Effects Of Single And Combined Pollution Of Cu And Cd On The Growth Of Brassica Napus L.

With the development of industry modernization, urban civilization andagriculture modernization, the release of heavy metals into the environment hasbeen accelerating annually. In this study, rape (Brassica napus L.), the oil cropplanted widely in our country, was used as the experimental materials. Throughwater culture, pot culture and other methods, the effects of single and combinedpollution of Cu and Cd on the whole growth process (seed germination, seedlingsgrowth, rapeseed yield, etc.) of rape, as well as the distribution law of Cu, Cdaccumulation in the rape plant were studied, which discussed the effects of heavymetals pollution on yield and quality of rape, and provided a reference for the rape(oil crops) planting in polluted farmland. The main results of this study were asfollows:(1) Through water cultivation, the effects of the single and combined pollutionof Cu and Cd on seeds germination and seedlings growth of rape had been studied.Under single Cu pollution, compared with the control groups, most of indicators onseed germination and growth of rape (germination energy, germination rate,germination index, vigor index, root length, shoot length, total length, root freshweight, bud fresh weight, total fresh weight and mitosis index, etc.), had a boostrole in the low Cu concentration (0-5mg·L-1); with the increasing of Cuconcentration (5-100mg·L-1), most of them showed a decreasing trend (P<0.05).The electric conductivities of seed outside exudate increased gradually (P<0.05).Because heavy metals Cu was an essential element of plant growth, but excess Cuwould hinder plant growth, so there was a phenomenon of the stimulating effects inlower Cu concentration and the inhibitory effects in high Cu concentration. Undersingle Cd pollution, with the increasing of Cd concentration (1-50mg·L-1),compared with the control groups, the index of rape seed germination and growth(germination energy, germination rate, germination index, vigor index, root length, shoot length, total length, root fresh weight, bud fresh weight, total fresh weightand mitotic index, etc.) all showed inhibitory effects, having a overall downwardtrend (P<0.05); but the electric conductivities of seed outside exudate increasedgradually (P<0.05). This was due to the toxicity of Cd and hindered seed growth.Under combined pollution of Cu and Cd, as the combined concentration increased(5/1-100/50mg·L-1), compared with the control groups, the index of rape seedgermination and growth (germination rate, germination energy, germination index,vigor index, total length, shoot length, root length, total fresh weight, bud freshweight root fresh weight and mitotic index) decreased gradually (P<0.05), whilethe electric conductivities of seed outside exudate increased gradually (P<0.05).And most of the index value of the above-mentioned seed germination and growthwere lower than the index value of at the same concentration of single Cu or Cdpollution, which indicated the synergistic effect of Cu, Cd pollution.And that the damage to the root of rape seed under single and combinedpollution of Cu and Cd was greater than the damage to the bud was found at thesame time.(2) The study showed the effects of single and combined pollution of Cu andCd on the growth and antioxidant enzyme systems of rape through pot experiment.Under single Cu pollution, the fresh weight of root/stem/leaf, soluble proteincontent, leaf pigment contents, SOD activity and CAT activity of rape seedlingswere increased slightly than the control groups in low Cu concentrations (0-50mg·kg-1), but with the increasing of Cu concentration (50-800mg·kg-1), each ofthese index decreased gradually (P<0.05); while leaf cell membrane permeability,content of malondialdehyde (MDA), content of proline and POD activity of rapeseedlings showed a rising trend (P<0.05), with the Cu concentration increased. Itpresent a phenomenon of the stimulating effects in lower Cu concentration and theinhibitory effects in high Cu concentration. Under single Cd pollution, comparedwith the control groups, the fresh weight of root/stem/leaf, soluble protein contents,leaf pigment contents, SOD activity and CAT activity of rape seedlings had adownward trend with the increased of Cd concentration (P<0.05), while leaf cellmembrane permeability, MDA content, proline content and POD activity of rape seedlings present a consistent upward trend, with increasing of Cd concentration(P<0.05). Because of the toxicity of heavy metals Cd, the rape seedlings weredamaged, caused a series of physiological and biochemical disorders, showedinhibitory effect. Under the combined pollution of Cu and Cd, the fresh weight ofroot/stem/leaf, leaf protein content, leaf pigments contents, SOD activity and CATactivity of rape seedlings mostly decreased gradually after a slight increasing；whilethe electric conductivity, MDA content, proline content increased gradually(P<0.05). Under the combined pollution of low Cu and Cd concentration (50/1mg·L-1), the index values of fresh weight of root/stem/leaf, protein content of rapewere higher than the value at the same concentration under single Cd pollution; theindex values (e.g., the leaf pigments contents, SOD activity, CAT activity and PODactivity) were higher than the values at the same concentration under single Cu orCd pollution; while the index values of electric conductivity and MDA contentwere lower than at the same concentration under single Cu or Cd pollution indexvalue. These showed that the antagonism action produced under the combinedpollution of low concentration of Cu and Cd (50/1mg·L-1), so the toxicity effect torape decreased; but with increasing of combined concentration (50/1-800/40mg·L-1), the synergistic action produced and the toxicity aggravated, so the harmeffect to rape increased.(3) Through the pot experiment, the effects of single and combined pollutionof Cu and Cd on the rapeseed yield and heavy metal (Cu/Cd) distribution in therape had been studied.(a) Under single and combined pollution of Cu and Cd, compared with thecontrol, the index (e.g., pod number per plant, pod width, pod surface area, thenumber of grains per pod) present a gradual rising trend, with increasing of singleandcombined concentrations of Cu and Cd (P<0.05). As single and combinedconcentrations of Cu and Cd increased, the pod length and per1000seeds weightof rape present a little increase or decrease, but the trends were not obvious.According the relevant analysis, the pod surface area was correlated significantlywith number of grains per pod. Reduction of per plant oilseed rape pods couldreduce its seed quantity, the suppression to pod width reduced the pod surface area, which induced to reduce pod storage capacity and the assimilation substances intothe pod, thereby grain number and grain yield reduced.(b) Under single and combined pollution of Cu and Cd, the Cu or Cdconcentrations and enrichment factors in root/stem/leaf of rape all present the trendof Curoot>Culeaf>Custemand Cdroot>Cdleaf>Cdstemin the period of rape seedlings. AndCu concentrations under combined pollution of Cu and Cd were higher than thoseunder single Cu pollution; Cd concentrations under combined pollution were lowerthan those under single Cd pollution. In the period of mature rape, Cuconcentrations and enrichment factors all present the trend of Curoot>Culeaf>Custem,while Cd concentrations and enrichment factors all present the trend ofCdroot>Cdstem>Cdleaf, furthermore the enriched capability of Cd was stronger thanthat of Cu. And Cu or Cd concentrations in maturity rape were all greater thanthose in rape seedlings.