brunnichia
ovata (Walt.) Shinners] (Shaw et al. 1991), S. dulcis (Jain and Singh 1989) and hairy nightshade (Solanum sarrachoides Sendtner) (Zhou et al. 2005) have been reported to germinate in a wide range of pH. The relative low germination at pH 5 or 7 may be biologically significant. Most YunnanGuizhou Plateau soils have a pH range of 5–7 (Table 1), which is within the range of Crofton weed germination. These results also suggest that Crofton weed prefers neutral to slightly acidic soil conditions. The potential distribution for Crofton weed in China predicted in a genetic algorithm of rule-set prediction model used by Papes and Peterson (2003) did not consider the effect of pH on seed germination. Our data suggest pH may be a limiting factor for spread of Crofton weed. Germination of Crofton weed seeds was inversely related to NaCl concentration (Figure 2C). Germination was greater than 65% at less than 100 mM NaCl, greater than 10% at 5 mM NaCl, and no germination occurred at 300 mM NaCl. These data suggest that even at high soil salinity, Crofton weed seed may germinate. Crofton weed seems to have salt tolerance greater than trumpetcreeper [Campsis radicans (L.) Seem. ex Bureau] (Chachalis and Reddy 2000) and texasweed [Caperonia palustris (L.) St. Hil.] (Koger et al. 2004). Lu et al.: Crofton weed germination
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As osmotic stress increased, Crofton weed seed germination decreased (Figure 2D). Crofton weed germination was 95, 85, 81, 43, and 41% at osmotic potential of 0, 20.1, 20.2, 20.3, and 20.4 MPa, respectively. Only 29 and 23% of seed germinated at osmotic potentials of 20.5 and 20.6 MPa, respectively. No germination occurred at a water potential lower than 20.7 MPa. Optimum germination occurred at osmotic potentials between 0 and 20.2 MPa, where germination exceeded 80%. This result helps explain the association between rain events and flushes of Crofton weed in the field, which occurs during the rain season (May to October) in Yunnan. Several weedy species, such as goatweed (Scoparia dulcis L.) (Jain and Singh 1989), and Virginia buttonweed (Diodia virginiana L.) (Baird and Dickens 1991), have shown similar sensitivity to osmotic stress. However, Crofton weed germination is more sensitive to osmotic stress than mayweed chamomile (Anthemis cotula L.) (Gealy et al. 1985) and tropical soda apple (Solanum viarum Dunal) (Akanda et al. 1996). Therefore, Crofton weed spread may be restricted to well-drained, moist soil due to its inability to germinate under low soil moisture conditions.
Light and Planting Depth When Crofton weed seeds were exposed to continuous darkness, the germination was 17% (SE 3%). This was significantly lower (P , 0.05) than the 93% (SE 3%) germination under 10-h photoperiod. This shows that Crofton weed seeds are light sensitive, and our results may help explain why it usually invades areas that experience frequent disturbance, particularly where soils are bare and exposed. This suggests that successful Crofton weed germination and establishment require a high-light environment. A light requirement for seed germination is common (Egley and Duke 1985), especially in species that have small seeds (Taylorson 1987). However, because some Crofton weed seeds also germinated in complete darkness, this could explain why germination occurs in dense, shaded areas such as pine forests. Emergence of Crofton weed seedlings decreased rapidly with increased planting depth. Emergence was maximum (84%) for seeds placed on the soil surface, and no seedlings emerged from seeds placed at a depth of 1.5 cm (Figure 3). This reduction in germination at even shallow soil depths could, in part, be attributed to a reduction in light or to inability of germinated Crofton weed seedlings to survive before they emerged. Because of the small size of Crofton weed seeds (He and Liu 2003), resources may have been limited, preventing sustained seedling growth. Decreased emergence due to increased planting depth has been reported in milkweedvine (Morrenia odorata Lindl.) (Singh and Achhireddy 1984), hairy beggarticks (Bidens pilosa L.) (Reddy and Singh 1992), redvine (Shaw et al. 1991), and trumpetcreeper (Chachalis and Reddy 2000). Shen and Liu (2004) indicated that Crofton weed is characterized by the accumulation of long-lived seed bank, which serves as a source of regeneration of new plants in the event of disturbance. The mean soil seed density, from the soil surface down to 10 cm, was estimated to be 2,202 seeds m22 (Shen and Liu 2004). So a potential advantage of photoblastic seeds is that they would not germinate when deeply buried in the soil, which allows seedling emergence 456
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FIGURE 3. Effect of planting depth on emergence of Crofton weed seeds. Vertical bars represent standard errors of the means. Different letters indicate significant differences (P , 0.05) according to Duncan’s multiple range test.
