The study examined the interrelationships between chemical and microbiological quality indicators... more The study examined the interrelationships between chemical and microbiological quality indicators of soil and their ability to differentiate plots under contrasting fertilization regimes. The study was based on a long-term field experiment established on an Udic Ustocrepts in 1966. The soil was cropped with maize (Zea mays L.) and winter wheat (Triticum aestivum L.) and received no organic fertilization (control), wheat straw and maize stalk (crop residue) or cattle manure (manure) in combination with increasing levels of mineral N (N 0 and N 200 ). To asses whether seasonal fluctuations of measured properties might mask the effects of fertilization, soil samples were collected four times within a growing season. Manure amendment increased soil TOC and TN, while crop residue amendment had no significant effects. Mineral N increased TN only in April, while in September it decreased water extractable organic C (WEOC). Data of diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) gave evidence for a higher relative contribution of the aliphatic peak at 2930 cm −1 and a lower relative contribution of the aromatic peaks at 1620 cm −1 and 1520 cm −1 under manure. Manure amendment stimulated enzymatic activities, increased microbial biomass carbon (C mic ) and total phospholipids (PLFAs), and reduced the metabolic quotient (qCO 2 ). Patterns of PLFAs indicated that manure amendment increased the ratio of Gram-positive to Gram-negative bacteria. Crop residue amendment had no significant effects, while in September mineral N inhibited protease activity and reduced the Gram-positive to Gram-negative ratio. Microbial-related parameters fluctuated over time but their seasonality did not hamper the identification of fertilization-induced effects. The selected properties proved to be valuable indicators of long-term changes of soil quality and were strongly interrelated: changes in soil organic matter content and composition induced by manure amendment were accompanied by changes in abundance and function of the soil microbial community. Partial least square analysis obtained relating DRIFTS spectra to measured soil properties produced accurate predictive models for TOC and PLFAs, and moderately accurate models for C mic , showing the potential of DRIFTS to be used as a rapid soil testing technique for soil quality monitoring.
Trophic interactions in cryptic belowground systems are difficult to assess, either experimentall... more Trophic interactions in cryptic belowground systems are difficult to assess, either experimentally or by direct observation. We used lipid analysis to determine feeding strategies in Collembola raised on various bacterial, fungal, plant, or nematode diets. Dietary fatty acids (FAs) were conserved and transferred through the trophic cascade into the neutral lipids of consumers. The presence of vaccenic type FAs (7 family) was indicative of a bacterial diet in general. More specifically, methyl-branched (iso, anteiso) and cyclic forms of FAs were markers for consumption of gram-positive and gram-negative bacteria, respectively. Fungal-feeding Collembola comprised a higher proportion of linoleic acid, whereas the profile of plant feeders showed an increased amount of oleic acid. The FA 20:1 9 was only present in Collembola with nematodes as prey. Based on the assigned marker FAs, field populations of Collembola in three deciduous forest stands were ascribed to feeding guilds (i.e., fungivores, bacterivores, herbivores, predators). In conclusion, FA biomarkers provide a high-resolution method to define feeding strategies of decomposer invertebrates and to determine their diets in situ. Lipid analysis has considerable potential as a new tool in soil food web studies.
Soil food webs are important determinants for the carbon flow through terrestrial systems, with t... more Soil food webs are important determinants for the carbon flow through terrestrial systems, with the trophic networks between microbes and microfaunal grazers forming the basis for processing plant resources. At an agricultural field site cropped with maize or wheat, plant carbon input to soil was experimentally manipulated by amendment with maize litter. The community structure of dominant micro-food web components, the bacteria, fungi, protozoa and nematodes, was investigated across a depth gradient comprising plough layer, rooted soil below plough horizon, and deeper root free soil. The community composition and diversity within micro-food webs, and the response to resource supply, were assessed in summer, the vegetation period with highest root exudation. In the plough layer amendment with plant residues increased microbial biomass as well as density of fan shaped amoeba morphotypes and of bacterial-and fungal-feeding nematodes. Diversity of food web assemblages was assessed by operational taxonomic units (OTU) for bacteria and fungi, protozoa morphotypes and nematode families. Changes in diversity were either not apparent (fungi, protozoa), negatively related to litter (bacteria) or positively linked to the presence of a specific crop plant (bacteria, nematodes). Based on nematode functional guilds and the related enrichment and structure index, general food web conditions were assigned as nutrient enriched, with a high degree of disturbance, and a dominance of the bacterial energy channel. In sum, litter amendment fostered the abundance but not the diversity of organisms as food webs remained bottom heavy with only small amounts of carbon conserved at higher trophic levels. Food web structure was more affected by the abiotic (soil profile) and biotic (crop plant) environment than by the supply with litter resources.
