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所有论文

22761. 题目: Drying and rewetting conditions differentially affect the mineralization of fresh plant litter and extant soil organic matter
文章编号: N18062536
期刊: Soil Biology and Biochemistry
作者: Luis Lopez-Sangil, Iain P. Hartley, Pere Rovira, Pere Casals, Emma J. Sayer
更新时间: 2018-06-25
摘要: Drought is becoming more common globally and has the potential to alter patterns of soil carbon (C) storage in terrestrial ecosystems. After an extended dry period, a pulse of soil CO2 release is commonly observed upon rewetting (the so-called ‘Birch effect’), the magnitude of which depends on soil rewetting frequency. But the source and implications of this CO2 efflux are unclear. We used a mesocosm field experiment to subject agricultural topsoil to two distinct drying and rewetting frequencies, measuring Birch effects (as 3-day cumulative CO2 efflux upon rewetting) and the overall CO2 efflux over the entire drying-rewetting cycle. We used 14C-labelled wheat straw to determine the contribution of fresh (recently incorporated) plant litter or extant soil organic matter (SOM) to these fluxes, and assessed the extent to which the amount of soil microbial biomass + K2SO4-extractable organic C (fumigated-extracted C, FEC) before rewetting determined the magnitude of Birch effect CO2 pulses. Our results showed a gradual increase in SOM-derived organic solutes within the FEC fraction, and a decrease in soil microbial biomass, under more extreme drying and rewetting conditions. But, contrary to our hypothesis, pre-wetting levels of FEC were not related to the magnitude of the Birch effects. In the longer term, rewetting frequency and temperature influenced the overall (31-day cumulative) amount of CO2–C released from SOM upon rewetting, but the overall 14CO2–C respired from fresh straw was only influenced by the rewetting frequency, with no effect of seasonal temperature differences of 15 °C. We conclude that the mineralization of fresh plant litter in soils is more sensitive to water limitations than extant SOM in soils under drying-rewetting conditions. Moreover, we found little evidence to support the hypothesis that the availability of microbial and soluble organic C before rewetting determined the magnitude of the Birch effects, and suggest that future work should investigate whether these short-term CO2 pulses are predominantly derived from substrate-supply mechanisms resulting from the disruption of the soil organo-mineral matrix.

22762. 题目: Effects of artificial warming on different soil organic carbon and nitrogen pools in a subtropical plantation
文章编号: N18062535
期刊: Soil Biology and Biochemistry
作者: Yiqing Li, Yanxia Qing, Maokui Lyu, Shidong Chen, Zhijie Yang, Chengfang Lin, Yusheng Yang
更新时间: 2018-06-25
摘要: Uncertainty about the effects of climate warming on belowground processes of tropical and subtropical forests limits our ability to predict the response and feedback of such ecosystems to future climate change. Few field experiments in the tropics and subtropics have been conducted on the effects of manipulating warming on microbial community, enzyme activities and soil organic carbon (C) decomposition of forest ecosystems. Here, using buried cable techniques, we conducted a microcosm warming experiment to investigate extractable and acid resistant C and nitrogen (N) pools, microbial community composition, and enzyme activity after about 1.5 years of soil warming (+5 °C) in a subtropical plantation in southeastern China. The microbial community structure was quantified with phospholipid fatty acid (PLFA) analysis. Soil extractable and acid resistant C and N fractions were determined using a two-step sulfuric acid hydrolysis. We found that warming increased soil extractable C by 28% and acid resistant N decomposition by 20%. Soil warming decreased soil microbial N use efficiency by 31% but did not alter microbial C use efficiency. Warming differentially affected bacteria, fungi and enzymes activities. Our results suggest that climate warming can alter microbial community structure and enzyme activity and consequently lead to a serious imbalance between soil N and C decomposition in subtropical tree plantations.

22763. 题目: Experimentally testing the species-habitat size relationship on soil bacteria: A proof of concept
文章编号: N18062534
期刊: Soil Biology and Biochemistry
作者: Manuel Delgado-Baquerizo, David J. Eldridge, Kelly Hamonts, Peter B. Reich, Brajesh K. Singh
更新时间: 2018-06-25
摘要: The species-area relationship is one of the most widely reported ecological theories accounting for biodiversity of plants and animals. However, we lack solid experimental data demonstrating whether this key ecological theorem also applies in the microbial world. Here, we conducted a microcosm study to evaluate the role of habitat area in driving the diversity, abundance, composition and functioning (i.e., four enzyme activities linked to organic matter decomposition) of soil bacterial communities. Thus, we aim to evaluate whether the principle of species-area relationship is potentially applicable to soil microbes. We established a fully factorial experimental design of three island sizes ( 9, 50 and 150 cm2) by two sterile soils (low, high resources). After six months of glasshouse incubation, habitat-area was positively related to bacterial richness, relative abundance of Chloroflexi, Verrucomicrobia and δ-proteobacteria, and soil functions in both soils. Soil with higher resources always had the greatest bacterial richness and functions. Our findings provide a proof of concept by demonstrating the potential importance of both habitat-area and resource availability in driving soil bacterial biodiversity and functioning.

