| Constructed wetlands have been widely used to dispose many kinds of wastewater. However, during the process for treating wastewater by constructed wetland, the contamination in the wastewater may negatively affect the growth of wetland plants in the mean time. Ammonia and organic pollutants are common pollutants in the sewage. The research on the tolerance of wetland plants to ammonia and organic pollutants and their mechanisms has important significance to guarantee the disposal efficiency of constructed wetlands and to maintain the sustainable development of ecosystem.In this paper, we studied the physiological response mechanism of typical wetland plants, Phragmites australis, Lemna minor and Vallisneria natans, under the stress of ammonia and organic pollutants using physiology and biochemistry method. The tolerability of wetland plants to ammonia and organic pollutants and the recovery law after stress removal was definite according to our study. Further more, in order to study the molecular mechanism of ammonia and organic pollutants stress to wetland plants, we analyzed differential proteomics of wetland plants by the technology of proteomics. The research shows the results as follows:(1) The physiological activity of wetland plants were affected at various degrees under ammonia and organic pollutants stress, like the membrane system damage and total chlorophyll contents decreasing. However, the plant has self-defense ability so that stresses to a certain degree could be resisted by itself. By studying their physiological and biochemical responses under ammonia and organic pollutants, this study makes clear the tolerability of typical wetland plants to ammonia and organic pollutants.CD Phragmites australis can resist high level of ammonia and organic pollutants. Even the concentrations of ammonia and organic pollutants (CODCr) were160mg L-1and200mg L-1, the contents of total chlorophyll, nutrition elements and osmotic adjustment substance, stability of membrane system and antioxidant defense system were all still at normal stage. Phragmites australis could grow well under80mg L- ammonia and400mg L-1CODCr stress according to our study.②Lemna minor can resist certain level of ammonia and organic pollutants. When the concentrations of ammonia and organic pollutants (CODCr) were80mg L-1and400mg L-1, the contents of total chlorophyll, nutrition elements and osmotic adjustment substance, stability of membrane system and antioxidant defense system were all at normal stage. The results showed that Lemna minor could grow well under80mg L-1ammonia and400mg L-1CODCr stress.③Vallisneria natans can was sensitive at ammonia and organic pollutants stress and had low tolerability to the stress. When the concentrations of ammonia and organic pollutants (CODCr) were2mg L-1and100mg L-1, the contents of total chlorophyll, nutrition elements and osmotic adjustment substance, stability of membrane system and antioxidant defense system were all at normal stage.. The results showed that Vallisneria natans could only grow well under2mg L-1ammonia and100gL-1CODCr.(2) Plants have a self-repair capability after the injury. Under a certain stage of stress, reversible injuries happen inside plants, and then plants could be back to normal through self-recovery after the stress removal. In this study, the recovery ability of typical wetland plants by investigating the recovery law of wetland plants after removal stress was made clear. The results show as follows:①30days under320mg L-1ammonia and400mg L-1CODCr stress, after stress removal, the the relative electrolyte leakage, MDA, ROS, total chlorophyll and nutrition elements contents, antioxidant defense system and osmotic adjustment substance contents all recoverd to normal in Phragmites australis. While the stress level of ammonia and CODCr was too high (≥640mg L-1,800mg L-1respectively), which exceed its tolerance range, Phragmites australis was irreversibly damaged and could not recover to normal after the stress removal.②14days under1600mg L-1ammonia and800mg L-1CODCr stress, after the stress removal, the relative electrolyte leakage, MDA, ROS, total chlorophyll and nutrition elements contents, antioxidant defense system and osmotic adjustment substance contents recoverd to normal in Lemna minor. However, when the stress level of ammonia and CODCr was too high (≥320mg L-1,1000mg L-1respectively), which exceed the tolerance range, Lemna minor was irreversibly damaged and could not recover to normal after the stress removal.③14days under4mg L-1ammonia and200mg L-1CODcr stress, after the stress removal, the relative electrolyte leakage, MDA, ROS, total chlorophyll and nutrition elements contents, antioxidant defense system and osmotic adjustment substance contents recoverd to normal in Vallisneria natans, While the stress level of ammonia and CODcr was too high (≥8mg L-1,300mg L-1respectively), which exceed the tolerance range, Vallisneria natans was irreversibly damaged and could not recover to normal after the stress removal.(3) Differential proteomics of typical wetland plants were identifed and analysed in order to study the molecular mechanism of wetland plants resistence to ammonia and organic pollutant. Besides, we compared the resistence capbility of these typical wetland plants. The results are as follows:①Injury mechanisms of ammonia stresses on Phragmites australis Lemna minor and Vallisneria natans were similar. A high level of ammonia would cause down-regulated expression of glutamine synthase and Ribulose-1,5-bisphosphate carboxylase/oxygenase which are the key enzymes of nitrogen metabolism and photosynthesis, repcetively. Therefore, excessive accumulation of free ammonia and suppression of photosynthesis happened in plants, which lead to inhibition to the normal growth of wetland plants.②Tolerant mechanisms of ammonia stresses were different for Phragmites australis Lemna minor and Vallisneria natans. Some proteins, which were related to the antioxidant defense, were up-regulated to resist ammonia injury. However, up-regulating expression of proteins in Phragmites australis were CAT and GST, while CAT and Mn-SOD in Lemna minor and Mn-SOD in Vallisneria natans.③Injury mechanisms of organic pollutant stresses on Phragmites australis Lemna minor and Vallisneria natans acted differently. Under organic pollutants stress, ribulose-1,5-bisphosphate carboxylase/oxygenase was down-regulated in Phragmites australis, which caused weak photosynthesis and suppression of plant growth. Adenosine triphosphate synthetase was down-regulated in Lemna minor and Vallisneria natans, which caused suppression of synthese of adenosine triphosphate, thereby, lacked enough energy to keep plants in normal stage.④Tolerant mechanisms of organic pollutant stresses on Phragmites australis Lemna minor and Vallisneria natans were in different ways. Uridine diphosphate glucose pyrophosphorylase was up-regulated in Phragmites australis under organic pollutant stress, which promoted the synthese of sugar to supply enough energy and hence increased the ability of resistance. While glyceraldehyde-3-phosphate dehydrogenase and glutathione stransferase were up-regulated in Lemna minor, they promoted the energy supply and antioxidant defence ability. Glutathione stransferase was up-regulated in Vallisneria natans.⑤For the tolerance of wetland plants to ammonia stress, Phragmites australis was suitable for treatment of wastewater with the concentration of ammonia less than160mg L-1, while80mg L-1for Lemna minor and2mg L-1for Vallisneria natans. As to the tolerance of wetland plants to organic pollutants stress, Phragmites australis was suitable for treatment of wastewater with the concentration of CODCr less than200mg L-1, while400mg L-1for Lemna minor and100mg L-1for Vallisneria natans.
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