The Effect Of Dissolved Oxygen On The Transfer And Transformation Of Ammonia And Ammonia-oxidizing Microorganism In The Jiulong River Wetland Sediment

There are several active biogeochemical processes in wetland ecosystem. Thenitrogen cycle is particularly significant. Wetland sediment was source and sink ofnitrogen, which directly affect the level of water eutrophication. Dissolved oxygen(DO) is an important environmental factor that affect ammonia release from sedimentand the ammonia oxidation in overlying water. Therefore, two kinds of surfacesediments (mangroves, mudflat) in the Mangrove wetland of Jiulong river estuarywere selected as experimental materials. In situ investigation and laboratorysimulation were applied. The effect of dissolved oxygen on release of ammonia fromsediment and ammonia oxidation in sediment-water interface were studied. Influenceof dissolved oxygen on ammonia-oxidizing microorganism community structure andabundance in surface sediments were explored by establishing clone library andreal-time PCR. And then examination of the survival of ammonia-oxidizingmicroorganism in enrichment culture conditions and effect of dissolved oxygen onammonia-oxidizing microorganism community structure also conducted throughDGGE. The main conclusions are as follows:The ways of NH4+–N release and oxidation in sediments with different vegetationwere significantly different under four dissolved oxygen conditions. Firstly, therelease of NH4+–N from mangrove sediments to overlying water was0.9~3.5timesthan mudflat sediments. The amount of NH4+–N release was lower at high DOcondition than that at low DO condition. Secondly, the release rate and oxidation rateof NH4+–N in the mangrove sediments were higher than that in the mudflat sediments.The reason was possibly that the microorganism species in mangrove sediments werericher than mudflat sediments, resulting in the higher degree of the mineralization andnitrification in mangrove sediments.In contrast to reports that AOA were far more abundant than AOB in bothterrestrial and marine systems, the real-time PCR estimates in this study indicated thatAOB amoA copy numbers were greater than AOA amoA in unvegetated bare mudflat zone, AOA was only significantly more abundant in hypoxic condition in mangrovesediment. AOB diversity index (Shannon-Wiener index)(0.367~1.999) in sedimentswas much higher than that of ammonia oxidizing archaea (0~0.896). AOBcommunity composition showed more sensitive to DO than AOA. Both AOA andAOB recovered from the sediments seemingly had regional specificity. All of theAOB sequences were grouped into Nitrosospira cluster and Nitrosomonas cluster. AllAOA sequences fell in cluster S (soil/sediment) and were closely related to thosefound in a variety of environments such as the mangrove sediments, estuarinesediments or some kinds of soil. The nitrification rate was positively related withAOA abundance but not AOB abundance, demonstrating the ecological importance ofAOA.A large portion of ammonia-oxidizing microbes were survived after140denrichment culture. DO affected not only the community structure ofammonia-oxidizing microorganism, but also the rate of ammonia oxidation. Thediversity of AOB was2.00and2.05under saturated and aerobic condition, it was2.29and2.03for AOA, while it was1.76and1.80respectively for AOB underhypoxia and anaerobic condition, and1.27and2.21for AOA. At higher DO level(saturated and aerobic) the ammonia-oxidizing rate were14.20mg·L-1·d-1and13.36mg·L-1·d-1and the conversation rate of NH4+-N were93.8%and88.2%respectively;however, at lower DO level (hypoxia and anaerobic) the ammonia-oxidizing ratewere7.82mg·L-1·d and5.66mg·L-1·d-1while the conversation rate of NH4+-N were51.7%and37.4%-1. It showed that ammonia oxidation rate have highly significantpositive correlation with DO level and Shannon index of AOB community and hadsignificant positive correlation with AOB community Simpson index, however, it hadno significant correlation with AOA.In summary, the DO influence ammonia the release and oxidation in sediment, thereason is the dissolved oxygen affects the community structure and abundance ofammonia-oxidizing microorganisms. This paper will provide basic data for thecomprehension of nitrogen biogeochemical cycle in coastal estuarine wetlands.