Evolution history dominantly regulates fine root lifespan in tree species across the world

Understanding the drivers of variations in fine root lifespan is key to informing nutrient cycling and productivity in terrestrial ecosystems.However,the general patterns and determinants of forest fine root lifespan at the global scale are still limited.We compiled a dataset of 421 fine root lifespan observations from 76 tree species globally to assess phylogenetic signals among species,explored relationships between fine root lifespan and biotic and abiotic factors,and quantified the relative importance of phylogeny,root system structure and functions,climatic and edaphic factors in driving global fine root lifespan variations.Overall,fine root lifespan showed a clear phylogenetic signal,with gymnosperms having a longer fine root lifespan than angiosperms.Fine root lifespan was longer for evergreens than deciduous trees.Ectomycorrhizal(ECM)plants had an extended fine root lifespan than arbuscular mycorrhizal(AM)plants.Among different climatic zones,fine root lifespan was the longest in the boreal zone,while it did not vary between the temperate and tropical zone.Fine root lifespan increased with soil depth and root order.Furthermore,the analysis of relative importance indicated that phylogeny was the strongest driver influencing the variation in forest fine root lifespan,followed by soil clay content,root order,mean annual temperature,and soil depth,while other environmental factors and root traits exerted weaker effects.Our results suggest that the global pattern of fine root lifespan in forests is shaped by the interplay of phylogeny,root traits and environmental factors.These findings necessitate accurate representations of tree evolutionary history in earth system models to predict fine root longevity and its responses to global changes.

Effects of Thinning and Litter Fall Removal on Fine Root Production and Soil Organic Carbon Content in Masson Pine Plantations

Soils play a critical role in the global carbon cycle, and can be major source or sink of CO2 depending upon land use, vegetation type and soil management practices. Fine roots are important component of a forest ecosystem in terms of water and nutrient uptake. In this study the effects of thinning and litter fall removal on fine root production and soil organic carbon content were examined in 20-year-old Masson pine （Pinus resinosa） plantations in Huitong, Hunan Province of China in the growing seasons of 2004 and 2005. The results showed that fine root production was significantly lower in the thinning plots than in the control plots, with a decrease of 58% and 14% in 2004 and 2005 growing seasons, respectively. Litter fall removal significantly increased fine root production by 14% in 2004. Soil temperature （Tsoil） and soil moisture （Msoil） were higher in the thinning plots than those in the controls. Litter fall removal had significant effects on Tsoil and Msoil. Soil organic carbon content was higher in the thinning plots but was lower in the plots with litter fall removal compared with that in the controls. Our results also indicated that annual production of fine roots resulted in small carbon accumulation in the upper layers of the soil, and removal of tree by thinning resulted in a significant increase of carbon storage in Masson pine plantations.

Experimental study on the moving characteristics of fine grains in wide grading unconsolidated soil under heavy rainfall

The initiation mechanism of debris flow is regarded as the key step in understanding the debrisflow processes of occurrence, development and damage. Moreover, migration, accumulation and blocking effects of fine particles in soil will lead to soil failure and then develop into debris flow. Based on this hypothesis and considering the three factors of slope gradient, rainfall duration and rainfall intensity, 16 flume experiments were designed using the method of orthogonal design and completed in a laboratory. Particle composition changes in slope toe, volumetric water content, fine particle movement characteristics and soil failure mechanism were analyzed and understood as follows: the soil has complex, random and unstable structures, which causes remarkable pore characteristics of poor connectivity, non-uniformity and easy variation. The major factors that influence fine particle migration are rainfall intensity and slope. Rainfall intensity dominates particle movement, whereby high intensity rainfall induces a large number of mass movement and sharp fluctuation, causing more fine particles to accumulate at the steep slope toe. The slope toe plays an important role in water collection and fine particleaccumulation. Both fine particle migration and coarse particle movement appears similar fluctuation. Fine particle migration is interrupted in unconnected pores, causing pore blockage and fine particle accumulation, which then leads to the formation of a weak layer and further soil failure or collapses. Fine particle movement also causes debris flow formation in two ways: movement on the soil surface and migration inside the soil. The results verify the hypothesis that the function of fine particle migration in soil failure process is conducive for further understanding the formation mechanism of soil failure and debris flow initiation.

