The Remediation Effects And Their Mechanisms Of Biochar And Polygonum Lapathifolium Linn.Cultured In Manganese Mine Soil

Guangxi is known as the Town of Nonferrous Metals,the reserves and production of manganese（Mn）ranks the first in China.Manganese mining activities produced many abandoned Mn mine abandoned areas and induced serious Mn pollution,needing to be solved in urgent.Biochar is widely used as a soil amendment to remediate heavy metals contaminated soil in recently years.But the usage of biochar on Mn contaminated soil was scarce.Polygonum lapathifolium Linn.has been verified as a Mn hyperaccumulator in our previous study,and has promising prospect in remediation of Mn-polluted environment because of its high biomass and widely distruibution.At present,the effects of the sole biochar addition and combined with P.lapathifolium were used to study the effects and their mechanisms on Mn mine area soil.The Mn mine soil sampled from Ertang Mn mine（110°47’43.44"E,24°40’41.52"N）,Guangxi Province.The 5%corn straw biochar（BC）and eggshell/corn straw biochar（EBC）were added,the soil without biochar addition as the control（CK）.Meanwhile,biochar combined with P.lapathifolium were used to study.The soil physicochemical properties,Mn forms,soil enzyme activities,plant growth and Mn bioaccumulation characteristics as well as the biochemical parameters were studied.The main results are as following.1.Soil experiment with biochar addition（1）The soil Mn forms changed greatly after BC and EBC added at different culture days.Among which,the fractions of weak-acid-extractable Mn and reducible Mn decreased,while the fractions of oxidation Mn and residue Mn increased,indicating the bioavailable Mn decreased,thus reducing the harmful of Mn mine soil.（2）Compared with CK,the concentrations of weak-acid-extractable Mn in soil decreased by 9.77%and 22.97%with BC and EBC addition culturing for 7 days.The corresponding values were 6.07%and 17.90%for 15 days and the corresponding values were 1.90%and 3.88%for 30 days.（3）Compared with CK,soil p H,conductivity,available potassium,organic matter,total carbon and total nitrogen contents were significant increased with BC and EBC addition over time.Meanwhile,the total phosphorus,available phosphorus and soil enzyme activities（sucrase,urease,protease,alkaline phosphatase and dehydrogenase）generally exhibited positive effects,but the contents of nitrate nitrogen and ammonium nitrogen decreased over time.In conclusion,BC and EBC addition could effectively improve the physicochemical properties of Mn contaminated soil throughout the whole culture stage.2.Biochar addition combined with plant cultivating（1）The soil Mn concentrations decreased by P.lapathifolium plantation as supplemented with BC and EBC.Compared with CK,soil Mn decreased by 9.69%and 5.44%with BC and EBC addition.The concentrations of weak-acid-extractable Mn decreased by10.24%and 12.49%in BC and EBC,the corresponding values for reducible Mn were 17.83%and 6.24%,respectively;for oxidation Mn were 18.45%and 1.06%,respectively.And the concentrations of residue Mn increased by 92.38%and 9.47%.（2）The soil p H value,conductivity,ammonium nitrogen,nitrate nitrogen,available potassium,available potassium,organic matter,total carbon and total nitrogen contents generally exhibited positive effects by P.lapathifolium cultivating with BC and EBC addition.The soil enzyme activities（urease,protease,alkaline phosphatase,dehydrogenase and catalase）generally exhibited positive effects,but the soil sucrase activity decreased.（3）The results of biochar addition combined with plant cultivating showed that:Compared with CK,plant weight,root weight,stem weight and leaf weight,plant height and stem height increased by 29.17%,40.62%,28.10%,20.71%,6.74%and 4.18%with BC addition,the corresponding values of were 9.84%,12.64%,10.08%,7.07%,8.07%and 9.50%with EBC addition,respectively.（4）The concentrations of soil available Mn were decreased by P.lapathifolium cultivating with BC and EBC addition,and the tissue Mn concentrations decreased in accordingly.However,the increase of biomass eventually led to the increase of total manganese concentration in plants with BC addition.Compared with CK,the Mn concentration in the roots of P.lapathifolium decreased by 8.66%and 20.69%with BC and EBC addition,the Mn concentration in the stems decreased by 34.90%and 45.40%,and the Mn concentration in the leaves decreased by 4.16%and 5.80%.Compared with CK,the total manganese content of P.lapathifolium increased by 8.34%with BC addition.（5）The contents of active oxygen,malondialdehyde and proline in the leaves of P.lapathifolium were significant decreased with BC and EBC addition.The activities of antioxidant enzymes（POD,CAT,APX）efficiently decrease,the contents of non-enzyme substances and osmotic regulatory substances（soluble protein,total sugar）increased,and alleviated the damage of lipid membrane peroxidation.Compared with CK,the contents of·O^2-,H₂O₂ and MDA in the leaves of P.lapathifolium were significant decreased by32.71%,31.10%and 27.81%with BC addition,respectively,the corresponding values were50.62%,27.88%and 29.67%with EBC addition,respectively.Compared with CK,the activities of POD,CAT and APX in the leaves of P.lapathifolium decreased by 13.54%,10.94%and 48.98%with BC addition,the corresponding values were 47.69%,21.15%and65.31%with EBC addition,respectively.The contents of GSH,-SH and ascorbic acid in the leaves of P.lapathifolium increased by 12.56%,11.33%and 21.01%with BC addition,respectively,the corresponding values were 9.12%,61.35%and 28.20%with EBC addition,respectively.Compared with CK,the content of proline in the leaves of P.lapathifolium were significant decreased by 18.53%and 23.43%with BC and EBC addition,soluble protein content significant increased by 16.83%and 50.05%,total sugar increased by 20.38%and35.79%,respectively.In conclusion,the damage of Mn pollution on P.lapathifolium alleviated with BC and EBC addition,which is beneficial to maintain the normal growth of P.lapathifolium.In summary,the combination of biochar and P.lapathifolium showed better remediation efficiency than those of sole biochar addtion.Although the tissue concentrations decreased as corn straw biochar,but the biomass increased,resulting whole plant Mn increased.The mechanisms reasons could be attributed two aspects.On the one hand,the reason is that biochar decreased soil Mn bioavailable and improve soil fertility;on the other hand,it is to alleviate its stress by increasing its non-enzymatic substances and osmotic regulatory substances.Therefore,the application of P.lapathifolium combined with biochar in Mn contaminated soil remediation has a promising prospect.