The lipid composition of Collembola and their potential food resources was assessed in three deci... more The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by their phospholipid fatty acid (PLFA) composition. Both the amount and the pattern of PLFAs differed between sites and soil depth, in particular the bacterial and plant marker FAs in the upper soil layer. Thus, the availability of resources for micro-detritivores varied due to forest and soil layer. The lipid composition of vital and senescent beech leaves was predominantly influenced by metabolic status and represented a quite homogenous FA resource across forest stands. Comparing Folsomia quadrioculata, Lepidocyrtus lignorum, Neanura muscorum and Pogonognathellus longicornis between the different forests revealed FA profiles to be predominantly affected by site, suggesting a diet shift depending on resources at hand. However, species-specific differences in individual FAs occurred, likely related to feeding strategy and physiological activity. Lipids of Collembola comprised low amounts of bacterial marker FAs, and bacterial consumption may occur to some extent, particularly on Gram-positives. The marker FA for predatory feeding, 20: 1o9, was found in several species, although in low amounts. This contradicts known feeding habits and caution is advisable in using 20: 1o9 as trophic marker. Overall, as indicated by high proportions of oleic ð18: 1o9Þ or linoleic ð18: 2o6; 9Þ acid, most species were either plant litter or fungal feeders, with some transitions. The ratio 18: 1o9=18: 2o6,9 is proposed as a tool to distinguish between these two major feeding strategies in Collembola. r
Increased carbon translocation to the rhizosphere via 'leakage' induced by low amounts of plant p... more Increased carbon translocation to the rhizosphere via 'leakage' induced by low amounts of plant parasitic nematodes can foster microorganisms. The effects of the root-knot nematode Meloidogyne incognita on microbial biomass (C mic ) and community structure (phospholipid fatty acids) in the rhizosphere of barley were studied. Inoculation densities of 2000, 4000, and 8000 nematodes were well below the threshold level for plant damage. A 13 CO 2 pulse-labelling was performed to assess the distribution of assimilated 13 C in the rhizosphere. Infection with M. incognita increased the carbon concentration in shoots, and enhanced root biomass slightly. The presence of nematodes did not affect microbial biomass, but significantly changed the allocation of the recent photosynthate. Less plant carbon was sequestered by microorganisms with increasing nematode abundance. Microbial community structure was distinctly altered in the early stages of the plant-nematode interactions. Both, bacteria and fungi, showed a positive response with 2000, and a negative one with 4000 and 8000 M. incognita added. The results suggest that low-level root herbivory still imposes a considerable carbon demand, and that proliferation of microorganisms due to increased rhizodeposition may be short-termed. The carbon flow to rhizosphere microbial communities is likely dependent on the specific nematode-plant association and the developmental stage of the nematode in the host.
Soil food webs are important determinants for the carbon flow through terrestrial systems, with t... more Soil food webs are important determinants for the carbon flow through terrestrial systems, with the trophic networks between microbes and microfaunal grazers forming the basis for processing plant resources. At an agricultural field site cropped with maize or wheat, plant carbon input to soil was experimentally manipulated by amendment with maize litter. The community structure of dominant micro-food web components, the bacteria, fungi, protozoa and nematodes, was investigated across a depth gradient comprising plough layer, rooted soil below plough horizon, and deeper root free soil. The community composition and diversity within micro-food webs, and the response to resource supply, were assessed in summer, the vegetation period with highest root exudation. In the plough layer amendment with plant residues increased microbial biomass as well as density of fan shaped amoeba morphotypes and of bacterial-and fungal-feeding nematodes. Diversity of food web assemblages was assessed by operational taxonomic units (OTU) for bacteria and fungi, protozoa morphotypes and nematode families. Changes in diversity were either not apparent (fungi, protozoa), negatively related to litter (bacteria) or positively linked to the presence of a specific crop plant (bacteria, nematodes). Based on nematode functional guilds and the related enrichment and structure index, general food web conditions were assigned as nutrient enriched, with a high degree of disturbance, and a dominance of the bacterial energy channel. In sum, litter amendment fostered the abundance but not the diversity of organisms as food webs remained bottom heavy with only small amounts of carbon conserved at higher trophic levels. Food web structure was more affected by the abiotic (soil profile) and biotic (crop plant) environment than by the supply with litter resources.
