Friedrich Beese

Signature fatty acids in phospholipids and lipopolysaccharides as indicators of microbial biomass and community structure in agricultural soils

Abstract Soil samples were taken from eight long-term agricultural monoculture and rotation experimental plots and examined for their profiles of fatty acids in either phospholipid or lipopolysaccharide fractions. The more specific constituents related to microorganisms were tested for their ability to estimate the biomass and to differentiate community structure.More than100 fatty acids, including unsubstituted, straight- and branched-chain,unsaturated and hydroxy fatty acids were detected in the soils sampled.Good correlations between the total amounts of fatty acids derived from phospholipids and the microbial biomasses and activities obtained by different classical procedures were observed (correlation coefficients were above 0.97). This indicates that the fatty acids were closely linked to soil microorganisms and that this method can be used in the study of soil microbial ecology.In addition,each of the eight soils was characterized by its own pattern of fatty acids, either as phospholipids,or as lipopolysaccharides.This shows that this method has the potential to differentiate between the soils,even on a management level.The most apparent difference was registered in terms of the relation of the monoenoic to the normal fatty acids among the eight soils.The black fallow and the fields cultivated with potatoes showed approximately equal amounts of both, the green fallow and the fields cultivated with wheat displayed a ratio of 1.7:1.0 and the grassland 1.3:1.0. The soil with crop rotation showed considerably more fatty acids in terms of the number in the normal fraction,while the grassland contained more hydroxy fatty acids than the soils from arable land.

Seasonal variation of N2O and CH4 fluxes in differently managed arable soils in southern Germany

Agricultural practices are assumed to contribute significantly to the increase in atmospheric nitrous oxide (N 2 O) concentrations observed in the last decades, and they might influence the consumption of atmospheric methane (CH 4 ) by soil. The aim of this study was to quantify the effects of management intensity, soil type, and frost periods on the emission of N 2 O and the consumption of CH 4 in rotations in southern Germany. Fluxes of N 2 O and CH 4 were monitored over 12 months, using a closed chamber technique. The extensively managed system was cropped to sunflower and fertilized with farmyard manure (12 t ha −1 ). The intensively managed field was planted with spring wheat and fertilized with a total of 190 kg N ha −1 given as calcium ammonium nitrate (30 kg N) and urea-NH 4 NO 3 solution (160 kg N). Variation in the N 2 O emissions with time was extremcly high, with flux rates ranging from 0 to 2700 μg m −2 h −1 . The N 2 O fluxes were influenced by soil properties, management practices, and weather. The highest release rates were measured in the winter during thawing of the frozen soil. During the growing season, N 2 O emission was highest after heavy precipitation. No strong relationship was found between N 2 O emission rates and soil factors such as soil temperature, soil moisturc, and soil nitrate content. Annual fluxes of N 2 O from the extensively managed field were 9.4 and 12.9 kg N 2 O-N ha −1 yr −1 for a sandy soil and a clay soil, respectively. Total N 2 O-N losses from the intensively fertilized field amounted to 9.6 kg ha −1 yr −1 for a silty soil with a tendency to waterlogging during wintertime and to 16.8 kg ha −1 yr −1 for a loamy colluvial soil. Up to 46% of the annual N 2 O evolution was emitted during December and January when frost/thaw cycles induced extremely high N 2 O production. The application of urea-NH 4 NO 3 solution significantly increased N 2 O emission rates. Of the 160 kg N applied, 2.9 kg N or 1.8% was lost as N 2 O within a period of 8 weeks. Rates of CH 4 -C uptake varied from 0 to 17 μg m −2 h −1 . Soil temperature correlated positively and soil moisture correlated negatively with the CH 4 consumption. Stepwise multiple linear regression, including these soil factors, explained up to 44% of the variation in CH 4 fluxes. Annual CH 4 -C uptake was rather similar for the intcnsively and extensively managed Eutrochrepts, ranging from 348 to 395 g ha −1 . Significantly higher CH 4 -C consumption of 567 g ha −1 yr −1 occurred in the colluvial soil (Typic Udifluvent). N fertilizers had no effect on the CH 4 flux rates.

