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11461. 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.

11462. 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.

11463. 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.

11464. 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.

11465. 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).

11466. 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.

11467. 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.

11468. 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.

11469. 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.

11470. 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.

11471. 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.

11472. 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.

11473. 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.

11474. 题目: Distinct bioenergetic signatures in particulate versus mineral-associated soil organic matter
文章编号: N18062516
期刊: Geoderma
作者: Elizabeth K. Williams, Marilyn L. Fogel, Asmeret Asefaw Berhe, Alain F. Plante
更新时间: 2018-06-25
摘要: Physical and chemical stabilization, environmental conditions, and organic matter composition all play vital roles in determining the persistence of soil organic matter (SOM). Fundamentally, SOM stability depends on the balance of microbial bioenergetics between the input of energy needed to decompose it (i.e., activation energy; Ea) and the net energy gained (i.e., energy density; ED) from its decomposition. This relationship is complicated in soils by chemical and physical protection mechanisms, which require additional energies to overcome for decomposition to occur. In this study, we analyze the bioenergetics of soil density fractions, which vary in their degrees of organic matter-mineral association, and show that the relationship of ED and Ea has the ability to provide information about relative differences in SOM chemical composition and stability. Our results demonstrate distinct bioenergetic signatures between particulate, light (free and occluded) fractions versus mineral-associated, heavy fractions isolated from soil samples collected at two depths from a climosequence along an elevation gradient in the Sierra Nevada, California. While there were no significant differences in ED and Ea within each fraction across climates, the light fractions (LF) were characterized by larger ED and Ea values, whereas the heavy fractions (HF) were characterized by smaller ED and Ea values. Combined with CHN analyses, we conclude that SOM in HF pools is likely comprised of relatively simple organic compounds that have long turnover rates because of chemical association with soil minerals, whereas the LF pools are comprised of more chemically complex molecules with low chemical reactivity and high Ea.

11475. 题目: Elevated [CO2] changes soil organic matter composition and substrate diversity in an arid ecosystem
文章编号: N18062515
期刊: Geoderma
作者: Malak M. Tfaily, Nancy J. Hess, Akihiro Koyama, R.D. Evans
更新时间: 2018-06-25
摘要: Little is known about how elevated atmospheric [CO2] will impact the dynamics of soil organic matter (SOM) in arid ecosystems. Evans et al. (2014) reported greater ecosystem carbon (C) and nitrogen (N) concentrations following 10 years exposure to elevated atmospheric [CO2] at the Nevada Desert Free-Air Carbon dioxide Enrichment (FACE) Facility (NDFF). In this study, we investigated potential mechanisms of SOC and total N accumulation and potential SOM stabilization using high resolution mass spectrometry. Samples were collected from soil profiles to 1 m in depth with 0.2 m increment under the dominant evergreen shrub Larrea tridentate and were air dried at room temperature. SOM was extracted sequentially with solvents with different polarity. The differences in the molecular composition and diversity of SOM in the different extracts were more evident in surface soils and declined with depth, and were consistent with higher SOC and total N concentrations under elevated than ambient [CO2]. Our results support the hypothesis that increased root exudation and/or microbial necromass from stabilization of labile C and N can contribute to SOM and N pools. We found that plant-derived compounds were primary substrates for microbial activity under elevated [CO2] and microbial necromass were the main constituents of stabilized SOM. Our results suggest that arid ecosystems are a potential large C sink under elevated [CO2], given arid ecosystems constitute 47% of the terrestrial land surface, and that labile compounds are transformed to stable SOM via microbial processes. Arid systems are limited by water, and thus may have a different C storage potential under changing climates than other ecosystems that are limited by nitrogen or phosphorus.

