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101.
To reduce soil destruction by urban sprawl, land use planning has to promote the use of soils within cities. As soil functions are now protected by law in Germany, urban soil quality has to be evaluated before soil management. We studied contributions from elemental carbon (EC) and soil organic matter (SOM) quality in topsoil horizons at seven sites in Stuttgart, Germany, differing in impurities by technogenic substrates. The most disturbed site was found at a disused railway area while high-density areas, public parks and garden areas showed varying degrees of disturbance by anthropogenic activities. For most soils, compounds derived from plant litter dominated organic matter (OM) quality characterized by nuclear magnetic resonance (NMR) spectroscopy. Although high contents of EC (up to 70% of soil organic carbon) were indicated by thermal oxidation, this was not confirmed by aromatic C intensities in NMR spectra. Only for the highly aromatic railway soil were results for elemental carbon by thermal oxidation and NMR similar. As other technogenic substrates beside EC like plastics may also contribute in the long-term to OM in urban soils, new analytical techniques are therefore required. This knowledge will promote the evaluation of urban soil properties and their sustainable use. 相似文献
102.
A greenhouse experiment was conducted by growing oats (Avenasativa L.) in a continuously 13CO2 labeled atmosphere. The allocation of 13C-labeled photosynthates in plants, microbial biomass in rhizosphere and root-free soil, pools of soil organic C, and CO2 emissions were examined over the plant's life cycle. To isolate rhizosphere from root-free soil, plant seedlings were placed into bags made of nylon monofilament screen tissue (16 μm mesh) filled with soil. Two peaks of 13C in rhizosphere pools of microbial biomass and dissolved organic carbon (DOC), as well as in CO2 emissions at the earing and ripeness stages were revealed. These 13C maxima corresponded to: (i) the end of rapid root growth and (ii) beginning of root decomposition, respectively. The δ13C values of microbial biomass were higher than those of DOC and of soil organic matter (SOM). The microbial biomass C accounted for up to 56 and 39% of 13C recovered in the rhizosphere and root-free soil, respectively. Between 4 and 28% of 13C assimilated was recovered in the root-free soil. Depending on the phenological stage, the contribution of root-derived C to total CO2 emission from soil varied from 61 to 92% of total CO2 evolved, including 4-23% attributed to rhizomicrobial respiration. While 81-91% of C substrates used for microbial growth in the root-free soil and rhizosphere came from SOM, the remaining 9-19% of C substrates utilized by the microbial biomass was attributable to rhizodeposition. The use of continuous isotopic labelling and physical separation of root-free and rhizosphere soil, combined with natural 13C abundance were effective in gaining new insight on soil and rhizosphere C-cycling. 相似文献
103.
Christiane Kramer 《Soil biology & biochemistry》2006,38(11):3267-3278
In this study we used compound specific 13C and 14C isotopic signatures to determine the degree to which recent plant material and older soil organic matter (SOM) served as carbon substrates for microorganisms in soils. We determined the degree to which plant-derived carbon was used as a substrate by comparison of the 13C content of microbial phospholipid fatty acids (PLFA) from soils of two sites that had undergone a vegetation change from C3 to C4 plants in the past 20-30 years. The importance of much older SOM as a substrate was determined by comparison of the radiocarbon content of PLFA from soils of two sites that had different 14C concentrations of SOM.The 13C shift in PLFA from the two sites that had experienced different vegetation history indicated that 40-90% of the PLFA carbon had been fixed since the vegetation change took place. Thus PLFA were more enriched in 13C from the new C4 vegetation than it was observed for bulk SOM indicating recent plant material as preferentially used substrate for soil microorganisms. The largest 13C shift of PLFA was observed in the soil that had high 14C concentrations of bulk SOM. These results reinforce that organic carbon in this soil for the most part cycles rapidly. The degree to which SOM is incorporated into microbial PLFA was determined by the difference in 14C concentration of PLFA derived from two soils one with high 14C concentrations of bulk SOM and one with low. These results showed that 0-40% of SOM carbon is used as substrate for soil microorganisms. Furthermore a different substrate usage was identified for different microorganisms. Gram-negative bacteria were found to prefer recent plant material as microbial carbon source while Gram-positive bacteria use substantial amounts of SOM carbon. This was indicated by 13C as well as 14C signatures of their PLFA. Our results find evidence to support ‘priming’ in that PLFA indicative of Gram-negative bacteria associated with roots contain both plant- and SOM-derived C. Most interestingly, we find PLFA indicative of archeobacteria (methanothrophs) that may indicate the use of other carbon sources than plant material and SOM to a substantial amount suggesting that inert or slow carbon pools are not essential to explain carbon dynamics in soil. 相似文献
104.
