Shear resistance characteristics and influencing factors of root-soil composite on an alpine metal mine dump slope with different recovery periods

Artificial vegetation restoration is the main measure for vegetation restoration and soil and water conservation in alpine mine dumps on the Qinghai-Tibet Plateau,China.However,there are few reports on the dynamic changes and the influencing factors of the soil reinforcement effect of plant species after artificial vegetation restoration under different recovery periods.We selected dump areas of the Delni Copper Mine in Qinghai Province,China to study the relationship between the shear strength and the peak displacement of the root-soil composite on the slope during the recovery period,and the influence of the root traits and soil physical properties on the shear resistance characteristics of the root-soil composite via in situ direct shear tests.The results indicate that the shear strength and peak displacement of the rooted soil initially decreased and then increased with the increase of the recovery period.The shear strength of the rooted soil and the recovery period exhibited a quadratic function relationship.There is no significant function relationship between the peak displacement and the recovery period.Significant positive correlations(P<0.05)exists between the shear strength of the root-soil composite and the root biomass density,root volume density,and root area ratio,and they show significant linear correlations(P<0.05).There are no significant correlations(P>0.05)between the shear strength of the root-soil composite and the root length density,and the root volume ratio of the coarse roots to the fine roots.A significant negative linear correlation(P<0.05)exists between the peak displacement of the rooted soil and the coarse-grain content,but no significant correlations(P>0.05)with the root traits,other soil physical property indices(the moisture content and dry density of the soil),and slope gradient.The coarse-grain content is the main factor controlling the peak displacement of the rooted soil.

Soil physical properties and maize root growth under different tillage systems in the North China Plain

The standard cultivation system in the North China Plain is double cropping of winter wheat and summer maize. The main effects of this cultivation system on root development and yield are decreases in soil nutrient content and depth of the plow layer under either long-term no-tillage or rotary tillage before winter wheat sowing and no tillage before summer maize sowing. In this study, we investigated the combined effects of tillage practices before winter wheat and summer maize sowing on soil properties and root growth and distribution in summer maize. Zhengdan 958(ZD958) was used as experimental material, with three tillage treatments: rotary tillage before winter wheat sowing and no tillage before summer maize sowing(RTW + NTM), moldboard plowing before winter wheat sowing and no tillage before summer maize sowing(MPW + NTM), and moldboard plowing before winter wheat sowing and rotary tillage before summer maize sowing(MPW + RTM).Tillage practice showed a significant(P < 0.05) effect on grain yield of summer maize. Grain yields under MPW + RTM and MPW + NTM were 30.6% and 24.0% higher, respectively, than that under RTW + NTM. Soil bulk density and soil penetration resistance decreased among tillage systems in the order RTW + NTM > MPW + NTM > MPW + RTM. Soil bulk densities were 3.3% and 515% lower in MPW + NTM and MPW + RTM, respectively, than that in RTW + NTM, and soil penetration resistances were respectively 17.8% and 20.4% lower,across growth stages and soil depths. Root dry matter and root length density were highest under MPW + RTM, with the resulting increased root activity leading to a yield increase of summer maize. Thus the marked effects of moldboard plowing before winter-wheat sowing on root length density, soil penetration resistance, and soil bulk density may contribute to higher yield.

Influence of the roots of mixed-planting species on the shear strength of saline loess soil

In order to improve our knowledge of the mechanical effect of the roots of mixed-plantings on soil reinforcement and slope protection,the influence of roots of a mixed-planting with four herb species(Medicago sativa L.,Elymus nutans Griseb.,Puccinellia distanx(L.),and Poa pratensis L.)and one shrub species(Caragana korshinskii Kom.)were investigated on the shear strength characteristics of saline loess soil.The root distribution characteristics were assessed via a survey when the plants grew for one year.The effects of the root biomass density,the root mass ratio(RMR)of the fine roots to the coarse roots,the moisture content,and the salt content on the shear strength index of the rooted soil were analyzed via a triaxial compression test,and the mechanism of these effects was discussed.The results indicate that the biomass density decreased linearly with increasing depth.The RMR initially decreased with depth and then increased,exhibiting in a quadratic relationship.The cohesion of the rooted soil increased linearly as the biomass density increased.The cohesion of the rooted soil initially increased with increasing RMR and salt content,and then it decreased.The turning point of the cohesion occurred when the RMR was 0.6 and the salt content was 1.18%.The internal friction angle of the rooted soil initially increased with biomass density and then decreased,and the turning point of the internal friction angle occurred when the biomass density was 0.015 g/cm3.The relationships between the internal friction angle of the rooted soil and the RMR and salt content were exponential incremental and linear subtractive relationship,respectively.Both the cohesion and the internal friction angle of the rooted soil linearly decreased with increasing moisture content.

