Soil moisture condition is heterogeneous and a key causative factor of spatial variation of ecosystem structure and function in wetlands. Microorganisms mediate fundamental processes in wetland ecosystems, such as C and N turnover, and are sensitive to soil moisture conditions. However, effects of soil moisture on microbial community have been poorly studied in alpine wetland at low latitude. Zoige alpine wetland is located in the east part of the Qinghai-Tibetan Plateau. It is the highest wetland, with the altitude of approximate 3400 m, and characterized by low temperature as well as low latitude (32°10' 34°10'N). To clarify the influence of soil water content on microbial diversity in Zoige alpine wetland, community structures were characterized for soil microorganisms from two sites with contrastive soil moisture conditions.
Soil samples were collected to the depth of 10 cm from neighboring flooding (down slope) and non-flooding (upslope) sites, 6 km away from the Flower Lake side in April (cold season) and August (warm season), 2007. Soil physical and chemical properties were measured using traditional methods. Phospholipid fatty acids (PLFAs) analysis was applied to determine soil microbial biomasses and investigate microbial community structure. Dilution-plate method was used to compare bacterial colonies under temperature gradient of 15℃, 25℃, and 37℃.
Results showed that soil organic carbon content, total nitrogen content and pH value were significantly higher in flooding soil than non-flooding soil. It could be attributed to the low decomposition rate of organic matter due to permanent inundation in the former site. PLFA analysis identified 17 different fatty acids in all sampling sites. The PLFA profiles were dominated by 16 ∶ 1ω7c, i16 ∶ 0, 18 ∶ 1ω9c, 18 ∶ 1ω8c, which together accounted for approximately 51.02%-61.64% of the total PLFA. Three of them were the biomarkers of gram-negative bacteria. Total microbial biomass, bacterial biomass, gram-positive and gram-negative bacterial biomass were all higher in flooding soil, and were higher in April than in August. High soil organic carbon content in flooding soil might partially explain high microbial biomass there. Plate counting demonstrated higher bacterial colonies at 15 ℃ than at 25 ℃ and 37 ℃, which might account for higher bacterial biomass in cold season. Gram-negative bacterial biomass was higher than gram-positive bacteria in all sampling sites, which might be attributed to the high pH value of Zoige wetland soil. PLFA analysis revealed that the aerobic fungi and actinomycetes had higher biomass in non-flooding soil with more aeration pores than flooding site, and were all higher in cold season than in warm season. Fungi:bacteria PLFA ratio which reflected microbial community structure was also higher in non-flooding soil. However, the ratio hadn't been affected by the seasonal variation.
Principal component analysis exhibited a significant difference in microbial community structures between the two sites, in both cold and warm seasons. However, the difference was insignificant between cold and warm seasons in either site.
The results suggested that soil moisture condition was likely the main factor controlling the spatial and temporal variation of microbial community structure in Zoige alpine wetland. And there might be a lager quantity of cold-adaptive microbes in this ecosystem.