[Show abstract][Hide abstract] ABSTRACT: Climate scenarios predict increasing temperatures and higher precipitation rates in late autumn to early spring, both of which holding the potential to change the dynamics of plant residue decomposition and overall microbial activity in soil. In company with consequences for nutrient release patterns influences on the survival of fungal plant pathogens and their phytopathogenicity can be expected. Both, litter decomposition and pathogen survival, was analyzed in a 70-day litterbag incubation experiment. Continuous +4 °C was compared to permanent frost (−3 °C) and different freeze-thaw cycles for the decomposition of maize residues and disease potential of soil-borne plant pathogens Fusarium culmorum, Fusarium graminearum, and Rhizoctonia solani. Frost generally reduced maize residue decomposition. On the lower levels of CO2 production in the permanent or occasionally frost treatments pathogen inoculation had large effects on microbial maize use, indicating high saprotrophic activity of pathogens even in cold winter scenarios. Pathogen inoculation led to higher amino sugar contents of maize residue dwelling microbial organisms. At constant 4 °C remarkable high amounts of glucosamine were detected, indicating higher substrate use efficiency without frost. Both, temperature treatments as well as intra- and interspecific competition directed the development of pathogens after inoculation. F. culmorum took large advantage from the non-frost scenario, while no significant increase was found under continuous frost. F. graminearum was also able to increase its abundance at +4 °C. But this was strongly reduced when F. graminearum was in competition to the other two pathogens. In summary, F. culmorum was found to be highly frost tolerant and competitive against F. graminearum, particularly under conditions of freeze-thaw cycles since F. culmorum was able to take a large share of saprotrophic litter residue use under the cold conditions. Biomass of R. solani was strongly decomposed in all treatments. We conclude that constant mild conditions during winter can increase biomass of F. culmorum and F. graminearum in crop residues, causing increased infection pressure in the next season. In contrast to that, frost and freeze-thaw events can lower the build-up of Fusarium biomass and thus diminish the risk of crop infection.
Soil Biology and Biochemistry 10/2014; 77:141–149. · 4.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Long-term organic fertilization may control the accumulation of organic matter in subsoil. The objective of this study was to evaluate the effects of long-term farmyard manure application in comparison with mineral fertilization on the accumulation of amino sugars as indices for microbial residues down to 1 m depth at a sandy site that exhibits highly heterogeneous pH conditions. In relation to maximum values in topsoil at 90–100 cm depth, the SOC content decreased to roughly 24% and the total N content to 16% of the maximum values, leading to an increased soil C/N ratio from 11 to values around 16 in all treatments. The relative contribution of microbial residue C to SOC decreased with depth from 68% at 0–25 cm to 24% at 50–100 cm. In the subsoil, the stocks of microbial residue C were increased by manure in comparison with mineral fertilization, but not the stocks of SOC. This suggests that manure-induced priming effects increase the microbial turnover at 50–100 cm depth. Manure fertilization promoted the formation of bacterial residues in the topsoil at 0–25 cm depth, but not in the subsoil. Below the topsoil, the fungal C to bacterial C ratio decreased from 2.6 at 0–25 cm depth to 2.1 at 50–100 cm depth. Below the topsoil, the ratio of fungal to bacterial residues continuously decreased with depth from 2.7 to 1.7 at 90–100 cm depth, without fertilizer effects. Possible reasons for this decrease, such as effects of pH on the subsoil microbial community, a higher sensitivity of fungi to the absence of fresh organic matter or to an unfavourable composition of the subsoil atmosphere, need further investigations.