22764. 题目: High carbon use efficiency and low priming effect promote soil C stabilization under reduced tillage
文章编号: N18062533
期刊: Soil Biology and Biochemistry
作者: Marie Sauvadet, Gwena?lle Lashermes, Gonzague Alavoine, Sylvie Recous, Matthieu Chauvat, Pierre-Alain Maron, Isabelle Bertrand
更新时间: 2018-06-25
摘要: Increasing the accumulation of organic carbon (C) in soils is a crucial challenge both for soil fertility and for climate change mitigation. Heterotrophic microbial communities are key drivers of C cycling in the soil and are influenced by cultural practices, among other factors. However, whether changes in microbial communities in turn affect their C degradation functions is not well understood. Here, we studied the effects of prior soil management on the microbial taxonomic composition and activity of soils amended with wheat litter. Prior soil management was either conventional (CONV) (i.e., full inversion ploughing) or reduced tillage (RT) during a 5-year period in the same loamy soil in northern France. Soil samples taken from the top 5 cm of field plots were incubated with 13C-labelled litter of either flowering wheat or mature wheat for 29 days at 15 °C. We measured the C-CO2 and 13C-CO2, microbial biomass C (MBC) and 13C, and hydrolytic enzyme activities during decomposition. The initial bacterial and fungal community diversity was studied via high-throughput sequencing of ribosomal genes. The results showed that the MBC in the RT soil was initially 1.5-fold greater than that in the CONV soil; contrasting taxonomic compositions were also recorded. The soil biotic legacy impacted the degradation functions when the soils were amended with wheat litter. Compared with that in the CONV soil, the enzymatic efficiency of microorganisms in the RT soil increased by 49% and 61% in the presence of mature and flowering wheat litter, respectively. Enzyme efficiency was positively correlated with microbial litter C use efficiency (CUE) (r = 0.92, P-Value < 0.001) but negatively associated with the priming effect (PE) (r = 0.85, P-value < 0.001) across all soils and litter treatments. These findings demonstrated that the RT soil benefited both from an increase in litter C incorporated in the microbial biomass and from a reduction in soil C loss due to the PE, regardless of the quality of the decomposed litter. Our study indicated that agricultural practices such as RT, which enriches the amount of soil organic C (SOC) in the topsoil layer, can lead to positive feedback against C stabilization functions.

22765. 题目: Interactions of soil bacteria and fungi with plants during long-term grazing exclusion in semiarid grasslands
文章编号: N18062532
期刊: Soil Biology and Biochemistry
作者: Chao Zhang, Guobin Liu, Zilin Song, Jie Wang, Liang Guo
更新时间: 2018-06-25
摘要: Microbial succession has been extensively investigated during the restoration of degraded environments, but the interactions of microbes with plants and soils have not been well documented. We examined changes in the plant communities, soil variables, and microbial communities of grasslands after different periods of grazing exclusion (0, 10, 25, and 35 y) on the Loess Plateau in China. The microbial communities were characterized based on their biomass, enzymatic activities, quantity of functional microbes, and composition using high-throughput sequencing. Grazing exclusion increased the plant diversity, above- and belowground biomass, organic carbon content, total nitrogen content, microbial biomass, enzymatic activities, abundance of ammonia-oxidizing microbes, and diversities of the bacterial and fungal communities; however, the highest values of these variables occurred at the 25-y exclusion site and subsequently declined, indicating that long-term exclusion could have a negative effect on this grassland. Decreases in the abundances of Alphaproteobacteria and Leotiomycetes and increases in Acidobacteria and Sordariomycetes along the chronosequence indicated different successional patterns in the microbial communities. The patterns of change in the composition and diversity of the plant, bacterial, and fungal communities suggest that plant and bacterial succession occurred in parallel and proceeded faster than fungal succession. Indicators of the bacterial and fungal communities, including their biomass, enzymatic activities, and community composition and diversity, were affected by the plant diversity and organic carbon, total nitrogen, and nitrate nitrogen contents. Fungal succession was also susceptible to changes in the soil moisture content. These results suggest that plant diversity plays an important role in shaping the microbial communities, likely by altering the levels of soil nutrients and moisture.

