Microbial diversity in three floodplain soils at the Elbe River (Germany)
Introduction
Wetlands function as important links between terrestrial and aquatic systems. Past studies paid little attention to soils in semi-terrestrial ecosystems, their properties and ecological processes (Reddy and Patrick, 1993). Consequently, semi-terrestrial soils, especially floodplain soils have been researched relatively little in comparison to terrestrial soils.
Floodplain soils are underlying largely fluctuations in water table and therefore various soil moisture conditions. Frequently, they have an oxidized soil body that allows aerobic processes to occur. However, they can become reduced when submerged. Floodplain soils are often characterized through high carbon contents due to high intensity of accumulation of organic material (Rinklebe, 2004).
It is well known that water and its biological availability is an important factor influencing soil microbial diversity. The soil microbial biomass is the living portion of soil organic matter and a principle component of the decomposer subsystem regulating nutrient cycling, energy flow and ecosystem productivity (Wardle, 1998). The substrate-induced respiration (SIR) method (Anderson and Domsch, 1978) utilizes the physiological respiration response of soil organisms to substrate amendment to provide an estimate of soil microbial biomass carbon. It has frequently been shown that soil microbial biomass decline upon drying and increase upon rewetting (Orchard and Cook, 1983; West et al., 1988, West et al., 1992; Wardle, 1998), whereas drying and rewetting of soils caused a decrease in microbial biomass (Van Gestel et al., 1993). Nevertheless, positive relationships between soil moisture and microbial biomass are not universal, and negative relations between these variables, mostly in conditions of high soil moisture, have sometimes been detected (Wardle, 1998; Rinklebe, 2004).
Generally, soil microbial biomass can be limited by soil moisture under both dry and wet conditions. Exposure of microbial communities to fluctuating moisture may lead to selection for organisms better adapted to these conditions. Although some researchers studied the effect of dry/wet cycles on soil microbial communities under different farming systems (Lundquist et al., 1999a) or on available carbon sources in the laboratory (Lundquist et al., 1999b), there is a gap to quantify impacts of flooding duration and type of soil on microbial diversity in floodplain soils, both in the laboratory and in the field.
Phospholipid fatty acids (PLFAs) are major constituents of the cell membranes of all microorganisms (Vestal and White, 1989). The large variety of PLFAs present in living organisms and extracted from soil may provide a unique fingerprint of the viable microbial community of a given soil, at a given time (Bossio and Scow, 1998; Lundquist et al., 1999a). Using multivariate statistical analyses, this variation in fatty acid (FA) composition between microorganisms can be exploited, revealing differences between microbial communities (Bossio et al., 1998; Macalady et al., 2000; Pennanen, 2001). Certain PLFAs are related to functional groups of organisms and appear promising in their use as biomarkers for these organism groups (Vestal and White, 1989). Zelles (1999) proposed that the classification of PLFAs into a number of fractions should simplify the evaluating procedure and improve the assessment of soil microbial communities. The PLFA method can provide information on a variety of microbial characteristics, such as biomass, physiology, taxonomic and functional identity, and overall community composition (Green and Scow, 2000).
In the research of terrestrial soils (e.g. Frostegård et al., 1993a; Zelles, 1999; Pennanen, 2001), sediment microbiology (e.g. Rajendran et al., 1992; Macalady et al., 2000) or groundwater microbiology (e.g. Green and Scow, 2000) the use of lipid-based techniques is well established. Several studies determined the soil microbial biomass (Gaunt, 1993; Witt, 1997), the metabolic diversity of microbial communities (Bossio and Scow, 1995) or PLFA (Bossio and Scow, 1998; Bai et al., 2000; Nakamura et al., 2003) in paddy rice fields. Only a few reports investigated soil respiration (Megonigal et al., 1996) or the impact of inundation dynamics and different management systems on soil respiration, and diverse enzyme activities (Emmerling, 1993) in floodplain soils. However, the microbial diversity in floodplain soils is poorly understood.
We hypothesized that the environmental conditions to which floodplain soils have been exposed (mainly inundation regime) may affect soil microbial biomass, function and community composition. To examine and to quantify these impacts we determined soil microbial carbon (Cmic), basal respiration (BR), metabolic quotient (qCO2), Cmic/Corg ratio, and PLFA in three selected floodplain soils at the Elbe River (Germany). Our objectives were (i) to characterize microbial diversity in three floodplain soils, and (ii) to discriminate these soils with microbial parameters.
Section snippets
Site and soils
The study site is located at the Elbe River (stream kilometre 417), 102 km north-westerly of Berlin, Germany (52°48′00″N, 12°02′15″E). The long-term annual precipitation is 449 mm and the long-term annual mean air temperature is 8.0 °C. The study site is periodically flooded. High flood events are closely related to the hydrometeorological conditions in the catchment area, which are fed predominantly by snow melting (winter and spring) and heavy rainfall (spring and summer).