Experimental investigation on static and dynamic resilient moduli of compacted fine soil

To investigate the static and dynamic resilient modulus of fine soil,and adapting to the new design code and maintenance system of highway subgrade in China,a series of static and dynamic tests were carried out according to the standard laboratory test methods(JTG E40-2007 and JTG D30-2015,respectively).The effects of initial water content,compactness and freeze-thaw cycles on the static and dynamic resilient moduli of fine soil were investigated and analyzed.Experimental test results show that with increasing water content,dry density and freeze-thaw cycles,the static moduli reduces about10.2%~40.0%,14.4%~45.5%,and 24.0%~50.3%,and dynamic moduli reduces about 10.9%~90.8%,2.5%~38.4%,and0.0%~46.0%,respectively.Then,the empirical mathematical relationship between static and dynamic resilient moduli was established under different water content,dry density and freeze-thaw cycles.The investigation results can be used to determine the dynamic modulus of fine soil by widely used static modulus,which could meet the requirement of adopting dynamic modulus index in new specification.

Influence of fines content on the anti-frost properties of coarse-grained soil

This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows： （1） the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; （2） the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; （3） with increasing numbers of freeze-thaw cycles, the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engi- neering design values; and （4） considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway sub,fade coarse-~rained soil fillings in frozen re^ions.

Response of density-related fine root production to soil and leaf traits in coniferous and broad-leaved plantations in the semiarid loess hilly region of China

Fine roots are the most active and functional component of root systems and play a significant role in the acquisition of soil resources. Density is an important structural factor in forest plantations but information on changes in fine roots along a density gradient is limited. In this study, plantations of black locust (Robinia pseudoacacia L.) and Chinese pine (Pinus tabuliformis Carr.) with four density classes were analyzed for the influence of soil and leaf traits on fine root growth. Fine root biomass increased with stand density. High fine root biomass was achieved through increases in the fine root production and turnover rate in the high-density black locust plantations and through an increase in fine root production in the pine plantations. In the high-density Chinese pine stand, there was a high fine root turnover which, coupled with high fine root production, contributed to a high fine root biomass. Overall, fine root production and turnover rate were closely related to soil volumetric water content in both kinds of plantations, while fine root biomass, especially the component of necromass, was related to soil nutrient status, which refers to phosphorous content in black locust plantations and nitrogen content in Chinese pine plantations. There was a close linkage between leaf area index and fine root dynamics in the black locust plantations but not in the pine plantations.

Removal of As and Heavy Metals （Cd, Cu and Pb） in Fine Soil from Soil Washing Process Using Chelating Agent

Fine soil generated from the soil washing process can be the second problem, as contaminants are concentrated in the fine soil, and also took the difficult forms to treat because soluble and exchangeable fractions are already removed by soil washing process; therefore, the fine soil is indicated to hazardous waste, and discarded in hazardous waste landfill. Thus, this research would be performed that arsenic and heavy metals formed difficult to remove in the fine soil were converted to more treatable fractions with chelating agents. Moreover, feasibility study to apply the second remediation targeted to the fine soil inquired. As a result, the chelating agent was decided 50 mM Na2EDTA, and it could develop the complex. In addition, the result of sequential extraction showed that Mn/Fe-oxide fraction, comprised about 28% of amount at first, was decreased about 16%, and organic fraction, consisted approximately 20%, was also decreased about 11%, while exchangeable fraction and carbonate fraction were increased. This result means that the difficult fractions removed could change fractions） by chelating agent. This research can provide the possibility hazardous waste because of difficulty to remediate. the more treatable fractions （exchangeable and carbonate to treat the fine soil, although the fine soil was regarded to

Experimental study of the effects of non-uniformly distributed fine soil on mechanical properties of Shenyang–Dandong Railway coarse-grained soil

