Influences Of Wildfire On Soil Microbial Community In A Shrubby Ecosystem

Object:Fire, as an important disturbance, not only affects ecological environment and biologic community of the upper storey, but also the belowground ecological system. Microorganisms is one of essential parts of soils, which are participants of transport and cycle of materials in the soils, and act as engineers and maintainers of soil structure and fertility. Microorganisms have their own characteristics to be different from other organisms, they are more sensitive to disturbance, so they can respone to the changes of environment immediately. The process and mode of succession in microbial community are different from vegetation post-fire. The study on the immediate changes and succession in soil microbial community structure can determine ecological processes of the microbes after wilfires, and improve our understanding of the ecological role of wilfires in forest ecosystems.Methods:Burned and unburned soils were sampled 18 hours after a shrubbery fire in Yumin county of Xinjiang, Northwest China. Two archaeal 16S rRNA gene clone libraries and two bacterial 16S rRNA gene clone libraries were generated from total genomic DNA in the two soils. We evaluated the immediate influences of the wildfire on the soil archaeal and baterial community structure through comparing between the two archaeal clone libraries, and between two bacterial clone libraries from burned and unburned soils. We sampled burned and unburned soils 1d,2,4,8, 10,12,15 monthes after the fire, and amplified bacterial 16S rRNA gene sequences labeled by fluorophores from total genomic DNA extracted of the two treatment soils. The variation in soil bacterial community structure after fire was monitored by comparing T-RFLP (Terminal Restriction Fragment Length Polymorphism) profiles of bacterial 16S rRNA sequences. We determined microbial functional diversity of burned soils sampled 1 d,2,4,8,10,12,15 months after the fire using BIOLOG technique.Results:The results of study on rapid responses of soil microbial community to wildfires showed that (1) Both Shannon index and Simpson index of archaeal community were low after 18 h after a shrubbery fire. Nine archaeal taxonomic units with low abundance in unburned soils did not detect in the burned soils. The relative aboundance of three dominant archaeal taxonomic units did not change significantly after the fire. (2) Bacterial community compostion in fire-impacted soil was significant different from the control unburned soils (p<0.05). The percentages of alphaproteobacteria, betaproteobacteria, gammaproteobacteria, actinobacteria, gemmatimona-detes were increased immediately after fire, certain groups in these bacterial phylum were concentrated and their relative aboundance increased.Through comparing profiles of T-RFLP of bacterial 16S rRNA gene sequences from soil sampled different time post fire, we found (1) 2 months after fire, the number of soil bacterial taxonomic group was lower and bacterial community structure of the burned soils was more significantly different from the control soil than other time after fire, and new dominant bacterial groups which may be from oxalobacteraceae generated. However, relative aboundance of population from acidobacteria which was dominant in soil pre-fire decreased significantly at this time. (2) Certain bacterial groups recovered in the burned soils 1 year post fire, and bacterial diversity increased more significantly than 2,4,8,10 months after fire. (3) 15 month after fire, bacterial diversity at burned sites was still lower than unburned sites, and baterial community structure was differernt from the control soils.The results of research on microbial functional diversity of burned soils different time after fire suggested that (1) Soil microbial activity was lower and metabolism characteristic was more significantly different from microbial community in the control soils 1d after fire than the other time after fire (2) Soil microbial activity and founctional diversity increased gradually along extending of the time after fire, and was similar to unburned sites at 15 months after fire.Conclusions:(1) When time after high severity shrubbery fire was at hourly scale, diversity of soil archaea was low, groups of archaea with low abundance were more sensitive to fire disturbance than those with high abundance. Bacterial community compostion was altered significantly, certain groups were concentrated and their relative aboundance increased immeditaly after fire. (2) Soil microbial community occurred obvious secondary succession in 15 months after fire. Recovery of microorganism was more significant at 1 year after fire (summer of the second year) than other time. (3) Soil microbial activity and founctional diversity were lowest 1 d after fire and increased processively among 15 monthes after fire.