We investigated microbial biomass, fungal biomass and microbial community structure at three alti... more We investigated microbial biomass, fungal biomass and microbial community structure at three altitudes (1000, 2000 and 3000 m) and in two soil layers [L/F layer (Layer I) and underlying H/Ah layer (Layer II)] of tropical mountain rain forests in southern Ecuador. Basal respiration, microbial biomass and concentration of ergosterol generally declined from Layer I to Layer II and peaked at 2000 m. Compared to temperate forest ecosystems microbial biomass and ergosterol concentrations were generally low. Patterns in phospholipid fatty acids indicated that the composition of microbial communities markedly changed from Layer I to Layer II. These differences between layers decreased with increasing altitude. The concentration of the arbuscular mycorrhizal fungal marker PLFA 16:1u5c decreased with altitude in Layer I but increased in Layer II. The fungal-to-bacterial ratio increased with altitude and was higher in Layer I than in Layer II. Presumably, low microbial biomass in soils of tropical forest ecosystems is due to high temperature associated with high respiration but also low litter quality, with the latter declining with altitude. These conclusions are supported by the fact that at higher altitude the microbial community changed from a bacterial-dominated to a fungal-dominated system. CCA showed that microbial biomass correlated closely with density of a number of putatively bacterial feeding testate amoeba species including Corythion dubium Taranek, 1871, Euglypha cristata Leidy, 1879, Trigonopyxis arcula Penard, 1912, Tracheleuglypha dentata Deflandre, 1928 and Trinema lineare Penard, 1890. Ergosterol concentrations, but not the PLFA 18:2u6c, strongly correlated with the putatively fungal feeding species Phryganella acropodia (Hertwig, Lesser, 1874) Hopkinson, 1909. Generally, parallel to microbial biomass and ergosterol concentrations the density of testate amoebae peaked at 2000 m. However, compared to microbial parameters changes in testate amoebae communities between two layers were less pronounced. The data suggest that density and community structure of testate amoebae are driven by the availability of food resources (bacteria and fungi) which at high altitude decrease with increasing moisture and decreasing pH.
The effect of a single cut (simulated grazing) and regrowth of Lolium perenne on CO2 efflux from ... more The effect of a single cut (simulated grazing) and regrowth of Lolium perenne on CO2 efflux from soil (loamy Haplic Luvisol), on below-ground C translocation and on the distribution of plant C among different soil particle size fractions was investigated under controlled conditions with and without N fertilization by pulse labelling with 14C 7 times (four before and three after the cutting). The amount of 14C respired from the rhizosphere of Lolium decreased by a factor of about 3 during 1 month of growth. At the same time the amount of 14C stored in soil increased. Cut and non-fertilized plants respired less C in the rhizosphere compared to the uncut plants and cut fertilized plants. About 80% of the root-derived CO2 efflux originated from the C assimilated after defoliation, and 20% originated from the C assimilated before cutting. N fertilization decreased the below-ground C losses (root respiration and exudation) during regrowth. The shoot is the main sink of assimilated C before and after the defoliation. N fertilization led to higher C incorporation into the shoot parts growing after defoliation compared to unfertilized plants. A lower incorporation of 14C was observed in the roots of N fertilized plants. The relative growth rates (expressed as 14C specific activity) of roots and stubble were minimal and that of shoot parts growing after defoliation was maximal. Twelve percent of 14C was found in the newly grown leaves after regrowth; nevertheless, 4.7% and 2.4% of 14C in the new shoot parts were translocated from the root and shoot reserves of unfertilized and fertilized plants, respectively. Most of the C retranslocated into the new Lolium leaves originates from the stubble and not from the roots. Between 0.5% and 1.7% of 14C recovered in shoots and below-ground C pools was found in the soil microbial biomass. Cutting and fertilization did not change 14C incorporation into the microbial biomass and did not affect xylanase, invertase, and protease activities. Tracing the assimilated C in particle size fractions revealed maximal incorporation for the sand and clay fraction.
ABSTRACT Modifications in temperature and precipitation due to climate change will likely affect ... more ABSTRACT Modifications in temperature and precipitation due to climate change will likely affect carbon cycling and soil respiration in terrestrial ecosystems. Despite the important feedback mechanism of ecosystems to climate change, there is still a lack of experimental observation in agricultural ecosystems. In July 2008, we established the Hohenheim Climate Change (HoCC) experiment to investigate effects of elevated temperature and altered precipitation on soil respiration in an arable soil (mean annual temperature and precipitation 8.7 °C and 679 mm, respectively). We elevated soil temperature to 4 cm depth by 2.5 °C, reduced the amount of summer precipitation by 25%, and extended dry intervals between precipitation events. For two years, CO2 fluxes were measured weekly and aboveground plant biomass and soil microbial biomass was determined. The results of the two-year study underline the importance of soil moisture as a driving factor in ecosystem response to climate change. Soil warming did not increase soil respiration in the first year; in the second year, a 27% increase was measured. The differential response of soil respiration to warming was most likely driven by soil moisture. In summer 2009, water limitation reduced microbial biomass in the heated plots thereby suppressing the stimulatory effect of elevated temperature on soil microorganisms. In summer 2010, the reduction in soil moisture was less pronounced and microbial biomass and respiration were not affected by water limitation. Temperature elevation significantly reduced Q10 values of soil respiration by 0.7–0.8. Altered precipitation showed only minor effects during the first two years of the experiment. We conclude from our study that the moisture regime of soils under elevation of temperature will largely determine whether different soils will serve either as carbon sources or as carbon sinks.
