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Berlin Brandenburg

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  • 1
    Language: English
    In: Biology and Fertility of Soils, 2011, Vol.47(5), pp.523-532
    Description: The objective of the present study was to determine whether substrate-induced priming effects in soils are sensitive to increasing levels of Cu and Zn. Soils were collected from ten plots of two Australian field experiments (Spalding and Avon) where increasing amounts of Cu or Zn had been added 2 years prior to sampling, reaching maximum values of 5,880 mg kg −1 for Cu and 7,400 mg kg −1 for Zn. In a 21-day incubation experiment, the effect of uniformly 14 C-labeled fructose and alanine on the mineralization of the soil organic carbon (SOC) was investigated. With increasing heavy metal content, the initial peak of soil respiration after substrate addition was retarded, indicating that the microorganisms utilizing these substrates were inhibited in soils highly contaminated with heavy metals. Both substrates strongly changed the mineralization of the soil organic matter (SOM), i.e., priming effects were induced. In the soil samples with high Cu concentrations from Spalding, fructose induced a stronger additional mineralization of the SOC than in the lower contaminated samples. In the samples with the highest Zn contamination level, negative priming effects, i.e., a reduced mineralization of SOM, were observed. In contrast, heavy metal effects in the Avon soil (pH 7.6) were less pronounced since substrate mineralization and priming effects were not directly related to the increasing heavy metal content. Apart from direct toxic heavy metal effects, the tested microbial activity parameters were also indirectly affected through the toxic heavy metal effects on plant growth. At the highest heavy metal contaminations, no fresh biomass inputs occurred during the past 2 years so that microorganisms in these soils were highly substrate-limited. As a consequence, complex interactions between different levels of heavy metal contamination, the microbial activity, and the input of SOC via plant biomass have to be considered.
    Keywords: Priming effect ; Soil organic matter ; Carbon turnover ; Soil respiration ; Heavy metals ; Biosolids
    ISSN: 0178-2762
    E-ISSN: 1432-0789
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  • 2
    Language: English
    In: Plant and Soil, 2013, Vol.367(1), pp.579-589
    Keywords: Litter fall manipulation ; Lignin degradation ; Fungi-to-bacteria ratio ; Temperate forest ; Field experiment
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 3
    Language: English
    In: Plant and Soil, 1 June 2013, Vol.367(1/2), pp.579-589
    Description: Background and aims We studied the response of lignin oxidation in soils of a beech/oak forest to changes in litter fall. Additionally we considered possible factors in lignin oxidation, including altered (i) input of fresh organic matter and (ii) fiingi-to-bacteria ratios. Methods The field-based experiment included (i) doubling and (ii) exclusion of litter fall and (iii) controls with ambient litter fall. Soil (0-20 cm depth) was sampled after 8 years. We analyzed (i) lignin using the CuO oxidation method, (ii) stocks of free and mineral-bound organic carbon (OC), (iii) the response of soil organic matter (SOM) decomposition to addition of labile organic compounds in laboratory incubations, and (iv) ratios of fungal-vs. bacterialderived amino sugars (F/B ratios). Results Litter exclusion increased stocks of free-light fraction OC, F/B ratios, the ability of the microbial community to use labile compounds for SOM decomposition, as well as acid-to-aldehyde ratios of vanillyltype lignin phenols in A horizons. Litter addition had no such effects. We assume that litter exclusion caused enhanced transport of organic debris from lower forest floor horizons with rainwater into the A horizon. Enhanced input of organic debris might have increased (i) the availability of labile compounds and (ii) F/B ratios. Consequently, lignin oxidation increased. Conclusions Enhanced input of organic debris from forest floors can increase lignin oxidation in mineral topsoils of the studied forest. The expected gradual changes in litter fall due to climate change likely will cause no such effects.
    Keywords: Physical sciences -- Chemistry -- Chemical compounds ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Biology -- Botany ; Biological sciences -- Agriculture -- Agricultural sciences ; Applied sciences -- Materials science -- Materials ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Biological sciences -- Agriculture -- Agricultural sciences ; Physical sciences -- Chemistry -- Chemical reactions ; Biological sciences -- Agriculture -- Agricultural sciences
    ISSN: 0032079X
    E-ISSN: 15735036
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  • 4
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2007, Vol.170(4), pp.551-559
    Description: It is well known that the addition of easily available substrates to soils can affect microbial activity and thus the mineralization of soil organic carbon (SOC). Up to now, little is known about the processes leading to these priming effects and which fractions of organic matter (OM) are affected. The objectives of this study were to determine if SOC associated with isolated soil size fractions showed different susceptibility to priming effects, whether these pools are easily depleted, or whether the amount of substrate addition affects the extent of priming effects. In an incubation experiment, the effect of the uniformly C‐labeled substrates fructose and alanine on the mineralization of the SOC of a Bs horizon of a Haplic Podzol was investigated. The soil sample was fractionated into the three soil size fractions sand, silt, and clay by a mild sonication followed by sieving and sedimentation. Additionally, nonfractionated soil of the horizon was included in the experiment. Every soil sample received four substrate additions repeated at weekly intervals with 3.325 μg substrate‐C (mg SOC) and a final addition of 13.3 μg substrate‐C (mg SOC) after 4 weeks. The respiration was determined hourly and CO was analyzed every 2, 4, and 7 d after the respective substrate addition. After 56 d, between 42% and 58% of the added substrates had been mineralized. Both substrates strongly increased the mineralization of the OM in all fractions (positive priming effects). The priming effects were always higher after the addition of the high substrate dose than during the first 4 weeks when four small doses were added. In general, the priming effects increased with decreasing particle size. Alanine generally caused higher priming effects than fructose in the soil size fractions (up to 280% 231%, respectively). This indicates that alanine serves not only as an energy substrate but also as a N source and, thus, also promotes microbial growth. The strong priming effects in the silt and clay fraction (133% and 125% with fructose, 172% and 168% with alanine) showed, that not only the labile pool of OM is affected, but also a more stable pool characterized by higher C ages. We assume that the stability of the OM in these fractions is not only due to recalcitrance or to interactions with the minerals, but that it may also be caused by a substrate limitation of the degrading microorganisms.
    Keywords: Priming Effect ; Soil Organic Matter ; Carbon Turnover ; Soil Respiration ; Soil Size Fraction
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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