22766. 题目: Interactive effects of initial pH and nitrogen status on soil organic carbon priming by glucose and lignocellulose
文章编号: N18062531
期刊: Soil Biology and Biochemistry
作者: Nang Seng Aye, Clayton R. Butterly, Peter W.G. Sale, Caixian Tang
更新时间: 2018-06-25
摘要: Soil pH and the availability of carbon (C) substrate and nutrients to microorganisms are well recognized to influence C priming. However, the mechanisms underpinning such interplay so far remain elusive. Given that liming acid soils, residue retention and fertilization are common agricultural practices, small changes in SOC content by these practices could have a big impact on the global C budget. This study aimed to gain insight into the impact of initial pH and mineral N availability on the priming effect of two C substrates with contrasting biodegradability. Stable 13C-labelled substrates, glucose and lignocellulose, were applied at the rate of 0.5 mg C g 1 soil with or without NH4NO3 to the same soil matrix with three different initial pH levels; pH 4.1 (strongly acidic), 4.7 (moderately acidic) and 6.6 (slightly acidic). The N treatment was based on a C:N of 10 of the added substrate (0.05 mg N g 1 soil) to ensure N was non-limiting. Interestingly, the priming effect was not linearly related to soil pH; greatest at pH 4.1, followed by pH 6.6 and lowest at pH 4.7. The greater net increase in microbial biomass upon C supply in strongly acidic soils compared to the moderately and slightly acidic soils would have enhanced co-metabolic decomposition of native soil organic C (SOC). The cumulative amount of primed SOC during the 30-day incubation period was greater in glucose- (21 μg C g 1) than lignocellulose-amended soils (13 μg C g 1). Nitrogen application reduced the C priming effect of both C substrates at all pH levels. This reduction was more prominent with lignocellulose and in the moderately acidic soils. The results suggest that maintaining optimal soil pH for nutrient availability and N application that exceeds the microbial N requirements in agricultural fields may minimize SOC loss via the priming effect in the short term.

22767. 题目: Liming does not counteract the influence of long-term fertilization on soil bacterial community structure and its co-occurrence pattern
文章编号: N18062530
期刊: Soil Biology and Biochemistry
作者: Bin Ma, Xiaofei Lv, Yanjiang Cai, Scott X. Chang, Miles F. Dyck
更新时间: 2018-06-25
摘要: Chemical fertilizer application is a common agronomic practice to improve crop productivity and liming is often used to counteract the soil acidification caused by long-term fertilization; however, it is unclear whether liming will counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern. Here, we examined the influence of long-term fertilization (NPKS) and liming (L) on soil bacterial community structure and its co-occurrence networks by sequencing 16S rRNA gene amplicons. Our results showed that liming counteracted the influence of long-term fertilization on soil pH, but not on soluble organic carbon (SOC) and electrical conductivity (EC). Long-term fertilization affected the abundance of Acidobacteriia, Deltaproteobacteria and Gammaproteobacteria in the 0–10 cm soil, and that of Deltaproteobacteria, Gammaproteobacteria and Gemmatimonadetes in the 10–20 cm soil; whereas liming affected the abundance of Acidobacteriia, Gammaproteobacteria, and Chloracidobacteria in the 0–10 cm soil and that of Deltaproteobacteria in the 10–20 cm soil. The bacterial community structure in soils with the NPKS-L treatment was different from that with other treatments, and was mainly affected by SOC, EC, and NO3 concentration. The link numbers in bacterial co-occurrence networks were decreased by long-term fertilization or liming alone, but were increased by the NPKS-L treatment. Notwithstanding the fact that liming alleviates fertilization-induced soil acidification, this study indicates that liming did not counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern, hence cannot recuperate the soil microbial functionality that is changed by long-term fertilization.

22768. 题目: Litter chemistry influences earthworm effects on soil carbon loss and microbial carbon acquisition
文章编号: N18062529
期刊: Soil Biology and Biochemistry
作者: Yong Zheng, Shuai Wang, Michael Bonkowski, Xiaoyun Chen, Bryan Griffiths, Feng Hu, Manqiang Liu
更新时间: 2018-06-25
摘要: Earthworms could affect soil C and N cycling process to balance their energy and nutrients requirements, and they could also regulate soil microbial community structure and microbial acquisition for C and N. However, the connection between faunal and microbial stoichiometry in the coupling soil C and N cycling remains poorly understood. In a controlled laboratory experiment, we amended soil with five litters differing in litter chemistry (clover, maize stover, wheat straw, Rumex and bagasse fiber) including a no litter control and treated them without or with earthworms (Metaphire guillelmi). After 90 d incubation, we examined changes in earthworm tissue and microbial stoichiometry and different soil C and N fractions. Earthworm tissue C content was rather stable compared with the fluctuation in tissue N, implying that C is under stronger control and associated with higher demand than N. The presence of earthworm significantly enhanced CO2 emissions and decreased particulate organic carbon (POC) and soil organic carbon (SOC) contents in the low lignin litter species clover, maize stover and wheat straw. Meanwhile, earthworm presence increased N2O cumulative emissions but exerted negligible effects on particulate organic nitrogen (PON) and soil total nitrogen (TN) contents irrespective of litter species. Correspondingly, earthworm regulated microbial C and N acquisition as C to N-degrading enzyme activity ratio were nearly doubled in the low lignin litter species clover, maize stover and wheat straw, while it was decreased in the high lignin litter species Rumex and bagasse fiber. However, the structural equation modeling indicated C loss induced by earthworms was mainly attributed to their effects on soil fungi and bacteria abundance, while much less related to C-degrading enzyme activities. In conclusion, litter species controlled earthworm effects on soil C and N loss and associated microbial acquisition for C and N, highlighting the pivotal role of resource chemistry in the regulation of soil fauna impact on soil functioning and ecosystem services.