ABSTRACT According to the method for estimating soil aggregate stability (SAS) described by Kempe... more ABSTRACT According to the method for estimating soil aggregate stability (SAS) described by Kemper and Koch, a new sieving device has been constructed to improve manipulation and the rapidity of the analysis. The method of determination is described. Multiple replications of several samples that have been carried out by the members of the Austrian Soil Physics Research Group, showed a small standard deviation on the same soil samples. Storage of soil samples before measuring may cause a variation (increase) in SAS. The spatial variability of SAS on three field plots turned out to be relatively low. However, statistically significant differences were obtained, which proofs the high precision of the modified machine. Furthermore a significant influence of cattle slurry treatments on SAS of permanent grassland soil could be detected.
The lipid composition of Collembola and their potential food resources was assessed in three deci... more The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by
Earthworms are key agents in organic matter decomposition, as they remove surface plant litter ma... more Earthworms are key agents in organic matter decomposition, as they remove surface plant litter material and mix it with mineral soil. Plant litter material is comminuted in the gizzard of anecic earthworms and this is enhanced if sand particles are available. We hypothesize that this comminution of soil and litter will result in changes in the distribution of soil organic
Die Bodengenetik ist die Lehre von der Entwicklung der Böden. Ein Boden ist ein Naturkörper, der ... more Die Bodengenetik ist die Lehre von der Entwicklung der Böden. Ein Boden ist ein Naturkörper, der an der Erdoberfläche unter einem bestimmten Klima, einer bestimmten streuliefernden Vegetation und Population von Bodenorganismen durch bodenbildende Prozesse (Verwitterung und Mineralbildung, Zersetzung und Humifizierung, Gefügebildung und verschiedene Stoffumlagerungen) aus einem Gestein entsteht.
Alle Böden unserer Erde sind nützlich. Sie dienen dem Naturhaushalt, der Pflanzen- und Tierproduk... more Alle Böden unserer Erde sind nützlich. Sie dienen dem Naturhaushalt, der Pflanzen- und Tierproduktion oder vielfältigen Zwecken der Zivilisation (vgl. Kap. 1.2). Je größer die Bevölkerung unserer Erde wird, desto mehr konkurrieren verschiedene Nutzungen um ein und denselben Boden. Deshalb wird häufiger die Grundfrage gestellt: Ist dieser Boden für eine bestimmte Nutzung geeignet? Diese Frage ist so alt wie der
Böden sind Naturkörper und als solche vierdimensionale Ausschnitte aus der Erdkruste, in denen si... more Böden sind Naturkörper und als solche vierdimensionale Ausschnitte aus der Erdkruste, in denen sich Gestein, Wasser, Luft und Lebewelt durchdringen. Wichtig ist dabei, dass die Böden belebt sind. Sie dürfen nicht als Lebewesen, sondern müssen als ein komplexes Poren- und Festkörpersystem betrachtet werden. Böden bestehen dabei aus vier Phasen, aus der gasförmigen, der flüssigen, der festen mineralischen und der festen
Böden sind Naturkörper und als solche durch jeweils typische physikalische Eigenschaften gekennze... more Böden sind Naturkörper und als solche durch jeweils typische physikalische Eigenschaften gekennzeichnet; Farbe (Kap. 6.8) und Körnung (Kap. 6.1) fallen am meisten ins Auge. Sie sind daher wichtige Bestandteile einer jeden Bodenbeschreibung.
Low amounts of root infestation by plant parasitic nematodes are suggested to increase nutrient s... more Low amounts of root infestation by plant parasitic nematodes are suggested to increase nutrient supply and in turn enhance microbial activity and net mineralization rate in the rhizosphere. These effects are generally related to "leakage" of plant-derived metabolites from damaged roots. Besides leakage, the present study examines other nematode-host interactions such as alterations in root exudation and morphology, which were almost not considered yet. This includes undamaged root parts in order to assess systemic plant response. The root-knot nematode Meloidogyne incognita (Kofoid and White 1919; Chitwood 1949) and barley (Hordeum vulgare L. cv. Europa) was used as model system. Host plants were grown in minirhizotrons inoculated with 0, 2,000, 4,000 or 8,000 M. incognita for 4 weeks. Root morphology, rhizodeposition (sugars, carboxylates, amino acids), and rhizosphere microbial communities (PLFAs) were assessed. In treatments with 4,000 nematodes, shoot biomass, total N and P content increased by the end of the experiment. Generally, an enhanced release of plant metabolites (sugars, carboxylates, amino acids) from the apical root zone occurred 1 week after inoculation with 4,000 and 8,000 M. incognita, indicating root leakage. Low levels of root herbivory stimulated root hair elongation in both infected and uninfected roots. These systemic changes in root morphology likely contributed to the increased sugar exudation in uninfected roots in all nematode treatments at 3 weeks after inoculation. Root-knots formed a separate microhabitat within the root-system. They were characterised by decreased rhizodeposition and increased fungal to bacterial ratio in the adhering rhizosphere soil. The present study provides the first evidence that, apart from leakage, nematode root herbivory at background levels induces local and systemic effects on root morphology and exudation, which in turn may affect plant performance.
