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Environmental Pollution 120 (2002) 445–453 www.elsevier.com/locate/envpol
Lead, zinc and copper accumulation and tolerance in populations of Paspalum distichum and Cynodon dactylon
W.S. Shua, Z.H. Yeb, C.Y. Lana, Z.Q. Zhanga, M.H. Wongb,* aSchool of Life Sciences and State Key Laboratory for Biocontrol, Zhongshan University, Guangzhou 510275, People’s Republic of China bInstitute for Natural Resources and Environmental Management, and Department of Biology, Hong Kong Baptist University, Kowloon, Hong Kong, People’s Republic of China
Received 29 March 2001; accepted 28 December 2001
‘‘Capsule’’: Metal-tolerant populations of the plants Paspalum distichum and Cunodon dactylon were identified.
Abstract Both Fankou and Lechang lead/zinc (Pb/Zn) mine tailings located at Guangdong Province contained high levels of total and DTPA-extractable Pb, Zn and Cu. Paspalum distichum and Cynodon dactylon were dominant species colonized naturally on the tailings. Lead, zinc and copper accumulation and tolerance of different populations of the two grasses growing on the tailings were investigated. Tillers of these populations including those from an uncontaminated area were subjected to the following concentra- tions: 5, 10, 20, 30 and 40 mg l 1 Pb, 2.5, 5, 10, 20 and 30 mg l 1 Zn, or 0.25, 0.50, 1 and 2 mg l 1 Cu for 14 days, respectively, then tolerance index (TI) and EC50 (the concentrations of metals in solutions which reduce 50% of normal root growth) were calculated. The results indicated that both Lechang and Fankou populations of the two grasses showed a greater tolerance to the three metals than those growing on the uncontaminated area, which suggested that co-tolerant ecotypes have evolved in the two grasses. P. distichum collected from Fankou tailings had the highest tolerance to Cu while Lechang population the highest tolerance to Pb and Zn among the tested populations, and tolerance levels in P. distichum were related to metal concentrations in the plants. P. dis- tichum had a better growth performance than C. dactylon when both of them were grown on the tailings sites. Tolerant populations of these species would serve as potential candidates for re-vegetation of wastelands contaminated with Pb, Zn and Cu. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Heavy metal; Tolerance; Accumulation; Paspalum distichum; Cynodon dactylon
1. Introduction (Baker, 1987). The ecology, physiology, biochemistry, molecular biology, evolutionary aspects of metal toler- Metal tolerance refers to specific individuals of a spe- ance in plants have been extensively studied (Baker and cies which are able to withstand greater amounts of Walker, 1990; Macnair, 1993; Ye et al., 1997a, b; Kar- toxicity than their immediate relatives on normal soil enlampi et al., 2000). The metal tolerant plant materials (Antonovics et al., 1971). Tolerance is therefore con- are not only of scientific interest, but they are also ferred by the possession of specific physiological adopted in several aspects of environmental protection, mechanisms which effectively enable it to function nor- such as revegetation of mined wastelands and phyto- mally even in the presence of high concentrations of remediation of lands polluted with heavy metals, for potential toxic elements (Baker, 1987). The phenom- long-term stabilization of wasteland surface and reduc- enon of heavy metal tolerance in plants has attracted tion of potentially toxic elements (Bradshaw and Chad- the interests of scientists for 50 years since the discovery wick, 1980; Raskin and Enseley, 2000; Terry and of Pb-tolerance of Agrostis tenuis grass (Bradshaw, Ban˜ uelos, 2000). Although some tolerant plant materi- 1952), and so far a substantial number of tolerant spe- als are now commercially available for restoration of cies or ecotypes have been identified around the world metalliferous wastelands, there has been continuous interest in searching for native tolerant plant materials * Corresponding author. Tel.: +852-2339-7050; fax: +852-2339- which adapt to local climatic conditions and are able 5995. to colonize metal-enriched soils for use in land recla- E-mail address: [email protected] (M.H. Wong). mation (Williamson et al., 1982; Sudhakar et al., 1992;