22769. 题目: Microbial communities in soil profile are more responsive to legacy effects of wheat-cover crop rotations than tillage systems
文章编号: N18062528
期刊: Soil Biology and Biochemistry
作者: Anil Somenahally, Jesse I. DuPont, Jeffrey Brady, Javid McLawrence, Brian Northup, Prasanna Gowda
更新时间: 2018-06-25
摘要: Declining trends in soil health under continuous monoculture systems of winter wheat are a concern for sustainable production in the Southern Great Plains of the US. This study was conducted to evaluate the long-term implementation of conservation tillage in combination with nitrogen treatments and summer cover crop (cowpeas) rotations with winter wheat, for their legacy effects on soil health attributes of microbial communities and soil organic carbon (SOC). Microbial biomass and composition were estimated, along with soil physico-chemical parameters in the soil profile during the annual rotation cycle of wheat and cover crops. Positive legacy effects of cover crop rotations were evident, as arbuscular mycorrhizal fungi (AMF) biomass during the wheat-growing season was significantly higher in cover crop treatments (by around 30-70%) compared to summer fallow treatment. Some dominant taxons such as Acidobacteria, Actinobacteria, Proteobacteria (>70% of prokaryotic relative abundance) and Ascomycota (>50% of fungal relative abundance) were detected in all experimental treatments. Microbial composition did not significantly change at phylum level, although some reorganization at OTU level was evident throughout the soil profile, mostly because of nitrogen treatments. Several Glomeromycota OTUs were significantly altered by soil depth and by nitrogen fertilization suggest distinct mycorhizosphere interactions in subsurface soil than the surface soil. Tillage treatment did not significantly alter the microbial abundance and their diversity. Differences in microbial biomass-C concentration among experimental treatments did not result in a change in SOC concentrations within the soil profile. Results of this study demonstrated that summer cowpea appeared to be an effective cover crop for enhancing beneficial microbial biomass and expansion of the mycorrhizosphere to deeper soil layers. Cover crop rotations appeared to be a suitable option for rapidly enhancing soil health in winter wheat production systems.

22770. 题目: Organic amendments increase crop yields by improving microbe-mediated soil functioning of agroecosystems: A meta-analysis
文章编号: N18062527
期刊: Soil Biology and Biochemistry
作者: Gongwen Luo, Ling Li, Ville-Petri Friman, Junjie Guo, Shiwei Guo, Qirong Shen, Ning Ling
更新时间: 2018-06-25
摘要: Although numerous studies suggest that organic amendments are better at maintaining soil fertility and crop production than mineral-only fertilization, it is unclear if this occurs in different agricultural systems on a global scale. Here we report a comprehensive meta-analysis of 690 independent experiments comparing the performance of organic amendments and mineral-only fertilization on crop yields, the soil organic carbon (SOC) and total nitrogen (TN) contents, soil nutrient dynamics and biological properties. Our analysis shows that organic amendments increased crop yields on average of 27% than mineral-only fertilization. Farmyard manure (FYM) had the highest effect (49% increase) and this was especially clear in wheat croplands (40% increase). Organic amendment increased the amount of SOC (38%), TN (20%), microbial biomass carbon (MBC; 51%) and microbial biomass nitrogen (MBN; 24%) than mineral-only fertilization. Organic amendments also increased the soil microbiome enzyme activity in terms of soil hydrolytic C acquisition (C-acq; 39%), N acquisition (N-acq; 22%), P acquisition (P-acq; 48%) and oxidative decomposition (OX; 58%). Increased nutrient acquisition and oxidative decomposition could explain the positive effects of organic amendment on crop yields. These observed patterns were consistent for most organic amendments and cropping systems in diverse regions of the world. In summary, our analysis suggests that organic amendments can improve microbe-mediated soil ecosystem functioning, long-term soil fertility and crop productivity, relative to mineral fertilization, on a global scale.

