| The atmosphere greenhouse gases mainly include carbon dioxide(CO2), methane(CH4) and nitrous oxide(N2O). Although there are abundant CO2 in the atmosphere, the single molecule CH4 has the warming potential of 20-30 times than CO2. There are many soures of CH4, the major sinks of methane are photochemical oxidation by the hydroxyl radical in the atmosphere and biological oxidation by the methanotrophs in the aerobic soil. The soil of grassland is loose, and it is a major sink of CH4. Despite the great number of studies about methane uptake in grasslands and its response to grazing, only a few focused on the change in methanotrophic community structure and activity. This study aimed to investigate the methanotrophic community structure and methanotrophs abundance in different enclosure time, and try to reveal the relationship between methanotrophic community structure and CH4 flux.In this study we chose typical grasslands in Xilin River Basin of Inner Mongolia, China to investigate methanotrophic community structure and activity under different enclosure treatments: 79E(grassland enclosed since 1979), 99E(grassland enclosed since 1999) and G(freely-grazed grassland). The soil DNA was extracted in three treatments, then the DNA was used to amplify the functional gene(pmoA) using specific primer, the PCR products was analyze by the clone library. The methanotrophs abundance was confirmed by real PCR. At the same time, in order to confirm the methanotrophic activity, the incubation experiment was conducted at 18°C and 28°C.The results showed that Type I was the main methanotrophic cluster in three treatments, Type II metahnotrophs was the barely cluster to which only one OUT belonged and it only existed in G. Cluster analysis showed that with the increase of enclosure time, methantrophic community composition of 99 E first clustered with 79 E, then with G. In combination with that of previous study, this result indicated that methanotrophic community structure has a obvious change with the increasing enclose time. Methanotrophic abundance(represented by the pmoA gene copies per gram of dry weight soil) decreased with the enclosure time as G(4.5×107) > 99E(2.8×107) >79E(2.0×107), This indicated that methanotrophic abundance decreased with the increasing enclose time, and the USC-γ cluster had the largest abundance in three treatments. Seen from the incubation experiment, the activity of methanotrophs increased with the increasing of temperature. Among the three types of grassland, 79 E had the lowest temperature sensitivity, indicating that its methanotrophic community structure should be the most tolerant to environmental change. Therefore, 79 E was more likely to maintain the stability of methanotrophic activity under global change. With the highest temperature sensitivity, 99 E is an instable grassland ecosystem since it situates in the transition period. Competition among microbes in the instable environment of 99 E may cause greater fluctuation in methanotrophic activity. However, with time it would gradually become as resilient to the global change as 79 E is today. For free grazing grassland, although it has high methanotrophic activity at a certain stage in this plot, the higher temperature sensitivity showed that the methanotrophic activity was still uncertain, depending on the environmental conditions. All in all, the activity of methanotrophs will be strengthen under global warming. |
PDF Full Text Request