1,721,032 research outputs found
Microbial use of N-15-labelled maize residues affected by winter temperature scenarios
No full textA 56-day incubation experiment was carried out to investigate decomposition and microbial use of N-15-labelled maize (Zea mays L.) residues incubated under four winter temperature scenarios. The residues were mixed to mesocosms equivalent to 1.2 mg C and 42.5 mu g N g(-1) dry soil, after which the samples were incubated at a constant temperature of +4 degrees C, a constant -3 degrees C, and under multiple and single freeze thaw conditions. A constant +4 degrees C was most favourable for microbial substrate use, with 4- and 6-fold higher total and maize-C mineralization, respectively, in comparison with constant frost. The cumulative maize mineralization was not determined by the frequency of freeze thaw events, but regulated by the overall time of frost and thaw conditions. The decomposition of maize straw significantly increased soil organic C mineralization (in all scenarios) and incorporation into microbial biomass (in the freeze thaw scenarios only). The positive priming effects observed were equivalent to an additional loss of total soil organic C of between about 0.2 (continuous frost) and 0.8% (single freeze thaw). Microbial biomass was significantly increased after maize straw amendment, with constant frost and freeze thaw scenarios not having any negative effect on microbial biomass C compared with constant +4 degrees C. Highest fungal biomass was found after constant frost without fresh substrates and also after extended frost followed by a warm period when fresh plant residues were present. On average, 50% of the added maize N were recovered in the soil total N after 56 days of constant 4 degrees C and in the freeze thaw scenarios, with the strongest effect after single freezing and thawing. (C) 2013 Elsevier Ltd. All rights reserved.University of Kasse
Winter decomposition of maize leaf litter at arable silt and clay sites, using a reciprocal soil transplantation approach
No full textEffect of litter quality and soil fungi on macroaggregate dynamics and associated partitioning of litter carbon and nitrogen
No full textWe investigated the effect of plant residue decomposability and fungal biomass on the dynamics of macroaggregate (250-2000 mu m) formation in a three months' incubation experiment and determined the distribution of residue-derived C and N in the microbial biomass and in aggregate size fractions (250-2000 mu m, 53-250 mu m and <53 mu m) using (13)C and (15)N data. A silty loam soil (sieved <250 mu m) was incubated with and without addition of (15)N labelled maize leaves (C/N = 27.4) and roots (C/N = 86.4). Each treatment was carried out with and without fungicide application. The addition of maize residues enhanced soil respiration and microbial biomass C and N and resulted in increased macroaggregate formation with a higher and more rapid maximum macroaggregation in the soil amended with maize leaves than in that with addition of roots. Fungicide application led to a significant decline of microbial biomass C and mineralization of the added residues compared to untreated soils, which demonstrates a successful suppression of part of the active microbial biomass by the fungicide. However, this was not confirmed by a generally lower ergosterol concentration. Consequently, ergosterol was no reliable fungal biomarker in periods of rapid decline of the fungal biomass. A single addition of fungicide was insufficient for continued inhibition of the fungal biomass. Yet, a significant delay (28-42 days) in macroaggregation in fungicide treated compared to untreated samples highlighted the importance of the fungal biomass in macroaggregate formation. Macroaggregates were enriched in maize-derived (13)C and (15)N compared to microaggregates or the fraction <53 mu m. They turned over rapidly with decreasing substrate availability, which entailed a transfer of maize-derived C and N stored within macroaggregates during the first weeks of incubation to microaggregates with proceeding incubation time. Our results indicate that this transfer happened within macroaggregates, because no considerable amount of free particulate organic matter (POM) was released upon macroaggregate breakdown. We conclude that substrate decomposability and fungal activity are key factors determining extent and dynamics of macroaggregation during decomposition processes. Macroaggregate formation implied rapid incorporation and thereby short-term protection of maize-derived C and N. Moreover, macroaggregates allowed a transfer of maize-derived organic matter into microaggregates within macroaggregates, which prevented the release of significant amounts of free POM upon macroaggregate breakdown. Consequently, macroaggregates constitute to the transfer of recently added C into more stable soil organic matter fractions. (C) 2008 Elsevier Ltd. All rights reserved
Earthworm communities in temperate beech wood forest soils affected by liming
No full textTo monitor the effects of liming on forest ecosystems, experimental plots were installed in forests in mid-western Germ any. In addition to soil chemical indices, earthworm communities were investigated on these plots about IS years after first lime applications took place. As a "natural reference", communities were compared to earthworm records that derived from a beech forest on limestone. In the non-acidified plots that had never been limed only epigeic earthworms were detected in small numbers and low species richness. Forest liming caused higher pH and a higher base saturation in the mineral topsoils. To a large extent, epigeic earthworm species seemed to benefit from this and had increased in number and biomass at all three different locations selected for the investigations. The epigeic dominated communities were completed by anecic Lumbricus terrestris that was rarely found in some of the samples from one location and a number of endogeic species that showed a very patchy distribution in limed plots. In contrast to this, the soil of the beech forest on limestone showed a different community composition. It was dominated by endogeic species in abundance and by anecic species in biomass. On limestone the total biomass of earthworms clearly exceeded the biomass values from all other plots. In conclusion, a long-term support of forest earthworm fauna due to liming was detected. This support was mainly effective for epigeic species, but in some cases for endogeic and anecic species, too. (c) 2007 Elsevier Masson SAS. All rights reserved
Below and aboveground responses to lupines and litter mulch in a California grassland restored with native bunchgrasses