The stress produced by repeated train loads decreases with increasing railway subgrade bed depth, and slightly weathered coarse particles of subgrade bed fillings can be broken at different levels under continuous load. Thus, the mass of fine soil, with a diameter of not more than 0.075 mm, is different at different depths. Fine soil is also sensitive to frost heave and thaw settlement. In order to study the effects of non-uniformly distributed fine soil on the mechanical properties of coarse-grained soil of the Shenyang-Dandong Railway, triaxial tests were conducted with three types of specimens, un- dergoing six freeze-thaw cycle numbers （0, 1, 3, 7, 9, 12） and three confining pressures （100, 200, 300 kPa）. The freezing temperature is -5 ~C and the thawing temperature is ＋15 ~C. The stress-strain behavior, static strength, resilient modulus, cohesive force and the angle of internal friction were measured for different tested specimens. As a result, the law of static strength and resilient modulus of different specimens following the increase of freeze-thaw cycles under three confining pressures is obtained. The changing law of cohesive force and friction angle of three specimens following the increase of freeze-thaw cycles is also calculated, and the different results of different specimens are also compared.

Performance of a Nonwoven Geotextile Reinforced Wall with Unsaturated Fine Backfill Soil

The use of marginal backfills in GSE （geosynthetic stabilized earth） walls has not been recommended by different standards specifications. Restrictions are motivated by the poor hydraulic conductivity of fine soils that are capable of developing of water pressures. However, the use of granular materials can expend the cost of the construction. As a result, local soils, granular or not, have been increasingly used. Unsaturated conditions of fine soils may result in convenient performance even using extensible reinforcements. This paper evaluates the performance of a full scale model of a nonwoven geotextile reinforced wall constructed with fine grained soil backfill. The unsaturated condition was maintained and matric suctions, displacements and reinforcement strains were monitored during the test. Results have shown that the unsaturated condition of the backfill allowed maximum reinforcement peak strain of 0.4 %. For the case of a wrap faced wall on a firm foundation the performance and good agreement between measured strains and factors of safety from limit equilibrium analyses have shown the maintenance of unsaturated conditions as an economical alternative to the use of high quality fill.

Microstructure of Fine Clay Soils Stabilized with Sugarcane Molasses

Sugar cane molasses has proved cohesive and excellent performance on soil aggregates (fine particles). However, the microstructure of consolidated soil by the molasses is not yet subjected to research. The analysis results of sample without molasses (0%) and consolidated samples at 8%, 12%, and 16% show that the molasses acts on the structure of clayey fine soil developing its microstructure of airy matrix type (sample without molasses (0%) to a microstructure of a qualified type, more solid. Consolidated samples to 8%, 12%, 16% of molasses). We also observe the presence of inter-aggregate pores (mesopores) of similar size in all samples. The results of porosimetrical analyses (BJH) of the sample without molasses and consolidated samples to 8%, 12%, and 16% show that simultaneous porous volumes of samples are reduced with the increasing of molasses quantity. This latter, therefore, acts on the porous volume (micropore 2 nm and mesopore 9 nm) by reducing them which really means, molasses occupies the porous volume of the sample. However, this sample seems not to have any effect on the size of mesopores 9 nm. Thus, this product induces the evolution of the soil structure towards the highly dense and condensed structure. Consequently, materials in consolidated soil by molasses will have mechanical properties far superior to those of materials consolidated soil without molasses.

Application of Nanotechnology in Soil Stabilization

Nano-technology is expanding its horizon in various science and technology fields.In civil engineering,soil is a complex material and used for various functions and applications.Meanwhile,sometimes an effective soil stabilization technique is needed to fulfil the site criteria and can be achieved by adopting various methods e.g.,physical,chemical,thermal or reinforcement using geotextiles and fabrics.The mechanism of soil stabilization using nanomaterials is still unexplored and open to prospective researchers.The present article attempts to touch and explore the possibilities of nano-technology in soil improvement and its applications in various civil engineering works.Microstructural analysis of the nanomaterials treated soils using the latest equipment has also been discussed.The study interprets that the use of nano materials is still limited,due to their high cost and sophisticated handling procedures.Though the use of nanoparticles in soil stabilization results in extraordinary improvements in various soil properties,the improved soil properties could be utilized for various geotechnical projects.The present study bridges the past findings to the present scenario of nanomaterials in soil improvement.