22771. 题目: Physical and microbial mechanisms of decomposition vary in importance among root orders and tree species with differing chemical and morphological traits
文章编号: N18062526
期刊: Soil Biology and Biochemistry
作者: Anthony J. Minerovic, Oscar J. Valverde-Barrantes, Christopher B. Blackwood
更新时间: 2018-06-25
摘要: Decaying roots are the major source of carbon that is stabilized in soil, but our understanding of plant decomposition is primarily based on decay patterns observed in leaf tissues. Chemical traits that impact microbial activity are the primary intrinsic control over leaf decomposition, and it is usually assumed that similar mechanisms control root decay. We hypothesized that root morphological traits may be an alternative control over root decay because root tissue is embedded in soil and is similar in size to soil minerals and aggregates. We compared decomposition of roots from two coexisting tree species with contrasting traits: tulip poplar (Liriodendron tulipifera) and American elm (Ulmus americana). If morphological traits are a stronger control over decomposition than chemical traits, Ulmus roots should decompose faster due to their thinner structure and increased surface area. Alternatively, if chemical traits are more important, then Liriodendron roots should decompose faster because of greater nutrient and energy availability. Unlike previous studies, the experiment was conducted in the field using root litterbags that also included mineral soil to simulate realistic physical processes and root-soil mineral interactions. Our results indicate that controls over decomposition depend on root order. For 3–4th order roots, mass loss in Liriodendron roots was double that in Ulmus roots, reflecting chemical control, but the pattern was reversed for 1–2nd order roots, consistent with morphological control. In addition, tissue chemistry shifted dramatically during decomposition for all Liriodendron root orders, but not for Ulmus. In contrast, root morphology shifted for Ulmus, with large reductions in specific root length and tip abundance, but not for Liriodendron. These results indicate that Liriodendron decomposition occurs evenly across root orders through microbial activity, which is regulated by traditional chemical measures of recalcitrance. Ulmus roots are more chemically recalcitrant, but the finer 1–2nd order Ulmus roots still lost mass very rapidly through physical fragmentation. These differing mechanisms of decomposition have implications for how root carbon is deposited into differing pools of soil organic matter. Thick, labile roots may contribute more C to soil microbial biomass and clay-associated simple organic molecules, whereas thin, recalcitrant roots would be expected to contribute to particulate organic matter.

22772. 题目: Prokaryotic assemblages within permafrost active layer at Edmonson Point (Northern Victoria Land, Antarctica)
文章编号: N18062525
期刊: Soil Biology and Biochemistry
作者: Maria Papale, Antonella Conte, Anu Mikkonen, Luigi Michaud, Rosabruna La Ferla, Maurizio Azzaro, Gabriella Caruso, Rodolfo Paranhos, S. Cabral Anderson, Giovanna Maimone, Alessandro Ciro Rappazzo, Carmen Rizzo, Nunziacarla Spanò, Angelina Lo Giudice, Mauro Guglielmin
更新时间: 2018-06-25
摘要: This study was aimed at gaining insights on the prokaryotic community (in terms of both taxonomic composition and activities) inhabiting the active layer at Edmonson Point, an ice-free area on the eastern slope at the foot of Mount Melbourne (Northern Victoria Land, Antarctica). Samples were collected during the thawing period, when microbial physiological activities are restored to utilize previously frozen organic substrates. Despite the very small cell sizes (<0.1 μm3), indicating the occurrence of stressed, dormant and/or starved cells, the prokaryotic communities appeared to be metabolically active in the decomposition of high molecular weight (>600 Da) substrates, as indicated also by the obtained rates of enzymatic hydrolytic activities over proteolytic, glycolitic and phosphoric compounds. Taxonomical composition showed that Proteobacteria, Actinobacteria and Firmicutes dominated the prokaryotic community, with most of their members playing crucial roles in organic matter turnover, as well as nitrogen cycling, or entering a viable but not cultivable state to cope with continuously changing environmental conditions, such as in the case of the active layer. Finally, non-autochthonous bacteria (mainly of marine origin) were detected and they probably contribute to the organic matter turnover within such cold terrestrial habitat. This research provides the first comprehensive account of the prokaryotic communities inhabiting the Antarctic permafrost and contributes to existing information on the response of their abundance and metabolism in a permafrost area that undergoes to seasonal changes (e.g. in terms of temperature, water availability and ice presence).

22773. 题目: Relative abundance of denitrifying and DNRA bacteria and their activity determine nitrogen retention or loss in agricultural soil
文章编号: N18062524
期刊: Soil Biology and Biochemistry
作者: Martina Putz, Philipp Schleusner, Tobias Rütting, Sara Hallin
更新时间: 2018-06-25
摘要: Dissimilatory nitrate reduction to ammonium (DNRA) competes with denitrification for nitrate (NO3 ) and can result in conservation of nitrogen (N), whereas denitrification leads to gaseous losses in the form of nitrogen gas or the greenhouse gas nitrous oxide (N2O). Thus, promoting DNRA bacteria in agricultural soils would be tractable, but little is known about what controls them in these systems and if management or cropping regimes can affect the competition between denitrifiers and DNRA bacteria. We hypothesized that cropping systems conserving soil organic matter (SOM) and resulting in higher C/NO3 ratios would favour DNRA over denitrification, and thereby lower the N2O emissions due to shifts in the abundances of the microbial communities involved. To test this hypothesis, we compared soil of an annual cereal rotation with a ley rotation (including barley) from a long-term field experiment, each with two different N fertilizer application rates. We quantified the gross rates of denitrification and DNRA in a15N tracing experiment and quantified the abundances of the functional genes for denitrification (nirK, nirS), DNRA (nrfA) and N2O reduction (nosZI, nosZII). The annual crop rotation had changed the soil properties, whereas the ley rotation prevented depletion of SOM resulting in higher C/NO3 ratios. The abundances of both nrfA and nosZ relative to the nir genes were higher in the ley soils, which correlated with significantly higher DNRA rates and lower N2O production, compared to the annual cereal rotation. We conclude that conservation of soil N and mitigation of N2O emissions can be mediated by the soil microbiome by management of SOM.

