N2O emissions of karst wetlands,rice fields,and abandoned rice fields and their correlation with communities of nitrifying and denitrifying bacteria
In order to study the effect of land use on nitrifying and denitrifying bacteria and nitrous oxide(N2O)emission in karst wetlands,natural wetlands,rice paddies and rice paddies abandoned land in Huixian karst wetlands were used as research site,and the relative abundance and absolute abundance of nitrifying and denitrifying bacteria communities,as well as the N2O emission rate and flux were determined by high-throughput sequencing,real-time PCR and static dark box combined with gas chromatography.The results showed that the overall in situ N2O emission rates in NWs were significantly higher than those in PF and in APF during the growth period of rice.The N2O flux in NW,PF,and APF were 1.07,0.38,0.20 kg·hm-2,respectively.During the mature stage,the absolute abundance of nitrifying bacteria in PF was significantly higher than in NW and in APF,whereas there was no significant difference in the absolute abundance of both nitrifying and denitrifying bacteria between NW and APF.The relative abundance of Nitrosospira,the most abundant nitrifying bacteria,was significantly higher in APF(83.28%)and PF(82.75%)than in NW(68.52%).The relative abundance of Pseudogulbenkiania,the most abundant denitrifying bacteria,was highest in APF(29.49%),followed by PF(21.24%),and lowest in NW(16.26%).The above research results indicate that long-term rice planting in karst wetlands reduces N2O emissions during the rice-growing season and changes the diversities of nitrifying and denitrifying bacterial populations during the mature stage.Therefore,in terms of N2O emissions alone,it is reasonable to maintain rice cultivation in karst wetland systems.
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