Geoderma 08/2014; s 226–227:79–84. · 2.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: C mineralization and aggregate stability directly depend upon organic matter and clay content, and both processes are influenced by the activity of microorganisms and soil fauna. However, quantitative data are scarce. To achieve a gradient in C and clay content, a topsoil was mixed with a subsoil. Single soils and the soil mixture were amended with 1.0 mg maize litter C g soil−1 with and without endogeic earthworms (Aporrectodea caliginosa). The differently treated soils were incubated for 49 days at 15 °C and 40% water holding capacity. Cumulative C mineralization, microbial biomass, ergosterol content and aggregate fractions were investigated and litter derived C in bulk soil and aggregates were determined using isotope analyses. Results from the soil mixture were compared with the calculated mean values of the two single soils. Mixing of soil horizons differing in carbon and clay content stimulated C mineralization of added maize residues as well as of soil organic matter. Mixing also increased contents of macro-aggregate C and decreased contents of micro-aggregate C. Although A. caliginosa had a stimulating effect on C mineralization in all soils, decomposition of added litter by A. caliginosa was higher in the subsoil, whereas A. caliginosa decreased litter decomposition in the soil mixture and the topsoil. Litter derived C in macro-aggregates was higher with A. caliginosa than with litter only. In the C poor subsoil amended with litter, A. caliginosa stimulated the microbial community as indicated by the increase in microbial biomass. Furthermore, the decrease of ergosterol in the earthworm treated soils showed the influence of A. caliginosa on the microbial community, by reducing saprotrophic fungi. Overall, our data suggest both a decrease of saprotrophic fungi by selective grazing, burrowing and casting activity as well as a stimulation of the microbial community by A. caliginosa.
[Show abstract][Hide abstract] ABSTRACT: The relationship between microbial biomass, residues and their contribution to microbial turnover is important to understand ecosystem C storage. The effects of permanent grassland (100 % ryegrass-PG), conversion to modified grassland (mixture of grass and clover-MG) or maize monoculture (MM) on the dynamics of soil organic C (SOC), microbial biomass, fungal ergosterol and microbial residues (bacterial muramic acid and fungal glucosamine) were investigated. Cattle slurry was applied to quantify the effects of fertilisation on microbial residues and functional diversity of microbial community across land use types. Slurry application significantly increased the stocks of microbial biomass C and S and especially led to a shift in microbial residues towards bacterial tissue. The MM treatment decreased the stocks of SOC, microbial biomass C, N and S and microbial residues compared with the PG and MG treatments at 0-40 cm depth. The MM treatment led to a greater accumulation of saprotrophic fungi, as indicated by the higher ergosterol-to-microbial biomass C ratio and lower microbial biomass C/S ratio compared with the grassland treatments. The absence of a white clover population in the PG treatment caused a greater accumulation of fungal residues (presumably arbuscular mycorrhizal fungi (AMF), which do not contain ergosterol but glucosamine), as indicated by the significantly higher fungal C-to-bacterial C ratio and lower ergosterol-to-microbial biomass C ratio compared with the MG treatment. In addition to these microbial biomass and residual indices, the community level physiological profiles (CLPP) demonstrated distinct differences between the PG and MG treatments, suggesting the potential of these measurements to act as an integrative indicator of soil functioning.
[Show abstract][Hide abstract] ABSTRACT: In a field experiment, peas (Pisum sativum L.) and oats (Avena sativa L.) were grown as sole crops and intercrops, fertilized with horse manure and yard-waste compost derived from shrub and garden cuttings at 10 t C ha−1 each. The objectives were to compare the effects of these organic fertilizer and cropping system in organic farming on (a) yield of peas and oats, grown as the sole crop or intercropped, as well as N2 fixation and photosynthetic rates, (b) the yield of wheat as a succeeding crop, (c) microbial biomass indices in soil and roots, and (d) microbial activity estimated by the CO2 evolution rate in the field and the amount of organic fertilizers, recovered as particulate organic matter (POM). In general, organic fertilizer application improved nodule dry weight (DW), photosynthetic rates, N2 fixation, and N accumulation of peas as well as N concentration in oat grain. Averaged across fertilizer treatments, pea/oat intercropping significantly decreased nodule DW, N2 fixation and photosynthetic rate of peas by 14, 17, and 12%, respectively, and significantly increased the photosynthetic rate of oats by 20%. However, the land equivalent ratio (LER) of intercropped peas and oats exceeded 1.0, indicating a yield advantage over sole cropping. Soil microbial biomass was positively correlated with pea dry matter yields both in sole and intercropped systems. Organic fertilizers increased the contents of microbial biomass C, N, P, and fungal ergosterol in soil and CO2 production, whereas the cropping system had no effects on these microbial indices. According to the organic fertilizer recovered as POM, 70% (manure) and 64% (compost) of added C were decomposed, but only 39% (manure) and 13% (compost) could be attributed to CO2–C during a 101-day period. This indicated that horse manure was more readily available to soil microorganisms than compost, leading to increased grain yields of the succeeding winter wheat.