22774. 题目: Root penetration in deep soil layers stimulates mineralization of millennia-old organic carbon
文章编号: N18062523
期刊: Soil Biology and Biochemistry
作者: Tanvir Shahzad, Muhammad Imtiaz Rashid, Vincent Maire, Sébastien Barot, Nazia Perveen, Ga?l Alvarez, Christian Mougin, Sébastien Fontaine
更新时间: 2018-06-25
摘要: Climate and land-use changes modify plant rooting depth, signifying that organic matter with long residence times in deep soil layers can be exposed to rhizospheres and associated microbial activities. The presence of roots in soils stimulates mineralization of native soil C, via a process termed the rhizosphere priming effect (RPE), which may in consequence lead to loss of soil C. By growing a deep rooting grass, Festuca arundinacea, on soil columns and under continuous dual labelling (13C- & 14C-CO2), we show that root penetration up to 80 cm into a soil profile stimulated mineralization of 15,000 year-old soil C. The RPE, after normalization with root biomass, was similar along the soil profile indicating that deep C is as vulnerable to priming as surface C. The RPE was strongly correlated with respiration of plant-derived C, and a PLFA marker representative of saprophytic fungi (18:2 6c) across all soil layers. Moreover, experimental disruption of soil structure further stimulated soil C mineralization. These findings suggest that the slow soil C mineralization in deep layers results from an impoverishment of energy-rich plant C for microorganisms (especially for saprophytic fungi), combined with a physical disconnection between soil C and microorganisms. Based on our results, we anticipate higher mineralization rates of deep millennia-old SOM in response to deeper root penetration which could be induced by changes in agricultural practices and climate.

22775. 题目: Significant release and microbial utilization of amino sugars and d-amino acid enantiomers from microbial cell wall decomposition in soils
文章编号: N18062522
期刊: Soil Biology and Biochemistry
作者: Yuntao Hu, Qing Zheng, Shasha Zhang, Lisa Noll, Wolfgang Wanek
更新时间: 2018-06-25
摘要: Amino sugars and d-amino acid enantiomers are major components of bacterial and fungal cell walls (i.e. peptidoglycan and chitin) and are often used as biomarkers of microbial residue turnover in soils. However, little is known about the in situ decomposition rates of microbial cell wall residues and how soil physicochemical properties affect this process. In this study, we investigated the in situ gross production and consumption rates of free amino sugars (glucosamine and muramic acid) and amino acids (meso-diaminopimelic acid, l-alanine, and d-alanine) by a novel isotope pool dilution assay using 15N-labeled amino compounds. Soils were obtained from six sites differing in land management (cropland, pasture, and forest) and bedrock (silicate and limestone) and incubated at three temperatures (5, 15, and 25 °C). Free glucosamine released during the decomposition of peptidoglycan and chitin contributed significantly to the extractable soil organic nitrogen pool. Gross production and consumption rates of glucosamine were higher than those of individual amino acids, i.e. L- and d-alanine. Muramic acid had a longer mean residence time (68 h compared to 2.7 h for glucosamine, L- and d-alanine) and made a negligible contribution to soil organic nitrogen fluxes, indicating that free muramic acid was not a major decomposition product of peptidoglycan in soils. Meso-diaminopimelic acid and d-alanine exhibited comparable gross production and consumption rates with l-alanine. These amino acids can be used as indicators to estimate the decomposition of peptidoglycan from bacterial cell wall residues. We found that chitin decomposition was greater in silicate soils, while peptidoglycan decomposition dominated in limestone soils. Glucosamine production rates were not correlated with soil total amino sugars, microbial community structure, or hydrolytic enzyme activities, but were highest in soils with low pH and high sand content, indicating that soil texture and soil pH may strongly influence the decomposition of amino sugar polymers. In contrast, mDAP, L- and d-alanine gross production and consumption rates were positively correlated with soil pH and clay content, due to greater depolymerization of peptidoglycan stem peptides in limestone soils. This isotope pool dilution approach strongly improves our understanding of the mechanisms and environmental controls on microbial cell wall decomposition in soils.