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446 W.S. Shu et al. / Environmental Pollution 120 (2002) 445–453
Archambault and Winterhalder, 1995; Wierzbicka, and the average annual precipitation is 1537 mm, with 1999; Monni et al., 2000). the rainfall season from March to August. Samples of Second only to agriculture, mining is one of the oldest P. distichum were collected from the waterlogged areas and most important industries in the world. Mining of Fankou and Lechang tailings ponds, respectively and activities, however, also produced greater volumes of samples of C. dactylon were collected from the dry area waste materials, such as tailings, overburden and waste of Lechang tailings pond. The Fankou and Lechang rocks. These waste materials frequently contain high tailings have been abandoned for 15 and 5 years concentrations of heavy metals (notably, Pb, Zn, Cu accordingly, at the time of sample collection. The con- and Cd) which are well above the toxic thresholds for trol populations for the two grasses were collected from most plants or which are at least high enough to restrict an uncontaminated pasture at the campus of Zhong- plant growth (Bradshaw and Chadwick, 1980). The shan University, Guangzhou, located approximately vegetation growing on tailings is subjected to a harsh 200 km south of Lechang and Fankou mine. P. dis- environment especially the various adverse edaphic fac- tichum generally grows on the edge of the pasture which tors besides the elevated heavy metals. Heavy metals is seasonally water-logged. Associated soil samples from can cause severe phytotoxic action, and may act as the study sites were also collected from rooting zone of powerful force for the evolution of tolerant populations. plants. There were four replicates for each tailings and It is easy to identify metal tolerant species from the soil sample. natural vegetation of metalliferous mine wastes (McNeilly and Bradshaw, 1968; Baker and Proctor, 2.2. Soil and plant analysis 1990; Wu, 1990). From 1995 to 1997, natural colonization of plants on Tailings and soil samples were air-dried for 7 days five Pb/Zn mine tailings including Fankou and Lechang until totally dry, and ground to pass through a 1-mm tailings in Guangdong Province; and Huangshaping, sieve. Paste pH and electrical conductivity (EC) were Shuikoushan and Taolin tailings in Hunan Province in measured using a pH meter and an EC meter accord- southern China was investigated. In general, the five ingly. Total [digested with concentrated HNO3 (16 tailings had high concentrations of heavy metals (Pb, M)+concentrated HClO4 (12 M), 5:1, v/v] and diethy- Zn, Cu and Cd), and low contents of N, P and organic lenetriaminepentaacetic acid (DTPA)-extractable Pb, matter (Shu, 1997). Toxic levels of heavy metals and Zn and Cu contents (tailings: DTPA, 1:2, w/v) were deficiency of major nutrients were the major constraints determined by flame atomic absorption spectrophot- on revegetation of these Pb/Zn tailings (Lan et al., 1997, ometry (AAS; Page et al., 1982). Plant samples were 1998; Shu et al., 1997). The natural colonization of washed with deionised water, divided into roots and plants on the five tailings was limited, with only some shoots, dried at 80 C for 24 h, and then milled to pass small patches distributed mainly on the edge of tailings, through a 2-mm mesh sieve, digested with concentrated and very few patches occurred at the center of tail- HNO3, and the contents of Pb, Zn and Cu in digestates ings. There were totally 54 species among 51 genera and were determined by AAS (Allen, 1989). 