The study examined the interrelationships between chemical and microbiological quality indicators... more The study examined the interrelationships between chemical and microbiological quality indicators of soil and their ability to differentiate plots under contrasting fertilization regimes. The study was based on a long-term field experiment established on an Udic Ustocrepts in 1966. The soil was cropped with maize (Zea mays L.) and winter wheat (Triticum aestivum L.) and received no organic fertilization (control), wheat straw and maize stalk (crop residue) or cattle manure (manure) in combination with increasing levels of mineral N (N 0 and N 200 ). To asses whether seasonal fluctuations of measured properties might mask the effects of fertilization, soil samples were collected four times within a growing season. Manure amendment increased soil TOC and TN, while crop residue amendment had no significant effects. Mineral N increased TN only in April, while in September it decreased water extractable organic C (WEOC). Data of diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) gave evidence for a higher relative contribution of the aliphatic peak at 2930 cm −1 and a lower relative contribution of the aromatic peaks at 1620 cm −1 and 1520 cm −1 under manure. Manure amendment stimulated enzymatic activities, increased microbial biomass carbon (C mic ) and total phospholipids (PLFAs), and reduced the metabolic quotient (qCO 2 ). Patterns of PLFAs indicated that manure amendment increased the ratio of Gram-positive to Gram-negative bacteria. Crop residue amendment had no significant effects, while in September mineral N inhibited protease activity and reduced the Gram-positive to Gram-negative ratio. Microbial-related parameters fluctuated over time but their seasonality did not hamper the identification of fertilization-induced effects. The selected properties proved to be valuable indicators of long-term changes of soil quality and were strongly interrelated: changes in soil organic matter content and composition induced by manure amendment were accompanied by changes in abundance and function of the soil microbial community. Partial least square analysis obtained relating DRIFTS spectra to measured soil properties produced accurate predictive models for TOC and PLFAs, and moderately accurate models for C mic , showing the potential of DRIFTS to be used as a rapid soil testing technique for soil quality monitoring.
Trophic interactions in cryptic belowground systems are difficult to assess, either experimentall... more Trophic interactions in cryptic belowground systems are difficult to assess, either experimentally or by direct observation. We used lipid analysis to determine feeding strategies in Collembola raised on various bacterial, fungal, plant, or nematode diets. Dietary fatty acids (FAs) were conserved and transferred through the trophic cascade into the neutral lipids of consumers. The presence of vaccenic type FAs (7 family) was indicative of a bacterial diet in general. More specifically, methyl-branched (iso, anteiso) and cyclic forms of FAs were markers for consumption of gram-positive and gram-negative bacteria, respectively. Fungal-feeding Collembola comprised a higher proportion of linoleic acid, whereas the profile of plant feeders showed an increased amount of oleic acid. The FA 20:1 9 was only present in Collembola with nematodes as prey. Based on the assigned marker FAs, field populations of Collembola in three deciduous forest stands were ascribed to feeding guilds (i.e., fungivores, bacterivores, herbivores, predators). In conclusion, FA biomarkers provide a high-resolution method to define feeding strategies of decomposer invertebrates and to determine their diets in situ. Lipid analysis has considerable potential as a new tool in soil food web studies.
Soil food webs are important determinants for the carbon flow through terrestrial systems, with t... more Soil food webs are important determinants for the carbon flow through terrestrial systems, with the trophic networks between microbes and microfaunal grazers forming the basis for processing plant resources. At an agricultural field site cropped with maize or wheat, plant carbon input to soil was experimentally manipulated by amendment with maize litter. The community structure of dominant micro-food web components, the bacteria, fungi, protozoa and nematodes, was investigated across a depth gradient comprising plough layer, rooted soil below plough horizon, and deeper root free soil. The community composition and diversity within micro-food webs, and the response to resource supply, were assessed in summer, the vegetation period with highest root exudation. In the plough layer amendment with plant residues increased microbial biomass as well as density of fan shaped amoeba morphotypes and of bacterial-and fungal-feeding nematodes. Diversity of food web assemblages was assessed by operational taxonomic units (OTU) for bacteria and fungi, protozoa morphotypes and nematode families. Changes in diversity were either not apparent (fungi, protozoa), negatively related to litter (bacteria) or positively linked to the presence of a specific crop plant (bacteria, nematodes). Based on nematode functional guilds and the related enrichment and structure index, general food web conditions were assigned as nutrient enriched, with a high degree of disturbance, and a dominance of the bacterial energy channel. In sum, litter amendment fostered the abundance but not the diversity of organisms as food webs remained bottom heavy with only small amounts of carbon conserved at higher trophic levels. Food web structure was more affected by the abiotic (soil profile) and biotic (crop plant) environment than by the supply with litter resources.