11476. 题目: Impact of drainage and soil hydrology on sources and degradation of organic matter in tropical coastal podzols
文章编号: N18062514
期刊: Geoderma
作者: Josiane Millani Lopes-Mazzetto, Judith Schellekens, Pablo Vidal-Torrado, Peter Buurman
更新时间: 2018-06-25
摘要: In podzols important environmental issues converge, including dissolved organic matter (DOM) transport, DOM-metal binding, and carbon storage in the subsoil. Therefore, it is important to understand the formation and degradation of podzols in relation to (changes in) environmental conditions. For this purpose a Holocene barrier island with coastal sand dunes (Ilha Comprida, SE Brazil) was chosen as study area. The island is build-up of five geomorphic units that have different age (from >5000 to 325 y BP), vegetation (restinga ecosystems), soil hydrology (flat units or units with ridges and swales) and drainage (poorly drained, well-drained, and improved drainage). Representative profiles were studied for each geomorphic unit, resulting in 100 samples from A, E, B, and C horizons, from which soil organic matter (SOM) was isolated by alkaline extraction. To better understand carbon sources and dynamics, we additionally sampled litter from different vegetation types and DOM from various sources. The molecular composition of SOM, DOM and litter was analyzed with pyrolysis gas chromatography mass spectrometry (pyrolysis-GC/MS). Comparing the pyrolysates of all samples (DOM, SOM and litter) factor analysis demonstrated that the major difference in molecular composition (factor 1) was related to the contribution from DOM (phenol, acetic acid, benzofurans, pyridine, benzene and naphthalene) or in-situ root material (straight chain aliphatics and methoxyphenols from the biomacromolecules suberan and lignin, respectively). The contribution from DOM or roots was characteristic for a profile i.e. without much change with depth. Factor 2 reflected decomposition processes, and showed that the predominantly DOM-derived B horizons were relatively enriched in aromatics compared to DOM, indicating selective decay and/or selective precipitation. In geomorphic units with swales and ridges that received DOM via groundwater flow from the catchment area, the B horizon was predominantly DOM-derived; these profiles showed large differences in the contribution from black carbon (BC; (poly)aromatics), with the younger profiles showing a larger contribution from BC in precipitated DOM. B horizons with a relatively large contribution from in-situ root materials were found in well-drained soils and in some of the poorly drained soils without lateral groundwater flow from the catchment area, i.e., the flat geomorphic unit without ridges and swales. Microbial material (N-containing compounds and sugars) was associated with relatively recent SOM and with well-drained conditions at present. i.e., well-drained profiles, and profiles with improved drainage.

11477. 题目: Irrigation with sediment-laden river water affects the soil texture and composition of organic matter fractions in arid and semi-arid areas of Northwest China
文章编号: N18062513
期刊: Geoderma
作者: Linlin Dong, Haidong Zhang, Lingqing Wang, Dongsheng Yu, Feixia Yang, Xuezheng Shi, Hafsa Saleem, M. Saleem Akhtar
更新时间: 2018-06-25
摘要: Soil organic carbon (SOC) is the largest reservoir of organic carbon in the terrestrial ecosystem, and is an effective mean of enhancing crop production in the irrigated area of the arid and semi-arid regions. Understanding long-term changes in composition of SOM under irrigation from sediment-laden Yellow River water is essential to manage sustainability issues in the agro-ecosystem. A total of 45 soils, including 39 of irrigated fields differing in irrigation history and 6 of non-cultivated and non-irrigated natural fields as the control, were sampled at 0–20 cm depth. The soil was analyzed for total SOC content, partitioning of light (LFOM) and heavy (HFOM) fraction organic matter based on NaI solution density of 1.7 g m3 and for particle size distribution. Compared to the non-irrigated and non-cultivated control soil, the LFOM and HFOM in irrigated soils increased with the duration of irrigation though SOM existed dominantly as the heavy fraction. The soils irrigated for <50 years have overall lesser LFOM and HFOM and more sand compared to those with >50 years irrigation. Further, a positive relationship existed between the fine particle and the SOM or its fractions (negative relation with coarse particle) suggesting either SOM accumulated as fine particles or the fine mineral particles better preserved SOM. In addition, field soil moisture at the time of sampling during October 2009 correlated with HFOM (p < 0.001) and LFOM (p < 0.01). The study suggested that the long-term irrigation with water diverted from Yellow River increased fine particle, SOC and the light and heavy fraction in the Ningxia Irrigation Zone.

11478. 题目: Modelling of sand/dust emission in Northern China from 2001 to 2014
文章编号: N18062512
期刊: Geoderma
作者: Heqiang Du, Tao Wang, Xian Xue, Sen Li
更新时间: 2018-06-25
摘要: Wind erosion is a major contributing factor to soil degradation and environmental pollution. As a hot spot of wind erosion, Northern China suffers from severe wind erosion hazards. Besides, there is an ongoing controversy regarding the magnitudes of sand/dust emissions of anthropogenic sources. To understand the mechanism of soil degradation and environmental pollution caused by wind erosion, and to resolve the controversy whether sand/dust emissions is from natural or anthropogenic sources in Northern China, accurate spatio-temporal distributions of sand/dust emission should be obtained. Herein, a wind erosion model with a high spatio-temporal resolution was developed and employed to identify the sand and dust emissions of areas with different land cover types. The sand and dust emission hot spots from 2001 to 2014 were mainly distributed in the Gashun Gobi and Kumutage Deserts, those are all natural areas. In these regions, the average sand and dust emissions exceeded 10,000 kg/m/y (year) and 240 g/m2/y, respectively. The intensities of sand and dust emissions demonstrated significant decreasing trends during this time. According to Moderate Resolution Imaging Spectroradiometer (MODIS) land cover data, the average sand/dust emission rates in natural sources were much higher than that in anthropogenic areas, e.g. from 2001 to 2014, the average annual dust emission of Northern China was about 130 Tg/y, and only approximately 3.7% of dust emissions originated from anthropogenic areas. Dust deflation correspondingly caused the entrainment of soil nutrients into atmosphere and result in soil degradation. Our results also show that the Soil Organic Carbon (SOC) loss due to wind erosion in Northern China was about 0.9 Tg/y and that 32.5% and 7.5% of the SOC loss originated from grasslands (including woody savannas, savannas, and grasslands) and farmlands (including croplands and cropland/natural vegetation mosaics), respectively. With regard to such severe sand and dust emissions, we believe that the results of this study could provide valuable information for the creation of strategies to cope with wind erosion hazards and measures to control the extent of wind-blown sand. In addition, the proposed model could be of interest to ecological and environmental researchers.

