异质土壤对地网接地电阻的影响

分别讨论了异质土壤电阻率、截面积以及深度对地网接地电阻的影响。通过仿真研究得出:异质土壤电阻率越大,其对地网接地电阻的影响越小;异质土壤横截面积小于地网面积的10%时,其对地网接地电阻的影响可忽略,否则,需考虑其影响;在一定的深度范围内,异质土壤越深,其对地网接地电阻的影响越大。

异质Pb胁迫对超富集植物金丝草根系生长及生物量分配的影响

以Pb超富集植物金丝草(Pogonatherum crinitum)为试验材料,设置不同Pb浓度的土壤异质胁迫室内模拟试验,定量测定不同Pb胁迫浓度和斑块中金丝草的根长、体积、表面积、平均直径等形态指标,以及根系和地上部分的生物量,比较不同异质Pb胁迫下金丝草根系形态指标及生物量分配的差异。结果表明,异质Pb胁迫对金丝草根长、根体积、表面积影响较明显,但对根平均直径的影响较小;随Pb胁迫浓度的增加,金丝草在Pb胁迫斑块和无Pb斑块的根长、根体积和表面积均呈逐渐增大的趋势,但无Pb斑块均大于Pb胁迫斑块;无Pb左室、Pb胁迫右室及整株根冠比均随Pb胁迫浓度的增加表现为先增大后减小的变化规律,表明轻度Pb胁迫条件下金丝草根系生物量分配较多,但随Pb胁迫浓度的增大,地上部的生物量所占比例逐渐增大。

Phenotypic Plasticity in Response to the Heterogeneous Water Supplyin the Rhizomatous Grass Species, Calamagrostis epigejosin the Mu Us Sandy Land of China

Calamagrostis epigejos (L.) Roth. is a perennial grass with slender and long rhizome segments between interconnected neighbor ramets. To investigate the phenotypic plasticity in response to the heterogeneous soil water supply, ramet pairs of the species were subjected to heterogeneous water supply by which either mother ramets or daughter ramets were in high or low soil water supply, respectively, in the Maowusu (Mu Us) Sandy Land of Nei Mongol. The results showed that the phenotypic characteristics of the individual ramets of C epigejos were greatly influenced by the heterogeneous water supply. The ramets treated with high water supply significantly produced more new rhizomes and more offspring (ramets), and accumulated more shoot biomass, and allocated more biomass to their shoots than those treated with low water supply. In comparison with the daughter ramets in homogeneous soil water supply, phenotypic characteristics, in terms of new rhizome growth, the production of new offspring, and the biomass allocation pattern, of the daughter ramets within the pairs of the species were not significantly changed, no matter that high or low soil water supply to mother ramets. The phenotypic responses of mother ramets to soil water supply were similar to those of daughter ramets. From these results, it is inferred that the interconnected ramets of C epigejos response phenotypically to their local soil water rather than to the soil water experienced by the interconnected ramets. The interconnected ramets of C epigejos might be independent of each other in water relationship, although they are physically interconnected with rhizome segments. The physiological independence of interconnected ramets might facilitate the risk spreading and thus enhance the genet survivorship under the frequent drought stresses in Mu Us Sandland.

Heterogeneity in Soil Seed Banks in a Mediterranean Coastal Sand Dune

Characteristics of total soil seed banks and permanent soil seed banks in three microhabitats in a Mediterranean coastal sand dune were investigated by using natural germination method combined with physically scanning separation method. The composition and structure of soil seed banks were analyzed between the microhabitats by using functional group method. The distribution patterns of soil seed bank were also analyzed between the microhabitats. We also analyzed the relationship between seed size and seed persistence in soil. The results show greatly spatial heterogeneity existed in soil seed bank of the Mediterranean coastal sand dune, even in the same microhabitats seed distribution was uneven. Sometimes a great difference occurred between them. Microhabitats significantly affected the distribution patterns of total soil seed banks and seed banks of the functional groups. The open area generally had the greater densities of seeds, but the seed densities under shrub and in trail were lower than that in the open area. Legumes seeds accounted for 76.0% total persistent seed banks. Annual and perennial grasses produced transient seed banks as no seeds were retrieved from the sieved soils. Seed persistence of legumes, umbeliferaes, perennial forbs, compositaes, annual forbs, crucifer decreased gradually. They were 50.1%, 45.6%, 40.6%, 6.3%, 5.6% and 0.6% respectively in the soil. There was a positive relationship between seed size and seed persistence. Bigger seeds had higher persistence, and vice versa.

