Changes Of Heavy Metal's Content In Greenhouse And The Absorbtion And Accumulation Of Cr⁶⁺ In Celery

The greenhouses in seven regions, Guanzhong district Shaanxi province were studied in this study. The contents of heavy metals in soils and vegetables have been detected by atomic absorption spectrophotometric(FAAS) and atomic fluorescence spectrophotometry (AFS), as well as analysed the physical and chemical properties of soils, including soil pH, soil organic matter(OM), basic nutrientions, electrical conductivity (EC) cation exchange capacity (CEC) and so on. At the same times, using differential centrifugation method and step extracting methds, the accumulation, subcellular distribution and chemical forms of chromium (Cr) were studied in potted celery (Apium graveolens). Moreover, the content of proline (Pro), and Vc et al were also investigated to study the effect of Cr to the growth of celery. It is provided a theoretical basis for greenhouse vegetable products. The results in this study are as follows:1.The contents of Cd and Hg were exceeding the limit value of"greenhouse vegetable producing environmental quality evaluation standards"HJ333-2006 in seven greenhouse soil in Guanzhong district. The contents of As ,Pb and Cr were under the limit value. The heavy metal pollution index(HPI) in soil is the oder:Sanyuanï¹¥Dongbaiï¹¥Xiwangï¹¥Nanzhuangï¹¥Fanyaoï¹¥Wenchangï¹¥Dongzhang. The greehouse soils had been polluted by heavy metals(HPIï¹¥1.00). Heavy metal contents were increasing in greenhouse soils were related to using large amount of the chemical fertilizer and pesticide.2.The contents of heavy metals in three species of greenhouse vegetables in the order:celeryï¹¥tomatoï¹¥cucumber. Pb were exceeding the limit value in three species of vegetables. Cd was exceeding the limit value in Sanyuan and Dongbai in three vegetables, and also Cd exceeding the limit value in Xiwang and Nanzhuang in celery; Cr, Pb and Hg were not exceeding the limit value in three types vegetables. The heavy metals polluted soils and using the pesticides which contain metals element leading to heavy metals accumulated in vegetables.3.The greenhouse soils were becoming acidification year by year.Soil pH, OM, soil available nitrogen, available phosphorus, available potassium, CEC and EC were more high than commonly vegetable fields. Using the correlation analysis in this study, according to these impact factors, OM, pH, available phosphorus, EC and CEC have the obvious effect to Cr and Hg, however, the effects of available nitrogen and available potassium were not significant.4.With the increasing concentration of Cr⁶⁺ treatments, malondialdehyde (MDA), Pro, soluble sugars and nitrate content in leaves of celery were increasing. Therefore, chlorophyll content, Vc content and roots activity were decreasing. In addition, soluble protein concentration was raising under low concentration(5mg·kg^-1) Cr⁶⁺ and decreasing in high concentration(60mg·kg^-1). It demonstrates that the effects is not obvious under low concentration of Cr⁶⁺ treatments, and harmed high concentrations of Cr⁶⁺ treatments in celery.5.In control subcellular distribution in roots and shoots with the order: F3 (soluble fraction)ï¹¥F2 (cell organs and membrane)ï¹¥F1 (cell wall and residue). However, under 40 mg·kg^-1 Cr ⁶⁺ treatment, the order: F1ï¹¥F3ï¹¥F2, so cell wall is the subcellular distribution area of Cr accumulation in celery. Moreover, acetic acid extractable-Cr were dominant in both roots and shoots, the mass of chromium extracted by NaCl and HCl were also considerable. It is documente that existence of insoluble phosphate, combined protein as well as oxalate were the main chemical forms for chromium in celery.6.There was no obvious effects on biomass under low concentration (5 mg·kg^-1 ) of Cr⁶⁺ treatment, whereas it was declined significantly when planted in high Cr⁶⁺concentrations (60 mg·kg^-1) (P﹤0.01), with the reducing of tolerance index simultaneously. The exposure to Cr⁶⁺ caused markedly increase of chromium content in both roots and shoots(P﹤0.01),and the retention function was great in roots.It demoetrates that the contents and the amounts of chromium in presented in the order: rootï¹¥leaveï¹¥stem. The resultes demonstrated that roots were the main Cr accumulated organ in celery.