The Distribution And Ecological Stoichiometry Characteristics Of Carbon,Nitrogen And Phosphorus In The System Of Plants And Indigenous Zinc Smelting Slag

The zinc smelting activities in the northwest of Guizhou province lasted for more than 300 years.It was basically banned around 2000.Due to the continuous accumulation over the years,a large number of fine-grained lead-zinc smelting wastes with heavy metals were left in the area.These particles are easily migrated to the surrounding water,soil and atmospheric environment by hydraulic and wind diffusion,posing potential risks to the surrounding ecological environment.Therefore,it becomes particularly important that effective measures are taken to control diffusion of heavy metal pollution.Compared with traditional physical,chemical and physicochemical remediation technologies,phytoremediation is a emerging treatment measure for waste residue yard,which has the characteristics of high efficiency,green and economy,and has been widely used for in-situ control of pollution release of waste residue yard.Although ameliorant-plants combined remediation can significantly increase the content of nutrients and organic matter in the waste residue,but the general metal smelting slag has the characteristics of poor nutrient,poor structure,heavy metal toxicity and other unfavorable plant growth.The demand of the restorative plants for major nutrients?carbon,nitrogen and phosphorus?that essential for plant growth and development and how to achieve stable growth for years in the waste residue yard have always been a hot issue for scientists.At present,the bioavailability of C,N and P in the slag of metal smelting waste yard after phytoremediation,the distribution characteristics of C,N and P in waste residue-plant system,and whether the ecosystem is restricted by N or P have not been systematically studied.Therefore,the zinc smelting waste slag yard has revegetated plants for 6 years in northwestern Guizhou was selected as the study area,and the six dominant plants?Lolium perenne L.,Chenopodium ambrosioides L.,Arundo donax,Robinia pseudoacacia L.,Broussonetia papyrifera and Cryptomeria fortunei?growth well on the waste slag yard were selected as study objects.The distribution and stoichiometry of C,N and P in waste-plant-litter were studied.The limitation of C,N and P in the waste residue-plants system is going to carried out,the paper is intended to provide a theoretical basis for the restoration of plants during the ecological restoration of similar metallurgical waste dumps.The conclusions are as follows:?1?The contents of organic carbon?OC?,total nitrogen?TN?,total phosphorus?TP?and their components in the slag profile of different phytoremediation were significantly different,OC and its components,TN,available nitrogen?AN?,and available phosphorus?AP?,organophosphorus?Po?,Ca₂-P,Ca₈-P,Al-P and Fe-P all showed a gradual decrease with increasing sampling depth,except for OC,HOC,TN and Fe-P.the others showed obvious phenomena of aggregation,while TP and Ca₁₀-P showed no obvious change with depth,and Oc-P was slightly lower than other depths.In addition,the oxidation stability factor?Kos?of organic carbon showed an increase with the increase of depth.The average value of phosphorus activation coefficient?PAC?of surface waste was more than 2%,and the PAC of 10 cm or less was less than 2%.In summary,the improvement of carbon,nitrogen and phosphorus in the waste residue by plants in ecological restoration is mainly concentrated in the surface layer.In addition.Pi accounted TP in waste residues for 58.91-62.85%and the percentageofPi'seachformintotalinorganicphosphoruswas:Oc-P?46.63%?>Fe-P?31.59%?>Ca₁₀-P?12.23?>Al-P?4.79%?>Ca₈-P?3.17%?>Ca₂-P?1.60%?,mainly Oc-p.?2?Correlation analysis showed that there was a significant positive correlation between OC and Kos in the surface slag?0-10cm?,?FA+HA?was negatively correlated with OC and HOC,and positively correlated with EOC.There was a significant positive correlation between AP and Ca₂-P,Ca₈-P,and Po in waste slag,and a significant positive correlation between Ca₂-P and Ca₈-P,Al-P and Po,a significant positive correlation between Ca₈-P and Al-P,Fe-P,Po.It can be seen that Ca₂-P,Ca₈-P and Po are effective phosphorus sources for plant absorption of P,Al-P and Fe-P are used as slow-acting phosphorus sources.The correlation between Ca₁₀-P and various forms of phosphorus was not significant.and a negative correlation between Oc-P and AP,Ca₂-P,Ca₈-P,Fe-P and Al-P.It is indicated that Ca₁₀-P and Oc-P in waste residue are potential phosphorus sources for plant absorption of P,and there are mutual transformation and mutual restriction between different phosphorus forms.?3?The contents of C in different organs and litter of plants was relatively stable,belonging to weak variability,and its distribution among different components was as follows:stems>branches>coarse roots>thin roots>leaves>litter.The content of N and P in each organ of different plant variation is larger,The distribution rules of N and P in plants are consistent,and the order is leaves>fine roots>litter>coarse roots>branches>stems.?4?C:N in the residue under different phytoremediation is stable in the vertical section.The mean values of C:P and N:P show that the surface layer is larger than the bottom layer.The variation coefficients of C:N,C:P and N:P of waste residues under different phytoremediation were lower than C,N and P,and they were of weak variability,indicating that the content variability of C,N and P in waste residues was greater than its ecological stoichiometric ratio.?5?The rules of C:N and C:P in plant vegetative organs and litter are consistent,the order is stems>branches>coarse roots>litter>thin roots>leaves.This is contrary to the distribution rules of N and P in plants,indicating that C:N and C:P in plants are mainly determined by the distribution of N and P in plants.The N:P of plants was:leaves>branches>litter>stems>thin roots>coarse roots.Correlation analysis shows that the N:P and contents of N in different components of plants are highly significantly positively correlated,and highly significantly negatively correlated with the contents of P in leaves,indicating that the N:P of plants was mainly affected by the contents of N in plants,at the same time,the N:P was affected by the content of P in leaves.Only the N:P in leaves of Robinia pseudoacacia L.was greater than 16 in the study,indicating that the growth of Robinia pseudoacacia L.in barren waste residue is not restricted by N,while the others are restricted by N.Therefore,it is important to select leguminous plants as pioneer plants to improve the nutrient status of waste residue dumps with poor nutrient status.?6?In waste residue and plant system,there were significant correlation between C:N,C:P,N:P of indigenous zinc smelting slag and C:N,C:P of plants,basically.The content of N in fine roots,the content of P and C:N,C:P in litter and fine roots had significant positive correlation or significant negative correlation with the contents of N and P,C:N,C:P and N:P in the waste residue.It explained the close relation between fine roots,litter and waste residue.In summary,after 6 years of ecological restoration,the OC,TN and TP in the waste residue have been significantly improved after being repaired,EOC,?FA+HA?,AN,AP,Ca₂-P?Ca₈-P?Al-P and Po and so on,these main active components of C,N and P has an obvious phenomenon of aggregation.The Pi in the residue under 6 plants remedial was mainly Oc-P,and there were mutual transformation and mutual restriction between different phosphorus forms.In the plants,the distributional characteristic of C was stable,but the contents of N and P were more variability.The distribution of C in different components of plants is:stems>branches>coarse roots>fine roots>leaves>litter.The distribution of N and P in the different components of the plant is the same,both were leaves>fine roots>litter>coarse roots>branches>stems.The N:P analysis of plant leaves indicated that the plant growth was limited by N in the ecological restoration system.The C:N and C:P of plants were affected by the distribution of N and P,respectively.Correlation analysis showed that plant N:P was mainly affected by N content.In addition,the fine roots and litter of plants were closely related to the nitrogen and phosphorus contents and stoichiometric characteristics of the waste residue.