Soil water repellency and its implications for organic matter decomposition – is there a link to extreme climatic events?

Earth system models associate the ongoing global warming with increasing frequency and intensity of extreme events such as droughts and heat waves. The carbon balance of soils may be more sensitive to the impact of such extremes than to homogeneously distributed changes in soil temperature (T_s) or soil water content (θ_s). One parameter influenced by more pronounced drying/rewetting cycles or increases in T_s is the wettability of soils. Results from laboratory and field studies showed that low θ_s, particularly in combination with high T_s can increase soil water repellency (SWR). Recent studies have provided evidence that the stability of soil organic matter (SOM) against microbial decomposition is substantially enhanced in water repellent soils. This review hypothesizes that SWR is an important SOM stabilization mechanism that could become more important because of the increase in extreme events. We discuss wettability‐induced changes in soil moisture distribution and in soil aggregate turnover as the main mechanisms explaining the reduced mineralization of SOM with increasing SWR. The creation of preferential flow paths and subsequent uneven penetration of rainwater may cause a long‐term reduction of soil water availability, affecting both microorganisms and plants. We conclude that climate change‐induced SWR may intensify the effects of climatic drought and thus affects ecosystem processes such as SOM decomposition and plant productivity, as well as changes in vegetation and microbial community structure. Future research on biosphere–climate interactions should consider the effects of increasing SWR on soil moisture and subsequently on both microbial activity and plant productivity, which ultimately determine the overall carbon balance.     

Soil structure formation and management effects on gas emission

The aim of this paper is to clarify the effect of soil management and thus also of soil aggregation on physical and chemical properties of structured soils both on a bulk soil scale, for single aggregates, as well as for homogenized material. Aggregate formation and aggregate strength depend on swelling and shrinkage processes and on biological activity and kinds of organic exudates as well as on the intensity, number and time of swelling and drying events. Thus, soil management like conventional or conservation tillage alter not only the mechanical strength but also the pore continuity and the hydraulic, gas and heat fluxes, and also alter the accessibility of exchange places for nutrients and for carbon storage (global change aspects). The possibility to predict physical properties on these various scales depends on the rigidity of the pore system. In general this rigidity depends on the above-mentioned physical and chemical processes both with respect to intensity and frequency, which again are linked to the soil management systems.     

Forms and Functions of Meso and Micro-niches of Carbon within Soil Aggregates

Soil aggregates include sand/silt/clay, water, ion and organic matter contents combined with natural dry/wet (D/W) cycling alters both the formation and function of intra-aggregate pore continuity, connectivity, dead-end storage volumes, and tortuosity. Surface aggregates in the 0-5 cm depths of most soils experience from 34 to 57 D/W cycles that exceed differences in water contents >10%. Both the rates of drying or wetting, (intensity) and the D/W range of soil water contents (severity) alter the transport of water, C and N through micro and mesofaunal habitats among multiple size domains. This report identifies micro-niche locations of accumulating soil C within soil aggregate regions that may affect nematode residence sites and migration pathways. Recent advances in X-ray microtomography enable the examination of intact pore networks within soil aggregates at resolutions as small as 4 microns. Geostatistical and multi-fractal methods provide concise characteristics of pore spatial distributions within the aggregates and are useful for comparing these alterations among soils. Aggregates subjected to multiple D/W cycles developed greater spatial correlations that parallel increases in the (13)C sorption within aggregate interiors were compared with locations of soil microbial communities. Past research indicates microbial activities within the soil aggregate matrix are spatially heterogeneous due to complex pore geometries within aggregates. Illumination of the "blackbox" interiors of soil aggregates includes a discussion of natural and anthropogenic alterations of solution flow and carbon sequestration by soil aggregates containing biophysical gradients.     

