5种湿地植物对生活污水的生理响应及其去污能力的研究

人工湿地是选用耐污染能力和净化能力强的水生植物，模拟自然湿地构建的用于污水净化的湿地系统，利用植物的吸收、基质的吸附、微生物的分解，综合了物理、化学和生物三方面的作用处理污水，作为一种处理费用和建设成本低的环境友好型污水处理技术，近年来在国内外各地区得到广泛的应用.本研究选用宁夏黄河流域分布较广的芦苇Phragmites australis)、水葱(Scirpus validus)、千屈菜(Lythrum salicaria)、扁秆藨草(Scirpus planiculmis)和长苞香蒲(Typha angustata)，共5种湿地植物，构建人工湿地污水处理小试系统，开展湿地植物对污水的生理响应，植物净化过程中污染物的动态变化规律以及植物根区土壤中微生物多样性的研究，主要取得了如下结果:1、湿地植物对污水的生理响应研究.通过测定清水培养和污水处理的5种湿地植物的光合生理参数、Fv/Fm值、叶绿素相对值和生物量变化，研究植物对污水的生理响应.结果表明:污水处理使5种植物叶片的净光合速率(Pn)和蒸腾速率(Tr)均高于清水培养植物，胞间CO2浓度(Ci)随季节的变化呈逐渐升高趋势，与Pn和气孔导度(Gs)随季节的变化呈逐渐下降趋势，说明Pn降低的原因可能是非气孔因素造成的.污水处理各植物的Fv/Fm值大体上高于清水培养，说明污水处理植物叶绿体光系统Ⅱ活性比清水培养高.各个指标表明，污水处理植物的生长状况好于清水培养植物.2、湿地植物对污水净化效果研究.通过测定污水中污染物的变化及氮磷元素在植物体-土壤-污水中的分布，综合评价植物对污水的净化能力.结果表明:(1)随处理时间延续，处理系统中污水的CODcr，铵态氮、总氮和总磷浓度均呈现下降趋势，且有植物去除效果显著高于无植物对照;湿地植物对污水NH4+-N和TP的去除率分别在试验验第18天和24天达到较高水平，对污水CODcr和TN在实验第31天达到较好净化效果.(2)5种植物能吸收污水中89.7%~97.9%的磷元素，污水中剩余量较少(2.1%-10.3%)，土壤中无滞留;污水中氮元素在植物体、污水和土壤中分布因植物种类不同有很大差异，芦苇、水葱和长苞香蒲吸收了污水中76.1%~83.4%的大部分氮元素，而千屈菜和扁干藨草对氮元素吸收量较少(分别为45.0%和46.8%)，在污水和土壤中滞留的氮元素较多(21.7%~31.6%).(3)5种湿地植物对生活污水的综合净化能力从高到低依次为芦苇>长苞香蒲>水葱>扁秆藨草>千屈菜.3、湿地植物根区微生物物种多样性研究.采用PCR-DGGE技术测定了湿地植物根区微生物物种多样性.结果显示:5种湿地植物根区分布的微生物包括5个类群，分别为变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)、和不可培养细菌(Uncultured bacterium).与清水对照相比，污水处理植物根区微生物物种数和多样性指数高于清水培养植物，这与污水中氮、磷、有机物等营养物质有关.

Constructed wetland is a wetland system for sewage purification constructed by simulating natural wetlands using aquatic plants with strong pollution tolerance and purification capacity. It utilizes plant absorption, matrix adsorption and microbial decomposition, integrating physical, chemical and biological processes to treat sewage. As an environmentally friendly sewage treatment technology with low treatment and construction costs, it has been widely applied in various regions at home and abroad in recent years.
This study selected five wetland plant species widely distributed in the Ningxia section of the Yellow River Basin, namely *Phragmites australis*, *Scirpus validus*, *Lythrum salicaria*, *Scirpus planiculmis* and *Typha angustata*, to construct a pilot-scale constructed wetland sewage treatment system. We conducted studies on the physiological responses of wetland plants to sewage, the dynamic changes of pollutants during the plant purification process, and the microbial diversity in the rhizosphere soil of plants, and obtained the following main results:
1. Study on the physiological responses of wetland plants to sewage. The physiological responses of plants to sewage were investigated by measuring photosynthetic physiological parameters, Fv/Fm values, relative chlorophyll content and biomass changes of the five wetland plants cultured in clear water and treated with sewage. The results showed that: the net photosynthetic rate (Pn) and transpiration rate (Tr) of the leaves of the five plants under sewage treatment were higher than those of plants cultured in clear water. The intercellular CO2 concentration (Ci) showed a gradual increasing trend with seasonal changes, while Pn and stomatal conductance (Gs) showed a gradual decreasing trend with seasonal changes, indicating that the decrease in Pn may be caused by non-stomatal factors. The Fv/Fm values of plants under sewage treatment were generally higher than those of plants cultured in clear water, indicating that the photosystem Ⅱ activity of chloroplasts in sewage-treated plants was higher than that in clear water-cultured plants. Various indicators showed that the growth status of sewage-treated plants was better than that of clear water-cultured plants.
2. Study on the sewage purification effect of wetland plants. The purification capacity of plants for sewage was comprehensively evaluated by measuring the changes of pollutants in sewage and the distribution of nitrogen and phosphorus elements in the plant-soil-sewage system. The results showed that:
(1) With the extension of treatment time, the concentrations of CODcr, ammonium nitrogen, total nitrogen and total phosphorus in the sewage of the treatment system all showed a downward trend, and the removal effect of planted systems was significantly higher than that of unplanted controls. The removal rates of NH4+-N and TP from sewage by wetland plants reached relatively high levels on the 18th and 24th days of the experiment, respectively, and the purification effects of CODcr and TN in sewage reached good levels on the 31st day of the experiment.
(2) The five plants could absorb 89.7%~97.9% of phosphorus in sewage, with a small remaining amount in sewage (2.1%~10.3%) and no retention in soil. The distribution of nitrogen in sewage among plants, sewage and soil varied greatly depending on plant species. *Phragmites australis*, *Scirpus validus* and *Typha angustata* absorbed most of the nitrogen (76.1%~83.4%) in sewage, while *Lythrum salicaria* and *Scirpus planiculmis* absorbed less nitrogen (45.0% and 46.8%, respectively), with more nitrogen retained in sewage and soil (21.7%~31.6%).
(3) The comprehensive purification capacity of the five wetland plants for domestic sewage from high to low was: *Phragmites australis* > *Typha angustata* > *Scirpus validus* > *Scirpus planiculmis* > *Lythrum salicaria*.
3. Study on microbial species diversity in the rhizosphere of wetland plants. The microbial species diversity in the rhizosphere of wetland plants was determined using PCR-DGGE technology. The results showed that the microorganisms distributed in the rhizosphere of the five wetland plants included 5 groups, namely Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and Uncultured bacterium. Compared with the clear water control, the number of microbial species and diversity index in the rhizosphere of sewage-treated plants were higher than those of clear water-cultured plants, which was related to nutrients such as nitrogen, phosphorus and organic matter in sewage.