查看更多>>摘要：Soil oxidases play a vital role in soil organic carbon decomposition. However, the question how biotic and abiotic factors interactively affect spatial variations of soil oxidase activities within ecosystems remains unresolved. Here, we identified soil oxidase (peroxidase (PER) and polyphenol oxidase (PPO)) activities at different locations within two afforested systems (coniferous woodland and leguminous shrubland), and investigated the associated variables of vegetation, soil environments, microbial communities and spatial structure to explore their relative importance in regulating oxidase activities. Our results showed that 32.5%-46.9% of variations in oxidase activities could be explained by the localized effects of vegetation, soil environments and microbial communities. Plant-soil-microbe interactions explained more variations of oxidases compared to the sole fraction of each group. High oxidase activities were closely associated with high pH and low present litter biomass. Meanwhile, the abundance of gram-negative bacteria was the key microbial factor on oxidase activities in the woodland, while the abundance of gram-positive bacteria was the key factor on PER activity in the shrubland. Taken together, our results provide novel experimental insight into spatial variability of soil oxidases, and reveal a profound impact of key vegetation, soil and microbial factors and their localized interactions on spatial patterns of soil oxidases at ecosystem-level.
查看更多>>摘要：Soil microorganisms play key roles in agricultural ecosystems. However, little is known about their dynamic diversity patterns and community assembly processes, especially in the rare microbial biosphere in agriculture systems. In this study, we determined the responses of diversities and assembly processes of abundant and rare bacterial and fungal subcommunities to agricultural practice (i.e. cover crop) in a semiarid orchard soil by using 16S and ITS rRNA gene sequencing. We found that the community structures of abundant and rare taxa exhibited a similar response to cover crop or growth periods. Growth periods significantly changed the bacterial and fungal subcommunities structure. Only the fungal subcommunities structure was affected by cover crop. The community assembly of abundant and rare fungi was respectively dominated by stochastic process and deterministic process and less affected by cover crop and growth period. For abundant bacteria, the assembly process was dominated by heterogeneous and undominated processes, and the importance of heterogeneous selection process was increased by cover crop at setting and maturing period. The assembly process of rare bacterial community was dominated by a homogeneous selection and the relative importance of dispersal limitation was increased at maturing period. We also found that the assembly processes of abundant taxa were significantly related to the soil DON, NH4+-N, NO3--N and pH, while the assembly processes of rare taxa were significantly related to the soil DOC, AP and SOC. Our results provide new insights into the formation of the microbial community in orchard soil under a cover crop, especially the seasonal succession of abundant and rare bacterial and fungal subcommunities.
查看更多>>摘要：Reliable estimations of soil organic carbon (SOC) deficits in agroecosystems are crucial in evaluating the atmospheric C sequestration potential of agricultural soils and supporting management decisions. Nonetheless, the co-benefit on soil quality resulting from SOC accrual is rarely considered. Here, we assessed SOC saturation and soil physical quality in permanent grasslands (PG) and croplands (CR) by applying the C-saturation concept and the SOC:clay ratio as an indicator of soil physical quality to a set of long-term monitoring sites in western Switzerland. For this goal, we produced a new relationship between the silt + clay (SC) particles and the C stored in the mineral-associated fraction (MAOM(C)) and we assessed the assumption that grasslands can be used as C-saturated reference sites. The saturation in PG was not coincidental as it depended on the C accrual history. Hence, PG with the lowest MAOM(C) have not reached their C-saturation level and present a potential SOC storage under optimal management. The MAOM(C) saturation in CR was low (62 +/- 4%) and corresponded to a deficit of -8.8 +/- 1.2 mg C g(-1 )soil as compared to the current level in PG. The saturation was mainly affected by the proportion of temporary grassland in the crop rotation. The relative distribution of C between MAOM (similar to 80%) and the fine and coarse particulate organic matter (POM) was not affected by land-use types. The MAOM(C) saturation in this study (MAOM(C) = 0.372 x SC + 4.23) was similar to that reported in the litterature, but discrepancies appeared when the silt and clay contents were considered separately. SC was by far the main factor explaining MAOM(C) amount in PG (semi-partial R-2 : 0.66). In contrast to other studies, the C content of MAOM in PG (43 mg C g(-1) SC) was not related to the SC content, suggesting a fixed maximal value in C-saturated soils. Nonetheless, MAOM(C) saturation may be underestimated as the least saturated PG might still accumulate MAOM(C). Finally, the SOC:clay ratio was correlated with MAOM(C) saturation level in CR, but not in PG suggesting that targeting SOC accrual in CR optimizes the benefits between soil C storage and soil quality.