增温下土壤资源异质分布对杉木幼苗生长的影响

在福建三明森林生态系统与全球变化研究站陈大观测点开展大气温度控制、土壤温度控制和土壤资源分布3因子试验,探讨土壤资源异质分布和增温对杉木幼苗地下和地上生长的影响,以及增温是否能改变杉木幼苗细根对土壤资源异质分布的识别度,以明确杉木人工林在全球变暖背景下对土壤资源异质分布的响应.结果表明:杉木对土壤资源异质分布的识别度主要体现在吸收根(0~1 mm径级)上,而1~2 mm径级细根则不具有识别度.除了单独大气增温处理对杉木1~2 mm径级细根的避贫系数具有显著影响外,不同增温处理均未对杉木幼树细根的贫富比、趋富系数和避贫系数产生显著影响.与土壤资源均质分布相比,土壤资源异质分布增加了0~1 mm径级细根生物量,降低了树高.与无大气增温相比,大气增温降低了0~1和0~2 mm径级细根生物量,增加了树高.与无土壤增温相比,土壤增温降低了1~2 mm径级细根生物量,但增加了树高和侧枝长度.大气增温控制、土壤增温控制和土壤资源异质分布对杉木地下、地上生长都无显著交互作用.杉木幼苗吸收根本身对土壤资源异质分布具有识别度,但增温并不会改变杉木幼苗细根对土壤资源异质分布的识别度.

Heterogeneity of Physico-Chemical Properties in Structured Soils and Its Consequences

Structured soils are characterized by the presence of inter- and intra-aggregate pore systems and aggregates, which show varying chemical, physical, and biological properties depending on the aggregate type and land use system. How far these aspects also affect the ion exchange processes and to what extent the interaction between the carbon distribution and kind of organic substances affect the internal soil strength as well as hydraulic properties like wettability are still under discussion. Thus, the objective of this research was to clarify the effect of soil aggregation on physical and chemical properties of structured soils at two scales: homogenized material and single aggregates. Data obtained by sequentially peeling off soil aggregates layers revealed gradients in the chemical composition from the aggregate surface to the aggregate core. In aggregates from long term untreated forest soils we found lower amounts of carbon in the external layer, while in arable soils the differentiation was not pronounced. However, soil aggregates originating from these sites exhibited a higher concentration of microbial activity in the outer aggregate layer and declined towards the interior. Furthermore, soil depth and the vegetation type affected the wettability. Aggregate strength depended on water suction and differences in tillage treatments.

Available Contents of Trace Nutrient Element and Factors Affecting Their Availability in Western Jilin

Based on the assay of the total content and available content of the trace nutrient elements and the soil pH and organic matter of the soil samples,the characteristic of the available content of the trace nutrient elements and their affecting factors are studied. The results show that the available B in western Jilin is in a middle level,the content in Nong'an is higher than that in the others; the available Mn is extremely abundant; the available Cu in Nong'an is obviously higher than other areas,and the content in Da'an differs greatly; the available Zn is in a middle level; the severe shortage of available Mo differs between different areas; and the available Fe is extremely abundant. The available Mn,Cu and Fe have significantly positive correlation with their total content; the available B has significantly positive correlation with pH,and Zn has obviously negative correlation with pH; the available Mn and Fe had significantly positive correlation with soil organic matter.