24 families recorded on the five tailings. Paspalum dis- tichum and Cynodon dactylon were the most common 2.3. Root elongation test and dominant ones, which indicated that these two grasses might have evolved heavy metal tolerance and Root elongations of tillers of the grasses collected have some potential use in revegetation of Pb/Zn tail- from three different sites were tested using the method ings (Shu, 1997). Therefore, the objectives of the present described by Wilkins (1957, 1978). Healthy tillers from experiment were to study: (1) whether populations of each population were selected and the roots were cut, these two species growing on Fankou and Lechang mine leaving the junction of root and the shaving stem intact. tailings have evolved metal tolerant ecotypes to Pb, Zn Six tillers of each population were placed in each 1000 and Cu; and (2) whether the degree of metal tolerance in ml beaker containing 500 ml of various aerated treat- 1 these two species were related to metal concentrations ment solutions: 500 mg l Ca(NO3)2 with Pb, Zn or Cu in plant tissues and/or associated substrata. ions in the form of Pb(NO3)2, ZnSO4 7H2O or CuSO4 5H2O, respectively. The working concentrations of the above metals were 5, 10, 20, 30 and 40 mg l 1 Pb, 2.5, 5, 2. Materials and methods 10, 20 and 30 mg l 1 Zn and 0.25, 0.50, 1 and 2 mg l 1 Cu. Ca(NO3)2 was employed to reduce metal toxicity so 2.1. Sample collection that the working metal concentration could be increased (Wilkins, 1957, 1978). Both Fankou and Lechang Pb/Zn mines are located The tillers were kept under a natural 16 h/8 h (light/ at northern Guangdong Province, with a subtropical dark) cycle at temperature of 25 5 C. The solutions climate. The average annual air temperature is 14 C, were changed every three days to provide aeration and 中国科技论文在线 http://www.paper.edu.cn
W.S. Shu et al. / Environmental Pollution 120 (2002) 445–453 447 to maintain the metal concentrations. The duration of C. dactylon had the lowest pH and highest EC among the experiment was 14 days and the root lengths of the the three tailings samples associated with plants. The grasses were measured at the end of the experiment. total and extractable contents of all the metals were The three populations (Fankou, Lechang tailings and significantly higher in three tailings sites than those uncontaminated soil) of P. distichum and two popula- of normal soil (P<0.05). Lechang tailings contained tions (Lechang and uncontaminated soil) of C. dactylon the highest total Cu and Fankou tailings contained the received the same treatments. Culture solution con- highest total Pb, and Lechang tailings associated with P. 1 taining 500 mg l Ca(NO3)2 without metal was distichum the highest total Zn. DTPA-extractable Pb, used as control. There were triplicates for each treat- Zn and Cu concentrations in tailings were similar ment. The tolerant index (TI) of the plants to Pb, Zn (P>0.05) among the tailings samples, and significantly and Cu were calculated by the following equation higher than those of normal soil. (Wilkins, 1978): 3.2. Heavy metal concentrations in plants Mean length of the longest Tolerant root in solution with metal Table 2 compares the contents of Pb, Zn and Cu in ¼ 100% index Mean length of the longest roots and shoots of two grasses collected from different sites. In general, all grasses collected from Fankou and root in solution without metal Lechang tailings contained higher metal concentrations in their tissues than those growing on normal soil (P<0.05). Higher metal contents were also observed in 2.4. Statistical analysis roots than shoots of plants collected from different sites, except Cu concentrations in P. distichum collected from Data were analyzed using t-test, one-way ANOVA Fankou tailings, of which the shoots contained the and LSD test as available in the SPSS statistical pack- highest amount of Cu (32 mg kg 1). It was also found age. that P. distichum accumulated significantly higher Pb and Zn than C. dactylon (Table 2).
3. Results 3.3. Root elongation of plants in metal solutions
