The Studies On Microbial Ecology Of The Rhizosphere Of Emergent Plants

Emergent plants are important component of aquatic ecosystems. The studies have shown that plants can remove nitrogen, phosphorus and other pollutants by absorption and accumulate of heavy metals. In addition, plant root exudates can also provide nutrition for the rhizosphere microbial to the degradation of organic compounds. In this work, studies on microbial ecology of the rhizosphere of emergent plant were carried out by field sampling and laboratory simulation and as follows:(1)Field sampling: The field study was conducted in two adjacent shallow lakes (Qingnian Lake and Aiwan Lake; P. australis and T. orientalis grew seperately in Qingnian Lake, while grew together in Aiwan Lake) located in Tianjin University to investigate the effect of plant species and growth strategy on the rhizosphere microbial ecology and plant root exudates. Phospholipid fatty acids analysis showed that the number of microorganisms in rhizosphere sediment was significantly higher than non-rhizosphere sediment; the numbers and diversity indices of T. orientalis rhizosphere microbial were greater than P. australis, indicating that the rhizosphere effect of T. orientalis more obvious. Emergent plant root exudates inclued amino acids, organic acids, sugars and fatty acids, phenolic acids, aromatic acids, phenols, esters, amines and so on. The results showed that there was significant difference in types and contents of amino acid and organic acid between the two plants. The root exudates content of T. orientalis was higher than P. australis, while small difference in root exudates content between T. orientalis and P. australis when they mixed growed.(2)Laboratory simulation: On the basis of field sampling, effect of sediment organic matter content and initial concentration of phthalate esters on rhizosphere microbial ecology and phthalate-degrading bacteria was studied in the lab by using P. australis as experimental material. The results showed that the content of organic carbon had a significant impact on the rhizosphere microbial ecological characteristics. The number of microorganisms in sediment (taken from Qingnian Lake) with high organic carbon was mainly affected by organic carbon, and the microbial amounts in the rhizosphere was similar to those in the non-rhizosphere, while microbial amounts in the rhizosphere were significantly higher than those in the non-rhizosphere of sediment (from the Mati Lake and Jingye Lake) with low organic carbon content. As for the total amount of microbiological, in the unplanted group, microbial amounts in non-spiked sediments from Jingye Lake and Mati Lake were higher, indicating that phthalic acid ester had a significant affect on the growth of microorganisms in the unplanted sediments with lower organic carbon content. Different with the other two lakes, there was no obviously difference in degrader numbers of phthalate acid esters between planted group and unplanted group in Qingnian Lake, because organic carbon content in sediments from Qingnian Lake was higher, leading to lower effective concentration of phthalate acid esters.