含泥量对砂类硫酸盐渍土工程特性的影响分析

为了明确含泥量对砂类硫酸盐渍土的盐胀和力学特性的影响,人工配制了不同细粒土含量的砂类硫酸盐渍土,在1%和3%(质量分数,下同)含盐量单向冻结盐胀试验的基础上,选取了细粒土含量为5%、15%、30%和40%的砂样进行常温、低温三轴剪切试验。研究结果表明:此试验条件下,不同级配砂类硫酸盐渍土的冻结温度为-0.7~-0.1℃,当砂样孔隙溶液浓度在冻结温度之上达到饱和时,降温过程中会首先生成盐结晶;1%含盐量条件下,高细粒土含量(≥30%)砂样的起胀温度在4~9℃之内,而低细粒土含量砂样的起胀温度在0℃附近,3%含盐量砂样的起胀温度为20~23℃;试验含水率和细粒土含量通过影响土体中自由水的含量对盐冻胀产生显著影响。在力学特性方面,随着细粒土掺量的增加,砂类硫酸盐渍土的抗剪强度表现出先增大后减小的趋势,细粒土由增强摩擦转变为颗粒间的“润滑”作用;此外,冻结后砂土转变为承载能力更强的“土-盐-冰骨架结构”,抗剪强度大幅提高,并呈现出明显的脆性破坏特征,由于冻结砂土受相对温度的影响,随着含盐量的增加,破坏应力呈先减小后增大的趋势。

球状风化花岗岩类土质边坡土-岩界面优势流潜蚀特性研究

受降雨作用,球状风化花岗岩类土质边坡的土-岩差异风化界面极易演化为优势渗流通道而发生渗流潜蚀,进而加速该类边坡的变形失稳,然而当前有关其渗流潜蚀作用特征、细颗粒迁移规律等的研究仍鲜见开展。基于多孔介质非饱和渗流理论,综合考虑细颗粒运移、潜蚀启动响应与非饱和渗流的耦合关系,提出一种可准确描述土-岩界面渗流潜蚀过程的数值计算框架。采用有限元方法,构建优势流作用下非饱和花岗岩残积土的渗流潜蚀模型,并以均质土柱的渗流潜蚀过程为参考,系统研究3种典型土-岩界面埋藏状态下的优势流潜蚀特性。结果表明:球状风化花岗岩类土质边坡的土-岩界面与基质渗透性存在高度差异性,湿润锋形成向下凹陷的渗透漏斗,且随着降雨的持续,湿润锋的凹陷程度愈发明显;细颗粒流失程度与土-岩界面的埋藏状态相关,其中下填土体工况的优势流潜蚀最为显著,其界面处甚至出现超孔隙水压力,最不利于该类边坡的稳定性。研究成果可为降雨条件下球状风化花岗岩类土质边坡稳定性的准确评价提供科学依据。

细粒土与粗粒土动力流化的孔压差异辨析

地基土体在动力作用下的液化对工程会产生灾害性影响。孔隙水压力是研究饱和土体转变为流体的重要表征,已有研究发现,细粒土在液化过程中即使孔压比(孔压/围压)未达到1,也已进入液化状态。本文将土颗粒概化为球体,考虑颗粒吸附水膜的影响,对由砂粒、粉粒、黏粒组成的饱和土体,在可发生流动的情况下,建立产生动力流化的理论模型,并分析了动三轴和振动台实验中孔压的变化。结合土体微结构特征,指出细粒土处于流化状态时,孔隙水压力因受结合水膜影响而导致孔压值减小,同时因颗粒形状(如板片等)的框架支撑作用也可减小孔压值。这一从土体微观组成的物理性质上进行的理论分析,有助于厘清以孔隙水压力判别细粒土与粗粒土发生动力流化标准不同的原因,有助于研究者深入理解土体液化的内在机制。