3.1. Soil analysis Figs. 1 and 2 illustrate the results of root growth in populations of P. distichum and C. dactylon exposed to The pH and EC values of Fankou and Lechang tail- different metal concentrations. For P. distichum, it was ings were significantly higher than those of the normal noted that when only Ca(NO3)2 was added into the soil (P<0.05; Table 1). Lechang tailings associated with solution, root growth of normal (soil) population was
Table 1 The pH, EC (mS cm 1) and metal concentrations (mean S.D., n=4, mg kg 1) of Fankou and Lechang tailings and normal soila
Fankou tailings Lechang tailings Lechang tailings Normal soil (Paspalum distichum) (P. distichum) (Cynodon dactylon) pH 7.25 0.24a 7.38 0.61a 6.13 0.46b 5.32 0.36c
EC 2.13 0.18b 2.36 0.16b 3.57 0.42a 0.56 0.09c
Pb T 5686 621a 2335 1234b 2785 1160b 119 25c E 219 47a 269 56a 225 50a 6.82 1.32b
Zn T 3009 78b 7607 2088a 3562 903b 79 21c E 258 78a 326 135a 249 116a 3.79 1.07b
Cu T99 6.42b 191 33a 198 22a 2.55 0.56c E10 2.61a 7.38 3.26a 6.95 2.15a 1.10 0.09b
a T, total content; E, DTPA-extractable content. Data with different letters within the same horizontal row indicate a significant difference at 5% level according to LSD test. 中国科技论文在线 http://www.paper.edu.cn
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Table 2 Concentrations of Pb, Zn and Cu (mean S.D., n=4, mg kg 1)inPaspalum distichum and Cynodon dactylon collected from different sitesa
Shoot Root
Fankou Lechang Normal soil Fankou Lechang Normal soil
P. distichum Pb 79.08 23.63 c 705.50 131.10 b 15.24 2.45 c 610.42 142.86 b 1899.07 172.65 a 26.08 3.14 c Zn 116.22 30.10 c 816.58 55.44 b 78.38 14.79 c 663.92 267.92 b 1864.77 300.96 a 121.54 13.90 c Cu 32.27 14.43 a 8.79 1.83 c 13.35 3.40b c 21.48 2.90 b 21.38 2.29 b 20.30 6.69 b
C. dactylon Pb 351.15 99.23 b 12.37 1.81 c 644.90 107.79 a 18.10 2.43 c Zn 688.76 120.47 b 66.30 18.85 c 1015.35 97.05 a 79.27 11.48 c Cu 22.26 1.72 b 14.81 5.05 b 45.56 6.53 a 20.75 4.83 b
a Data with different letters within the same horizontal row indicate a significant difference at 5% level according to LSD test.
Fig. 1. Root growth of different populations of Paspalum distichum at different concentrations of (a) Pb, (b) Zn and (c) Cu for a period of 14 days (n=18, *: Lechang population, : Fankou population, &: normal population). somewhat more rapid than those of the two tailings 3.4. Index of tolerance populations. However, when more than 20 mg l 1 Pb, 10 mg l 1 Zn or 0.25 mg l 1 Cu was added to the solu- The tolerance index of different populations of P. tion, root length of the control population was severely distichum and C. dactylon subjected to various con- inhibited. Distinctive population differences were found centrations of Pb, Zn and Cu are listed in Tables 3 when the tillers subjected to higher metal concentra- and 4. For P. distichum (Table 3), TIs of Fankou and tions, for example, 30–40 mg l 1 Pb, 10–30 mg l 1 Zn or Lechang populations were significantly higher than 0.25 mg l 1 Cu. those of the control population in all the metal con- For C. dactylon, the root length of the control popu- centrations tested. In general, Lechang population was lation was shorter than that of tailings population when less sensitive to Pb and Zn than Fankou population, tillers were subjected to control solution or lower metal while Fankou population was the least sensitive to Cu. concentrations. When subjected to higher metal con- TIs of Fankou population in all Cu treatments were centrations, root elongation of both control and tailings significantly higher than those of Lechang population populations was inhibited markedly. Furthermore, there (P<0.05). According to Table 4, index of tolerance in was no root growth for the two populations when different populations of C. dactylon collected from the exposed to 2 mg l 1 of Cu. two sites had a significant difference (P<0.05) only at 中国科技论文在线 http://www.paper.edu.cn
W.S. Shu et al. / Environmental Pollution 120 (2002) 445–453 449
Fig. 2. Root growth of different populations of Cynodon dactylon at different concentrations of (a) Pb, (b) Zn and (c) Cu for a period of 14 days (n=18, *: normal population, : Lechang population).