Spatial Heterogeneity of Soil Mineral Oxide Components in Depression Between Karst Hills,Southwest China

In karst regions,the spatial heterogeneity of soil mineral oxides and environmental variables is still not clear.We investigated the spatial heterogeneity of SiO2,Al2O3,Fe2O3,CaO,MgO,P2O5,K2O,and MnO contents in the soils of slope land,plantation forest,secondary forest,and primary forest,as well as their relationships with environmental variables in a karst region of Southwest China.Geostatistics,principal component analysis(PCA),and canonical correlation analysis(CCA)were applied to analyze the field data.The results show that SiO2was the predominant mineral in the soils(45.02%–67.33%),followed by Al2O3and Fe2O3.Most soil mineral oxide components had a strong spatial dependence,except for CaO,MgO,and P2O5in the plantation forest,MgO and P2O5in the secondary forest,and CaO in the slope land.Dimensionality reduction in PCA was not appropriate due to the strong spatial heterogeneity in the ecosystems.Soil mineral oxide components,the main factors in all ecosystems,had greater influences on vegetation than those of conventional soil properties.There were close relationships between soil mineral oxide components and vegetation,topography,and conventional soil properties.Mineral oxide components affected species diversity,organic matter and nitrogen levels.

Modeling of forest soil and litter health using disturbance and landscape heterogeneity indicators in northern Iran

This paper focuses on the indicators of soil and litter health, disturbance, and landscape heterogeneity as a tool for prediction of ecosystem sustainability in the northern forests of Iran. The study area was divided into spatial homogenous sites using slope, aspect, and soil humidity classes. Then a range of sites along the disturbance gradient was selected for sampling. Chemical and physical indicators of soil and litter health were measured at random points within these sites. Structural equation modeling(SEM) was applied to link six constructs of landscape heterogeneity, three constructs of disturbance(harvest, livestock, and human accessibility), and soil and litter health. The results showed that with decreasing accessibility, the total N and organic matter content of soil increased and effective bulk density decreased. Harvesting activities increased soil organic matter. Therefore, it is concluded that disturbances through harvesting and accessibility inversely affect the soil health. Unexpectedly, it was found that the litter total C and C:N ratio improved with an increase in the harvest and accessibility disturbances, whereas litter bulk density decreased. Investigation of tree composition revealed that in the climax communities, which are normally affected more by harvesting activities, some species like Fagus orientalis Lipsky with low decomposition rate are dominant. The research results showed that changes in disturbance intensity are reflected in litter and soil indicators, whereas the SEM indicated that landscape heterogeneity has a moderator effect on the disturbance to both litter and soil paths.

Reciprocal Effects of Plant-Soil Relationships at Two Spatial Scales in a Semiarid Land of Central Mexico

We studied the influence of soil heterogeneity on plant community structure in a semiarid region of Central Mexico using Bray-Curtis Ordination. The results showed that some edaphic factors, such as soil depth, organic matter, and potassium and calcium content, explained 80% of the total variation in structure of the studied communities. We found that soil resources were heterogeneously distributed in the study area, indicating that the edaphic variables considered in this study explain the existing plant community variability, moreover the presence of some shrubs as Krameria cytisoides influences the soil properties, suggesting that there is a reciprocal effect between plant and soil.

Scaling of Soil Carbon,Nitrogen,Phosphorus and C:N:P Ratio Patterns in Peatlands of China

Inspired by the importance of Redfield-type C:N:P ratios in global soils,we looked for analogous patterns in peatlands and aimed at deciphering the potential affecting factors.By analyzing a suite of peatlands soil data(n = 1031),mean soil organic carbon(SOC),total nitrogen(TN) and total phosphorous(TP) contents were 50.51%,1.45% and 0.13%,respectively,while average C:N,C:P and N:P ratios were 26.72,1186.00 and 46.58,respectively.C:N ratios showed smaller variations across different vegetation coverage and had less spatial heterogeneity than C:P and N:P ratios.No consistent C:N:P ratio,though with a general value of 1245:47:1,was found for entire peatland soils in China.The Northeast China,Tibet,Zoigê Plateau and parts of Xinjiang had high soil SOC,TN,TP,and C:P ratio.Qinghai,parts of the lower reaches of the Yangtze River,and the coast zones have low TP and N:P ratio.Significant differences for SOC,TN,TP,C:N,C:P and N:P ratios were observed across groups categorized by predominant vegetation.Moisture,temperature and precipitation all closely related to SOC,TN,TP and their pairwise ratios.The hydrothermal coefficient(RH),defined as annual average precipitation divided by temperature,positively and significantly related to C:N,C:P and N:P ratios,implying that ongoing climate change may prejudice peatlands as carbon sinks during the past 50 years in China.