砂砾土渗流侵蚀中细粒迁移-沉积-滤通的物理水力临界条件

细粒迁移机制是理解砂砾土渗流侵蚀过程的基础与关键,对研究砂砾土斜坡雨水侵蚀过程的细观致灾机制具有重要意义。目前其运移模式及运移状态发生转变的临界条件并不清晰,不同物理水力条件下的细粒运动类型有所不同。为掌握砂砾土侵蚀过程中细粒的整体运动类型及其发生改变的临界条件,采用可视圆柱入渗试验和离散元数值模拟,分析了细粒迁移的影响因素和内部机理。结果表明:(1)细粒迁移受级配和水力梯度影响显著,而受初始孔隙率影响不显著,且级配的影响大于水力梯度;(2)水力作用下细粒整体运动状态可分为沉积和滤通2种模式,内部结构不稳定的砂砾土细粒运动处于滤通状态,内部结构稳定和稳定性过渡型砂砾土随水力梯度升高细粒的运动状态从整体沉积转变为整体滤通;i=3.4-(3)细粒运动状态在粒径比和水力梯度共同作用下存在明显界限,最终得到细粒沉积-滤通转变的临界条件为0.12e(D15/d85)/1.5。研究可为砂砾土斜坡渗蚀失稳防护提供理论指导。

砂质土与建筑垃圾制备可控性低强度材料

利用砂质土与建筑垃圾细骨料复掺制备可控性低强度材料(CLSM),研究了砂质土与建筑垃圾细骨料不同质量比下CLSM的流动度、泌水率、凝结时间和抗压强度的变化规律,并通过XRD和SEM探究物相组成和微观形貌。结果表明,随着砂质土与建筑垃圾细骨料质量比的降低,CLSM的泌水率及流动度减小、凝结时间缩短、抗压强度提高。利用砂质土与建筑垃圾细骨料复掺解决了泌水率高的问题,且当两者质量比为1∶1时,流动度、泌水率、凝结时间和抗压强度符合市政管道回填施工要求。

复合水泥固化剂固化泥炭土渗透性研究

针对泥炭土工程性质差、改良难度高的问题,本文提出了一种由超细水泥(UFC)和普通硅酸盐水泥(OPC)组成的复合水泥固化剂(CCS)用于固化模拟泥炭土,并通过渗压试验和X射线衍射(XRD)测试研究UFC对水泥土试样渗透性的影响规律。渗压试验结果表明:CCS掺入量相同时,试样渗透系数k随UFC质量分数的增加而减小,UFC质量分数大于12%时k值下降趋势显著减缓;CCS中UFC质量分数为12%时,k随CCS掺入量的增加而减小,CCS掺入量大于25%时下降趋势明显减缓。XRD测试结果显示,试样中水化硅酸钙(C-S-H)的衍射峰强度随UFC质量分数及养护龄期的增加而增强。相较于OPC,CCS以更少的水泥用量便能达到优异的固化效果,从而实现减碳目标。

泸定水电站坝基覆盖层深部潜蚀对土骨架变形影响评价试验研究

泸定水电站因坝基覆盖层深部(1)层潜蚀诱发涌水险情,潜蚀过程中大量细颗粒持续流失能否诱发明显土骨架变形关系到电站自身、下游梯级电站及泸定县城的安全。土体颗粒级配、应力状态及细颗粒流失比例等均有可能影响土骨架变形,但其影响机制尚不清楚。为全面评价(1)层潜蚀对土骨架变形的影响,自行研制了可以模拟现场(1)层土体原始级配特征和应力状态的高应力、大直径的土体渗透稳定试验装置,建立了土骨架发生明显变形的判据,即潜蚀过程中试样累计体积应变大于等于1%时,表明土骨架已发生明显变形,提出了细颗粒运移比作为衡量细颗粒流失比例的评价指标。针对(1)层土体,开展了一系列极端不利水力条件下的渗流应力耦合潜蚀试验研究,重点探讨了颗粒级配、应力状态及细颗粒运移比对土骨架变形的影响规律。研究表明:所有试样潜蚀全过程的累计体积应变介于0.1%~0.49%,均小于1%,即(1)层土体中细颗粒大量甚至全部流失也不会诱发明显骨架变形,(1)层潜蚀诱发防渗墙开裂、折断,甚至突然溃坝的风险不大。颗粒级配显著影响细颗粒运移比、潜蚀临界和破坏坡降,5 mm以下颗粒含量越少,细颗粒运移比越大,潜蚀临界和破坏坡降越小;上覆压力对细颗粒运移比影响不大,但对潜蚀临界和破坏坡降影响显著,上覆压力越大,潜蚀临界和破坏坡降越大。研究成果为科学评价泸定水电站深部渗透稳定提供了重要依据,同时,也为其他类似工程安全评价提供了重要借鉴。