用δ~(13)C法研究黑土添加有机物料后有机碳的变化规律 总被引:1,自引:0,他引:1
通过室内短期培养实验,利用δ13C的方法研究了外源有机物料分解过程中黑土有机碳的变化规律。结果表明:黑土中添加有机物料后,土壤有机碳的数量明显增加。在有机物料分解过程中,随着培养时间的延长,土壤有机碳的总量在逐渐下降,总的变化趋势是先快后慢,渐趋平缓,到培养结束(30天),有机物料在土壤中净残留率小于50%。黑土有机碳的δ13C值受进入土壤中有机物料的种类所影响,从数量上土壤有机碳的δ13C值可以反映土壤中不同来源有机碳的变化。在小麦秸秆分解过程中,新进入黑土中的有机碳转化较快,而土壤中固有的有机碳转化较慢,添加有机物料可以增加土壤中有机碳的固定。 相似文献
105.
106.
S.M. Kristiansen M. Brandt E.M. Hansen B.T. Christensen 《Soil biology & biochemistry》2004,36(1):99-105
Analyses of the spatial and temporal variations in the natural abundance of 13C are frequently employed to study transformations of plant residues and soil organic matter turnover on sites where long continued vegetation with the C3-type photosynthesis pathway has been replaced with a C4-type vegetation (or vice versa). One controversial issue associated with such analyses is the significance of isotopic fractionation during the microbial turnovers of C in complex substrates. To evaluate this issue, C3-soil and quartz sand were amended with maize residues and with faeces from sheep feed exclusively on maize silage. The samples were incubated at 15 °C for 117 days (maize residues) or 224 days (sheep faeces). CO2 evolved during incubation was trapped in NaOH and analysed for C isotopic contents. At the end of incubation, 63 and 50% of the maize C was evolved as CO2 in the soil and sand, respectively, while 32% of the faeces C incubated with soil and with sand was recovered as CO2. Maize and faeces showed a similar decomposition pattern but maize decomposed twice as fast as faeces. The δ13C of faeces was 0.3‰ lower than that of the maize residue (δ13C −13.4‰), while the δ13C of the C3-soil used for incubation was −31.6‰. The δ13C value of the CO2 recovered from unamended C3-soil was similar or slightly lower (up to −1.5‰) than that of the C3-soil itself except for an initial flush of 13C enriched CO2. The δ13C values of the CO2 from sand-based incubations typically ranged −15‰ to −17‰, i.e. around −3‰ lower than the δ13C measured for maize and faeces. Our study clearly demonstrates that the decomposition of complex substrates is associated with isotopic fractionation, causing evolved CO2 to be depleted in 13C relative to substrates. Consequently the microbial products retained in the soil must be enriched in 13C. 相似文献
107.
Human activity has increased the amount of N entering terrestrial ecosystems from atmospheric NO3− deposition. High levels of inorganic N are known to suppress the expression of phenol oxidase, an important lignin-degrading enzyme produced by white-rot fungi. We hypothesized that chronic NO3− additions would decrease the flow of C through the heterotrophic soil food web by inhibiting phenol oxidase and the depolymerization of lignocellulose. This would likely reduce the availability of C from lignocellulose for metabolism by the microbial community. We tested this hypothesis in a mature northern hardwood forest in northern Michigan, which has received experimental atmospheric N deposition (30 kg NO3−-N ha−1 y−1) for nine years. In a laboratory study, we amended soils with 13C-labeled vanillin, a monophenolic product of lignin depolymerization, and 13C-labeled cellobiose, a disaccharide product of cellulose degradation. We then traced the flow of 13C through the microbial community and into soil organic carbon (SOC), dissolved organic carbon (DOC), and microbial respiration. We simultaneously measured the activity of enzymes responsible for lignin (phenol oxidase and peroxidase) and cellobiose (β-glucosidase) degradation. Nitrogen deposition reduced phenol oxidase activity by 83% and peroxidase activity by 74% when compared to control soils. In addition, soil C increased by 76%, whereas microbial biomass decreased by 68% in NO3− amended soils. 13C cellobiose in bacterial or fungal PLFAs was unaffected by NO3− deposition; however, the incorporation of 13C vanillin in fungal PLFAs extracted from NO3− amended soil was 82% higher than in the control treatment. The recovery of 13C vanillin and 13C cellobiose in SOC, DOC, microbial biomass, and respiration was not different between control and NO3− amended treatments. Chronic NO3− deposition has stemmed the flow of C through the heterotrophic soil food web by inhibiting the activity of ligninolytic enzymes, but it increased the assimilation of vanillin into fungal PLFAs. 相似文献
108.