Soil organic matter turnover is governed by accessibility not recalcitrance

Mechanisms to mitigate global climate change by sequestering carbon (C) in different ‘sinks' have been proposed as at least temporary measures. Of the major global C pools, terrestrial ecosystems hold the potential to capture and store substantially increased volumes of C in soil organic matter (SOM) through changes in management that are also of benefit to the multitude of ecosystem services that soils provide. This potential can only be realized by determining the amount of SOM stored in soils now, with subsequent quantification of how this is affected by management strategies intended to increase SOM concentrations, and used in soil C models for the prediction of the roles of soils in future climate change. An apparently obvious method to increase C stocks in soils is to augment the soil C pools with the longest mean residence times (MRT). Computer simulation models of soil C dynamics, e.g. RothC and Century, partition these refractory constituents into slow and passive pools with MRTs of centuries to millennia. This partitioning is assumed to reflect: (i) the average biomolecular properties of SOM in the pools with reference to their source in plant litter, (ii) the accessibility of the SOM to decomposer organisms or catalytic enzymes, or (iii) constraints imposed on decomposition by environmental conditions, including soil moisture and temperature. However, contemporary analytical approaches suggest that the chemical composition of these pools is not necessarily predictable because, despite considerable progress with understanding decomposition processes and the role of decomposer organisms, along with refinements in simulation models, little progress has been made in reconciling biochemical properties with the kinetically defined pools. In this review, we will explore how advances in quantitative analytical techniques have redefined the new understanding of SOM dynamics and how this is affecting the development and application of new modelling approaches to soil C.     

Increasing the organic carbon stocks in mineral soils sequesters large amounts of phosphorus

Despite the fact that phosphorus (P) is critical for plant biomass production in many ecosystems, the implications of soil organic carbon (OC) sequestration for the P cycle have hardly been discussed yet. Thus, the aims of this study are, first, to synthesize results about the relationship between C and P in soil organic matter (SOM) and organic matter inputs to soils, second, to review processes that affect the C:P ratio of SOM, and third, to discuss implications of OC storage in terrestrial ecosystems for P sequestration. The study shows that the storage of OC in mineral soils leads to the sequestration of large amounts of organic phosphorus (OP) since SOM in mineral soils is very rich in P. The reasons for the strong enrichment of OP with respect to OC in soils are the mineralization of OC and the formation of microbial necromass that is P‐rich as well as the strong sorption of OP to mineral surfaces that prevents OP mineralization. In particular, the formation of mineral‐associated SOM that is favorable for storing OC in soil over decadal to centennial timescales sequesters large amounts of OP. Storage of 1,000 kg C in the clay size fraction in the topsoils of croplands sequesters 13.1 kg P. In contrast, the OC:OP ratios of wood and of peatlands are much larger than the ones in cropland soils. Thus, storage of C in wood in peatlands sequesters much less P than the storage of OC in mineral soils. In order to increase the C stocks in terrestrial ecosystems and to lock up as little P as possible, it would be more reasonable to protect and restore peatlands and to produce and preserve wood than to store OC in mineral soils.     

Reappraisal of drying and wetting effects on C and N mineralization and fluxes in soils

In the next decades, many soils will be subjected to increased drying/wetting cycles or modified water availability considering predicted global changes in precipitation and evapotranspiration. These changes may affect the turnover of C and N in soils, but the direction of changes is still unclear. The aim of the review is the evaluation of involved mechanisms, the intensity, duration and frequency of drying and wetting for the mineralization and fluxes of C and N in terrestrial soils. Controversial study results require a reappraisal of the present understanding that wetting of dry soils induces significant losses of soil C and N. The generally observed pulse in net C and N mineralization following wetting of dry soil (hereafter wetting pulse) is short‐lived and often exceeds the mineralization rate of a respective moist control. Accumulated microbial and plant necromass, lysis of live microbial cells, release of compatible solutes and exposure of previously protected organic matter may explain the additional mineralization during wetting of soils. Frequent drying and wetting diminishes the wetting pulse due to limitation of the accessible organic matter pool. Despite wetting pulses, cumulative C and N mineralization (defined here as total net mineralization during drying and wetting) are mostly smaller compared with soil with optimum moisture, indicating that wetting pulses cannot compensate for small mineralization rates during drought periods. Cumulative mineralization is linked to the intensity and duration of drying, the amount and distribution of precipitation, temperature, hydrophobicity and the accessible pool of organic substrates. Wetting pulses may have a significant impact on C and N mineralization or flux rates in arid and semiarid regions but have less impact in humid and subhumid regions on annual time scales. Organic matter stocks are progressively preserved with increasing duration and intensity of drought periods; however, fires enhance the risk of organic matter losses under dry conditions. Hydrophobicity of organic surfaces is an important mechanism that reduces C and N mineralization in topsoils after precipitation. Hence, mineralization in forest soils with hydrophobic organic horizons is presumably stronger limited than in grassland or farmland soils. Even in humid regions, suboptimal water potentials often restrict microbial activity in topsoils during growing seasons. Increasing summer droughts will likely reduce the mineralization and fluxes of C and N whereas increasing summer precipitation could enhance the losses of C and N from soils.     