only when their establishment is more likely. Crofton weed produces a large amount of small seeds with no primary dormancy (Shen and Liu 2004) and the ability to germinate over a wide range of temperatures, so the deeply buried seeds have the potential for germination when they are relocated to near the soil surface by disturbance. This can increase the time and effort needed to control Crofton weed, so we suggest that a long-term management system be established to control this invasive weed. In summary, Crofton weed seed did not tolerate water stress, was photoblastic, and only seeds near the soil surface germinated. The range of pH (5–7) required for seed germination is within the range of most soil of the YunnanGuizhou Plateau. Therefore, alkalinity or other alteration of soil acidity will probably limit the establishment of this weed. Crofton weed occurs over a broad range of salt concentrations; a proportion of Crofton weed seeds may germinate at high soil salinity, so it may invade some coastal areas (Auld 1969b; Auld and Martin 1975). Germination of Crofton weed seed may occur over a wide range of temperatures (10–30 C). Therefore, it should be controlled as soon as possible in spring or early summer, when temperatures are 15 to 25 C. The lack of tolerance to high temperatures indicates that Crofton weed is most competitive in the temperate climate of the Yunnan-Guizhou Plateau, and suggests that the range of this species as a significant pest is not likely to extend into southeastern China. Crofton weed also tends to be a sporadic problem in other regions, where the climatic and edaphic conditions are suitable for the seed germination. The Yunnan-Guizhou Plateau has similar climatic and geographic conditions to the native regions (Mexico and Costa Rica) of Crofton weed. The Yunnan-Guizhou, Mexico, and Costa Rica Plateaus are also low latitude plateaus (Yunnan Meteorological Bureau 2000). The annual mean temperature of most of the Yunnan-Guizhou Plateau region is 14–24 C (Zhao and Chen 2001), which is again similar to the annual mean temperatures of Mexico (17–27 C) and Costa Rica (16–25 C) (Sino Maps Press 1987). This study has shown that germination of Crofton weed is influenced by a range of environmental factors, and our results suggest that the successful invasion of Crofton weed in southwestern
China can be explained in part by these conditions and interactions of climatic and edaphic conditions.
Sources of Materials 1 Parafilm from Pechiney Plastic Packaging, 8770 West Bryn Mawr Avenue, Chicago, IL 60631.
Acknowledgments We thank Weibin Gu, Yulong Feng, Zhiming Zhong, Lihong Han, and Zhiquan Liu for their assistance in this research. And we also thank F. Andrew Smith, Li Zhu, Xingjun Yu, and two anonymous reviewers for their suggestions about this paper and for giving much constructive advice. The work was supported by Knowledge Innovation Project of Chinese Academy of Sciences (Contract No. KSCX1-SW-13-03), National Natural Science Foundation of China (Contract No. 30470337) and K. C. Wong Fellowship, Royal Society of U.K.
Literature Cited Akanda, R. U., J. Mullahey, and D. G. Shilling. 1996. Environmental factors affecting germination of tropical soda apple (Solanum viarum). Weed Sci. 44:570–574. Auld, B. A. 1969a. Incidence of damage caused by organisms which attack crofton weed in the Richmond-Tweed region of New South Wales. Aust. J. Sci. 32:163. Auld, B. A. 1969b. The distribution of Eupatorium adenophorum Spreng, on the far north coast of New South Wales. J. Proc. R. Soc. NSW 102:159–161. Auld, B. A. 1970. Eupatorium weed species in Australia. PANS 16(1):82– 86. Auld, B. A. and P. M. Martin. 1975. The autoecology of Eupatorium adenophorum Spreng. in Australia. Weed Res. 15:27–31. Baird, J. H. and R. Dickens. 1991. Germination and emergence of Viginia buttonweed (Diodia virginiana). Weed Sci. 39:37–41. Baskin, J. M. and C. C. Baskin. 1989. Physiology of dormancy and germination in relation to seed bank ecology. Pages 53–65 in M. Leck, V. Parker, and R. Simpson, eds. Ecology of Soil Seed Banks. San Diego, CA: Academic. Chachalis, D. and K. N. Reddy. 2000. Factors affecting Campsis radicans seed germination and seedling emergence. Weed Sci. 48:212–216. Clark, W. M. and H. A. Lubs. 1916. Hydrogen electrode potentials of phthalate, phosphate, and borate buffer mixtures. J. Biochem. 