Costa, Rodolfo FagundesFirmano, Ruan FranciscoColzato, MarinaCosta Crusciol, Carlos Alexandre...
15页
查看更多>>摘要：Sulfur (S) is present mainly in organic forms in the most superficial layers of well-drained soils, despite sulfate (SO42-) being the main S-species absorbed by plants. Coupled broadcast application of lime and phosphogypsum (PG) is widely deployed as an agricultural practice to improve soil chemical properties and increase crop yields in highly weathered tropical soil areas under no-tillage system (NTS). However, the effects of large-scale application of these soil amendments to S-species distribution in soil in NTS are largely unknown. We combined S wet-chemical analysis with Synchrotron-based X-ray Absorption Near-Edge Structure Spectroscopy (XANES) to evaluate the effects of lime and PG application to S-species distribution along the soil profile (up to 150 cm). Soil samples were collected from a field-scale experiment under NTS for over 15 years. Soil was amended with lime and PG, either individually or in combination, four times during the experiment. Soil sampling was conducted 16 months after the last amendments' application, and treatments (lime, PG and lime + PG) were compared to a control (under NTS without amendments' application) and with soil samples from a native forest (reference for an undisturbed site). Broadcast PG application increased the contents of Ca-phosphate extractable S and pseudototal S (microwave assisted acid digestion) contents in the deeper layers. Two peaks representing reduced and oxidized S species were detected in S K-edge XANES spectra of all treatments and NF soil. The oxidized S peak gets sharper with increase in depth, as reduced S peak intensity decreases, and fingerprint analysis suggested a greater contribution of reduced organic S species in the most superficial soil layer followed by an increase in highly oxidized S species as depth increased. Linear combination fitting analysis confirmed a greater contribution of highly oxidized S species to the total S-species as depth increased, especially in soil samples that received PG application.
查看更多>>摘要：It has been recently reported that silicon (Si) increases methane (CH4) emission from peats through mobilizing phosphorus and organic carbon bound to iron minerals and stimulating microbial activities. However, it is unknown whether this effect of Si applies in other environments, such as warm temperate forest soils that function primarily as a CH4 sink but occasionally as a CH4 source. We tested our hypothesis that CH4 emission should increase with Si availability in warm temperate forest soils under anaerobic conditions, by incubating four soil samples collected from a variety of topographic positions in the Kiryu Experimental Watershed, in Shiga, Japan. The soil characteristics including soil pH and total phosphorus and iron contents varied among the soils. Much greater CH4 emission was observed in the soils from the riparian wetland areas than in those from the upland areas. The onset of methanogenesis was not accelerated by Si addition during the incubation. At the end of the incubation, the Si addition did not increase total CH4 production from the soils. A lack of the Si effects would be due to low quantities of phosphorus retained by iron minerals in the entire area of this watershed and high abundance of more potent electron acceptors in the upland. Overall, our results suggest that increasing Si availability exerts little influence on CH4 emissions from warm temperate forest soils under the used experimental conditions in this watershed.