11479. 题目: Moderate thinning increases soil organic carbon in Larix principis-rupprechtii (Pinaceae) plantations
文章编号: N18062511
期刊: Geoderma
作者: Junyong Ma, Fengfeng Kang, Xiaoqin Cheng, Hairong Han
更新时间: 2018-06-25
摘要: Forest thinning management practices such as thinning play a major role in the process of soil organic carbon (SOC) sequestration, however, the mechanism for SOC variations is still unclear. The objectives of this study were to estimate SOC stock and its active chemical components following a short term density adjustment of stand woods. Three treatments, low intensity thinning (removal of 15% of the trees, three 25 25 m repeated plots), moderate thinning (30% removal), and heavy intensive thinning (50% removal) were compared to control plots with no thinning three years before sampling of soil carbon composition. A number of carbon components (i.e. SOC; soil total nitrogen, TN; permanganate oxidizable C, POXC; dissolved organic carbon, DOC; microbial biomass carbon, MBC) were measured in five soil layers within the Larix principis-rupprechtii plantation throughout the growing seasons of 2015 and 2016. Results indicated both SOC content and its active component, POXC content, were maximized under the moderate density adjustment (p < 0.01). Density adjustment significantly affected POXC/SOC ratio (p < 0.001), with maximum POXC content per unit SOC content also under moderate density adjustment. However, density adjustment hardly had any impact on DOC or MBC, both of which showed more obvious seasonal dynamics than SOC, TN and POXC. Summer affected SOC storage by altering the POXC, TN and MBC. Our results suggest that effects of density adjustment on POXC drive variation in SOC.

11480. 题目: No-tillage with continuous maize cropping enhances soil aggregation and organic carbon storage in Northeast China
文章编号: N18062510
期刊: Geoderma
作者: Yan Zhang, Xiujun Li, Edward G. Gregorich, Neil B. McLaughlin, Xiaoping Zhang, Yafei Guo, Aizhen Liang, Ruqin Fan, Bingjie Sun
更新时间: 2018-06-25
摘要: In Northeast China, conventional tillage practices involve removal of crop residue after harvest and prior to moldboard plowing; this has been shown to cause a decline of soil organic carbon (SOC) and degradation of soil structure. No-tillage has been suggested to be an effective way to increase SOC storage but its effectiveness in some soils and climates has been questioned. Different cropping systems also influence SOC storage. Hence, we established an experiment to evaluate how a combination of different tillage and cropping systems could improve soil aggregation and organic carbon storage. We included five treatments: a) NTMS: no tillage with maize (Zea mays L.)-soybean (Glycine max Merr.) (MS) rotation; b) MPMS: moldboard plowing with maize-soybean rotation; c) NTMM: no tillage with continuous maize (MM); d) MPMM: moldboard plowing with continuous maize; e) CTMM: conventional tillage with continuous maize (the conventional farming practice in Northeast China). All crop residues were returned to the soil except in the CTMM treatment. Returning residue to the soil significantly increased SOC storage in all tillage/cropping systems with NTMM having the highest increase in rate of SOC storage at 0.80 Mg C ha 1 yr 1 relative to the start of the experiment. The CTMM depleted SOC storage at rate of 0.52 Mg C ha 1 yr 1 relative to the start of the experiment. Soil under NTMS exhibited a significant SOC decline deep in the soil (5–30 cm) but overall SOC storage in 0–30 cm profile was equal to that under MPMS. The NTMM had the highest SOC storage and the highest proportion and associated organic carbon (OC) in occluded micro-aggregates (53–250 μm, inside of 250 μm aggregates) across all experimental treatments. The OC in occluded micro-aggregates was much higher than that associated with unprotected micro-aggregates (53–250 μm, outside of 250 μm aggregates). The effects of tillage on aggregate size and OC concentration occurred mainly in the surface layer (0–5 cm) whereas the effect of cropping system on aggregate size and OC concentration occurred at deeper depths. The MS cropping system increased the proportion of silt-clay (<53 μm, outside of 250 μm aggregates) over MM while occluded silt-clay (<53 μm, inside of 250 μm aggregates) in MM was greater than in MS in all layers. The NTMM treatments improved SOC storage and aggregation over the other treatments.

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