The lipid composition of Collembola and their potential food resources was assessed in three deci... more The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by their phospholipid fatty acid (PLFA) composition. Both the amount and the pattern of PLFAs differed between sites and soil depth, in particular the bacterial and plant marker FAs in the upper soil layer. Thus, the availability of resources for micro-detritivores varied due to forest and soil layer. The lipid composition of vital and senescent beech leaves was predominantly influenced by metabolic status and represented a quite homogenous FA resource across forest stands. Comparing Folsomia quadrioculata, Lepidocyrtus lignorum, Neanura muscorum and Pogonognathellus longicornis between the different forests revealed FA profiles to be predominantly affected by site, suggesting a diet shift depending on resources at hand. However, species-specific differences in individual FAs occurred, likely related to feeding strategy and physiological activity. Lipids of Collembola comprised low amounts of bacterial marker FAs, and bacterial consumption may occur to some extent, particularly on Gram-positives. The marker FA for predatory feeding, 20: 1o9, was found in several species, although in low amounts. This contradicts known feeding habits and caution is advisable in using 20: 1o9 as trophic marker. Overall, as indicated by high proportions of oleic ð18: 1o9Þ or linoleic ð18: 2o6; 9Þ acid, most species were either plant litter or fungal feeders, with some transitions. The ratio 18: 1o9=18: 2o6,9 is proposed as a tool to distinguish between these two major feeding strategies in Collembola. r
Increased carbon translocation to the rhizosphere via 'leakage' induced by low amounts of plant p... more Increased carbon translocation to the rhizosphere via 'leakage' induced by low amounts of plant parasitic nematodes can foster microorganisms. The effects of the root-knot nematode Meloidogyne incognita on microbial biomass (C mic ) and community structure (phospholipid fatty acids) in the rhizosphere of barley were studied. Inoculation densities of 2000, 4000, and 8000 nematodes were well below the threshold level for plant damage. A 13 CO 2 pulse-labelling was performed to assess the distribution of assimilated 13 C in the rhizosphere. Infection with M. incognita increased the carbon concentration in shoots, and enhanced root biomass slightly. The presence of nematodes did not affect microbial biomass, but significantly changed the allocation of the recent photosynthate. Less plant carbon was sequestered by microorganisms with increasing nematode abundance. Microbial community structure was distinctly altered in the early stages of the plant-nematode interactions. Both, bacteria and fungi, showed a positive response with 2000, and a negative one with 4000 and 8000 M. incognita added. The results suggest that low-level root herbivory still imposes a considerable carbon demand, and that proliferation of microorganisms due to increased rhizodeposition may be short-termed. The carbon flow to rhizosphere microbial communities is likely dependent on the specific nematode-plant association and the developmental stage of the nematode in the host.
Soil food webs are important determinants for the carbon flow through terrestrial systems, with t... more Soil food webs are important determinants for the carbon flow through terrestrial systems, with the trophic networks between microbes and microfaunal grazers forming the basis for processing plant resources. At an agricultural field site cropped with maize or wheat, plant carbon input to soil was experimentally manipulated by amendment with maize litter. The community structure of dominant micro-food web components, the bacteria, fungi, protozoa and nematodes, was investigated across a depth gradient comprising plough layer, rooted soil below plough horizon, and deeper root free soil. The community composition and diversity within micro-food webs, and the response to resource supply, were assessed in summer, the vegetation period with highest root exudation. In the plough layer amendment with plant residues increased microbial biomass as well as density of fan shaped amoeba morphotypes and of bacterial-and fungal-feeding nematodes. Diversity of food web assemblages was assessed by operational taxonomic units (OTU) for bacteria and fungi, protozoa morphotypes and nematode families. Changes in diversity were either not apparent (fungi, protozoa), negatively related to litter (bacteria) or positively linked to the presence of a specific crop plant (bacteria, nematodes). Based on nematode functional guilds and the related enrichment and structure index, general food web conditions were assigned as nutrient enriched, with a high degree of disturbance, and a dominance of the bacterial energy channel. In sum, litter amendment fostered the abundance but not the diversity of organisms as food webs remained bottom heavy with only small amounts of carbon conserved at higher trophic levels. Food web structure was more affected by the abiotic (soil profile) and biotic (crop plant) environment than by the supply with litter resources.