The influence of plant root system architectural properties upon the stability of loess hillslopes,Northeast Qinghai,China

To investigate the influence of root system architectural properties of three indigenous(coldadapted) shrubs on the hillslope stability of loess deposits in the Xining Basin,northeast part of Qinghai-Tibet Plateau(QTP),indoor direct shear tests have been conducted on the remolded rooted soil of three shrubs.Test results show that root system architectural indices(root area ratio(RAR),root length density(RLD) and root density(RD)) of the shrubs decline with depth and the relationship between RAR,RD and depth is exponential,while a power relationship describes the relationship between RLD and depth.The cohesion force of remolded rooted soil for the shrubs initially increases withdepth,but it then demonstrates a slightly decreasing trend,which can be described with a power relationship.Power relationships also describe relationships between cohesion force and RAR,RLD and RD for the shrubs.As the growth period increases from 10 to 17 months,the incremental increase in RAR is 48.32% ~ 210.25% for Caragana korshinskii Kom and 0.56% ~ 166.85% for Zygophyllum xanthoxylon(Bunge) Maxim.This proportional increase is notably larger than that for RLD and RD.The increment in RAR is marginally greater for C.korshinskii than it is for Z.xanthoxylon.Correspondingly,the cohesion force incremental rates of remolded rooted soil for C.korshinskii and Z.xanthoxylon are 12.41% ~ 25.22% and 3.45% ~ 17.33% respectively.Meanwhile,as root content increases,the contribution by roots to cohesion force increases markedly until a threshold condition is reached.

Root length density distribution and associated soil water dynamics for tomato plants under furrow irrigation in a solar greenhouse

Furrow irrigation is a traditional widely-used irrigation method in the world. Understanding the dynamics of soil water distribution is essential to developing effective furrow irrigation strategies, especially in water-limited regions. The objectives of this study are to analyze root length density distribution and to explore soil water dynamics by simulating soil water content using a HYDRUS-2D model with consideration of root water uptake for furrow irrigated tomato plants in a solar greenhouse in Northwest China. Soil water contents were also in-situ observed by the ECH_2O sensors from 4 June to 19 June and from 21 June to 4 July, 2012. Results showed that the root length density of tomato plants was concentrated in the 0–50 cm soil layers, and radiated 0–18 cm toward the furrow and 0–30 cm along the bed axis. Soil water content values simulated by the HYDRUS-2D model agreed well with those observed by the ECH_2O sensors, with regression coefficient of 0.988, coefficient of determination of 0.89, and index of agreement of 0.97. The HYDRUS-2D model with the calibrated parameters was then applied to explore the optimal irrigation scheduling. Infrequent irrigation with a large amount of water for each irrigation event could result in 10%–18% of the irrigation water losses. Thus we recommend high irrigation frequency with a low amount of water for each irrigation event in greenhouses for arid region. The maximum high irrigation amount and the suitable irrigation interval required to avoid plant water stress and drainage water were 34 mm and 6 days, respectively, for given daily average transpiration rate of 4.0 mm/d. To sum up, the HYDRUS-2D model with consideration of root water uptake can be used to improve irrigation scheduling for furrow irrigated tomato plants in greenhouses in arid regions.