查看更多>>摘要：Soil organic carbon (SOC) mineralization is essential for nutrient cycling; however, it also increases carbon emission as CO2 to the atmosphere (CO2-C). Therefore, detailed information is required to design land use practices promoting positive C balances and soil health. Short-term SOC mineralization is sensitive to soil properties. Short-term soil C mineralization at a landscape scale has been poorly describe, despite the need to understand the variability of C dynamics among environments. The objectives of this work were to 1) estimate the parameters of short-term soil C mineralization kinetics in different locations within a region and 2) explore correlations among site-specific kinetic parameters and edaphoclimatic properties of sampled sites. The study involved 150 sites with different soil and climatic characteristics sampled from a 165,000 km(2) area in central Argentina. CO2-C data were obtained from 28-day laboratory incubation experiments of the 150 soil samples. We tested three models (exponential, hyperbolic and power), which depend non-linearly on their parameters, to describe the population average cumulative CO2-C. Using nonlinear mixed models, we tested the significance of random site effects to explain variability in curve parameters among soils. Random forest was used to explain C mineralization parameters from edaphoclimatic properties. The best fit was provided by the power model with random effects on two parameters: initial C mineralization rate and mineralization rate coefficient. The results indicate heterogeneous C mineralization processes across central Argentina. The observed cumulative CO2-C after 28 days of soil incubation ranged between 250 and 1693 mg C kg(-1) soil with an average of 826 mg C kg soil(-1). Lower amounts of CO2-C (800 mg C kg(-1) soil) are expected at 28 days of mineralization in sandy loam soils with lower organic matter than in rich loam soils (more than 1000 mg C kg(-1) soil). A relational study explaining site-specific C mineralization from soil, climatic and management variables indicated a significantly higher short-term C mineralization in soils with high organic matter and soil chemical fertility, with soil properties being more important process drivers than climatic variables. Thus, short-term C mineralization kinetics can be predicted from soil properties at the large scale.
van Mourik, JanGehrt, ErnstKoegel-Knabner, IngridUrbanski, Livia...
14页
查看更多>>摘要：Plaggic Anthrosols are anthropogenic soils formed by former plaggen agriculture in north-western continental Europe. Here, we present an inventory of organic carbon (OC) concentrations and stocks of Plaggic Anthrosols and of reference soils in the vicinity without plaggen fertilization history from eight sites in northwest Germany (Lower Saxony, North Rhine-Westphalia) and the eastern parts of The Netherlands (North Brabant, Overijssel). To evaluate the enrichment of Plaggic Anthrosols with OC and the implications for OC stocks, soils were analysed for basic soil properties (bulk density, pH, OC - and nitrogen (N) concentrations), texture, and acid oxalate(Feox) and dithionite-citrate-bicarbonate-extractable iron (Fe DCB ) concentrations. Organic C stocks and plant-available water capacity (PAWC) were calculated. The plaggic topsoils are characterized by high OC concentrations (6.5-36.9 mg g(-1)) and a thickness of 53-124 cm, in contrast to the modern cultivated similar to 30 cm thick topsoils of the reference soils with 10.6-24.0 mg g(-1) OC concentration. The plaggen agriculture formed a soil with improved properties and conditions for plant growth. The addition of plaggen material to the topsoils induced a volume increase as well as higher OC concentrations in the Ap horizons, resulting in significantly higher OC stocks in the Plaggic Anthrosols (6.3-14.5 kg m(-2)) compared to the reference soils (4.9-10.5 kg m(-2)). The additional soil volume amounted to 30-56% to the total soil profile depth (1.0 to 1.6 m) and comprised 25-62% of the total OC stocks. Compared to the reference soils, the volume increase of the plaggic topsoil increased the PAWC in the effective rooting zone by 1.6 to 3.4 times. Plaggic Anthrosols represent a relic of historical farming with preserved high OC concentrations and improved storage capacity for plant-available water, causing higher nutrient availability and an increase in yields, which in turn result in higher in-situ OM input, additionally contributing to high OC stocks. The results of this study demonstrate the potential of soil melioration practices similar to the former plaggen management to induce high OC concentrations and increase OC stocks in sandy agricultural soils.