We investigated microbial biomass, fungal biomass and microbial community structure at three alti... more We investigated microbial biomass, fungal biomass and microbial community structure at three altitudes (1000, 2000 and 3000 m) and in two soil layers [L/F layer (Layer I) and underlying H/Ah layer (Layer II)] of tropical mountain rain forests in southern Ecuador. Basal respiration, microbial biomass and concentration of ergosterol generally declined from Layer I to Layer II and peaked at 2000 m. Compared to temperate forest ecosystems microbial biomass and ergosterol concentrations were generally low. Patterns in phospholipid fatty acids indicated that the composition of microbial communities markedly changed from Layer I to Layer II. These differences between layers decreased with increasing altitude. The concentration of the arbuscular mycorrhizal fungal marker PLFA 16:1u5c decreased with altitude in Layer I but increased in Layer II. The fungal-to-bacterial ratio increased with altitude and was higher in Layer I than in Layer II. Presumably, low microbial biomass in soils of tropical forest ecosystems is due to high temperature associated with high respiration but also low litter quality, with the latter declining with altitude. These conclusions are supported by the fact that at higher altitude the microbial community changed from a bacterial-dominated to a fungal-dominated system. CCA showed that microbial biomass correlated closely with density of a number of putatively bacterial feeding testate amoeba species including Corythion dubium Taranek, 1871, Euglypha cristata Leidy, 1879, Trigonopyxis arcula Penard, 1912, Tracheleuglypha dentata Deflandre, 1928 and Trinema lineare Penard, 1890. Ergosterol concentrations, but not the PLFA 18:2u6c, strongly correlated with the putatively fungal feeding species Phryganella acropodia (Hertwig, Lesser, 1874) Hopkinson, 1909. Generally, parallel to microbial biomass and ergosterol concentrations the density of testate amoebae peaked at 2000 m. However, compared to microbial parameters changes in testate amoebae communities between two layers were less pronounced. The data suggest that density and community structure of testate amoebae are driven by the availability of food resources (bacteria and fungi) which at high altitude decrease with increasing moisture and decreasing pH.
The effect of a single cut (simulated grazing) and regrowth of Lolium perenne on CO2 efflux from ... more The effect of a single cut (simulated grazing) and regrowth of Lolium perenne on CO2 efflux from soil (loamy Haplic Luvisol), on below-ground C translocation and on the distribution of plant C among different soil particle size fractions was investigated under controlled conditions with and without N fertilization by pulse labelling with 14C 7 times (four before and three after the cutting). The amount of 14C respired from the rhizosphere of Lolium decreased by a factor of about 3 during 1 month of growth. At the same time the amount of 14C stored in soil increased. Cut and non-fertilized plants respired less C in the rhizosphere compared to the uncut plants and cut fertilized plants. About 80% of the root-derived CO2 efflux originated from the C assimilated after defoliation, and 20% originated from the C assimilated before cutting. N fertilization decreased the below-ground C losses (root respiration and exudation) during regrowth. The shoot is the main sink of assimilated C before and after the defoliation. N fertilization led to higher C incorporation into the shoot parts growing after defoliation compared to unfertilized plants. A lower incorporation of 14C was observed in the roots of N fertilized plants. The relative growth rates (expressed as 14C specific activity) of roots and stubble were minimal and that of shoot parts growing after defoliation was maximal. Twelve percent of 14C was found in the newly grown leaves after regrowth; nevertheless, 4.7% and 2.4% of 14C in the new shoot parts were translocated from the root and shoot reserves of unfertilized and fertilized plants, respectively. Most of the C retranslocated into the new Lolium leaves originates from the stubble and not from the roots. Between 0.5% and 1.7% of 14C recovered in shoots and below-ground C pools was found in the soil microbial biomass. Cutting and fertilization did not change 14C incorporation into the microbial biomass and did not affect xylanase, invertase, and protease activities. Tracing the assimilated C in particle size fractions revealed maximal incorporation for the sand and clay fraction.
ABSTRACT Modifications in temperature and precipitation due to climate change will likely affect ... more ABSTRACT Modifications in temperature and precipitation due to climate change will likely affect carbon cycling and soil respiration in terrestrial ecosystems. Despite the important feedback mechanism of ecosystems to climate change, there is still a lack of experimental observation in agricultural ecosystems. In July 2008, we established the Hohenheim Climate Change (HoCC) experiment to investigate effects of elevated temperature and altered precipitation on soil respiration in an arable soil (mean annual temperature and precipitation 8.7 °C and 679 mm, respectively). We elevated soil temperature to 4 cm depth by 2.5 °C, reduced the amount of summer precipitation by 25%, and extended dry intervals between precipitation events. For two years, CO2 fluxes were measured weekly and aboveground plant biomass and soil microbial biomass was determined. The results of the two-year study underline the importance of soil moisture as a driving factor in ecosystem response to climate change. Soil warming did not increase soil respiration in the first year; in the second year, a 27% increase was measured. The differential response of soil respiration to warming was most likely driven by soil moisture. In summer 2009, water limitation reduced microbial biomass in the heated plots thereby suppressing the stimulatory effect of elevated temperature on soil microorganisms. In summer 2010, the reduction in soil moisture was less pronounced and microbial biomass and respiration were not affected by water limitation. Temperature elevation significantly reduced Q10 values of soil respiration by 0.7–0.8. Altered precipitation showed only minor effects during the first two years of the experiment. We conclude from our study that the moisture regime of soils under elevation of temperature will largely determine whether different soils will serve either as carbon sources or as carbon sinks.
