模拟咸水入侵对崇明岛河岸带根际土壤微生物及反硝化作用的影响

通过模拟咸水入侵,研究了其对崇明岛河岸带根际土壤微生物及其反硝化过程的影响.结果表明:模拟咸水入侵后4种不同植被型河岸带土壤根际微生物区系发生显著变化,除放线菌菌群数量稍有增加外,细菌、真菌以及硝化和反硝化细菌数量均出现不同程度下降,特别是反硝化功能细菌数量较对照平均下降51.8％,说明河岸带土壤不同微生物区系对咸水入侵的响应存在显著差异.模拟咸水入侵后,河岸带土壤与氮转换相关的酶活性普遍受到抑制,且抑制作用随酶类型不同而存在差异,亚硝酸还原酶对咸水入侵最敏感,其活性较对照平均下降了43.5％,脲酶活性次之,其降幅为37.4％,而脱氢酶受咸水影响较小,其活性平均下降29.5％.模拟咸水入侵明显削弱了河岸带土壤反硝化作用,其速率平均下降34.9％.不同植被型河岸带土壤微生物对咸水入侵的生态生理响应存在显著差异,与对照相比,茭白根际土壤微生物数量和酶活性受咸水入侵的平均抑制率最大,土壤反硝化速率最小,其次是菖蒲和芦苇.在模拟咸水入侵下,菖蒲与芦苇混合群落根际土壤微生物数量、酶活性和反硝化速率抑制率明显低于单一植物模式,表明混合植被群落根际土壤微生物过程及反硝化作用对咸水入侵具有较好的缓冲性能.

Effects of saltwater incursion on the microbiological characteristics and denitrification in a riparian rhizosphere soil in Chongming Island of Shanghai, East China

A simulation test was conducted to study the effects of saltwater incursion on the microbiological characteristics and denitrification in the riparian rhizosphere soils vegetated with different plants in Chongming Island of Shanghai. Saltwater incursion changed the microflora in the rhizospheric soils. Except for actinomycete whose quantity had slight increase, the quantities of bacteria, fungi, nitrifiers, and denitrifiers all decreased to some extent by saltwater incursion, with the denitrifiers decreased by 51.8%, suggesting that the riparian soil microflora responded differentially to saltwater incursion. The activities of soil nitrogen-transforming enzymes were significantly inhibited by saltwater incursion, and the inhibitory effects differed with the enzymes. Nitrite reductase activity was most sensitive to saltwater incursion, with an inhibition rate of 43.5%, followed by urease activity, with 37.4% inhibition, and by dehydrogenase (29.5% inhibition). Saltwater incursion inhibited the denitrification, with the average denitrification rate decreased by 34.9%. There existed significant differences in the eco-physiological responses of the microbes in the rhizosphere soils vegetated with different plants to the saltwater incursion. The microbial quantities and enzyme activities showed the highest inhibition percentages in the rhizosphere soil of Zizania aquatica, followed by in the rhizosphere soils of Acorus calamus and Phragmites australis. Under saltwater incursion, the inhibition percentages of microbial quantities, enzyme activities, and denitrification rate in the rhizosphere soil of A. calamus-P. australis were significantly lower, as compared with those in the rhizosphere soils vegetated with Z. aquatica, A. calamus, and P. australis, respectively, suggesting that mixed vegetation showed a better buffer effect on the responses of riparian rhizosphere soil microbiological processes and denitrification to saltwater incursion.