European Journal of Agronomy 01/2014; 52:259–270. · 2.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A 56-d incubation experiment at 30 °C was carried out to study how salinity affects C and N mineralization of composted dairy manure and date palm straw. A low- and a high-saline soil were amended with (1) manure, (2) manure + low straw, (3) manure + straw, and (4) sole straw. The microbial and fungal biomass contents are very low in Omani soil abandoned for at least 6 years. Straw application revealed a highly significant increase in microbial biomass C, but especially in ergosterol in the low-saline soil. In contrast, straw led only to an increase in ergosterol in the high-saline soil, where only the combined application of manure with straw had significant positive effects on microbial biomass C. In the high-saline soil, the sum of C mineralized reached only 55% of SOC-derived CO2–C, 65% of manure-derived CO2–C, and 75% of straw-derived CO2–C in comparison with the respective treatments of the low-saline soil. The application of straw led always to a net N immobilization, which was markedly stronger in the high- than in the low-saline soil. The increase in salinity by composted cattle manure should be considered if this fertilizer is applied to soils sensitive to changes in salinity.
Journal of Arid Environments 01/2014; s 100–101:106–110. · 1.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background and aims Species rich, semi-natural grassland systems provide several ecosystem functions. The goal was to assess how aboveground composition and evenness affects soil substrate utilization pattern and soil microbial functional evenness. Methods At five German NATURA 2000 grassland sites, the interactions of plant functional groups (graminoids, forbs and legumes) and belowground microbial functional evenness were investigated in relation to soil properties and sampling date. Functional evenness of soil microorganisms was measured with high spatial resolution by community level physiological profiling (CLPP) using multi-SIR (substrate-induced respiration) at three sampling dates during the vegetation period. Evenness indices were used to compare plant functional group diversity and soil microbial functional diversity. Results All sites differed in the consistently high soil microbial functional evenness, which was strongly predicted by soil pH, but not by plant functional groups or aboveground plant dry matter production. However, soil microbial functional evenness was particularly decreased by an increasing legume proportion and showed seasonal changes, probably driven by shifts in resource availability and soil water content. Conclusions Our results suggest that changes in soil chemical properties or in a single key plant functional group may have stronger effects on soil microbial functional evenness than changes in plant functional group evenness.
[Show abstract][Hide abstract] ABSTRACT: The dynamics of fungal and bacterial residues to a one-season tillage event in combination with manure application in a grassland soil are unknown. The objectives of this study were (1) to assess the effects of one-season tillage event in two field trials on the stocks of microbial biomass, fungal biomass, microbial residues, soil organic C (SOC) and total N in comparison with permanent grassland; (2) to determine the effects of repeated manure application to restore negative tillage effects on soil microbial biomass and residues. One trial was started 2 years before sampling and the other 5 years before sampling. Mouldboard ploughing decreased the stocks of SOC, total N, microbial biomass C, and microbial residues (muramic acid and glucosamine), but increased those of the fungal biomarker ergosterol in both trials. Slurry application increased stocks of SOC and total N only in the short-term, whereas the stocks of microbial biomass C, ergosterol and microbial residues were generally increased in both trials, especially in combination with tillage. The ergosterol to microbial biomass C ratio was increased by tillage, and decreased by slurry application in both trials. The fungal C to bacterial C ratio was generally decreased by these two treatments. The metabolic quotient qCO2 showed a significant negative linear relationship with the microbial biomass C to SOC ratio and a significant positive relationship with the soil C/N ratio. The ergosterol to microbial biomass C ratio revealed a significant positive linear relationship with the fungal C to bacterial C ratio, but a negative one with the SOC content. Our results suggest that slurry application in grassland soil may promote SOC storage without increasing the role of saprotrophic fungi in soil organic matter dynamics relative to that of bacteria.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to determine the influence of leaf-litter type (i.e., European beech—Fagus sylvatica L. and European ash—Fraxinus excelsior L.) and leaf-litter mixture on the partitioning of leaf-litter C and N between the O horizon, the topsoil, the soil microbial biomass, and the CO2 emission during decomposition. In a mature beech stand of Hainich National Park, Thuringia, Germany, undisturbed soil cores (∅ 24 cm) were transferred to plastic cylinders and the original leaf litter was either replaced by 13C15N-labeled beech or ash leaf litter, or leaf-litter-mixture treatments in which only one of the two leaf-litter types was labeled. Leaf-litter-derived CO2-C flux was measured every second week over a period of one year. Partitioning of leaf-litter C and N to the soil and microbial biomass was measured 5 and 10 months after the start of the experiment. Ash leaf litter decomposed faster than beech leaf litter. The decomposition rate was negatively related to initial leaf-litter lignin and positively to initial Ca concentrations. The mixture of both leaf-litter types led to enhanced decomposition of ash leaf litter. However, it did not affect beech leaf-litter decomposition. After 5 and 10 months of in situ incubation, recoveries of leaf-litter-derived C and N in the O horizon (7%–20% and 9%–35%, respectively) were higher than in the mineral soil (1%–5% and 3%–8%, respectively) showing no leaf-litter-type or leaf-litter-mixture effect. Partitioning of leaf-litter-derived C and N to microbial biomass in the upper mineral soil (< 1% of total leaf-litter C and 2%–3% of total leaf-litter N) did not differ between beech and ash. The results show that short-term partitioning of leaf-litter C and N to the soil after 10 months was similar for ash and beech leaf litter under standardized field conditions, even though mineralization was faster for ash leaf litter than for beech leaf litter.
