Studying The Phytotoxicity Of Landfill Leachate To Arabidopsis Thaliana

With the rapid development of China's population and economic, as well as accelerated process of industrialization and urbanization, the generation of garbage is growing rapidly, and its dispose has become one of the main problems of the world's attention. At present, three types of waste disposal and recycle method are widely used, including sanitary landfill, high-temperature composting and waste-to-energy power generation technology. The sanitary landfill method has been adopting as the primary method of municipal waste disposal in the world due to its low processing cost, simple technology, easy operation and management. However, prevalence use of this technology, especially in the developing countries, has exerted terrible pollution of landfill leachate released from the landfills.Landfill leachate is the water that comes from the process of various physicochemical and biological reactions such as accumulation, compaction and degradation etc. Generally, landfill leachate has such characteristics as complicated element, great variation in either quality or flow rate, intricate species of organic pollutant and metals. In theory, nitrogen, phosphorus and other elements in it can provide nutrients for plant growth and promote plant growth and development, while high concentrations of organic pollutants and heavy metal ions will restrain plant growth and development. Up to date, mechanisms of comprehensive toxicity of landfill leachate to plants have not been elucidated completely, although more and more relative studies on the biological stress of landfill leachate were conducted.Arabidopsis thaliana is the first higher plant whose whole genome Sequencing was completed, for which it is always used as model plant for laboratory experiments. Our present study was designed to research the toxic effect of landfill leachate on the growth, development and reproduction of Arabidopsis thaliana, which obtained from a landfill in northern of China in winter. The results of Physical and chemical characteristic analysis showed that landfill leachate contained a variety of metal ions, Cu, Mn, Pb, Ni, Zn and Fe; salt content was up to157ms/cm, chroma was up to250times, pH was7.96, CODcr was2340mg/L, NH3-N content was958mg/L.After exposure A.thaliana seedlings to different concentrations of landfill leachate, we found that irragation of landfill leachate had an impact on Arabidopsis seed germination and seedling growth. Low concentrations of landfill leachate promote seed germination, but high concentrations of landfill leachate not only delayed the germination of seeds, but also reduced the rate of seed germination. In the same group, the inhibition of landfill leachate on Arabidops roots were stronger than their shoots.Examination of the injury effect of landfill leachate on Arabidopsis during ripening stage indicated that low concentrations of landfill leachate could promote plants growth, while high concentrations of landfill leachate could inhibit plants growth. Compared with the control group, the leaves in low concentrations of landfill leachate-treatment groups were more green, new leaves and whole plant grew faster; in high concentrations of landfill leachate-treatment groups, leaves were gradually atrophic and shriveled, new leaves and whole plant grew slower. In all landfill-treatment groups, the content of chlorophyll increased in the beginning, and then became lower Along with the extending of time. Oxidative stress levels including the content of MDA, activities of antioxidants (SOD,CAT,POD) in Arabidopsis plant after landfill leachate exposure at various concentrations were also investigated and the results showed that the content of MDA, as well as CAT and POD activity increased in both time-and concentration-dependent manners, while SOD activity was significantly decreased. Comparing of Early and mature Arabidopsisthe tolerance to landfill leachate displayed that tolerance of mustard seed was weaker than mature plants. Seed germination rate of just10%landfill leachate diluent treatment group was up to53%of the control group, but mature plants tolerated up to80%of the leachate diluent for two weeks. Finally, the mature Arabidopsis exposed to various concentrations of landfill leachate for two weeks was resuscitated, and then bolting rate and fruits number were determined. The results showed that low concentrations of landfill leachate promoted the bloting of mature Arabidopsis, increased the fruit number. On the contrary, high concentrations of landfill leachate caused unrecoverable injury to Arabidopsis plant, displaying lower bolting and podsless symptom.