Evaluation of Spatial Variability of Soil Properties in a Long-Term Experimental Tobacco Station in Southwest China

Analysis of the spatial variability of soil properties is important to arrange the experimental treatments in the experimental station. This paper aims to study the spatial structure of soil variables and their distribution in the Pengshui tobacco experiment station in Chongqing, China. Soil samples were taken from 289 soil points on 20 m grid in March 2012. Twenty-two soil chemical and physical properties were analyzed by classical statistical and geo-statistical methods. Soil pH, cation exchange capacity （CEC）, total phosphorus （TP）, available phosphorus （AP）, zinc （Zn）, magnesium （Mg） and sulphur （S） have the strong spatial dependence, with nugget/sill ratios of less than 25%. The others have the moderate dependence with nugget/sill ratios of 26.17% to 71.04%. Ranges of the spatial correlation varied from 51.30 m for chlorine （C1） to 594.90 m for TP. The clearly patchy maps of the nutrients showed the spatial distributions of the soil variables, which can be used for better management of experimental treatments, achieving reliable exoerimental results in the tobacco exnerimental station.Highlight： Scientific experimentation assumes the existence of random variability for soil attributes. This research was to evaluate the spatial variability of soil chemical and physical attributes and to interpolate the spatial distribution of soil properties in the tobacco experimental station in Chongqing. The result of this work can be used for the agricultural management of tobacco cultivation.

Effect of Heterogeneities in Soil on Spatial Variation of Peak Ground Acceleration

In the proximity of an active fault, spatial variation of peak ground motion is significantly affected by the faulting mechanism. It has been observed that near fault ground motions consists of different characteristics compared to the far fault ground motions. Near fault records, in the distance range of less than 100 m from the faults are not available except for few cases. Therefore numerical simulation of ground motions for such near-fault situations is necessary. In addition to the understanding of the phenomenon of near fault ground motion there is a need to enhance our understanding of the possible potential hazard that can be caused due to the future rupture activity by understanding the phenomenon of surface faulting. In this paper we propose numerical simulation based on discrete modeling to investigate the fault rupture propagation and its effect on the surface peak ground acceleration. In the present two dimensional study rupture propagation due to bedrock motion has been observed for different shear wave velocity. A model of size 1000× 150 m is selected for this purpose. It has been observed that as the stiffness of the media is decreasing, the affected surface is decreasing and also width of the shear crack zone is decreasing. Secondly, we attempted to study the ground motion on the surface due to the bedrock motion in presence of boulders in the soil media by keeping the boulder at different positions. We find that there is an increase in the shear zone as well as the PGA on the surface when the boulder is present on the foot wall and in the vicinity of the rupture zone. Finally, we performed the analysis using layered media and studied the affect of crack propagation and also the variation of peak accelerations. Findings from the study can be utilized to assess the damage potential of the near fault areas.

Neighbour effects on plant biomass and its allocation for forbs growing in heterogeneous soils

Focal plants are considerably affected by their neighbouring plants,especially when growing in heterogeneous soils.A previous study on grasses demonstrated that soil heterogeneity and species composition affected plant biomass and above-and belowground allocation patterns.We now tested whether these findings were similar for forbs.Three forb species(i.e.Spartina anglica,Limonium bicolor and Suaeda glauca)were grown in pots with three levels of soil heterogeneity,created by alternatively filling resource-rich and resource-poor substrates using small,medium or large patch sizes.Species compositions were created by growing these forbs either in monocultures or in mixtures.Results showed that patch size×species composition significantly impacted shoot biomass,root biomass and total biomass of forbs at different scales.Specifically,at the pot scale,shoot biomass,root biomass and total biomass increased with increasing patch size.At the substrate scale,shoot biomass and total biomass were higher at the large patch size than at the medium patch size,both in resource-rich and resource-poor substrates.Finally,at the community scale,monocultures had more shoot biomass,root biomass and total biomass than those in the two-or three-species mixtures.These results differ from earlier findings on the responses of grasses,where shoot biomass and total biomass decreased with patch size,and more shoot biomass and total biomass were found in resource-rich than resource-poor substrates.To further elucidate the effects of soil heterogeneity on the interactions between neighbour plants,we advise to conduct longer-term experiments featuring a variety of functional groups.