Determination of phospholipid- and lipopolysaccharide-derived fatty acids as an estimate of microbial biomass and community structures in soils

Several soils subject to different cultivation and management practices were examined by analysis of fatty acid profiles derived from phospholipids and lipopolysaccharides, using an improved sequential method which is capable of measuring ester-linked and non-ester-linked phospholipid fatty acids (EL-PLFA, NEL-PLFA, respectively) and the hydroxy fatty acids in lipopolysaccharides. A good correlation was obtained (r>0.90) between the soil biomass and total EL-PLFA in the soils investigated, which ranged from forest soils to a variety of agricultural soils. Elucidation of the composition of the community structure was an additional task. Eukaryotes can be differentiated from bacteria by the presence of polyunsaturated and ω-hydroxy fatty acids, both of which were much more abundant in the OF layer of the forest soil than in the remaining samples. A relatively low proportion of monomethyl branched-chain saturated fatty acids was obtained in the forest OF horizon, these being indicators for Gram-positive bacteria and actinomycetes. Various subclasses of proteobacteria produce β and mid-chain hydroxy fatty acids, which occur primarily in agricultural soils. The ratios between monounsaturated fatty acids and saturated fatty acids seem to be very useful parameters of soil environmental conditions. In addition, on the basis of the differences in composition of the NEL-PLFA and hydroxy fatty acids of lipopolysaccharides, clear indications for the community structure of various soils were obtained. In the forest soils much more abundant anaerobic micro-organisms and relatively less abundant proteobacteria were present than in the other soils. In the cultivated soils, however, the proportion of Gram-negative bacteria was considerably higher. Furthermore, eukaryotes appeared to be pre-dominant in the soils once used for a manure deposit site.

Nitrous oxide emissions from soil during freezing and thawing periods

In a laboratory investigation, the processes of N2O emissions during freezing/thawing periods were studied. Four undisturbed soil columns from an agricultural site were subjected to two freeze/thaw cycles. Two periods of higher N2O emissions were detected, a period of elevated N2O emissions during continuous soil freezing and a period of brief peak emissions during thawing. Soil respiration indicated that microorganisms were still active in both periods. We concluded that N2O was produced by microorganisms during continuous soil freezing in an unfrozen water film on the soil matrix. This thin liquid water film was covered by a layer of frozen water. The frozen water in form of an ice layer represents a diffusion barrier which reduces oxygen supply to the microorganisms and partly prevents the release of the N2O. Peak emissions during soil thawing were explained by the physical release of trapped N2O and/or denitrification during thawing.

Microbial biomass, metabolic activity and nutritional status determined from fatty acid patterns and poly-hydroxybutyrate in agriculturally-managed soils

Abstract Soil microbial biomass, fatty acid pattern, poly-β-hydroxybutyrate content and selected physiological variables were studied in agriculturally-managed soils with different cropping histories: crop rotation, hops and grassland. Significant correlation was observed between substrate-induced respiration, the amounts of adenine nucleotides and the total amounts of phospholipid fatty acids. The highest microbial biomass was found in a grassland soil, the lowest in soils which were formerly cultivated with hops. Additionally, the highest ratio of poly-β-hydroxybutyrate: total phospholipid fatty acids, the largest specific respiration rate and the lowest amounts of the adenylate energy charge were obtained in one of the former hop yards. Due to the frequent treatment of hop plants with fungicides a large amount of copper had accumulated in this former hop yard. The condition of the soil had resulted in the creation of a microbial community with markedly different biochemical characteristics compared to communities associated with grassland soil or crop rotation soil. The principal component analysis was able to discriminate the different soils when applied to hydroxy fatty acids. The profile of fatty acids in the copper-contaminated soil indicated an increase in numbers of Gram-negative bacteria. A lower concentration of branched chain fatty acids revealed a decreased proportion of Gram-positive bacteria in both former hop yard soils.