After 8 years research
Results
Cmic and PLFA-biomass increased in the order GLe<FLe<FLm (Table 2, Fig. 1) according to the elevational and hydrological gradient (Table 1). Cmic/Corg ratios ranged between 0.41 and 1.16 and revealed the same ranking over the three soils like Cmic (Table 2). Contrary, qCO2 and BR are highest in GLe and lowest in FLm (Table 2) according to flooding duration (Table 1).
PLFA patterns of 26 FAs were analysed for characterization of the microbial community structures. The identified FAs, the
Discussion
Differences in the topography of floodplains are usually slight but cause mostly in important hydrological differences, which generally correspond with type of soil. FLe, FLm and GLe are commonly found along the Elbe River (Rinklebe, 2004). The floodplains in the Elbe area are dominated of fine-grained sediments. This so-called “Auenlehm” (meadow loam) covers the surface of large areas of today's meadows at the Elbe River. Dominating soils are FLe. Flood channels and depressions are embedded in
Conclusion
PLFAs, Cmic, BR, qCO2, and Cmic/Corg ratio in the three floodplain soils were strongly influenced by the gradient in elevation, type of soil, flooding duration, and time since the soils were last flooded. Different plant communities and their residues as well as pH value may influence the microbial diversity additionally. The soil microbial properties chosen here are suitable to estimate microbial diversity in floodplain soils at the Elbe River. Additional data will be necessary to determine
Acknowledgements
We thank Mrs. A. Gurenowitz for laboratory assistance and the anonymous reviewers.
References (55)
Microbial eco-physiological indicators to asses soil quality
Agriculture, Ecosystems and Environment
(2003)- et al.
A physiological method for the quantitative measurement of microbial biomass in soils
Soil Biology & Biochemistry
(1978) - et al.
Ratios of microbial biomass carbon to total organic carbon in arable soils
Soil Biology & Biochemistry
(1989) - et al.
The metabolic quotient for CO2 (qCO2) as a specific activity parameter to assess the effects of environmental conditions, such as pH, on the microbial biomass of forest soils
Soil Biology & Biochemistry
(1993) - et al.
Relationship between SIR and FE estimates of microbial biomass C in deciduous forest soils at different pH
Soil Biology & Biochemistry
(1997) - et al.
Relationships between soil microbial biomass determined by chloroform fumigation-extraction, substrate-induced respiration, and phospholipid fatty acid analysis
Soil Biology & Biochemistry
(2002) - et al.
Microbial biomass measured as total lipid phosphate in soils of different organic content
J. Microbiol. Methods
(1991) - et al.
Shifts in the structure of soil microbial communities in limed forests as revealed by phospholipid fatty acid analysis
Soil Biology & Biochemistry
(1993) - et al.
Estimation of conversion factors for fungal biomass determination in compost using ergosterol and PLFA 18:2ω6,9
Soil Biology & Biochemistry
(2004) - et al.
Rapid response of soil microbial communities from conventional, low input, and organic farming systems to a wet/dry cycle
Soil Biology & Biochemistry
(1999)
Wet-dry cycles affect dissolved organic carbon in two California agricultural soils
Soil Biology & Biochemistry
Soil microbial eco-physiology as affected by short-term variations in environmental conditions
Soil Biology & Biochemistry
Size, activity and catabolic diversity of the soil microbial biomass as affected by land use
Applied Soil Ecology
Relationship between soil respiration and soil moisture
Soil Biology & Biochemistry
Microbial communities in boreal coniferous forest humus exposed to heavy metals and changes in soil pH—a summary of the use of phospholipid fatty acids, Biolog® and 3H-thymidine incorporation methods in field studies
Geoderma
Microbial biomass and activity in soils with fluctuating water contents
Geoderma
Controls of temporal variability of the soil microbial biomass: a global-scale synthesis. Review
Soil Biology & Biochemistry
A critique of the microbial metabolic quotient (qCO2) as a bioindicator of disturbance and ecosystem development
Soil Biology & Biochemistry
Phospholipid fatty acid profiles in selected members of soil microbial communities
Chemosphere
The use of neutral lipid fatty acids to indicate the physiological conditions of soil fungi
Microbial Ecology
Soil bacterial biomass, activity, phospholipid fatty acid pattern, and pH tolerance in an area polluted with alkaline crust deposition
Applied and Environmental Microbiology
Characterization of microbial consortia in paddy rice soil by phospholipid analysis
Microbial Ecology
Impact of carbon and flooding on the metabolic diversity of microbial communities in soils
Applied and Environmental Microbiology
Impacts of carbon and flooding on soil microbial communities: phospholipid fatty acid profiles and substrate utilization patterns
Microbial Ecology
Determinants of soil microbial communities: effects of agricultural management, season, and soil type on phospholipid fatty acid profiles
Microbial Ecology
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