Table 3 Zn, 0.19, 0.22 and 1.1 mg l 1 for Cu, respectively. As to The tolerance index (TI) of Paspalum distichum subjected to different C. dactylon,EC50 values of soil and Lechang popula- a concentrations of Pb, Zn and Cu for 14 days (mean S.D., n=3) tions were 8.2 and 11.1 mg l 1 for Pb, 1.8 and 2.5 mg l 1 1 Fankou Lechang Normal soil for Zn, 0.17 and 0.19 mg l for Cu, respectively. The results indicated that: (1) populations of P. distichum Pb (mg l 1) 5 69.5 1.1 b 91.5 11.3 a 53.0 2.3 c from the two tailings sites were more tolerant than tail- 10 50.1 2.1 b 69.0 7.8 a 46.0 2.3 c ings population of C. dactylon, (2) P. distichum collected 20 38.2 0.8 a 45.7 8.4 a 22.9 1.2 b from Fankou tailings had the highest tolerance to Cu 30 24.4 0.4 b 35.0 4.0 a 8.2 0.4 c while Lechang population had the highest tolerance to 40 21.3 0.7 a 22.6 4.4 a 2.3 0.1 b Pb and Zn among all the tested populations. Zn (mg l 1) 2.5 69.5 5.7 b 86.1 7.2 a 55.4 2.3 c 5 68.5 4.1 a 62.7 3.1 a 45.3 0.8 b 4. Discussion 10 45.2 2.6 b 56.7 3.5 a 12.1 0.7 c 20 38.6 1.6 a 43.4 0.7 a 8.3 0.3 b Mine tailings impose various adverse effects on plant 30 37.2 2.7 a 38.1 3.5 a 2.1 0.4 b growth, such as high levels of various heavy metals and Cu (mg l 1) other elements in toxic concentrations, low amounts of 0.25 84.2 3.9 a 43.2 4.6 b 27.1 1.3 c major plant nutrients, acidity, salinity and alkalinity, 0.5 74.1 3.1 a 34.6 4.1 b 19.7 0.7 c and poor physical structures (Bradshaw and Chadwick, 1.0 50.5 2.8 a 22.6 4.7 b 18.7 5.1 c 1980). Present results indicated that pH values (6.1–7.4) 2.0 18.2 2.0 a 13.5 0.5 b 2.9 0.6 c and EC values (2.1–3.6) of the three sites at Lechang and a Data with different letters in the same treatment indicate a sig- Fankou tailings were within the normal ranges for plant nificant difference at 5% level according to LSD test. growth (Williamson et al., 1982). In general, phytotox- icites of soil have been associated with 7–11 mg kg 1 specific metal concentrations, e.g. 30 mg l 1 Pb, 2.5, 5, DTPA-extractable and 300 mg kg 1 total Zn (Lepp, 10 and 30 mg l 1 Zn and 0.25 mg l 1 Cu, while in the 1981), 60–125 mg kg 1 total Cu (Ross, 1994) or 500 to other metal concentrations, performance of root growth 1000 mg kg 1 total Pb (Chaney, 1993). Therefore, the of these two populations was similar. elevated total and DTPA-extractable Pb, Zn and Cu of Fankou and Lechang tailings might impose phytotoxic 3.5. The 14-day EC50 values effects to higher plants (Table 1). However, field inves- tigation revealed that both P. distichum and C. dactylon The 14-day EC50 values (the concentrations of metals could thrive on tailings without any evident metal toxic in solutions which reduce root growth by 50%) of P. symptoms, such as cholorosis or stunting (Foy, 1978). distichum and C. dactylon were calculated and com- This indicated that populations of the two grasses pared with results of other studies on the same species growing on the Pb/Zn mine tailings could tolerate ele- as well as other species (Table 5). For P. distichum col- vated metal concentrations. lected from normal soil, Lechang and Fankou were 7.8, The higher TIs in tailings populations of C. dactylon 22 and 12.5 mg l 1 for Pb, 4.2, 17.8 and 9.5 mg l 1 for and P. distichum further confirmed that these populations 中国科技论文在线 http://www.paper.edu.cn
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Table 4 levels of both calcium and phosphate (Jowett, 1964). The tolerance index (TI) of Cynodon dactylon subjected to different Therefore, metal-tolerant plants, especially plants which a concentrations of Pb, Zn and Cu for 14 days (mean S.D., n=3) are co-tolerant to several metals had great advantage in Lechang Normal soil restoration of metalliferous wastelands. It has also been reported that P. distichum growing in waterlogged area Pb (mg l 1) 5 83.8 12.3 79.4 7.1 of iron ore tailings have evolved co-tolerance to Mn, Fe 10 52.7 6.4 44.5 2.3 and Cu (Wong et al., 1983). Furthermore, other species 20 24.1 5.8 18.7 2.1 of the genus Paspalum also possess higher tolerance to 30 8.9 1* 6.5 0.5 Pb and Zn, such as P. conjugatum (Lan et al., 1992), P. 40 