ABSTRACT According to the method for estimating soil aggregate stability (SAS) described by Kempe... more ABSTRACT According to the method for estimating soil aggregate stability (SAS) described by Kemper and Koch, a new sieving device has been constructed to improve manipulation and the rapidity of the analysis. The method of determination is described. Multiple replications of several samples that have been carried out by the members of the Austrian Soil Physics Research Group, showed a small standard deviation on the same soil samples. Storage of soil samples before measuring may cause a variation (increase) in SAS. The spatial variability of SAS on three field plots turned out to be relatively low. However, statistically significant differences were obtained, which proofs the high precision of the modified machine. Furthermore a significant influence of cattle slurry treatments on SAS of permanent grassland soil could be detected.
The lipid composition of Collembola and their potential food resources was assessed in three deci... more The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by
Earthworms are key agents in organic matter decomposition, as they remove surface plant litter ma... more Earthworms are key agents in organic matter decomposition, as they remove surface plant litter material and mix it with mineral soil. Plant litter material is comminuted in the gizzard of anecic earthworms and this is enhanced if sand particles are available. We hypothesize that this comminution of soil and litter will result in changes in the distribution of soil organic
Die Bodengenetik ist die Lehre von der Entwicklung der Böden. Ein Boden ist ein Naturkörper, der ... more Die Bodengenetik ist die Lehre von der Entwicklung der Böden. Ein Boden ist ein Naturkörper, der an der Erdoberfläche unter einem bestimmten Klima, einer bestimmten streuliefernden Vegetation und Population von Bodenorganismen durch bodenbildende Prozesse (Verwitterung und Mineralbildung, Zersetzung und Humifizierung, Gefügebildung und verschiedene Stoffumlagerungen) aus einem Gestein entsteht.
Alle Böden unserer Erde sind nützlich. Sie dienen dem Naturhaushalt, der Pflanzen- und Tierproduk... more Alle Böden unserer Erde sind nützlich. Sie dienen dem Naturhaushalt, der Pflanzen- und Tierproduktion oder vielfältigen Zwecken der Zivilisation (vgl. Kap. 1.2). Je größer die Bevölkerung unserer Erde wird, desto mehr konkurrieren verschiedene Nutzungen um ein und denselben Boden. Deshalb wird häufiger die Grundfrage gestellt: Ist dieser Boden für eine bestimmte Nutzung geeignet? Diese Frage ist so alt wie der
Böden sind Naturkörper und als solche vierdimensionale Ausschnitte aus der Erdkruste, in denen si... more Böden sind Naturkörper und als solche vierdimensionale Ausschnitte aus der Erdkruste, in denen sich Gestein, Wasser, Luft und Lebewelt durchdringen. Wichtig ist dabei, dass die Böden belebt sind. Sie dürfen nicht als Lebewesen, sondern müssen als ein komplexes Poren- und Festkörpersystem betrachtet werden. Böden bestehen dabei aus vier Phasen, aus der gasförmigen, der flüssigen, der festen mineralischen und der festen
Böden sind Naturkörper und als solche durch jeweils typische physikalische Eigenschaften gekennze... more Böden sind Naturkörper und als solche durch jeweils typische physikalische Eigenschaften gekennzeichnet; Farbe (Kap. 6.8) und Körnung (Kap. 6.1) fallen am meisten ins Auge. Sie sind daher wichtige Bestandteile einer jeden Bodenbeschreibung.
Low amounts of root infestation by plant parasitic nematodes are suggested to increase nutrient s... more Low amounts of root infestation by plant parasitic nematodes are suggested to increase nutrient supply and in turn enhance microbial activity and net mineralization rate in the rhizosphere. These effects are generally related to "leakage" of plant-derived metabolites from damaged roots. Besides leakage, the present study examines other nematode-host interactions such as alterations in root exudation and morphology, which were almost not considered yet. This includes undamaged root parts in order to assess systemic plant response. The root-knot nematode Meloidogyne incognita (Kofoid and White 1919; Chitwood 1949) and barley (Hordeum vulgare L. cv. Europa) was used as model system. Host plants were grown in minirhizotrons inoculated with 0, 2,000, 4,000 or 8,000 M. incognita for 4 weeks. Root morphology, rhizodeposition (sugars, carboxylates, amino acids), and rhizosphere microbial communities (PLFAs) were assessed. In treatments with 4,000 nematodes, shoot biomass, total N and P content increased by the end of the experiment. Generally, an enhanced release of plant metabolites (sugars, carboxylates, amino acids) from the apical root zone occurred 1 week after inoculation with 4,000 and 8,000 M. incognita, indicating root leakage. Low levels of root herbivory stimulated root hair elongation in both infected and uninfected roots. These systemic changes in root morphology likely contributed to the increased sugar exudation in uninfected roots in all nematode treatments at 3 weeks after inoculation. Root-knots formed a separate microhabitat within the root-system. They were characterised by decreased rhizodeposition and increased fungal to bacterial ratio in the adhering rhizosphere soil. The present study provides the first evidence that, apart from leakage, nematode root herbivory at background levels induces local and systemic effects on root morphology and exudation, which in turn may affect plant performance.
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Papers by Ellen Kandeler