查看更多>>摘要：Peatlands around the world have been drained for agriculture and forestry practices over the last century, leading to carbon loss, water loss, and soil degradation. Soil available water capacity (AWC, the amount of water a soil can provide for plants) is one of the most important soil properties regulating the water balance and plays a pivotal role in plant growth. Compared to most mineral soils, our understanding of the impact of land management on the AWC (applies to the root zone of 0.7 m) and water storage of peat (the amount of water that is stored over the whole peat profile) is limited. In this study, we aimed to deduce possible alterations of the AWC and water storage of peat following peatland drainage and rewetting. We analyzed a comprehensive dataset (676 measurements from boreal and temperate peatlands) to seek relations between bulk density (BD) as a proxy for soil degradation, and field capacity, wilting point as well as AWC. The analyses showed that the AWC increases with BD up to a value of 0.2 g cm(-3), and a further increase in BD leads to a considerable decrease in AWC. The function between BD and AWC enables to upscale the AWC to a regional scale using readily available peat BD data. The average AWC of agricultural peatlands in Germany was estimated to be 37.8 +/- 11.3 vol% (mean +/- standard deviation). Currently, the average water storage of agricultural peatlands in Germany is approximately 19.3 km(3) (1.3 m(3) per m(2)), which is less than half of the overall water storage in the natural peatlands in Germany prior drainage (39.6 km(3)). The conversion of pristine peatlands into agricultural land through artificial drainage resulted in a water storage loss of approximately 20.3 km(3), which roughly corresponds to 27 times the volume of the lake Muritz (largest lake entirely within German territory). We conclude that several decades of peatland rewetting would have a limited role in water storage recovery due to a substantial peat thickness loss prior rewetting and low porosity of (formerly) degraded peat.
查看更多>>摘要：High-quality plant inputs to the soil with low lignin to nitrogen ratios have been conceptualized to foster the formation of soil organic matter (SOM) and carbon (C) in stabilized soil compartments, such as aggregates and organo-mineral associations (MAOM), in dependence of the soil's capacity to store additional C (i.e., C saturation deficit). Yet, evidence for these conceptualizations from field experiments is scarce and it is unclear whether factors commonly not included in laboratory experiments (such as soil depth) may modulate the influence of substrate quality on SOM formation. We, thus, tested the effect of substrates with different qualities (from European alder and Scots pine) on C stocks in bulk soil, free particulate and aggregate-occluded organic matter, and MAOM in soils at various ages after reclamation and at different soil depths in a common-garden field experiment.
查看更多>>摘要：Soils may react to the impact of wheeling with volume-changed deformation by compaction and volume-constant deformation by shearing. The different deformation mechanisms with their deteriorated effects on soil pore functions have been studied frequently, but less is known about the compaction/shearing-induced deformation on structured soils as compared with homogenized substrates. In order to document both the effect of aggregation on soil deformation behaviors as well as the sensitivity due to texture, compaction and shearing measurements were performed on soil samples from the A- horizon of a homogenized Luvisol (a silt loam with a bulk density of 1.37 g cm(-3)) and two structured Gleysols (clay loam soils with bulk densities of 1.34 g cm(-3) and 1.11 g cm(-3)). The changes of vertical settlement (Delta H), air/water-filled pores (epsilon/theta), air permeability (k(a)), and pore water pressure (u(w)) during compaction and subsequent shearing were studied. Results showed that the soil deformation behaviors due to compaction and shearing depended highly on the level of applied normal stress, especially on structured soils. At a normal stress of 50 kPa, which was smaller than the precompression strength, the structured Gleysols had only minor compaction-induced deformation (Delta H: 0 similar to 1 mm) and a contractive shear behavior. At a high normal stress of 200 kPa, which exceeded the precompression strength, both homogenized and structured soils displayed greater compaction-induced deformation (Delta H: 3.5 similar to 6.0 mm) and a dilative shear behavior. Compared with static loading, cyclic loading resulted in further deformation and dilative shear behaviors in both structured and homogenized soils. In addition, the structured soils showed a smaller decrease in epsilon/theta and maintained 10 times higher k(a) value than homogenized soils. However, shearing reduced the inter-aggregate pore continuity and enhanced the relative functionality of the sheared intra-aggregate pores, as was proofed by the more pronounced changes of u(w) (Delta u(w)) in the structured soils (from -93.0 hPa to +335.6 hPa) compared with that in the homogenized silt loam (from +2.1 hPa to +140.2 hPa). In conclusion, the well-structured clayey soils exhibited less deformation during compaction compared with the homogenized (tilled) soil with coherent structure and more silty texture. The dynamic stress application and shearing resulted in more intense weakening of soil structure because the accessibility of particle surfaces for mobilized water coincides with an enhanced stress dependent swelling and sliding due to the rapidly increased u(w).
NSTL
Elsevier