Production Performance of Root Systems of Four Forage Legume Species and Their Development Characteristics in Loess Plateau,China

Production performance of four forage legumes species of Medicago sativa,Onobrychis viciifolia,Lotus corniculatus and Galega officinalis were determined,including plant height,above-ground biomass per unit area,tillers per unit area,fertile tillers per unit area,shoot /leaf ratio and fresh /dry matter weight ratio,and the distribution characteristics of their root systems in 0- 100 cm soil layers with 10 cm interval were studied. Results showed that the average aboveground fresh biomass(4 a and 5 a) of four forage legumes species successively were L. corniculatus 】 M. sativa 】 O. viciifolia 】 G. officinalis. The average plant heights in two years successively were O. viciifolia 】 M. sativa 】 G. officinalis 】 L. corniculatus. Tillers per unit area of four forage legume species in two years successively were M. sativa 】 L. corniculatus 】 O. viciifolia 】 G. officinalis. Fertile tillers per unit area in two years were O. viciifolia 】 M. sativa 】 L. corniculatus 】 G. officinalis. Average shoot /leaf ratio in two years were G. officinalis 】 M. sativa 】 O. viciifolia 】 L. corniculatus. Average moisture contents of four forage legume species in two years successively were G. officinalis 】 L. corniculatus 】 M. sativa = O. viciifolia. The distribution characteristics of root systems of four forage legumes species in 0- 100 cm soil layers were as follows: the root weights of M. sativa in 0- 40 cm soil layers accounted for about 98. 3% of total root weight,that of O. viciifolia in 0- 30 cm soil layers was 85. 8%,that of L. corniculatus in 0- 10 cm soil layers was 80%,and that of G. officinalis in 0- 40 cm soil layers was 81. 4%. The results suggested that L. corniculatus was suited to plant in slighter degraded pasture to control water and soil erosion in early stage,G. officinalis with strong lateral roots was adapted to degraded grassland in the Loess Plateau where soil nutrient was poor,while O. viciifolia and M. sativa with potentially strong main root were fit for water and soil conservation in the losses plateau for long term.

Optimal root system strategies for desert phreatophytic seedlings in the search for groundwater

Desert phreatophytes are greatly dependent on groundwater, but how their root systems adapt to different groundwater depths is poorly understood. In the present study, shoot and root growths of Alhagi sparsifolia Shap. seedlings were studied across a gradient of groundwater depths. Leaves, stems and roots of different orders were measured after 120 days of different groundwater treatments. Results indicated that the depth of soil wetting front and the vertical distribution of soil water contents were highly controlled by groundwater depths. The shoot growth and biomass of A. sparsifolia decreased, but the root growth and rooting depth increased under deeper groundwater conditions. The higher ratios of root biomass, root/shoot and root length/leaf area under deeper groundwater conditions implied that seedlings of A. sparsifolia economized carbon cost on their shoot growths. The roots of A. sparsifolia distributed evenly around the soil wetting fronts under deeper groundwater conditions. Root diameters and root lengths of all orders were correlated with soil water availabilities both within and among treatments. Seedlings of A. sparsifolia produced finer first- and second-order roots but larger third- and fourth-order roots in dry soils. The results demonstrated that the root systems of desert phreatophytes can be optimized to acquire groundwater resources and maximize seedling growth by balancing the costs of carbon gain.

Firm Roots in Tibetan Soil

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中国南北方植物对土壤加固机制的差异性

为深入分析植物对土壤加固的影响效益和机制,该研究选取重庆缙云山地区和陕西延安黄土丘陵区种植一年的乔木(火炬树、榆树)和灌木(荆条、酸枣),测定其根系形态、力学参数和土壤的抗剪强度,通过RBMw模型计算根系固土效益,综合评估不同植物的固土效能和贡献度。结果表明:2地种植的物种平均根直径的差异不显著(P>0.05),重庆种植的乔木(火炬树、榆树)的根长、分叉数和根尖数显著高于延安,灌木未出现显著差异(P<0.05)。根系的抗拉强度与直径都符合负幂函数关系,其中平均抗拉强度最大的为荆条。除荆条外,同种植物根系的抗拉强度并未因不同地区的种植产生显著差异。4个植物种根系的固土效率为0.65~4.12 kPa,各物种间存在显著差异(P<0.05)。重庆2种乔木种植下的根土复合体有效黏聚力高于裸地(约10%),灌木种植下则普遍略低于裸地。除酸枣外,种植于重庆的4种植物的根系固土作用和效率都显著的高于延安(P<0.05)。研究结果可为不同地区固土护坡的树种选择提供理论依据。

