Effects Of Nitrogen Fertilizer And Rice Straw Biochar On Ramie Growth,Copper Uptake And Resistance In Copper Contaminated Soils

Heavy metals pollution in agricultural soils is considered a serious environmental concern due to the toxic effects of heavy metals on soil-plant systems and humans.Particularly,copper?Cu?contamination is a concern in vast areas of the world,rendering productive lands into non-cultivated areas.Therefore,amelioration of Cu polluted soil is an important task to minimize its accumulation by edible plant parts and,thereby reduces its mobility in agricultural soils for higher production.Thus,the plant species which can adapt contaminated environment as well as cheap and less destructive technique?use of amendments?are inevitable.Therefore,cultivation of Ramie?Boehmeria nivea L.?cv.Zhongsizhu No.1 using various levels of nitrogen fertilizer and rice straw biochar has been established to get high fresh biomass and low Cu uptake by plant in artificially and naturally aged Cu contaminated soils.In present studies,the effects of copper,nitrogen fertilization,and rice straw biochar and their interactions on plant growth,gaseous exchange traits,antioxidant capacity,forage quality,Cu uptake by plants and post harvest soil characteristics were evaluated in the green house experiments.These findings could offer basis for the cultivation of B.nivea as a fodder crop using optimal level of nitrogen fertilizer or biochar for higher fresh fodder yield with low Cu uptake in Cu contaminated regions of China.The main results were summarized as follows.1.Morpho-physiological traits,antioxidant capacity and phytoextraction of copper by ramie?Boehmeria nivea L.?grown as fodder in copper contaminated soilFirstly,a green house study was conducted to investigate the growth potential and antioxidant capacity of B.nivea on Cu contaminated soil.Moreover,the potential of B.nivea for phytoextraction on Cu contaminated soil was also studied.Therefore,a pot experiment was conducted to examine the growth,antioxidative response and localization?distribution?of Cu in B.nivea plants under different Cu concentrations?0,50,100,200,300 and 400 mg kg^-11 soil?.Results revealed that B.nivea tolerated up to 100 mg kg^-1 Cu concentration without significant decrease in biomass,but further increase in Cu concentration from 200 to 400 mg kg^-1 exhibited significant reduction in chlorophyll contents,fresh and dry biomass,plant height and number of leaves per plant.In addition B.nivea accumulated more Cu in roots(26 to 53 mg kg^-1),followed by the leaves(23 to28 mg kg^-1)and stems(14 to 21 mg kg^-1).While the values for both bioaccumulation factor?BAF?and translocation factor?TF?at all treatments were less than 1.Moreover,activities of antioxidative enzymes?superoxide dismutase and peroxidase?were initially increased with the exposure of 50,100 and 200 mg kg^-1 Cu,but decreased by further increasing the Cu concentration to 300 and 400 mg kg^-1 indicating the oxidative stress which is manifested by high malondialdehyde?MDA?and proline contents also.Thus,based on results,it can be concluded that B.nivea accumulated relatively low Cu contents in above ground parts and could be grown as fodder crop on Cu contaminated sites?100mg kg^-11 Cu,with necessary precautions.2.Effective role of nitrogen to mitigate copper induced stress in ramie ?Boehmeria nivea L.?grown in contaminated soilAn additional experiment was carried out to investigate the effectiveness of nitrogen?N?fertilizer on B.nivea growth in Cu contaminated soil to get high fresh biomass and fodder quality.Therefore,combinations of Cu levels?0,100,300 mg kg-1?and N levels(0,140,280,420 kg ha^-1)were applied.The results showed that N at 280 kg ha^-1significantly??0.05?increase plant growth in terms of fresh biomass,plant height,stem diameter and number of leaves per plant up to 100 mg kg^-1 Cu in soil for all harvests?H1,H2,H3 and H4?.However,the interactive