Study On Pb Accumulation Characteristics And Tolerance Mechanisms Of Dwarf Bamboos Under Pb Stress

The objective of this study was to exmine the physiological growth and Pb accumulation characteristics of dwarf bamboos in Pb-containated soil,and then to estamate the potential application remediation of dwarf bamboos in Pb-contained environment.In this regard,six dwarf bamboos were treated with the common soil heavy metal pollutant-lead（Pb）to investigate the shoot development,physiological response and Pb accumulation/species.Meanwhile,for the purpose to provide more theoretical basis about the tolerance mechanisms of dwarf bamboos on Pb stress,Sasa argenteostriata（Regel）E.G.Camus,which was considered the Pb-tolerant one,being dedected to be exposed to 0,1500,3000,4500 mg/kg higer concentration soil Pb stress treatments as well as 0,300,600,900 mg/L Pb stress test by hydroponic treatment.The results were as follows.（1）In the aspect of shoot development,soil Pb stress mainly inhibited the number of shoots in the fast-growing stage（April～May）of all species,the shoot-emergency number of Shibataea lanceifolia C.H.Hu declined most in April,decreased 37.04%,48.15%,respectively,Sasa auricoma（Mitford）E.G.Camus showed the maximum decreases in May,respectively by 38.24%,58.82%.Pb300 treatment had no adverse effect on the total number of bamboo shoots,while Pb1500 treatment significantly reduced all of them.Duing to the bamboo returning rate of each bamboo species was reduced,there was no adverse effect on the number of new bamboo shoots under Pb300 treatment.On the contrary,Pb1500 treatment increased the bamboo returning rate,significantly reducing the new bamboos number of Sasaella glabra（Nakai）f.albo-striata Muroi and Shibataea lanceifolia C.H.Hu by 23.64%and 31.25%.As a result of the highest-new bamboo rate,lowest-bamboo returning rate,as well as the most about new bamboo shoot numbers,new shoot growth of Sasa auricoma（Mitford）E.G.Camus and Indocalamus decorus Q.H.Dai was minimally inhibited by soil Pb stress compered with other bamboo species（2）In the aspect of physiological-resistance of new bamboos,soil Pb stress of generally induced a surge in content of O₂^-and MDA in new bamboos.Both the two of them were presented with lowest-contained in Sasa auricoma（Mitford）E.G.Camus（9.96μg/g,0.016μmol/g）,while the highest-contained of O₂^-and MDA appeared in Shibataea lanceifolia C.H.Hu（15.99μg/g）and Sasa auricoma（Mitford）E.G.Camus（0.021μg/g）,respectively under Pb1500 treatment.As a result of being not capable of accumulating enormous free proline,which caused a weak osmotic regulation in Sasaella glabra（Nakai）f.albo-striata Muroi,Shibataea lanceifolia C.H.Hu,when compared with the other 4 species.Three shoot-growing indexes（including number of shoots,the rate of bamboo shoots,the rate of red bamboo）and eghit stress resistance-physiology indexes（including SOD,POD,CAT activity;O₂^-,MDA,SS,SP,Pro content）under Pb1500tratment were selected to be carried out by figure principal component analysis,combined with the membership function method,on the base of the above method,the tolerance to1500mg/kg Pb-contanined soi of six new species’new bamboo was evaluated as follows:Indocalamus decorus Q.H.Dai（0.78）>Sasa auricoma（Mitford）E.G.Camus（0.75）>Sasa fortunei（Van Houtte）Fiori（0.70）>Shibataea lanceifolia C.H.Hu（0.49）>Sasaella glabra（Nakai）f.albo-striata Muroi（0.39）>Sasa auricoma（Mitford）E.G.Camus（0.38）.（3）In the accumulation of biomass,the total biomass of Sasa auricoma（Mitford）E.G.Camus,Indocalamus decorus Q.H.Dai,increased by 15.92%and 14.41%under Pb300 treatment,while the other treatments decreased.In terms of distribution proportion of ariel and underground part,under Pb300 treatment,the ariel part proportion increased in Sasa fortunei（Van Houtte）Fiori,Sasa auricoma（Mitford）E.G.Camus and Indocalamus decorus Q.H.Dai,while decerased in Sasa auricoma（Mitford）E.G.Camus and Sasaella glabra（Nakai）f.albo-striata Muroi,no significant change was observed in Shibataea lanceifolia C.H.Hu.Arieal part proportion of all species decreased significantly under Pb1500 treatment,Sasa auricoma（Mitford）E.G.Camus showed the greatest decline（14.87%）;what’s more,the proportion of whip in all species increased,and the largest increase（33.74%）was found in the Sasa auricoma（Mitford）E.G.Camus under Pb1500treatment.Compared with the other four bamboo species,the biomass distribution pattern of Sasa auricoma（Mitford）E.G.Camus and Indocalamus decorus Q.H.Dai was more advantageous,which was conducive to the biomass reserve of the harvesting-old organs in the following year.（4）Old stem and whip were the organs possing the highest accumulation of Pb,while the new stem were the organs with the lowest accumulation.Six bamboo species formed three different Pb enrichment patterns:（1）“Whip&Old stem”Pb accumulation modle;（2）“Old stem&New root”Pb accumulation modle;（3）“Old stem&Whip”Pb accumulation modle.Above all,Sasa auricoma（Mitford）E.G.Camus and Indocalamus decorus Q.H.Dai hold the more optimized“Old stem-dominated”Pb accumulation model,which were considered as the best two choices of six dwarf bamboo species that could be applied to Pb-pollutted soil phytoremediation.（5）The Pb tolerance mechanism was analyzed both on the physiological resistance and organ Pb detoxification mechanism by selecting the Pb-tolerant Sasa auricoma（Mitford）E.G.Camus.In terms of physiological resistance response,it could regulate the activity of enzymes（SOD,POD,CAT,APX,GR,AAO）and non-enzymatic substances（Pro,SP,As A,GSH,NPT-SH,PCs）synergistically to resist the high concentration soil Pb stress damage.In terms of Pb detoxification mechanisms of different organs,in regard to segregation,.the cell wall retention was the dominant Pb detoxification mechanism of new roots,old roots,whip,new stem and old stem,the vacuolar compartmentalization was the dominant Pb detoxification mechanism of new leaf and old leaf.In the chemical form of Pb chemical forms transformation,the conversion of Pb to low-toxicity and low-mobility morphology was thre Pb detoxification mechanism of new bamboo roots,whip,stem,while was not obvious in leaf.On the mechanism of plant cell chelation,new roots,old roots,new leaves and old leaves all could alleviate Pb stress damage by massive synthesising of NPT-SH,PCs and GSH.The difference was that PCs played a leading role in new root and old root Pb detoxification,while GSH mainly conducted a major role in the new leaf and old leaf.