蚯蚓对湿地植物光合特性及净化污水能力的影响

以香蒲、芦苇和美人蕉为研究对象,并以土壤+沙子+有机质混合物为供试基质模拟人工湿地处理污水,采用向基质中加入蚯蚓与未加入蚯蚓2种处理。研究加入蚯蚓后,香蒲、芦苇和美人蕉光合速率、蒸腾速率、SPAD值和水分蒸发、蒸腾量的变化及其对净化污水能力的影响。结果表明:与未加入蚯蚓相比,加入蚯蚓后,香蒲、芦苇和美人蕉的净光合速率、蒸腾速率、SPAD值和水分蒸发、蒸腾量均增加,其中芦苇的净光合速率、蒸腾速率和水分蒸发、蒸腾量增加达到显著水平(P <0.05),而香蒲的水分蒸发、蒸腾量增加也达到显著水平(P <0.05);加入蚯蚓后,香蒲、芦苇和美人蕉对COD_Mn、NH₄⁺-N、NO₃^--N、TN和TP的去除率均增加,且香蒲和芦苇对COD_Mn的去除率显著增加 (P <0.05)。加入蚯蚓后,香蒲、芦苇和美人蕉的SPAD值均增加,说明蚯蚓能提高湿地植物对氮的吸收,增加植株中的氮含量,促进湿地植物的光合速率和蒸腾速率从而提高对污水的净化能力。

Effect of earthworms on the photosynthetic characteristics of wetland plants and their capacity to purify wastewater

Constructed wetlands are effective and useful treatment systems in developing countries since they use simple technology and have low operational and construction costs. Wetland plants are very important structural components of in constructed wetlands. The function of wetland plants in constructed wetlands is providing a structure for enhancing flocculation, sedimentation and filtration of suspended solids, and releasing the carbon from root exudates or decaying root thus enhancing microbial activity such as microbial biomass carbon, microbial biomass nitrogen, and enzyme activity. In addition, wetland plants directly take up nitrogen, phosphorus and heavy metals, and also play an important role during winter by insulating the water surface from cold temperatures thereby reducing heat loss. Typha angustifolia, Phragmites australis and Canna indica are wetland plants widely used in constructed wetlands to purify wastewater. Earthworms are important as ecosystem engineers, and play important roles in organic matter breakdown and soil structure improvement. They also affect nitrogen cycling, both directly through consumption of leaf and soil material and excretion, and indirectly by burrowing and casting and increasing the rate at which organic nitrogen is mineralized into inorganic forms. The response of wetland plants to earthworms in a constructed wetland that used a mixture of soil, sand and organic matter as substrate was investigated together with its influence on the removal efficiency of wastewater. The effects of added earthworms were studied to determine changes in photosynthetic rate, transpiration rate and SPAD value of T. angustifolia, P. australis and C. indica, and any relationship with the removal efficiency of wastewater. For the three wetland plant species, T. angustifolia, P. australis and C. indica, addition of earthworms increased their photosynthetic rate by 20.9%, 81.4% and 13.4%, respectively; their transpiration rate by 8.4%, 78.5% and 12.0%, respectively; and the SPAD vale of their leaves by 22.1%, 16.4% and 16.9%, respectively. Addition of earthworms to the substrates led to significant increases (P <0.05) in the photosynthetic rate and transpiration rate of P. australis and a significant increase (P <0.05) in the SPAD value of T. angustifolia. Addition of earthworms increased evapotranspiration losses of T. angustifolia, P. australis and C. indica by 29.6%, 92.1% and 24.6%, respectively. Evapotranspiration losses of T. angustifolia and P. australis were significantly increased (P<0.05). For the three wetland plant species, T. angustifolia, P. australis and C. indica, addition of earthworms increased their removal efficiency of COD_Mn by 8.5%, 79.6% and 8.7%, respectively; their removal efficiency of NH₄⁺-N by 6.4%, 6.6% and 5.5%, respectively; their removal efficiency of NO₃^--N by 7.8%, 26.2% and 6.8%, respectively; their removal efficiency of TN by 6.1%, 6.8% and 5.8%, respectively; and their removal efficiency of TP by 4.1%, 4.1% and 4.6%, respectively. Addition of earthworms significantly increased (P <0.05) the removal efficiency of COD_Mn, of T. angustifolia and P. australis and the rate of removal of NO₃^--N by Phragmites australis. The increased SPAD values of T. angustifolia, P. australis and C. indica showed that the N content of the wetland plants was increased due to addition of earthworms into the wetland substrates, resulting in enhanced photosynthetic and transpiration rates, and an increased capacity to purify wastewater.