| The effects of Cu, Zn, Cd, Pb stress on seed germination of three leguminous plants were studied using solution culture with the treatment concentrations as follows:Cu 0,400, 800,1200 mg·L-1; Zn 0,500,1000,1500 mg·L-1; Cd 0,1,10,20 mg·L-1; Pb 0,500,1000, 1500 mg·L-1. The three leguminous plants adopted as experimental materials include Medicago sativa, Trifolium pratense and Astragalus adsurgens, all of which have many advantages such as being good at resisting drought and frigidity, large biomass and high economic and applicable values. Furthermore, the effects of heavy metals stress on the physiological indexes of the three leguminous plants seedlings, growth condition in maturation period and the metal-absorption abilities were also studied via pot culture with adding heavy metals into soil. The additions of the heavy metals were as follows:Cu 0,400, 800,1200mg·kg-1 soil; Zn 0,500,1000,1500mg·kg-1 soil; Cd 0,1,10,20mg·kg-1 soil; Pb 0, 500,1000,1500 mg·kg-1 soil.The results showed:The effects of the heavy metals stress on the plants germination rate are different from each other. Under the stress of Cu, Zn and Pb, the germination index, germination rate and germination vigor decrease with the concentrations increase, showing highly significant negative correlation(P<0.01)with the concentrations; while under the treatment of Cd, the effect on the plants germination rate do not reach significant level. Under the stress of Cu, Zn, Cd and Pb, the radicle and embryonal elongation are inhibited, while the radicle length get a higher inhibited degree. With the increase of the heavy metals addition, the chlorophyll contents decrease, while the contents of proline and the activities of SOD and CAT present increasing tendencies at lower metal-addition treatments and decreasing tendencies at higher ones. The changes of POD activities vary with the plant and the metal kinds, and show incareasing tendencies in certain ranges.The three plants can normally grow at lower metal-addition treatment. Under the stress of Cu, Zn and Pb, the seedling length, dry biaomass aboveground and underground significantly decrease with the increase of the mount of metal added into the soil, therefore they show significantly negative correlation(P<0.05)with the metal-addition. While the treatment of Cd show insignificant influence on the plants growth. The stress of Cu has lest effect on the growth of T. pretense; Zn at a high metal-addition has serious effect on the growth of all the three plants; compared with A. adsurgens and T. pratense, Pb has more effects on M. sativa.The contents of heavy metals in the organs of the plants increase with the increase of the metal-additions, and the amount of the metals accumulated in the root system are more than those of in the aboveground parts. The abilities of metal absorbtion vary with the plants. Taking the contents of heavy metals in the root as the standard, the results show that the abilities of absorbing Cu and Zn are:T. pretense> A. adsurgens>M. sativa; the abilities of absorbing Cd are:T.pretense> M. sativa>A. adsurgens; the abilities of absorbing Pb are:A. adsurgens>T.pretense> M. sativa.As the aspect of the metal-absorption, although the ability of none of the three plants reaches the standard of hyperaccumulator, the total amount of the migration of heavy metals are still considerable because the leguminous plant has many advantages such as fast-growth and fast-increase of biomass and so on. In this study, besides of the total amount of metal-absorption, Cu and Cd acumulated in the aboveground part and the root system of M. sativa are more than those of the other two plants, so are Pb absorption in the A. adsurgens. Above all, it is feasible to use M. sativa to repair the soil polluted by Cu or Cd, and to use A. adsurgens to repair the soil polluted by Pb. However, the three plants are not suitable species to repaire Zn pullution soil as they have no big abilities for the metal-absorption.
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