Scale Dependence of Soil Spatial Variation in a Temperate Desert

Spatial variation is a ubiquitous feature of natural ecosystems, especially in arid regions, and is often present at various scales in these regions. To determine the scale dependence of the heterogeneity of soil chemical properties and the dominant scales(factors) for soil heterogeneity in arid regions, the spatial variability of soil resources was investigated in the Gurbantunggut Desert of Central Asia at the scales of 10-3, 10-2, 10-1, 100, 101, 102, 103and 104m(from individual plant to population or community to ecosystem). Soil chemical properties including pH, electrical conductivity(EC), organic carbon, total nitrogen, available nitrogen, total phosphorus, and available phosphorus were considered in the investigation. At a scale of 10-1m, which represented the scale of individual plant, significant enrichment of soil resources occurred under shrub canopy and "fertile islands" formed in the desert ecosystem. Soil EC exhibited the largest heterogeneity at this scale, indicating that individual plants exerted a great influence on soil salinity/alkalinity. Soil nutrients exhibited the greatest heterogeneity at a scale of 102m, which represented the scale of sand dune/interdune lowlands(between communities). The main important factors contributing to soil spatial heterogeneity in the Gurbantunggut Desert were individual plants and different topographic characteristics, namely, the appearance of vegetation, especially shrubs or small trees, and existing sand dunes. Soil salinity/alkalinity and soil nutrient status behaved differently in spatial heterogeneity, with an inverse distribution between them at the individual scale.

Field and Numerical Tests of the Two-Ponding Depth Procedure for Analysis of Single-Ring Pressure Infiltrometer Data

The two-ponding depth （TPD） analysis procedure of single-ring infiltrometer data can yield invalid results, i.e., negative values of the field-saturated soil hydraulic conductivity or the matric flux potential, denoting failure of the two-level run. The objective of this study was to test the performance of the TPD procedure in analyzing the single-ring infiltrometer data of different types of soils. A field investigation carried out in western Sici]y, Italy, yielded higher failure rates （40%） in two clay loam soils than in a sandy loam soil （25%）. A similar result, i.e., fine-textured soils yielding higher failure rates than the coarse-textured one, was obtained using numerically simulated infiltration rates. Soil heterogeneity and reading errors were suggested to be factors determining invalid results in the field. With the numerical data, allowing a less generic definition of soil heterogeneity, invalid TPD results were occasionally obtained with the simultaneous occurrence of a high random variation （standard deviation ≥ 0.5） and a well developed structural correlation for saturated hydraulic conductivity （correlation length 〉 20 cm）. It was concluded that a larger number of replicated runs should be planned to characterize fine-textured soils, where the risk to obtain invalid results is relatively high. Large rings should be used since they appeared more appropriate than the small ones to capture and average soil heterogeneity. Numerical simulation appeared suitable for developing improved strategies of soil characterization for an area of interest, which should also take into account macropore effects.

Spatial Heterogeneity of Soil Nutrients and Respiration in the Desertified Grasslands of Inner Mongolia,China

There is a limited knowledge of spatial heterogeneity in soil nutrients and soil respiration in the semi-arid and arid grasslands of China. This study investigated the spatial differences in soil nutrients and soil respiration among three desertified grasslands and within two shrub-dominated communities on the Ordos Plateau of Inner Mongolia, China in 2006. Both soil organic carbon （SOC） and total nitrogen （TN） were significantly different （P 〈 0.01） among the three desertified grasslands along a degradation gradient. Within the two shrub-dominated communities, the SOC and TN contents decreased with increasing distance from the main stems of the shrub, and this ＂fertile island＂ effect was most pronounced in the surface soil. The total soil respirations during the growing season were 131.26, 95.95, and 118.66 g C m^-2, respectively, for the steppe, shrub, and shrub-perennial grass communities. The coefficient of variability of soil respiration was the highest in the shrub community and lowest in the steppe community. CO2 effiuxes from the soil under the canopy of shrub were significantly higher than those from the soil covered with biological crusts and the bare soil in the interplant spaces in the shrub community. However, soil respiration beneath the shrubs was not different from that of the soil in the inter-shrub of the shrub-perennial grass community. This is probably due to the smaller shrub size. In the two shrub-dominated communities, spatial variability in soil respiration was found to depend on soil water content and C：N ratio.