Journal of Plant Nutrition and Soil Science 10/2013; · 1.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The site-specific contribution of bacterial and especially fungal
residues to a tillage-induced C sequestration is largely unknown,
although microbial residues contribute a significant percentage to
the soil organic C (SOC) pool. In the current study, the
co-accumulation of microbial residues and organic matter was
investigated in a mature, 15-year-old on-farm tillage experiment
(mouldboard plough (MBT), grubber (GRT), no tillage (NT)) on four
different arable silt-loam sites in central and southern Germany at 0
to 40 cm soil depth. The GRT and NT treatments increased the
stocks of SOC (+7 %) and microbial biomass C (+20 %) in
comparison with the MBT treatment. The differences between the
GRT and NT were small, but there were more positive effects for the
GRT treatment in most cases. Our results indicate significant tillage
effects in loess-derived silt loams suitable for rain-fed sugar beet
production, although strong site-specific differences occurred for
most of the soil chemical and microbiological properties analysed.
In the GRT and NT treatments, the increased stocks of SOC were
not caused by the preferential accumulation of fungal residues at
0–5 cm depth, whereas ergosterol-free biotrophic arbuscular
mycorrhizal fungi (AMF) was promoted at the expense of
saprotrophic fungi at 30–40 cm depth. Our results suggest that the
relationship between saprotrophic fungi and AMF is an important
factor for tillage-induced changes in microbial turnover of SOC.
Biology and Fertility of Soils 10/2013; · 3.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: As a consequence of their widespread use, e.g. as protective coatings for fabrics, and their resistance to thermal and biological breakdown, perfluorinated compounds are increasingly found in the environment, but little is known about their ecotoxicological properties. A 40-day microcosm experiment was carried out to examine the effects of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) on the endogeic geophagus earthworm Aporrectodea caliginosa, its survival and feeding on soil organic C and microbial biomass C. Three levels of concentration (1, 100, and 500mgkg(-1)) were chosen. The lowest represented the maximum found in sediments and soils and the other two are extreme concentrations that might occur in pollution hotspots and that have been shown to poison organisms. Earthworms promoted the production of CO2 and decreased microbial biomass C in soil, regardless of the presence of PFOA or PFOS. Both compounds significantly decreased the surviving numbers and dry weight of earthworms at concentrations of 100mgkg(-1). No earthworms survived at PFOA and PFOS concentrations of 500mgkg(-1). At concentrations of 1mgkg(-1), no negative effects were observed. The δ(13)C values of A. caliginosa did not differ between treatments. In contrast, the δ(15)N values were significantly increased after adding 1mgkg(-1) of PFOA, reflecting elevated portions of soil-derived N in the earthworm tissue. In contrast, these portions of soil-derived N were lower in the earthworms after addition of 100mgkg(-1) of PFOA and PFOS. In conclusion, extreme concentrations of PFOA and PFOS negatively affected endogeic A. caliginosa, whereas a concentration of 1mgkg(-1) of PFOA and PFOS was related to an increased uptake of soil N by the earthworms.
Ecotoxicology and Environmental Safety 06/2013; · 2.20 Impact Factor