Copper Sorption Behavior of Selected Soils of the Oasis in the Middle Reaches of Heihe River Basin,China

The mobility and bioavailability of copper (Cu) depends on the Cu sorption capacity of soil and also on the chemical form of Cu in soils. Laboratory batch experiments were carried out to study the sorption and distribution of Cu in nine soils differing in their physicochemical properties from the oasis in the middle reaches of Heihe river basin, China: desert soil (S-1), agricultural soils (S-2, S-3, S-8, and S-9), marshland soil (S-4), and hungriness shrub soils (S-5 and S-6). Copper sorption behavior was studied using the sorption isotherm and sequential extraction procedure. In general, the sorption capacity for Cu decreased in the order: S-4 > S-9 > S-2 > S-8 > S-3 > S-6 > S-5 > S-7 > S-1. The correlation results suggest that soils with higher CEC, silt, clay, CaCO3, and organic matter will retain Cu more strongly and in greater amounts than soils that are sandy with lower CEC, CaCO3, and organic matter. pH is not an important impact factor to Cu sorption in experimental soil samples because pH in soils used in this study had a narrow range. The distribution of sorbed Cu varied between nine soils studied and depended on both soil properties and initial added Cu concentration. There are significant differences in the distribution of Cu in each soil with the increase of initial Cu concentration. The predominance of Cu associated with the available fraction, which was over 50% of the total sorbed Cu in most cases, indicates that the change of geochemical conditions might promote the release of Cu back into soil solution thus impacting organisms in the soils. The added Cu has also the tendencies to locate in the residual fraction, which was larger than 5% of the total amount extracted from the four fractions in most soils.     

Desorption of Pyrene from Freshly-Amended and Aged Soils and its Relationship to Bioaccumulation in Earthworms

Desorption of pyrene was studied in freshly-amended and 120 d-aged samples of six different soils using a Tenax-assisted method in order to evaluate the influence of soil properties and aging time on desorption. The correlations between desorption percentage (P _d ), rapid desorption rate constant (k _rap ), and biota to soil accumulation factor (BSAF) were analyzed. Results showed that in soils with a relatively high soil organic matter (SOM) content (> 1% in this study), P _d and k _rap decreased with the increase of SOM content both in freshly amended and aged soils. This suggests that SOM is the key component for sorption organic pollutants by providing highly active combination sites, where the combined pollutant becomes difficult to desorb. In soils with a relatively low SOM content (< 1%), clay minerals played an important role through offering nanopores to entrap pollutant molecules, making it difficult for these molecules to diffuse out. Aging significantly reduced the rate and extent of pyrene desorption. It is reasonable to deduce that, during aging, some of the pyrene molecules moved from “readily desorbing sites” to “relatively slower desorbing sites,” which led to a reduction of desorption. Ln P _d showed a linear relationship with ln BSAF for both freshly-amended and aged soils, and ln k _rap only in aged soils. In freshly-amended soils, rapid desorption in some soils is too quick to be the limiting step for bioaccumulation, and, therefore, the elevation BSAF became insignificant when k _rap was larger than 3 × 10 ^{? 3} h ^{? 1} .     

Distinct microbial communities associated with buried soils in the Siberian tundra

Cryoturbation, the burial of topsoil material into deeper soil horizons by repeated freeze–thaw events, is an important storage mechanism for soil organic matter (SOM) in permafrost-affected soils. Besides abiotic conditions, microbial community structure and the accessibility of SOM to the decomposer community are hypothesized to control SOM decomposition and thus have a crucial role in SOM accumulation in buried soils. We surveyed the microbial community structure in cryoturbated soils from nine soil profiles in the northeastern Siberian tundra using high-throughput sequencing and quantification of bacterial, archaeal and fungal marker genes. We found that bacterial abundances in buried topsoils were as high as in unburied topsoils. In contrast, fungal abundances decreased with depth and were significantly lower in buried than in unburied topsoils resulting in remarkably low fungal to bacterial ratios in buried topsoils. Fungal community profiling revealed an associated decrease in presumably ectomycorrhizal (ECM) fungi. The abiotic conditions (low to subzero temperatures, anoxia) and the reduced abundance of fungi likely provide a niche for bacterial, facultative anaerobic decomposers of SOM such as members of the Actinobacteria, which were found in significantly higher relative abundances in buried than in unburied topsoils. Our study expands the knowledge on the microbial community structure in soils of Northern latitude permafrost regions, and attributes the delayed decomposition of SOM in buried soils to specific microbial taxa, and particularly to a decrease in abundance and activity of ECM fungi, and to the extent to which bacterial decomposers are able to act as their functional substitutes.     