根土微环境对早实核桃细根时空分布、养分特征的影响

以长势基本一致且处于稳产期的‘新新2号’早实核桃(Juglans regia L.)后代为研究对象,按照小格子法将根土连续体划分为144个采样小区。于2022年每月采集根、土样品,测定细根生物量并构建二维空间分布图,研究细根形态指标、养分特征以及土壤水、养质量分数并分析其对早实核桃细根时空分布、养分特征的影响。结果表明:早实核桃细根主要分布在垂直方向的0~0.4 m土层和距树干水平方向1.5 m范围内,占细根分布总量的80%。细根形态参数值(生物量、根长密度、根表面积密度、根体积密度)和养分质量分数均随土层加深呈下降趋势,细根在微环境水平变异时差异不明显。夏、秋季细根形态参数值均显著高于春、冬季。土壤全氮、全磷质量分数随土层加深逐渐减少,土壤全钾质量分数在整个空间分布上无明显差异。土壤含水率随土层加深而增加,距树干距离越远含水率越低。土壤各养分质量分数的季节性差异较大,全氮质量分数在夏、秋季较高,在春季最低;全磷质量分数在春季最高;全钾质量分数在冬季最高;土壤含水率在秋、冬季最高。细根形态、养分质量分数与土壤全氮、全磷、含水率的关系更密切,相关性存在一定季节差异。细根生长在细微变异的环境下仍具有一定的趋水趋肥性。对早实核桃进行肥水精细化管理时,可根据根土的时空关系,在根区适时灌溉,季节性调整肥料养分,施肥则以氮、磷肥为主。

碎石土细颗粒迁移特征及优先流形成路径

碎石土是一种非连续、非均质的结构性材料,由于内部含有大量碎石块,容易形成架空结构,使其内部形成复杂独特的渗流通道即优先流通道,碎石土优先流通道是包括水分运移和土体细颗粒迁移的复杂过程,但在研究其优先流路径时通常只考虑了水分的运移而忽略了细颗粒的迁移,颗粒迁移与通道形成密切相关。为此,对两种不同级配土柱(粗细颗粒连续级配和间断级配)分别进行饱和渗流-颗粒迁移试验,从细颗粒迁移的角度分析通道形成的时空发展规律。试验结果表明:细颗粒迁移一部分由于流失引起碎石土渗透性增大,另一部分由于重新沉积而堵塞局部孔隙,降低渗透性,两者作用结果最终加速优先流通道形成;连续级配的碎石土形成大面积交叉分布的管网状渗流通道,间断级配的碎石土则形成集中渗流通道;相同水力条件下,不同级配细颗粒迁移的空间分布特征不同,连续级配的碎石土细颗粒迁移不随空间位置的差异而发生变化,间断级配的碎石土细颗粒迁移随空间位置的差异而发生变化,两种级配下碎石土细颗粒主要流失量的粒径范围均在1~0.075 mm;不同水力梯度条件下,连续与间断级配试验细颗粒流失量均随水力梯度增加而增大,间断级配的碎石土破坏时水力梯度小于连续级配破坏时水力梯度,间断级配碎石土更容易发生破坏。研究成果为进一步揭示碎石土优先流形成机理提供试验依据。