宁夏南部黄土丘陵区3种草本根土复合体抗冲性及其与影响因素的关系

[目的]明确宁夏南部黄土丘陵区3种草本根土复合体抗冲性差异及其与相关影响因素的关系,为研究区生态建设质量提升及植被优化配置提供理论依据。[方法]以研究区常见草本百里香、星毛委陵菜、长芒草根土复合体为研究对象,采用室内原状土水槽冲刷法,并利用LA-S根系扫描分析系统,研究不同草本0—15 cm土层根土复合体抗冲性能及其与根、土的关系。[结果](1) 3种草本0—15 cm土层根土复合体抗冲性大小为星毛委陵菜(53.7 L·h/g)>百里香(36.5 L·h/g)>长芒草(14.2 L·h/g),星毛委陵菜根土复合体抗冲性最强。(2) 3种草本根系根长密度、表面积密度、体积密度和比根长分别为4.25~10.56 cm/cm^(3),42.95~111.51 mm^(2)/cm^(3),5.04~17.94 mm^(3)/cm^(3),35.06~67.96 m/g,根长密度等参数百里香明显大于其他草本。(3)各草本根系分布土壤的有机碳含量百里香(1.437%)>星毛委陵菜(1.290%)>长芒草(0.430%)。根系土壤黏粒含量百里香是星毛委陵菜、长芒草的1.14倍、1.20倍。3种草本土壤团聚体参数MWD,GMD,R_(>0.25)分别为13.80~18.23 mm, 7.15~11.11 mm, 43.06%~70.05%,各指标星毛委陵菜最大。(4)根系、土壤均能直接或间接、单独或共同影响根土复合体抗冲性。百里香土壤黏粒、粉粒、砂粒及团聚体直接影响土体抗冲性,其大部分根系还通过影响土壤机械组成和有机碳含量间接影响抗冲性。星毛委陵菜土壤粉粒和大部分细根直接影响土体抗冲性,其0~0.5 mm根、土壤黏粒、砂粒还通过影响土壤团聚体等间接影响抗冲性。长芒草土壤砂粒、0~1.0 mm根直接影响土体抗冲性,其特定细根还通过影响土壤团聚体和有机碳含量间接影响抗冲性。[结论]3种草本根土复合体抗冲性大小有明显差异,根系、土壤均能影响其抗冲性能,在宁夏南部黄土丘陵区进行生态建设应考虑不同草本(植被)的抗冲性能,并在改善相关影响因素的基础上加以科学配置。

Mechanisms for the Movement of Fe，Mn，Cn and Zn to Plant Roots in Loessal So il and Lon Soil

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北麓河青藏公路沿线多年冻土区热融滑塌型边坡植被防护力学效应研究

为评价青藏公路沿线多年冻土区高寒草甸和人工种植植物固土护坡力学贡献,本研究选取位于青藏公路沿线北麓河地区一处热融滑塌灾害作为研究区。以原生草甸(主要植物种为嵩草(Carex myosuroides Vill.)和藏嵩草(Kobresia tibetica Maxim.))和人工种植垂穗披碱草(Elymus nutans Griseb.)、星星草(Puccinellia tenuiflora(Griseb.)Scribn.&Merr.)、冰草(Agropyron cristatum(L.)Gaertn.)、早熟禾(Poa annua L.)、碱茅(Puccinellia distans(L.)Parl.)和中华羊茅(Festuca sinensis Keng ex S.L.Lu)等6种生长期为1 a草本为研究对象,通过开展室内原状根-土复合体剪切试验,探讨了草本根系增强热融滑塌型边坡体抗剪强度作用贡献,并采用静力平衡法对该热融滑塌型边坡稳定性进行了评价。主要得到如下结果:通过室内洗根试验得到根-土复合体试样平均含根量由高至低依次为原生草甸(33.33 mg·cm^(-3))、垂穗披碱草(16.95 mg·cm^(-3))、早熟禾(13.12 mg·cm^(-3))、中华羊茅(5.80 mg·cm^(-3))、冰草(3.89 mg·cm^(-3))、星星草(3.15 mg·cm^(-3))、碱茅(2.86 mg·cm^(-3));平均株高由高至低依次为垂穗披碱草(10.93 cm)、原生草甸(9.64 cm)、冰草(6.88 cm)、早熟禾(5.22 cm)、中华羊茅(3.90 cm)、碱茅(3.86 cm)、星星草(2.90 cm);区内原生草甸和6种人工种植草本根-土复合体抗剪强度均显著高于不含根系素土,其中原生草甸和人工种植垂穗披碱草根系增强土体抗剪强度作用增幅相对较大,分别为42.17%和30.96%;由静力平衡法计算得到含根系边坡安全系数均高于不含根系素土边坡,边坡安全系数由大至小依次为原生草甸(1.47)、垂穗披碱草(1.39)、早熟禾(1.38)、冰草(1.37)、碱茅(1.36)、星星草(1.32)、中华羊茅(1.32)、素土(0.96)。该研究结果对于有效防治青藏公路沿线北麓河地区热融滑塌灾害,同时为进一步有效防治青藏公路沿线热融滑塌灾害引发的水土流失、草地退化等灾害提供理论依据和实际指导。