No full textGoals of ecosystem restoration in California grasslands include the reestablishment of plant communities with a high proportion of native species, and simultaneously improve soil nutrient cycling. Addition of annual lupines and a litter mulch layer were hypothesized to be factors that would promote the growth of the native perennial bunchgrass. Nassella pulchra, in a restored California grassland. To test this hypothesis, field mesocosms were installed, each encircling a Nassella plant, at a perennial grassland restoration site in Carmel Valley, California. Two sets of treatments were imposed: (I) seeding of the annual N-fixing legume, Lupinus bicolor; and (2) exchanging the grassland litter for a thicker mulch layer of C(4) grass litter (C/N = 99). Stable isotope analysis allowed the tracking of fates of N fixed by the legume and the C(4)-litter derived C. Treatments continued for 28 months, from December 2002 to April 2005, when most of the destructive measurements were taken. In 2005, neither treatment had significantly increased the biomass of the annuals or the perennial bunchgrass, and there was little effect on total soil C and N. Lupinus decreased the delta(15)N content, but did not affect the biomass, N and P content of the litter, which was largely composed of annual plants from the previous year. Lupinus resulted in higher soil microbial biomass carbon (SMB-C), and distinct effects on soil microbial communities, especially soil fungi, as measured by phospholipid fatty acid analysis (PLFA) and ergosterol. The high C/N litter mulch tended to increase biomass of Nassella, despite its lower P concentration, and it reduced SMB-C, presumably due to lower decomposition rates compared to the ambient litter. Using a high C/N litter mulch thus is ambiguous for grassland restoration. Repeated increases of legumes over a longer time frame may potentially increase soil fertility and soil C pools in California grasslands, but this study suggests that native perennial grasses may be slow to benefit. (C) 2009 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Substrate use and survival of fungal plant pathogens on maize residues at winter temperatures around freezing point
No full textClimate 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 degrees C was compared to permanent frost (-3 degrees 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 degrees 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 degrees C. But this was strongly reduced when F. graminearum was in competition to the other two pathogens. In summary, E culmorum was found to be highly frost tolerant and competitive against E 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 E 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. (C) 2014 Elsevier Ltd. All rights reserved.University of Kassel; DFG [1397
Decomposition of maize residues after manipulation of colonization and its contribution to the soil microbial biomass
No full textA 28-day incubation experiment at 12 degrees C was carried out on the decomposition of maize leaf litter to answer the questions: (1) Is the decomposition process altered by chemical manipulations due to differences in the colonization of maize leaf litter? (2) Do organisms using this maize material contribute significantly to the soil microbial biomass? The extraction of the maize straw reduced its initial microbial biomass C content by 25%. Fumigation and extraction eliminated the microbial biomass by 88%. In total, 17% of added maize straw C was mineralized to CO(2) during the 28-day incubation at 12 degrees C in the treatment with non-manipulated straw. Only 14% of added C was mineralized in the treatment with extracted straw as well as in the treatment with fumigated and extracted straw. The net increase in microbial biomass C was 79 mu g g(-1) soil in the treatment with non-manipulated straw and an insignificant 9 mu g g(-1) soil in the two treatments with manipulated straw. However, the net increase did not reflect the fact that the addition of maize straw replaced an identical 58% (approximate to 180 mu g g(-1) soil) of the autochthonous microbial biomass C(3)-C in all three straw treatments. In the two treatments with manipulated straw, the formation of maize-derived microbial biomass C(4)-C was significantly reduced by 25%. In the three straw treatments, the ratio of fungal ergosterol-to-microbial biomass C ratio showed a constant 60% increase compared to the control, and the contents of glucosamine and muramic acid increased by 18%. The average fungal C/bacterial C ratio was 3.6 in the soil and 5.0 in the recovered maize straw, indicating that fungal dominance was not altered by the initial chemical manipulations of the maize straw-colonizing microorganisms
Crop residue displacement by soil inversion: Annelid responses and their impact on carbon and nitrogen dynamics in a lab-based mesocosm study
Full text linkIn the context of sustainable agriculture, a deeper knowledge of the effects of soil management on soil annelids is needed, as they play an important role in many soil processes. In a laboratory mesocosm experiment, we compared the simulated effect of ploughing by inverting the top soil (crop residues at 15 cm depth) to a non-inversion treatment (crop residues on the soil surface) using the soil type Haplic Luvisol. We investigated the response of earthworms and enchytraeids and the consequences for microbial and chemical soil parameters. Four treatments with soil fauna were established by adding: (i) endogeic earthworms (Octolasion cyaneum), (ii) anecic earthworms (Lumbricus terrestris), (iii) a combination of two enchytraeid species (Enchytraeus crypticus and
Enchytraeus christenseni) and (iv) having control columns (without annelids). Feeding behaviour of annelids was investigated using isotopic analysis (δ13C, δ15N), and chemical and microbial soil properties were measured. Carbon and nitrogen losses in the form of gas emissions (CO2, N2O) and leachate were recorded during the time
of incubation. We found no interactions of soil inversion and annelid addition on chemical and microbial soil properties; these properties were closely related to crop residue placement, indicated by the effect of soil inversion between 0 and 20 cm. Below 20 cm, this effect disappeared. Here, the presence of enchytraeids enhanced soil microbial properties, regardless of soil inversion. Stimulating microbial activity and increasing soil aeration seem to be the most important factors that increase CO2-C emissions in the presence of anecic earthworms. N2O-N emissions were consistently higher (+188%) in the inverted columns. Our results show that regardless of the placement of crop residues, anecic earthworms and enchytraeids fed more on crop residue derived carbon than endogeic earthworms, while endogeic earthworms appeared to avoid feeding at the soil surface. Moreover, it was found that the inversion and the annelid effects did not interact in an experimental setting where soil inversion is carried out in a form without detracting or impairing the annelids directly
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