5.4 1.9 3.2 0.4 thunbergii (Zhang et al., 2000) and P. notatum (Xia and Zn (mg l 1) Shu, 2001). Seed germination test also demonstrated 2.5 44.5 1.0* 28.3 2.5 that P. scrobiculatum possesses a high degree of toler- 5 35.8 1.5* 25.2 0.6 ance to Cu and Zn (Arora and Katewa, 1999). All of 10 28.8 0.4** 10.5 0.1 these suggested that the taxa of Paspalum might have 20 9.8 1.1 8.1 0.6 great potential for evolution of metal tolerance under 30 7.0 0.9* 4.8 0.2 metal toxicity pressure, which might be due to their Cu (mg l 1) inherent higher genetic variability. Metal tolerance in 0.25 20.9 1.5* 12.3 0.8 higher plants is systematically related at genus or even 0.5 5.9 0.1 5.0 0.2 family level, for example, the majority of widespread 1.0 3.2 0.3 3.2 0.4 British metal-tolerant taxa occur in only three families: 2.0 0 0 the Gramineae, Brassicaceae and Caryophyllaceae, while a Significant differences between C. dactylon populations of other large families such as the Cyperaceae, Asteraceae Lechang tailings and normal soil according to Student’s t-test: and Rosaceae are poorly presented (Baker and Proctor, *P<0.05, **P<0.01. 1990). Therefore, species in genus of Paspalum have high potential for evolution of metal tolerance and are were able to withstand higher metal concentrations than useful in revegetation of metal contaminated lands. It is the control populations, and might have evolved co-tol- also commonly known that C. dactylon can withstand erance to Pb, Zn and Cu (Tables 3 and 4). These results adverse edaphic condition including metal toxicity (Wu are also in line with the view that the degree of tolerance and Antonovics, 1976), is widespread in temperate and is mainly governed by the specific metal concentration in tropical areas (Wong and Lau, 1985) and also thriving contaminated areas (Gregory and Bradshaw, 1965; on toxic mine wastes (Bradshaw and Chadwick, 1980). Antonovics et al., 1971). It has been generally agreed that P. distichum is also a common lawn grass, and is also tolerance to more than one metal is dependent on the useful for holding banks of streams and ditches, for presence of these metals at elevated concentration in controlling water-soil erosion (Shu et al., 2000). It is contaminated areas (Jowett, 1958, 1964; Wong, 1982). envisaged that the metal tolerant populations of the two Therefore, in the populations of C. dactylon on Lechang grasses could be used for reclaiming the Pb/Zn tailings. tailings, and P. distichum on Lechang and Fankou tailings It has long been recognized that metal accumulation had the high tolerance to Pb, Zn and Cu might be caused capacity varies greatly between different species and by the elevated metal concentrations in the tailings. varieties, and is affected by various edaphic conditions. Lechang and Fankou populations of the two grasses It is also a common phenomenon that higher metal showed a greater tolerance level to the three metals than concentrations are located in root than shoot (Adriano, their normal counterparts, which suggested that co-tol- 1986). Therefore, the different amounts of heavy metals erant ecotypes have evolved for the two grasses. Plants accumulated by P. distichum and C. dactylon growing co-tolerant (multi-tolerant) to more than one metal on different substrata reflected both the edaphic condi- have been reported (Gregory and Bradshaw, 1965; Cox tions, and the difference between populations and spe- and Hutchison, 1979, 1980, 1981; Wong, 1982; von cies in terms of metal accumulation (Tables 1 and 2). Frenckell-Insam and Hutchinson, 1993). Due to the fact The results presented here also indicated a close rela- that tailings often contain more than one metal at toxic tionship between metal contents in plant tissues, and level, metal co-tolerant genotypes would have a higher those in substrata. For P. distichum, it was observed application value. Furthermore, tolerant plant materials that metal-tolerant levels were positively related to can withstand adverse site conditions other than those metal concentrations in plants. Lechang population associated with toxic metals. For example, it has been accumulated higher amounts of Pb and Zn while Fan- noted that tolerant plants survive drought on the coar- kou population a higher amount of Cu (Table 2). ser grades of mine soil and even on nontoxic soil better Lechang population had higher TIs of Pb and Zn, while than non-tolerant plants. Tolerant Agrostis tenuis plants Fankou populations higher TIs of Cu (Table 5). Baker from an acidic Pb mine were found to be adapted to low and Walker (1990) suggested that metal tolerance and 中国科技论文在线 http://www.paper.edu.cn
