Phospholipid fatty acid analysis was applied to study the microbial community structural characteristics and dynamic changes in different substrate layers, among different aggregate size classes and during winter operation period in Integrated Vertical-flow Constructed Wetland (IVCW). In conjunction with measurements of soil physical and chemical properties, microbial biomass and substrate enzyme activities, the relationship between wetland microbial community structure and function, and the influences of certain environmental factors on them, were discussed. The work could further clarify the purification mechanisms in IVCW and contribute to the theoretical basis for optimizing the operation and management of IVCW. The main results were summarized as followed:
1．PLFA composition of the substrate was dominated by the saturated fatty acid, branched fatty acid and monounsaturated fatty acid; the contents of polyunsaturated fatty acid and cyclopropane fatty acid were relatively small in amount. The ratios of characteristic fatty acids showed vertical distribution pattern. The aerobic prokaryotes in substrate were predominant groups, followed by the gram-positive bacteria and other anaerobic bacteria; and microeukaryotes accounted for the lowest proportion. The distribution of biomarker PLFAs of microbial functional groups indicated that there were distinct aerobic and facultative anaerobic function areas in the wetland system.
2．The contents of organic matter and total nitrogen (TN) showed a decreasing trend with the increase of aggregate size class; total phosphorus (TP) in substrate was greater in <0.5mm or >1.0mm aggregate size fractions. Aggregate size (0.25mm-2.0mm) had a minor influence on microbial PLFA profiles, and the differences between sampling sites would alter the distribution pattern of PLFA profiles in substrate aggregate. The relative contents of biomarker PLFAs of gram-negative bacteria and fungi correlated with aggregate size, but gram-positive bacteria proportions showed no significant differences among aggregate size classes.
3．In winter, wetland microbial biomass and activity were decreased drastically, while extracellular enzyme activities maintained at a certain level. With alteration of season, the unsaturation degree of total PLFA significantly increased, PLFA profiles clearly undergone a shift，which indicated that the gram-negative bacterial became the predominant group in substrate microbial community, and the microbial community diversity decreased significantly. The indicators of microbial community structure and function showed obvious different response patterns to seasonal change. This result revealed that wetland microbial community adapted to low temperature mainly by recomposing community structure, and the steady high level of extracellular enzyme activities reflected the response of microbial community to poor nutrients supply in winter.