Microbes Environ. Vol. 19, No. 2, 154–162, 2004
http://wwwsoc.nii.ac.jp/jsme2/
Microbial Biomass, Abundance and Community Diversity Determined by Terminal Restriction Fragment Length Polymorphism Analysis in Soil at Varying Periods after Occurrence of Forest Fire JHONAMIE A. MABUHAY1*, YUJI ISAGI1 and NOBUKAZU NAKAGOSHI1 1
Graduate School for International Development and Cooperation Hiroshima University, 1–5–1 Kagamiyama, Higashi-Hiroshima 739–8529, Japan
(Received January 29, 2004—Accepted April 7, 2004) This study was conducted to gain knowledge about how microbial communities are affected by burning, and to know their present conditions at various periods after the occurrence of forest fires. It aimed to determine the microbial community diversity, biomass carbon and microbial abundance in soil. Six different sites in Hiroshima prefecture, Japan were chosen for this study, 5 sites in burned forest areas (2 months, and 3, 6, 9 and 25 years, after fire) and a control site (an undisturbed forest). From a simple count of the number of TRFs (Terminal Restriction Fragments), the burned areas showed low community diversity even many years after fire. The biomass carbon in burned areas was low, even 25 years post fire. In terms of microbial abundance, the overall result showed that the undisturbed forest (control) had the largest number of gram-positive and gram-negative bacteria, actinomycetes and fungi, while of all the burned sites, the area burned 2 months before being studied had the highest microbial count. These results show that forest wildfires can have a long-term effect on microbial biomass, abundance and diversity in soil. Key words: Abundance, Community diversity, Forest fire, Microbial biomass, TRFLP, 16S rRNA genes
Wildfire, as an intrinsic part of natural and managed landscapes, can have short-term, detrimental effects and longterm importance6). Recently, fire disturbance has received a great deal of attention because of its critical role in the environment. Fire maintains the diversity of the ecosystem by decreasing the dominance of competitive species, regulating plant biomass and releasing nutrients retained for decades in recalcitrant organic compounds47). Temperatures generated by fire that are higher than 50°C result in the death of heat sensitive microbes, whereas temperatures higher than 70°C can kill vegetation18,33). Many microorganisms can be killed during forest fires, but the changes in habitat after fire affect the microbial population to a greater degree37). Also, the combustion of organic matter at exceedingly high temperatures can result in volatilization and potential loss of nitro* Corresponding author; E-mail:
[email protected], Tel & Fax: +81–82–424–6957
gen previously found in complex organic form17). Fire alters soil chemical composition15) directly, via the decomposition of clay minerals, and indirectly, by converting complex organic structures into simple inorganic forms8). The overall effects of fire on ecosystems are complex, ranging from the reduction or elimination of aboveground biomass, to impacts on belowground physical, chemical and microbially mediated processes. Since a key component of overall ecosystem sustainability occurs belowground, recovery is tied to the soil’s physical, chemical, and biological functions and processes33). Soil microbial communities are among the most complex, diverse, and important assemblages in the biosphere43). The greatest microbial diversity on a small scale is found in soil. Analysis of genetic diversity in soil communities by DNA renaturation suggests that there are approximately 1.3– 2.3´102 different genome equivalents per gram of soil42). Since soil microorganisms can respond rapidly, they are
Soil Microbiology after Forest Fire
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often considered when monitoring soil status. Microorganisms regulate the decomposition of organic matter and nutrient availability, initiate and maintain soil structure, and remove organic contaminants from soil profiles24). The microbial biomass plays an important role as a pool of mineral nutrients in the soil6). With the development of four widely used indirect methods, fumigation-incubation (FI), substrate-induced respiration (SIR), fumigation-extraction (FE), and ATP content3,20,21,30,45), a great deal of effort has gone into the measurement of the size of microbial biomass and its associated nutrient pools. All these methods are designed to quantify the microbial biomass carbon in different soil samples, soil horizons, soil profiles and sites12). Microbial biomass is a very important factor that influences C and N mineralization in soils, and can be an indicator of the present status of a soil’s health. Genetic approaches to the characterization of microbial diversity have gained popularity in the field of ecology. A rapid analysis of diversity in complex microbial communities has remained an elusive but important goal in microbial ecology11). The ability to amplify genes from the total microbial population has provided the potential to study microbial community structure and population dynamics in both natural and managed environments. Direct amplification of bacterial 16S rRNA genes from extracted soil DNA provides the most comprehensive and flexible means of sampling bacterial communities11). This study used the terminal restriction fragment length polymorphism (TRFLP) analysis11,16,26) for community fingerprinting, to obtain information about the relative diversity in the microbial community of soil after a forest fire. The reason for using this method is to give a picture of overall community diversity all at once16). Following wildfires, changes in physiological groups of microorganisms may occur1). Acea and Carballas1) pointed out that, in the shortterm, burning resulted in a decrease in the number of cellulase-producers, while amylase-produc-
Table 1.
ers and ammonifying microbes increased, but, in the long term, the effect of burning would be nil on ammonifiers, somewhat negative on cellulolytic and amylolytic microbes, and slightly positive on nitrite- and nitrate formers. Vazquez et al.46) showed that, in the shortterm, aerobic heterotrophic bacteria are stimulated by fire, while cyanobacteria, algae and fungi are depressed, but, in the longterm, positive effects on fungal propagules, cyanobacteria and algae were observed. This study aimed to determine the community diversity, microbial biomass carbon and microbial abundance in soil following a forest fire. We have not found studies analogous to this one describing the microbial diversity at various periods after the occurrence of wildfires. Most previous studies were conducted at the biomass and activity levels, and focused on few specific types of microorganisms. The aim of this study is to aid in our understanding of the status of microbial communities at different periods after fire.
Materials and Methods Study sites and soil sampling Six different sites in Hiroshima prefecture, Japan, were selected for this study (Table 1). This region has a warmtemperate monsoon climate. The monthly mean air temperature reaches its maximum in August and minimum in January or February. Precipitation is lower in winter and higher throughout the summer, except in August39). The study areas were selected according to the years since the occurrence of wildfires. Post-fire areas with similar geographical and climatic characteristics were chosen for a better comparison of the microbial status. The first site was on Etajima Island, where one of the largest forest wildfires in Japan in recent years occurred. The second site in Mihara was a secondary pine forest. The third site was in Yasuura-cho, and was previously dominated by pine trees, with some small patches of fruit-tree plantations. The fourth area, in Oono-cho, was
Characteristics of the study sites
Study sites
Period after fire
Date of occurrence of fire
Area burned
Season when fire occurred
Cryptomeria sp. 40 yrs old height (m)
Chamaecyparis sp. 40 yrs old height (m)
Pinus sp. 40 yrs old height (m)
Average slope (degrees)
Onomichi Oono-cho Yasuura Mihara Etajima Kagamiyama
2 months 3 yrs 6 yrs 9 yrs 25 yrs control
3 Dec 02 2 May 99 8 Mar 97 11 Aug 94 1 June 78 —
>10 ha 136 ha 185 ha 352 ha 1005 ha —
Winter Spring Spring Summer Summer —
8–