Effect of crop-specific field management and N fertilization on N2O emissions from a fine-loamy soil

Agricultural soils are a major source of atmospheric N2O. This study was conducted to determine the effect of different crop-specific field management and N fertilization rates on N2O emissions from a fine-loamy Dystric Eutrochrept. Fluxes of N2O were measured for two years at least once a week on plots cropped with potatoes (Solanum tuberosum) fertilized with 50 or 150 kg N ha−1 a−1, winterwheat (Triticum aestivum) fertilized with 90 or 180 kg N ha−1 a−1, corn (Zea mays) fertilized with 65 or 130 kg N ha−1 a−1, and on an unfertilized, set-aside soil planted with grass (mainly Lolium perenne and Festuca rubra). The mean N2O emission rate from the differently managed plots was closely correlated to the mean soil nitrate content in the Ap horizon for the cropping period (April to October, r2 = 0.74), the winter period (November to March, r2 = 0.93, one outlier excluded), and the whole year (r2 = 0.81). N2O emissions outside the cropping period accounted for up to 58% of the annual emissions and were strongly affected by frost-thaw cycles. There was only a slight relationship between the amount of fertilizer N applied and the annual N2O emission (r2 = 0.20). The mean annual N2O-N emission from the unfertilized set-aside soil was 0.29 kg ha−1. The annual N2O-N emission from the fertilized crops for the low and the recommended rates of N fertilization were 1.34 and 2.41 kg ha−1 for corn, 2.70 and 3.64 kg ha−1 for wheat, and 5.74 and 6.93 kg ha−1 for potatoes. The high N2O emissions from potato plots were due to (i) high N2O losses from the interrow area during the cropping season and (ii) high soil nitrate contents after the potato harvest. The reduction of N fertilization (fertilizer was applied in spring and early summer) resulted in decreased N2O emissions during the cropping period. However, the emissions during the winter were not affected by the rate of N fertilization. The results show that the crop-specific field management had a great influence on the annual N2O emissions. It also affected the emissions per unit N fertilizer applied. The main reasons for this crop effect were crop-specific differences in soil nitrate and soil moisture content.

Nitrous oxide emissions from frozen soils under agricultural, fallow and forest land

In a field study, N2O emissions were measured in an agricultural, a fallow, and a forest system once a week from December 1995 to November 1996. Elevated N2O emissions were detected during periods of both soil freezing and soil thawing. The dynamics of the N2O winter emissions were influenced by the changes in soil temperatures. The highest emission rates were observed during soil thawing. The N2O emissions during the entire winter period (December 1995 to March 1996) amounted to 2.8, 1.3, and 0.7 kg N2O–N for the agricultural land, fallow and forest, respectively, and contributed to 58, 45 and 50% of the annual N2O emissions from these systems. Differences in the winter emissions among the three sites could not be explained by means of nitrate concentration but rather by water-filled pore space (WFPS). Additionally, the upper organic layers of the forest and the grass vegetation of the fallow site delayed the time of soil freezing and reduced the depth of frost penetration. Both WFPS and vegetation control the N2O emissions in winter.

N2O and CH4 fluxes in potato fields: automated measurement, management effects and temporal variation

Abstract The large temporal variation in nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) flux rates is a major source of error when estimating cumulative fluxes of these radiative active trace gases. We developed an automated system for near-continuous, long-term measurements of N2O, CH4 and CO2 fluxes from cropland soils and used it to study the temporal variation of N2O and CH4 fluxes from potato (Solanum tuberosum L.) fields during the crop periods of 1997 and 1998, and also to determine the effects of management practices and weather. Additionally, we evaluated the error of other common methods, namely, weekly or monthly measurements, used for estimating cumulative fluxes. The fluxes were quantified separately for the ridges, uncompacted interrows and tractor-compacted interrows. Total N2O–N emission from the potato field during the growing period (end of May to September) was 1.6 kg ha−1 in 1997 and 2.0 kg ha−1 in 1998; emissions were highest for the tractor-compacted soil. Periods of increased N2O losses were induced by heavy precipitation (in particular in compacted soil) and by the killing of potato tops (on the ridges) by herbicide application. The total CH4–C uptake in the potato field during the growing period was 295 g ha−1 in 1997 and 317 g ha−1 in 1998. The major fraction of the total CH4 uptake (≈86%) occurred on the ridges. Weekly measurements of N2O fluxes complemented by additional event-related flux determinations provided accurate estimates of total emissions. The monthly flux determination was not adequate for determining the temporal variation of the N2O emission rates. Weekly measurements were sufficient to provide reliable estimates of the cumulative CH4 uptake.