Acidity and organic matter promote abiotic nitric oxide production in drying soils

Soils are an important source of NO, particularly in dry lands because of trade‐offs that develop between biotic and abiotic NO‐producing processes when soils dry out. Understanding how drier climates may offset the balance of these trade‐offs as soils transition toward more arid states is, therefore, critical to estimating global NO budgets, especially because drylands are expected to increase in size. We measured NO emission pulses after wetting soils from similar lithologies along an altitudinal gradient in the Sierra Nevada, CA, where mean annual precipitation varied from 670 to 1500 mm. Along the gradient, we measured field NO emissions, and used chloroform in the laboratory to reduce microbial activity and partition between biotic and abiotic NO‐producing processes (i.e., chemodenitrification). Field NO emission pulses were lowest in the acidic and SOM‐rich soils (4–72 ng NO‐N m^?2 s^?1), but were highest in the high‐elevation barren site (~560 ng NO‐N m^?2 s^?1). In the laboratory, NO emission pulses were up to 19× greater in chloroform‐treated soils than in the controls, and these abiotic pulses increased with elevation as pH decreased (6.2–4.4) and soil organic matter (SOM) increased (18–157 mg C g^?1). Drought can shift the balance between the biotic and abiotic processes that produce NO, favoring chemodenitrification during periods when biological processes become stressed. Acidic and SOM‐rich soils, which typically develop under mesic conditions, are most vulnerable to N loss via NO as interactions between pH, SOM, and drought stimulate chemodenitrification.     

Formation of aggregates by plant roots in homogenised soils

The influence of root growth and water regime on the formation of aggregates was studied in modified minirhizotrons under controlled conditions. Two soils, a black earth (67% clay) and a red-brown earth (19% clay) were ground and forced through a 0.5 mm sieve. Ryegrass, pea and wheat were grown for fifteen wetting and drying (wd) cycles for 5 months. Another set of minirhizotrons was not planted and served as a control. Measurements of aggregate size distribution (ASD), aggregate tensile strength (ATS), aggregate stability (AS), aggregate bulk density (ABD) and organic carbon (OC) were made on single aggregates of the 2–4 mm fraction. The results showed that aggregates of the black earth which has a high clay content and shrink/swell properties had more smaller aggregates with higher ATS, AS and ABD than those from the red-brown earth. It was also found that for both soils: (1) w/d cycles and higher root length density (RLD) increased the proportions of smaller aggregates and aggregate strength; (2) differences in the ability of the plant species to influence aggregation was evident and seemed to be related to the RLD. The RLD was in the order ryegrass > wheat > pea. Mechanisms likely to be involved in processes of aggregate formation and stabilization are discussed. They include cracking of soil due to tensile stresses generated during drying of a shrinking soil; changes in pore water pressure within the soil mass caused by water uptake by plant roots generating effective stresses; and biological processes associated with plant roots and root exudates.     

Influence of the Interactions Between Black Carbon and Soil Constituents on the Sorption of Pyrene

Biochar (a kind of black carbon (BC)) has been advocated as a promising additive to farmland, thus it is crucial to understand the influence of BC on the fate of hydrophobic organic chemicals (HOCs) when they exist in soil. This study explored the sorption of pyrene onto a BC sample obtained by pyrolyzing pine sawdust, two soils, clay (kaolinite), and the mixtures thereof to investigate the influence of the interactions between BC and soil constituents on the sorption of HOCs and the mechanisms therein. Sorption of pyrene onto soil?BC mixtures was significantly less than that predicted by the sum of the individual soil and BC sorption, indicating that the sorption of pyrene onto soil and BC did not occur independently. The reduction of BC sorption capacity in soil seemed primarily to be caused by soil dissolved organic matter (DOM), which attenuated pyrene sorption onto BC by 18.7%?40.3% (within pyrene equilibrium concentration range of 0.05?0.5 S _w). These were likely due to the blockage of micropores, reduced accessibility of sorption sites, and binding of pyrene by DOM in aqueous solution. In addition to the DOM effect, kaolinite also diminished pyrene sorption onto BC to some extent, which suggested additional interaction between BC and soil particles. Pyrene sorption onto the soil?BC mixtures varied with water content and contact time. The influence of wet versus dry conditions and contact time on the K_oc of pyrene was more obvious when pyrene equilibrium concentrations were lower. The effect of aging also varied with soil properties. In summary, BC could not behave independently in soil, and its sorption capacity was changed by its interactions with soil constituents, which may be influenced by soil properties, environmental condition, and contact time.     

