Processes Of Phytoremediation Coupled With Agro-production Of Cadmium And Nitrate Co-contaminated Soils

In recent decades,the world population is growing fast,and the demand for vegetables and fiber increased,as a result,green house production of vegetables was increasing.Because of this increasing industrial wastes emission,fertilizers and pesticides usage,a large number of lands and greenhouse soil were polluted by Cd and nitrate.It was a serious threat to agro-production and human health.In view of Cd and nitrate co-contamination in China and even all over the world,it is necessary to develop a resource-saving and environment-friendly phytoremediation technology in a right away.The characteristics determined for Cd and nitrate phytoremediation differ from each other,so the remediation strategies for plant and microorganism were limited.In this study,we investigated variations in Cd and nitrate co-accumulation among different genotyoes of Chinese cabbage and water spinach.The Cd uptake and accumulation processes of S.alfredii after CO2 or/and inoculate endophytic bacterium via hydroponics,rhizosphere,pot and field studies,the effects of Cd and nitrate uptake and accumulation with different water management technical models effects analysis of phytoremediation coupled with agro-production.Cd and nitrate co-contaminated soils with hyperaccumulator S.alfredii rotated with low-accumulator water spinach and Chinese cabbage with CO2 fertilization and endophyte inoculation is also effective way to remediate soils.The main results are summarized as follows:1.A field experiment was conducted to screen low co-accumulator genotypes of both Cd and nitrate from 62 Chinese cabbage genotypes.Cd concentrations showed a 63-fold difference from the highest to the lowest and 10-fold difference for nitrate in Chinese cabbage genotypes.Seven genotypes,i.e.,SIYM,TCCS,28TS,DGAF,CANB,FBSY and SJXH,were identified as low co-accumulators of Cd and nitrate.These genotypes were suitable for growing in slightly or moderately contaminated soils without risk to food safety.Improved management practices,such as reduced N,increased K application rate,and foliar application of water soluble Zn,may be useful for reducing Cd and nitrate concentrations in Chinese cabbages on contaminated soils.Besides,soil conditioners may also be used to improve calcareous soil so that plant-availability of Ca,Mg and Mn could be enhanced,thus reducing Cd and nitrate concentrations in edible parts of plants and improving vegetables quality.2.A field experiment was conducted to screen low co-accumulator genotypes of both Cd and nitrate from 38 water spinach genotypes.Cd concentrations among spinach genotypes was 39-fold from the highest to the lowest,and 6-fold for nitrate.Genotypes,i.e.,JXDY,GZQL,XGDB and B888 were identified as low co-accumulators of Cd and nitrate.These genotypes were suitable for growing in slightly or moderately contaminated soils without risk to food safety.Increasing P fertilizer application rates appears to prevent heavy metal and nitrate translocation to shoot tissues and other edible parts of water spinach on co-contaminated soil.3.The effects of phytoremediation efficiency of Cd contamination by enhancing CO2 or/and inoculate endophytic bacterium to S.alfredii was investigated via hydroponics and rhizosphere experiments.Superposition treatments resulted in the highest agronomic characters,photosynthesis,root exudates and Cd concentrations of both hyperaccumulating ecotype and non-hyperaccumulating ecotype S.alfredii.The differences were:In hyperaccumulating ecotype S.alfredii,most Cd was transported to shoots,especially in to leaves,in order to stimulate the roots uptake of Cd;In non-hyperaccumulating ecotypes of S.alfredii,most Cd was accumulatedin roots,the fraction of Cd was transported to shoots mainly in stem and low transportation was observed in to leaves,in order to alleviate Cd toxicity.These results proved there was great difference in response to Cd stress between two S.alfredii ecotypes.From this findings we can suggest there is a possibility to enhance phytoremediation efficiency of S.alfredii by CO2 and endophyte superposition treatment.4.The effects of Cd and nitrate uptake accumulation by flooding to water spinach was investigated via pot experiments.As a result,flooding treatment increased the agronomic characters and reduced Cd and nitrate concentrations and bioaccumulation factor of all water spinach genotypes.Flooding treatment increased soil pH,reduced soil DTPA Cd and nitrate concentrations.The soil DTPA Cd and nitrate with high-accumulator water spinach shown a tremendous increase of 30.86 and 27.81%,respectively,but the soil total Cd removal efficiency was reduced.High-accumulator water spinach has high removal efficiency to DTPA Cd and nitrate and these genotypes were identified as an useful materials for phytoremediation.Low-accumulator water spinach has lower Cd and nitrate transfer and bioaccumulation factor which are safe for consumption.5.Phytoremediation with hyperaccumulator S.alfredii,endophyte M002 inoculation,CO2 fertilization and fermentation residue being continuously applied,rotating with low-accumulator aquatic vegetables like water spinach and Chinese cabbage with reasonable water management via the field trials was investigated.After 1 and 2 years of phytoremediation,total Cd uptake by S.alfredii with superposition treatment was 2.57 and 2.48 times greater as compared to mono-planting of S.alfredii.Cd and nitrate concentrations of low-accumulative water spinach and Chinese cabbage genotypes were significantly decreased and safe for consumption when grown after planting with S.alfredii.This PCA system removed 56.5%total Cd,62.3%DTPA extractable Cd,and 65.4%nitrate,respectively from the co-contaminated soil in 2 years of phytoremediation,and this can be proved as an effective way of remediating moderately co-contaminated soil by Cd and nitrate.