Potential contribution of Lumbricus terrestris L. to carbon dioxide, methane and nitrous oxide fluxes from a forest soil

Abstract Potential effects of earthworms (Lumbricus terrestris L.) inoculated into soil on fluxes of CO2, CH4 and N2O were investigated for an untreated and a limed soil under beech in open topsoil columns under field conditions for 120 days. Gas fluxes from L. terrestris, beech litter and mineral soil from soil columns were measured separately in jars at 17  °C. The inoculation with L. terrestris and the application of lime had no effect on cumulative CO2 emissions from soil. During the first 3–4 weeks earthworms significantly (P<0.05) increased CO2 emissions by 16% to 28%. In contrast, significantly lower (P<0.05) CO2 emission rates were measured after 11 weeks. The data suggest that earthworm activity was high during the first weeks due to the creation of burrows and incorporation of beech litter into the mineral soil. Low cumulative CH4 oxidation rates were found in all soil columns as a result of CH4 production and oxidation processes. L. terrestris with fresh feces and the beech litter produced CH4 during the laboratory incubation, whereas the mineral soil oxidised atmospheric CH4. Inoculation with L. terrestris led to a significant reduction (P<0.02) in the CH4 oxidation rate of soil, i.e. 53% reduction. Liming had no effect on cumulative CH4 oxidation rates of soil columns and on CH4 fluxes during the laboratory incubation. L. terrestris significantly increased (P<0.001) cumulative N2O emissions of unlimed soil columns by 57%. The separate incubation of L. terrestris with fresh feces resulted in rather high N2O emissions, but the rate strongly decreased from 54 to 2 μg N kg–1 (dry weight) h–1 during the 100 h of incubation. Liming had a marked effect on N2O formation and significantly (P<0.001) reduced cumulative N2O emissions by 34%. Although the interaction of liming and L. terrestris was not significant, N2O emissions of limed soil columns with L. terrestris were 8% lower than those of the control.

Spatial variation of nitrate–N and related soil properties at the plot-scale

Neglecting the spatial variation in soil nutrient status may result in unused yield potential and in environmental damage. Site-specific management has been suggested to reduce inappropriate fertilization that can adversely affect soil, ground and surface water. Decision criteria for determining variable-rate nitrogen fertilization are, however, lacking. This paper analyses the spatial variation of nitrate nitrogen (NO3–N) and soil properties related to the N cycle at the plot-scale. Three 50×50 m plots were sampled in nested sampling designs of varying complexities. Classical statistics revealed a characteristic ranking in the variability of soil properties. Geostatistical analysis of the NO3–N data from two plots showed that the small-scale variation found in one small subgrid was not typical for the small-scale variation in the entire plot, indicating bias in the sampling design. A trend component was found in the NO3–N data and, consequently, the minimal requirement for the regionalized variable theory was not fulfilled. Problems due to design were overcome with a more complex nested sampling at the third plot. However, the spherical model fitted to the NO3–N data of the first year explained only 21% of the total variance, whereas a pure nugget effect was observed in the second year. The water content data also showed a low structural variance, which was different in the two years. In contrast, two thirds of the variance of total carbon (Ct) and total nitrogen (Nt) could be explained by the fitted models. Seasonal variations, such as varying duration of snow cover, and extrinsic management effects, such as growing of a cover crop, may have contributed to the observed differences in variability between the years. Due to the low proportion of structural variance and the observation that spatial distribution was not stable with time, geostatistical analysis of NO3–N and water contents data added only little information to classical statistical analysis. However, geostatistical analysis of total C and N contents provided a useful means to calculate spatial distribution patterns of these properties.