Soil‐specific response functions of organic matter mineralization to the availability of labile carbon

Soil organic matter (SOM) mineralization processes are central to the functioning of soils in relation to feedbacks with atmospheric CO₂ concentration, to sustainable nutrient supply, to structural stability and in supporting biodiversity. Recognition that labile C‐inputs to soil (e.g. plant‐derived) can significantly affect mineralization of SOM (‘priming effects’) complicates prediction of environmental and land‐use change effects on SOM dynamics and soil C‐balance. The aim of this study is to construct response functions for SOM priming to labile C (glucose) addition rates, for four contrasting soils. Six rates of glucose (3 atm% ¹³C) addition (in the range 0–1 mg glucose g^?1 soil day^?1) were applied for 8 days. Soil CO₂ efflux was partitioned into SOM‐ and glucose‐derived components by isotopic mass balance, allowing quantification of SOM priming over time for each soil type. Priming effects resulting from pool substitution effects in the microbial biomass (‘apparent priming’) were accounted for by determining treatment effects on microbial biomass size and isotopic composition. In general, SOM priming increased with glucose addition rate, approaching maximum rates specific for each soil (up to 200%). Where glucose additions saturated microbial utilization capacity (>0.5 mg glucose g^?1 soil), priming was a soil‐specific function of glucose mineralization rate. At low to intermediate glucose addition rates, the magnitude (and direction) of priming effects was more variable. These results are consistent with the view that SOM priming is supported by the availability of labile C, that priming is not a ubiquitous function of all components of microbial communities and that soils differ in the extent to which labile C stimulates priming. That priming effects can be represented as response functions to labile C addition rates may be a means of their explicit representation in soil C‐models. However, these response functions are soil‐specific and may be affected by several interacting factors at lower addition rates.     

原油污染对黄绵土和风沙土水分入渗的影响

原油进入土壤后会堵塞土壤孔隙,影响土壤斥水性,改变土壤水分运动状况。本研究利用土柱模拟的方法,研究了不同原油污染程度(0、0.5%、1%、2%、4%)对黄绵土和风沙土水分入渗过程的影响。结果表明: 随着原油含量的增加,两种土壤湿润锋的推进速度和入渗速率均减小,土壤原油污染程度为4%时湿润锋运移到土柱底部的所需时间最长,污染程度为0时湿润锋运移到土柱底部的所需时间最短,黄绵土湿润锋达到土柱底部所需最长时间是最短时间的5倍,风沙土最长时间是最短时间的48倍;当湿润锋运移到土柱底部时,黄绵土的累积入渗量随原油含量的增加而减小,而风沙土的累积入渗量先增大后减小;在高浓度(2%、4%)原油处理下,风沙土的累积入渗量曲线出现“翘尾”现象。Kostiakov入渗模型和Philip入渗模型比Green-Ampt模型能更好地模拟不同原油处理下的黄绵土土壤水分入渗过程,但对风沙土而言,两种模型对低浓度(0、0.5%、1%)原油处理的土壤水分入渗过程拟合较好。原油污染能够显著影响土壤水分入渗过程,且对风沙土的影响更大。     

Characteristics of Soil Organic Matter and Sorption of Phenanthrene,Naphthalene 1,3,5-TCB and o-Xylene

Nonlinear isotherm behavior has been reported for the sorption of hydrophobic organic compounds (HOCs) in soil/water systems, but the mechanisms are unclear. The model of “soft” and “hard” carbon domains has been extensively cited in the sorption literature to account for nonlinear sorption behaviors, but the structural compositions of soil organic matter (SOM) are not well understood. The objective of this study was to examine the characteristics of SOM and the effect of SOM heterogeneity on sorption isotherm by elemental analysis, organic petrographic examination, scanning electron microscopy, ¹³C nuclear magnetic resonance and studying the sorption behaviors of phenanthrene, naphthalene, 1,3,5-trichlorobenzene and o-xylene in soil and its isolated fractions, humic acid (HA) and humin (denser particulates and lighter particulates). DP mainly contained low maturation and high paraffinic carbon huminite. LP was composed of inertinite, huminite, vitrinite and exinite, with smaller particle size and higher maturation than DP. Humic acid approached the lignite coal rank.