22776. 题目: A mixed model for landscape soil organic carbon prediction across continuous profile depth in the mountainous subtropics
文章编号: N18062521
期刊: Geoderma
作者: Moritz Laub, Sergey Blagodatsky, Rong Lang, Xueqing Yang, Georg Cadisch
更新时间: 2018-06-25
摘要: Due to the spatial variability of soil resources in rapidly changing landscapes, such as rubber expansion areas in mountainous South East Asia, landscape based soil organic carbon (SOC) stock assessments need new approaches to obtain cost effective high-resolution soil maps. 3D modelling presents the opportunity to model changes of soil properties with soil depth and in space in one single model. While most 3D models make use of spatial autocorrelation to create soil maps, it might be feasible for upscaling to neglect the spatial autocorrelation and only model autocorrelation within the soil profiles. We propose a “mixed model over continuous depth” (MMCD), which uses a linear and quadratic term to model changes of soil properties with depth and predicts the spatial distribution of soil properties at the landscape level. As the study area of 43 km2 in South West China was subject to multiple constraints such as sparse road networks, steep terrain, and poor infrastructure, we applied the cost-constrained conditioned Latin hypercube sampling (CCLHS) scheme for soil sampling at 120 locations to a depth of 1 m. The MMCD provides information on the most important drivers of selected soil properties, and their relative importance. In this study, SOC was strongly linked to an interaction of elevation with mean horizon depth (p < 0.001) and to the land use type (p < 0.001). An iterative leave-one-third-out evaluation was performed to compare the MMCD to several established 2D and 3D mapping approaches. The MMCD proofed to be as powerful as these established techniques, with an overall modelling efficiency (EF) of 0.72. All tested models had a strong decrease of accuracy with depth, from an EF of about 0.8 in the topsoil to 0.2 at 0.8 to 1 m subsoil depth. The MMCD was further used to model highly unbalanced SOC density data with 120 independent topsoil observations and only 11 locations with subsoil observations (EF of 0.75), where the computed prediction intervals (95%) accurately covered the range of legacy measurements. Our approach allowed upscaling of SOC density predictions to the surrounding larger nature reserve of 270 km2. The resulting MMCD and 3D maps revealed that on average, 15 and 10% of SOC stocks are expected in the 0.6 to 0.8 m and 0.8 to 1 m soil depth intervals, respectively. The combination of CCLHS and MMCD is particularly suitable for mountainous subtropical areas with poor road networks. However, this approach requires a strong relationship of the soil property of interest with explanatory environmental covariates, as it does not consider spatial autocorrelation for soil mapping. The advantage of this restriction is that it is easy to apply to highly unbalanced datasets and easy to upscale, given that the environmental covariates in the surrounding area are similar to the calibration area.

22777. 题目: Aggregate-related changes in soil microbial communities under different ameliorant applications in saline-sodic soils
文章编号: N18062520
期刊: Geoderma
作者: Shasha Luo, Shaojie Wang, Lei Tian, Shaohua Shi, Shangqi Xu, Fan Yang, Xiujun Li, Zhichun Wang, Chunjie Tian
更新时间: 2018-06-25
摘要: Soil ameliorants can improve soil physico-chemical properties and activate microbial communities in saline-sodic soils. However, there has been less focus on how aggregate fractions affect soil microbial communities under different ameliorant applications. Here, we used the phospholipid fatty acid (PLFA) analysis to explore the effects of soil ameliorants on microbial communities within mega-aggregates (diameter of >2 mm, ME), macro-aggregates (diameter of 0.25–2 mm, MA), and micro-aggregates (diameter of <0.25 mm, MI), based on an 8-year rice (Oryza sativa L.) field experiment. The five treatments included CK, non-amended control; SS, amended with sandy soil; DG, amended with desulfurization gypsum; FM, amended with farm manure; and M, amended with a mixture of sandy soil, desulfurization gypsum, and farm manure. Relative to the CK treatment, the SS, DG, FM, and M treatments significantly decreased the soil pH and electrical conductivity and significantly increased the soil organic carbon (SOC) content of the MI, while the FM and M treatments also significantly improved the SOC content of the MA and ME. Irrespective of the ameliorant used, the absolute abundance of total PLFAs and most microbial groups generally varied with the SOC content as follows: MA > ME > MI. Meanwhile, the proportional abundance of arbuscular mycorrhizal fungi (AMF) varied between different aggregate fractions as follows: ME > MA > MI. Additionally, the DG treatment significantly enhanced the soil aggregate stability by increasing the AMF abundance, AMF/saprotrophic fungi ratio, and SOC content of the MI. Furthermore, soil microbial groups were highly correlated with soil SOC (P < 0.001), C/N ratio (P < 0.001), pH (P < 0.01), total nitrogen (P < 0.01), and the proportion of aggregates with a >0.25 mm diameter (P < 0.05). In conclusion, desulfurization gypsum is more effective for improving the properties of saline-sodic soils in the western Songnen Plain.