25:479. Egley, G. H. and S. O. Duke. 1985. Physiology of weed seed dormancy and germination. Pages 27–64 in S. O. Duke, ed. Weed Physiology. Volume I. Reproduction and Ecophysiology. Boca Raton, FL: CRC Press. Gealy, D. R., F. L. Young, and L. A. Morrow. 1985. Germination of mayweed (Anthemis cotula) achenes and seed. Weed Sci. 33:69–73. He, P. and Y. Liu. 2003. The investigation of invasive plant species in natural grassland at Liangshan, Sichuan Province. Pratacultural Sci. 20(4):31–33. [In Chinese with English abstract] Jain, R. and M. Singh. 1989. Factors affecting goatweed (Scoparia dulcis) seed germination. Weed Sci. 37:766–770. Koger, C. H., K. N. Reddy, and D. H. Poston. 2004. Factors affecting seed
germination, seedling emergence, and survival of texasweed (Caperonia palustris). Weed Sci. 52:989–995. Li, H. S., Q. Sun, S. J. Zhao, and W. H. Zhang. 2000. Pages 267–271 in Principles and Techniques of Plant Physiological Biochemical Experiment. Beijing: Higher Education Press. Liu, L. H., W. Y. Liu, Z. Zheng, and G. F. Jing. 1989. The characteristic research of autecology ecology of Pamakani (Eupatorium adenophorum). Acta Ecol. Sin. 9(1):66–70. [In Chinese with English abstract] Lu, P., W. G. Sang, and K. P. Ma. 2005. Progress and prospect in the researches of an exotic invasive species Eupatorium adenophorum. Acta Phytoecol. Sin. 29(6):1029–1037. [In Chinese with English abstract] Lu, Z. J. and K. P. Ma. 2004. The influence of topographical factors on the invasion of the alien species, Eupatorium adenophorum. Acta Phytoecol. Sin. 28(6):761–767. [In Chinese with English abstract] Lu, Z. J. and K. P. Ma. 2005. Scale dependent relationships between native plant diversity and the invasion of croftonweed (Eupatorium adenophorum) in southwest China. Weed Sci. 53:600–604. Michel, B. E. and M. R. Kaufmann. 1973. The osmotic potential of polyethylene glycol 6000. Plant Physiol. 51:914–916. Papes, M. and A. T. Peterson. 2003. Predicting the potential invasive distribution for Eupatorium adenophorum Spreng. J. Wuhan Bot. Res. 21: 137–142. Qiang, S. 1998. The history and status of the study on Crofton weed (Eupatorium adenophorum Spreng.) a worst worldwide weed. J. Wuhan Bot. Res. 16:366–372. [In Chinese with English abstract] Reddy, K. N. and M. Singh. 1992. Germination and emergence of hairy beggarticks (Bidens pilosa). Weed Sci. 40:195–199. Shaw, D. R., R. E. Mack, and C. A. Smith. 1991. Redvine (Brunnichia ovata) germination and emergence. Weed Sci. 39:33–36. Shen, Y. X. and W. Y. Liu. 2004. Persistent soil seed bank of Eupatorium adenophorum. Acta Phytoecol. Sin. 28(6):768–772. [In Chinese with English abstract] Singh, M. and N. R. Achhireddy. 1984. Germination and ecology of milkweedvine (Morrenia odorata). Weed Sci. 32:781–785. Sino Maps Press. 1987. Pages 71–72 in World Atlas. Beijing: Sino Maps Press. Taylorson, R. B. 1987. Environmental and chemical manipulation of weed seed dormancy. Rev. Weed Sci. 3:135–154. Yu, X. J., D. Yu, Z. J. Lu, and K. P. Ma. 2005. A new mechanism of invader success: exotic plant inhibits natural vegetation restoration by changing soil microbe community. Chinese Sci. Bull. 50(11):1105– 1112. Yu, X. J., D. Yu, and K. P. Ma. 2004. Relationships between allelopathy and invasiveness by Eupatorium adenophorum in different sites. Acta Phytoecol Sin. 28(6):773–780. [In Chinese with English abstract] Yunnan Meteorological Bureau. 2000. Meteorology Study on Low Latitude Plateau. http:// www.ynmb.net/dw/dwgy.htm. Zhao, G. J. and Y. P. Ma. 1989. The investigation research on the distribution and harmfulness of Eupatorium adenophorum Spreng. in Yunnan province. J. Weed Sci. 3:37–40. [In Chinese with English abstract] Zhao, J. and C. K. Chen. 2001. Pages 579–581 in Geography of China. Beijing: Higher Education Press. Zhou, J. K., E. L. Deckard, and W. H. Ahrens. 2005. Factors affecting germination of hairy nightshade (Solanum sarrachoides) seeds. Weed Sci. 53:41–45. Zhou, S., C. J. Tang, and X. Y. Zhang. 2004. The damage situation and control countermeasures for Eupatorium adenophorum in Sichuan province. Pratacult. Sci. 21(1):24–26. [In Chinese with English abstract]
Received November 28, 2005, and approved January 23, 2006.
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