毛乌素沙地不同植被恢复类型的土壤碳水效应

[目的]探讨不同植被恢复类型下土壤有机碳和水分含量特征及其关系,为毛乌素沙地植被恢复类型的选取提供科学依据。[方法]以毛乌素沙地自然恢复草地及沙蒿、沙柳、沙蒿×沙柳(灌灌混交)、樟子松、沙柳×樟子松(乔灌混交)为研究对象,并以裸沙地为对照,分析不同植被恢复类型对0-5.0 m土层土壤剖面碳、水的影响及其相关性。[结果](1)植被恢复增加土壤有机碳含量,沙柳×樟子松、樟子松、草地、沙蒿×沙柳、沙柳、沙蒿依次降低,0—0.2 m土层显著高于深层,表现为表聚效应;随着土层深度的增加,各植被类型的有机碳含量逐渐降低;沙蒿、沙柳、沙蒿×沙柳在0.8—2.2 m土层范围内表现为碳损失。(2)不同植被恢复类型在深层均存在不同程度的水分亏缺,主要集中在1.0—3.0 m土层,具体亏缺程度为沙柳×樟子松>樟子松>沙蒿×沙柳>沙柳>草地>沙蒿。(3)根系是影响土壤有机碳含量和水分消耗的主要因素;土壤有机碳含量与土壤含水量在0—5.0 m土层范围内负相关。[结论]植被固存有机碳以消耗深层土壤水分为代价,沙柳×樟子松固定同等单位量的碳消耗水分最少。因此,从土壤固碳和保水2个角度同时考虑,沙柳×樟子松在毛乌素沙地的植被恢复中具有较好的恢复效果。

土壤含水量对探地雷达探测植物根系构型精度的影响

根系是评价植被生态服务功能的关键基础要素,但快速、精确、无损确定根系的测量技术和方法是目前生态系统评估中的瓶颈。探地雷达是一种高效无损的地球物理学技术,可以在无损状态下获取土壤中的根系信息。但是探地雷达检测和识别根系的精度受土壤含水量、根系含水量、根径大小、根系埋藏深度等诸多因素影响,导致其在野外根系探测中适用性受限,为了探究土壤含水量对探地雷达探测根系精度的影响,本研究采用野外预埋根系的控制实验,根据探地雷达波速、振幅和根点反射系数的变化,分析了不同土壤含水量条件下根点识别率及根点距离均方根误差。结果表明:(1)根系探测中,探地雷达波速和振幅是判断土壤含水量变化的重要参数;(2)随着土壤含水量的增大,探地雷达波速减小,雷达振幅趋于平缓;(3)不同土层深度上随着根系直径的增大,探地雷达波速增大,雷达振幅趋于激烈;(4)根点识别率与土壤含水量成负相关(P<0.05),土壤含水量为15%~25%时探地雷达对活根的识别效果最佳。本研究表明探地雷达可以作为植物根系生物量无损和快速测定、评估的方法,但在利用探地雷达测定土壤中根系时,应在土壤含水量相对较低的时间段进行。