22778. 题目: An investigation of organic matter quality and quantity in acid soils as influenced by soil type and land use
文章编号: N18062519
期刊: Geoderma
作者: Qinhua Shen, Manuel Suarez-Abelenda, Marta Camps-Arbestain, Roberto Calvelo Pereira, Samuel R. McNally, Francis M. Kelliher
更新时间: 2018-06-25
摘要: Knowledge of the molecular composition of soil organic matter (OM) and the interaction of OM with soil minerals is needed to fundamentally understand how the persistence of OM is affected by land use. We investigated organic carbon (C) fractions, content of short-range order constituents (SRO) (i.e., Al and Fe oxy-hydroxides) and OM chemistry of 45 top soils across a range of soil orders and land uses in New Zealand. The objective of the study was to assess the influence of different land uses on the OM quality and quantity of soils that differed in their content of SRO constituents. The C fractions considered were cold + hot water-soluble C (CH2O), C recovered in the residuum after HF treatment (CHF-residuum), and C not so recovered (CHF-mobile). Carbon in particulate OM (CPOM) was determined in non-Allophanic soils, and C extractable with sodium pyrophosphate (Cp) in Allophanic soils. The chemistry of the HF-residual OM was investigated using pyrolysis-GC/MS. The highest C content was found under grazed grasslands and, among soil orders, in Allophanic soils, which had the largest CHF-mobile and CHF-residuum contents. Yet compared to non-Allophanic, Allophanic soils were more vulnerable to loss of C (CHF-mobile and CHF-residuum) when used for cropping. The relative contribution of microbial- vs. plant-derived OM was influenced by soil order and land use: microbial-derived OM increased as the presence of SRO constituents increased, these being more abundant in Allophanic soils; soils under ungrazed grasslands had the largest contribution of fresh plant-derived molecules to OM (and of CHF-residuum to total C) while cropping had a negative impact on the contribution of plant-derived OM, consistent with a decrease in CPOM. Overall, the results showed that not only is the ability of New Zealand soils to store C soil-specific, but so too is their vulnerability to losing it when under specific land use.

22779. 题目: Control of tillage disturbance on the chemistry and proportion of raindrop-liberated particles from soil aggregates
文章编号: N18062518
期刊: Geoderma
作者: Tingyu Hou, Timothy D. Berry, Sarmistha Singh, Madison N. Hughes, Yanan Tong, A.N. Thanos Papanicolaou, Kenneth M. Wacha, Christopher G. Wilson, Indrajeet Chaubey, Timothy R. Filley
更新时间: 2018-06-25
摘要: In most agricultural systems, the raindrop-induced breakdown of soil aggregates is the initial process of surface soil erosion and redistribution of soil organic matter. The physicochemical differences between the liberated and mobilized material and the residual raindrop-stable soil aggregates can be a critical factor controlling landscape-level heterogeneity in soil biogeochemical reactivity. Using an artificial rainfall simulator with soils from southeastern Iowa, we investigated the role of management intensity on the chemical characteristics of soil particles liberated through raindrop-induced breakdown of both small aggregates (0.25–2 mm; SMAGG) and large aggregates (>2 mm; LGAGG). At all sites LGAGG exhibited lower stability to raindrop energy than SMAGG. Both soil aggregate size classes from a restored prairie and an agricultural site using reduced ridge tillage exhibited higher raindrop stability than conventionally tilled sites. In the restored prairie, the chemical composition (i.e. lignin, substituted fatty acids, SOC and TN, δ15N values) of raindrop-liberated particles was nearly indistinguishable from raindrop-stable aggregates. Among all tilled sites, with the exception of SOC in the conservation tillage site, the raindrop stable particles had relatively higher concentration of measured chemical components versus raindrop-liberated particles. Additionally, the liberated particles in all tilled sites contained higher concentration of oxidized lignin phenols, a lower proportion of cinnamyl to vanillyl lignin, and, as evidenced by the δ15N values, a trend toward a higher proportion of microbially-processed nitrogen, indicating more decomposed microbial processed organic matter. These results are important for understanding the biogeochemical impacts and resulting spatial heterogeneity of raindrop liberated and transported soil particles among landscapes with different management intensity and efforts toward soil conservation.

22780. 题目: Decoupling of topsoil and subsoil controls on organic matter dynamics in the Swiss Alps
文章编号: N18062517
期刊: Geoderma
作者: Magalì Matteodo, Stephanie Grand, David Sebag, Mike C. Rowley, Pascal Vittoz, Eric P. Verrecchia
更新时间: 2018-06-25
摘要: Our understanding of mechanisms governing soil organic matter (OM) stability is evolving. It is gradually becoming accepted that soil OM stability is not primarily regulated by the molecular structure of plant inputs, but instead by the biotic and abiotic properties of the edaphic environment. Moreover, several experimental studies conducted in artificial systems have suggested that mechanisms regulating OM stability may differ with depth in the soil profile. Up to now however, there is very limited field-scale evidence regarding the hierarchy of controls on soil OM dynamics and their changes with soil depth. In this study, we take advantage of the high heterogeneity of ecological conditions occurring in the alpine belt to identify the major determinants of OM dynamics and how their significance varies with depth in the soil profile. Aboveground litter, mineral topsoil, and subsoil samples originating from 46 soil profiles spanning a wide range of soil and vegetation types were analysed. We used Rock-Eval pyrolysis, a technique that investigates the thermal stability of OM, as an indicator of OM dynamics. Our results show a clear divergence in predictors of OM thermal stability in the litter, topsoil, and subsoil layers. The composition of OM correlated with its thermal stability in the litter layer but not in mineral soil horizons, where the supply rate of fresh organic material and the physical and chemical characteristics of the pedogenic environment appeared important instead. This study offers direct confirmation that soil OM dynamics are influenced by different ecosystem properties in each soil layer. This has important implications for our understanding of carbon cycling in soils under a changing climate.

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