Effects of three-dimensional soil heterogeneity on seed germination in controlled experiments

Aims Seed germinations react to their local growing conditions,but the impacts of soil heterogeneity on seed germinations are not well known.Methods Effects of three-dimensional soil heterogeneity on seed germinations of grasses species were explored,where two levels of such soil heterogeneity were created via alternatively filling nutrient-poor and nutrientrich substrate in pot in all directions.Patch sizes of the two heterogeneity levels are around 7.5 and 15 cm,respectively.Fifty seeds of each of the grasses species(Lolium perenne and Elymus nutans)were set either in these heterogeneous soils or in petri dishes with distilled water.Seed germinations of these species were daily recorded.Important Findings We found that pots with smaller patches had relatively lower germination rate,which is con sistent with our expectati on that shorter distance between nutrient-rich and nu trient-poor patches in pots with smaller patches allows plants to reduce their germination rates and delay their germination,in order to reduce the negative impacts of the strong variation of soil resources in these pots.Our results also revealed that pots with smaller patches yielded more heterogeneous seed germination,i.e.seed germinations highly diverged among these pots.These findings highlight that the realistic three-dimensional design can improve our understanding of seed germination as driven by soil spatial heterogeneity.

Effects of plant intraspecific variation on the prediction of C_(3)/C_(4)vegetation ratio from carbon isotope composition of topsoil organic matter across grasslands

Aims Understanding the patterns and drivers of carbon isotope discrimination(13Δ)in C_(3)and C_(4)functional groups is critical for predicting C_(3)/C_(4)vegetation ratio from the isotopic composition of soil organic matter.In this study,we aimed to evaluate how intraspecific variation will modify functional group-level 13Δvalues and the associated prediction of C_(3)/C_(4)vegetation ratio.Methods We investigated 13Δof 726 individual plants(96 species;C_(3)and C_(4)functional groups)and topsoil organic matter in 26 grassland communities along an aridity gradient in northern China.The fraction of C_(4)contribution was calculated with mixing models that considered:(i)both intra-and interspecific effects on the 13Δvalues of C_(3)and C_(4)functional groups;(ii)only interspecific effects;or(iii)none of these effects.Important Findings We found divergent responses of plant 13Δat the intraspecific level to the changes of aridity across the gradient.The 13Δof both C_(3)and C_(4)functional groups was negatively correlated with an aridity index,with higher sensitivity for C_(3)than for C_(4)functional groups.Intraspecific 13Δvariation played a key role in driving the total 13Δvariations of C_(3)plants.Overlooking such intraspecific effect in mixing models led to a greatly increased fraction of C_(4)contribution to soil organic carbon.A correction for the effects of intraspecific variation is therefore essential for correctly inferring C_(3)/C_(4)vegetation ratio in the past.Our findings provide basic information for the reconstruction of past vegetation change from bulk materials in arid and semiarid biomes.

On the instability of offshore foundations: theory and mechanism

As the offshore engineering moving from shallow to deep waters, the foundation types for fixed and floating platforms have been gradually evolving to minimize engineering costs and structural risks in the harsh offshore environments. Particular focus of this paper is on the foundation instability and its failure mechanisms as well as the relevant theory advances for the prevailing foundation types in both shallow and deep water depths. Piles, spudcans, gravity bases, suction caissons, and plate anchors are detailed in this paper. The failure phenomena and mechanisms for each type of foundations are identified and summarized, respectively. The theoretical approaches along with sophisticated empirical solutions for the bearing capacity problems are then presented. The major challenges are from flow-structure-soil coupling processes, rigorous constitutive modeling of cyclic behaviors of marine sediments, and the spatial variability of soil properties for large-spreading structures. Further researches are suggested to reveal the instability mechanisms for underpinning the evolution of offshore foundations.