Study On The Effect Of Fire On Soil Microorganism And Enzyme Activity In Larix Gmelinii Forest

Our research object is the burned area in Larix gmelinii forest, the fire occurred in 1996,2003,2009 and 2012 respectively, in different degree of burned areas, soil microbial quantity, microbial biomass carbon and nitrogen and the change of soil enzyme activity, the mutual relationship between the indexes and environmental factors were studied. The results show that:1. The effect of fire on the number of microorganismsThe dynamic of soil microbial quantity is obvious at both burned and unburned areas, the number of bacteria and fungi shows a single peak trend, reaching the maximum in June and July respectively; the Number of actinomycetes is the biggest in May, showing a trend of decline, a peak appeared in September. The dynamic of soil microbial quantity in light burned area is the same with burned area, while there are some differences between severe burned area and burned area in some months.The change of soil microbial quantity is different in different years and different degrees of burned areas. The number of actinomycetes and fungi increased in light burned area, the number of bacteria decreased first and then increased, with the passage of time the difference narrowed, microbial quantity in severe burned area is lower to unburned area in a short period of time after fire, changing with the time is not obvious, but in the end, there were not significant difference between them.In different degree of burned areas, the impact of environmental factors on soil microbial quantity is different. Microbial quantity mainly affected by the organic carbon and total nitrogen in unburned areas. Microbial quantity, in the light burned areas, is not only related to the organic carbon and total nitrogen, also associated with available nutrients. Microbial quantity, in severe burns, mainly is affected by the available nutrients, pH and moisture content.2. The effect of fire on soil microbial biomass carbon and nitrogenThe dynamic of soil microbial biomass carbon and nitrogen is obvious at both burned and unburned areas, The dynamic of soil microbial biomass carbon and nitrogen, in light burned area, is the same with the unburned area, showing a peak in July, a minimum in June and September respectively. The dynamic of soil microbial biomass carbon and nitrogen, in severe burned area, appeared the maximum value in June and July respectively, and only one minimum in September.The soil microbial biomass carbon and nitrogen content in the burned areas belows to the unburned areas,1 year after the fire, and microbial biomass carbon and nitrogen content reduce more with the increase of the degree of fire. In 2 years after the fire, the soil microbial biomass carbon and nitrogen content, in light burned areas, is above to unburned areas, until 18 years after the fire. While it is lower in severe burned areas until 18 years after the fire.In different degree of burned areas, the impact of environmental factors on soil microbial biomass carbon and nitrogen content is different. Compared with unburned areas, in light burned areas, microbial biomass carbon is correlated with total nitrogen, available potassium, total nitrogen content, microbial biomass nitrogen is correlated with pH. In severe burned areas, microbial biomass carbon is correlated with total nitrogen, the correlation between microbial biomass nitrogen and organic carbon is weaken.3. The effect of fire on soil enzymeThe dynamic of soil enzyme is obvious at both burned and unburned areas, soil urease and sucrase were peaked in June and July, and in September for the minimum; Catalase activity reached minimum and maximum in June and August respectively. In addition to the catalase in severe burned areas, the dynamic soil enzyme activity in burned areas are similar with unburned areas.The change of soil enzyme is different in different years and different degrees of burned areas. In light burned areas, soil catalase recover faster, only 2 years after the fire has reached to the level of unburned areas, while urease and sucrase return to the normal level in 5 years and 11 years after fire. Soil enzyme activity in severe areas, after many years of recovery, is still lower than unburned areas.Soil urease and sucrase are more sensitive to fire, while catalase are less affected by the fire, soil invertase are greatly influenced by pH. The influence factor of soil enzyme activity changed after fire, compared with unburned areas, soil enzyme activity is affected by the microbial after fire. In light burned areas, invertase activity are affected by fungi; In severe burned areas, sucrase and urease are affected by fungi, catalase are correlated with the bacteria.