effect of Cu and N on Cu uptake by plant varied with levels of N fertilizer.Furthermore,N at 280 kg ha^-1 also improved the gas exchange characteristics viz.,net photosynthesis?Pn?,transpiration rate?Tr?and stomatal conductance?gs?while,decrease oxidative stress in B.nivea up to 100 mg kg^-1 Cu in soil,relative to control.Thus N at 280 kg ha^-1 can be considered an effective dose for high fresh biomass with lower Cu uptake by B.nivea grown as fodder in Cu contaminated soils(?100 mg kg^-1).Overall,present research highlighted the necessity of balanced or optimum N application for sustainable B.nivea forage production in Cu contaminated agricultural lands.3.Influence of rice straw biochar on growth,antioxidant capacity and copper uptake in ramie?Boehmeria nivea L.?grown as forage in aged copper-contaminated soilA pot study was conducted to examine the effectiveness of biochar derived from rice straw?RSB?at various application rates?0,2.5,5 and 10%w/w?to mitigate possible risks of Cu solubility and its uptake by ramie?Boehmeria nivea L.?,when grown as forage on highly Cu polluted soil.The plant growth parameters as well as soil chemical properties?pH,electrical conductivity and cation exchange capacity?notably improved with the increasing RSB application.Moreover,prominent reduction was observed in soil bioavailable Cu concentration by 96%with RSB application of 10%relative to control.In addition,Cu content in B.nivea roots,leaves and stems decreased by 60,28 and 22%,respectively,for 10%RSB application.It was noted that chlorophyll contents and gas exchange parameters in leaves were significantly higher at 10%RSB application than in control.Furthermore,10%RSB resulted in a greater reduction in oxidative stress from the Cu in soil.Thus,soil amended with RSB demonstrated positive results for Cu stabilization in aged Cu-contaminated soil,thereby reducing its accumulation and translocation in B.nivea and mitigating livestock feed security risks.4.Interactive effects of rice straw biochar and nitrogen fertilizer on ramie ?Boehmeria nivea L.?growth and post harvest soil characteristics in highly copper contaminated soilThis pot study was conducted to investigate the interactive influence of rice straw biochar?BC₀:0,BC₁:5,BC₂:10%w/w?and nitrogen fertilizer(N₀:0,N₁:140,N₂:280,N₃:420 kg ha^-1)on plant growth,Cu mobility and phytoavailability to B.nivea in highly Cu-contaminated soil.Results revealed that BC×N fertilizer had significantly?p?0.05?increased the growth of B.nivea in term of biomass,plant height,stem diameter and number of leaves.Furthermore,BC×N fertilizer resulted in significant changes in post harvest soil pH,EC and CEC,relative to the control.However,the effect of BC×N fertilizer on soil extractable Cu and Cu uptake by plant varied with levels of N fertilizer.The BC₂N₁ treatment significantly increased the fresh and dry shoot biomass of B.nivea by 635 and 452%,respectively,however reduced Cu concentrations in roots,leaves and stems i.e.52,34 and 23 mg kg^-1,respectively compared to control.Thereby,high dose of BC along with low N fertilizer could be considered as an efficient soil amendment combination for Cu stabilization and higher biomass production of B.nivea in highly Cu contaminated soil.In summary,B.nivea cv.Zhongsizhu No.1 can be cultivated as forage on Cu contaminated soil?100 mg kg^-1 Cu,due to low Cu accumulation in leaves or stems.However,medium N fertilizer(280 kg ha^-1)can support to higher fresh yield of B.nivea in normally Cu contaminated soil.Furthermore,RSB is a useful amendment for cultivation of B.nivea in highly Cu contaminated regions.It can reduce Cu solubility in soil and reduced its translocation to plant parts.In addition,addition of RSB has reduced the level of N fertilizer.Thus,high dose of biochar along with low N fertilizer could be considered efficient soil amendments for Cu stabilization and higher biomass of B.nivea in highly Cu polluted soils.