W.S. Shu et al. / Environmental Pollution 120 (2002) 445–453 451
Table 5 1 The concentrations (mg l ) of Pb, Zn and Cu in solutions which reduced 50% growth of roots from control (EC50) in different populations of Paspalum distichum and Cynodon dactylon compared with those of other species estimated from the published data
Species EC50 References Note
Pb Paspalum distichum 12.5 Present study Fankou tailings Paspalum distichum 22 Present study Lechang tailings Paspalum distichum 7.8 Present study Normal soil Cynodon dactylon 11.1 Present study Lechang tailings Cynodon dactylon 8.2 Present study Normal soil Festuca ovina 10 Polson and Adams, 1970 Zea mays (SR52) 11.2 Graig, 1978 Lolium perenne 1.7 Wong and Bradshaw, 1982 Typha latifolia 8.4 Ye et al., 1997a Pb/Zn tailings Phragmites australis 15.5–20 Ye et al., 1997b Pb/Zn tailings
Zn Paspalum distichum 9.5 Present study Fankou tailings Paspalum distichum 17.8 Present study Lechang tailings Paspalum distichum 4.2 Present study Normal soil Cynodon dactylon 2.5 Present study Lechang tailings Cynodon dactylon 1.8 Present study Normal soil Zea mays (SR52) 8.37 Graig, 1978 Lolium perenne 1.6 Wong and Bradshaw, 1982 Typha latifolia 3.29 Ye et al., 1997a Leaf elongation Phragmites australis 2.2–4.3 Ye et al., 1997b Pb/Zn tailings
Cu Paspalum distichum 1.1 Present study Fankou tailings Paspalum distichum 0.22 Present study Lechang tailings Paspalum distichum 0.19 Present study Normal soil Cynodon dactylon 0.19 Present study Lechang tailings Cynodon dactylon 0.17 Present study Normal soil Deschampsia cespitosa 0.72 Cox and Hutchinson, 1980 Cu/Ni smelter Paspalum distichum 0.33 Wong et al., 1983 Iron ore tailings Sporobolus virginicus 0.85 Wong et al., 1983 Iron ore tailings Festuca rubra <0.125 Wong, 1982 Cu mine Agrostis tenuis 0.6 Jowett, 1958 Cu mine Typha latifolia <0.1 Ye, 1995 Pb/Zn tailings
metal uptake might be functionally related, and that DTPA-extractable Pb, Zn and Cu, which would impose both metal exclusion and accumulation are the basic a high selection pressure for evolution of metal-tolerant strategies of metal uptake by tolerant plant, and differ- ecotypes and genotypes. ent tolerant species or genotypes have different metal Root elongation tests indicated that populations of P. uptake strategies. This could explain the different distichum and C. dactylon collected from Fankou and metal uptake behavior between populations of P. dis- Lechang tailings have evolved co-tolerance to Pb, Zn tichum, and the relationship between metal uptake and and Cu. The population of P. distichum from Lechang metal tolerance in plants. tailings was the most tolerant to Pb and Zn, while Although statistical analysis could not be used to com- another population from Fankou tailings was the pare the different of EC50 values of different species, it most tolerant to Cu. In comparison with P. distichum, seems obvious that P. distichum possessed one of the most metal tolerance of tailings (Lechang) population of C. tolerant genotypes (Table 5). According to the compari- dactylon was relatively low. The level of tolerance of son, P. distichum is even more tolerant to Cu than Agrostis plants also reflected the metal concentrations in plant tenuis and Festuca rubra, which are tolerant to Cu. tissues and their associated substrata.
5. Conclusions Acknowledgements
The Fankou and Lechang Pb/Zn mine tailings Financial support from Natural Science Foundation contained elevated concentrations of total and of China (No. 39770154, 30100024), Natural Science 中国科技论文在线 http://www.paper.edu.cn
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