All isotherms were nonlinear, and nonlinearity increased in the following order: HA > DP > soil > BE > LP. The sorption of HOCs in soil was primarily regulated by SOM. Humic acid seemed to be the soft carbon domain and insoluble condensed organic matter (humin) the hard carbon domain. Isotherm nonlinearity was negatively correlated with hydrophobicity and molecular size, while sorption capacity increased with increase of these parameters. Aliphatic structures of SOM, as observed for LP, could also contribute to both isotherm nonlinearity and large sorption capacity.     

Differentiating chernozemic soil organic matter by acriflavine adsorption

Summary 1. Acriflavine adsorption capacities of humic substances are not easy to interpret since factors such as acid pretreatment, strength of extractant, and time and temperature of extraction all affect the data. It is thus difficult to establish with this technique whether qualitative differences exist between organic matter formed under different plant associations. 2. Acriflavine sorption capacity of the acid-precipitable humus extracted may be a measure of the efficiency of humus carbon extraction as related to the organo-mineral complexes in the soil since it correlates negatively with the clay content of the samples. 3. Acriflavine adsorption values of the acid-precipitable humus of the aeolian soils are likely to represent true or total sorption capacities of this fraction in these soils, because the clay content of these soils is low and thus extraction of those sites responsible for the acriflavine sorption reaction will be more complete.     

The origin of soil organic matter controls its composition and bioreactivity across a mesic boreal forest latitudinal gradient

Warmer climates have been associated with reduced bioreactivity of soil organic matter (SOM) typically attributed to increased diagenesis; the combined biological and physiochemical transformation of SOM. In addition, cross‐site studies have indicated that ecosystem regime shifts, associated with long‐term climate warming, can affect SOM properties through changes in vegetation and plant litter production thereby altering the composition of soil inputs. The relative importance of these two controls, diagenesis and inputs, on SOM properties as ecosystems experience climate warming, however, remains poorly understood. To address this issue we characterized the elemental, chemical (nuclear magnetic resonance spectroscopy and total hydrolysable amino acids analysis), and isotopic composition of plant litter and SOM across a well‐constrained mesic boreal forest latitudinal transect in Atlantic Canada. Results across forest sites within each of three climate regions indicated that (1) climate history and diagenesis affect distinct parameters of SOM chemistry, (2) increases in SOM bioreactivity with latitude were associated with elevated proportions of carbohydrates relative to plant waxes and lignin, and (3) despite the common forest type across regions, differences in SOM chemistry by climate region were associated with chemically distinct litter inputs and not different degrees of diagenesis. The observed climate effects on vascular plant litter chemistry, however, explained only part of the regional differences in SOM chemistry, most notably the higher protein content of SOM from warmer regions. Greater proportions of lignin and aliphatic compounds and smaller proportions of carbohydrates in warmer sites' soils were explained by the higher proportion of vascular plant relative to moss litter in the warmer relative to cooler forests. These results indicate that climate change induced decreases in the proportion of moss inputs not only impacts SOM chemistry but also increases the resistance of SOM to decomposition, thus significantly altering SOM cycling in these boreal forest soils.     

冻融交替后不同尺度黑土结构变化特征

冻融交替是改变黑土结构、加剧土壤侵蚀的重要因子。以典型黑土区耕作土壤为研究对象,采用野外季节性冻融循环与室内模拟冻融循环相结合、X射线计算机断层摄影(CT)与扫描电子显微镜(SEM)相结合的方法,通过水分物理性质、团聚体破坏率、孔隙数目、孔隙面积、孔隙成圆率、孔隙Feret直径的测定与分析,研究了冻融交替后0—40 cm、40—80 cm和120—160 cm3个土层以及田间季节性冻融环刀、室内模拟冻融CT扫描和室内模拟冻融SEM3种方式下黑土结构特征的变化规律。结果表明:冻融交替能够对不同土层和不同尺度的耕地黑土结构产生不同程度的影响。季节性冻融后,表层土壤容重升高,非毛管孔隙度和持水能力显著降低(P0.05),40—80 cm土层团聚体破坏率增加40.97%(P0.05),土壤抗蚀性有所削弱,120—160 cm土壤没有受到季节性冻融的显著影响。CT扫描尺度上,3个土层均以1—2 mm径级的孔隙数目为最多,形状也相对规则、接近圆形;冻融循环没有对表层土壤大孔隙结构产生影响,却能够显著降低40—80 cm土层范围内大孔隙面积以及Feret直径(P0.05)。SEM扫描显示冻融后土壤表面粗糙度增加,颗粒松散、脱离,孔壁断裂,证明了冻融交替对土壤微结构的破坏作用;同时结合电子能谱的元素分析可知冻融交替能够改变土壤颗粒表面化学特征。