Various methods exist for the isolation of particulate organic matter (POM), one of the soil‐organic‐matter (SOM) fractions reacting most sensitive on land‐use or soil‐management changes. A combination of density separation and ultrasonic treatment allows to isolate two types of POM: (1) free POM and (2) POM occluded in soil aggregates. POM fractions are closely linked to their biochemical function for the formation and stabilization of aggregates, therefore methods using different aggregate sizes may result in different POM fractions isolated. We evaluated two physical fractionation procedures to reveal whether they yield different POM fractions with respect to amount and composition, using grassland and arable soils with sandy‐loam to sandy–clay‐loam texture and thus low macroaggregate stability. Method I used air‐dried aggregates of <2.0 mm size and a low‐energy sonication for aggregate disruption, method II used field‐moist aggregates <6.3 mm and a high‐energy–sonication procedure for aggregate disruption. POM fractions were analyzed by elemental analysis (C, N) and CPMAS 13C‐NMR spectroscopy. With both methods, about similar proportions of the SOM are isolated as free or occluded POM, respectively. The free‐ and occluded‐POM fractions obtained with method I are also rather similar in C and N concentration and composition as shown by 13C‐NMR spectroscopy. Method II isolates a free‐ and occluded‐POM fraction with significantly different C and N concentrations. NMR spectra revealed significant differences in the chemical composition of both fractions from method II, with the occluded POM having lower amounts of O‐alkyl C and higher amounts of aryl C and alkyl C than the free POM. Due to the use of larger, field‐moist aggregates with minimized sample pretreatment, two distinctly different POM fractions are isolated with method II, likely to be more closely linked to their biochemical function for the formation and stabilization of aggregates. High‐energy sonication as in method II also disrupts small microaggregates <63 µm and releases fine intraaggregate POM. This fraction seems to be a significant component of occluded POM, that allows a differentiation between free and occluded POM in sandy soils with significant microaggregation. It can be concluded, that microaggregation in arable soils with sandy texture is responsible for the storage of a more degraded occluded POM, that conversely supports the stabilization of fine microaggregates. 相似文献
109.
Soil microorganisms contribute to the formation of non-living soil organic matter (SOM) by metabolic transformation of plant-derived material. After cell death, their biomass components with a specific molecular character become incorporated into SOM imprinting its chemical properties, although this process has not yet been quantified. In order to elucidate the contribution to SOM formation, we investigated the fate of gram-negative bacterial model biomass (Escherichia coli usually introduced into soil with manure or feces) during incubation of soil with isotopically (13C) and genetically (lux gene) labeled cells. The decline of living cells was monitored by the loss of bioluminescence. The carbon turnover and mineralization was balanced by bulk soil stable isotope analysis, and the persistence of nucleic acids was investigated by PCR amplification of the lux gene. During incubation, the number of viable E. coli cells decreased rapidly (99.9% within the first 42 d) serving as substrate for other microorganisms or for the formation of SOM, and bioluminescent cells could only be detected during the first 56 d. However, the lux gene was still detected after 224 d, which indicates stabilization of DNA in SOM. Although the survival of E. coli in soil is limited, only about 65% of the added labeled biomass carbon was mineralized to 13CO2 and 51% remained in soil after 224 d with an average 13C recovery of 117%. The amount of 13C found in the PLFA representative of living cells had decreased to 25% of the initial value, suggesting a proportional decrease of the 13C in the soil microbial biomass. The extent of this decrease is higher than the mineralization of the bulk E. coli C and thus the difference of around 25% has to be stabilized as metabolites, or in non-living SOM. The data provide evidence that the genetic information and a considerable part of the carbon from dying bacterial biomass were retained in both the soil microbial food web and in non-living SOM. 相似文献
110.
土壤腐殖物质的组成和结构复杂,其中含有多种官能团,是土壤碳库中的重要组成部分.固态13C NMR是研究有机化合物结构的有效手段,特别对于不溶性HM,已成为其研究的重要技术方法.本文主要介绍了固体13C NMR在土壤腐殖物质中的应用概况,总结、归纳了土壤腐殖物质中不同官能团所对应的信号区间,对比分析了腐殖物质中不同组分的结构区别,讨论分析了固体13C NMR在土壤腐殖物质结构与形态研究中的应用,以期借助固体13C NMR更加深入地对腐殖物质整体结构进行研究,推进对腐殖物质形成、转化的探讨. 相似文献