不同密度可降解防草布对柑橘幼树生长及土壤性质的影响

本研究分析不同密度可降解防草布(低密度:52 g·m^(-2);中密度:72 g·m^(-2);高密度:82 g·m^(-2))对幼树生长及土壤性质的影响,旨在为柑橘幼树果园如何选择可降解防草布提供参考。结果表明,与对照相比,低密度和中密度可降解防草布对植株地上部分生长、根系在不同土层深度的分布比例均无显著性影响,但能造成根系总数量发生显著性减少。高密度可降解防草布能显著促进植株地上部分生长,不会引起根系总数量减少,但易造成根系分布在浅土层(0~<20 cm土层深度)。3种防草布对土壤容重无显著性影响,但能造成表层土壤含水量增加和深层土壤含水量减少,这可能是根系分布在浅土层的原因之一。因此,建议柑橘幼树果园选择高密度可降解防草布覆盖,但应考虑防草布覆盖前进行深层土壤改良,避免根系上浮。

接种AMF对西部煤矿区紫穗槐根系分布和水分利用效率的影响

西部干旱半干旱煤矿区井工开采导致了大面积采煤沉陷区的出现,矿区生态复垦难度较大,利用菌根微生物技术进行生态修复已经成为当前的研究热点。为探究接种丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)对紫穗槐根系分布特征和水分利用效率(Water Use Efficiency,WUE)的影响,研究通过室内土柱试验,设置了对照不种植紫穗槐幼苗(CK1)、种植紫穗槐幼苗(CK)、种植紫穗槐幼苗并接种AMF(+AM)3组试验处理,并对植物生长指标和土壤水分等进行了测定。结果表明:①接种AMF有效促进了紫穗槐的生长,其株高、SPAD(Soil and plant analyzer development)值、地上生物量和地下生物量相较CK处理分别提升38.5%、27.5%、11.1%、69.4%;②接菌改变了紫穗槐的根系分布,使总根系长度和根尖数分别增加329.0%和586.1%,平均根直径显著减小22.9%,2 mm以下细根根长比例提升370.1%。同时,接菌影响了土壤水分分布和紫穗槐的水分利用模式,使0~20 cm的土壤含水率较CK处理分别提高8.9%、7.8%,20~50 cm的含水率又分别降低16.8%、4.0%、11.6%;接菌增加了紫穗槐对表层5 cm以下土壤的水分利用比例,在5~30、30~50 cm分别提升15.4%、9.9%;③接菌使紫穗槐植株的WUE增加了27.5%,主成分分析结果表明,紫穗槐根系中的细根长(0.50~1.00 mm)和根尖数是干旱胁迫下接种AMF对土壤水分高效利用的关键根系特征。综上,接菌可对紫穗槐幼苗有明显的促生作用,通过对紫穗槐细根根系特征参数的显著改善,促进了对土壤水分的吸收及再分配能力,进而使紫穗槐植株表现出较高的WUE,该研究结果可为西部采煤沉陷区生物联合修复技术提供科学指导和技术支持。

甘蔗/花生间作对根系生理及根际土壤养分的影响

为探明甘蔗/花生间作对根系生理及根际土壤养分的影响,本文设置了甘蔗单作、花生单作、甘蔗/花生间作模式,系统分析了不同种植模式下根系分泌物、根系浸提物和根际土壤养分的变化及其相关性。结果表明:间作甘蔗根系分泌的总氨基酸及根系浸提液中的总糖显著高于单作,间作花生根系分泌的总糖显著高于单作。间作甘蔗根际土壤的碱解氮(alkali-hydrolyzed nitrogen,AN)、有效磷(available phosphorus,AP)、速效钾(available potassium,AK)和土壤有机质(soil organic matter,SOM)显著高于单作甘蔗,间作种植显著降低了花生根际土壤的有效磷、速效钾和pH。间作和单作甘蔗的酸性磷酸酶、过氧化氢酶、脲酶和蔗糖酶差异不显著,间作花生的过氧化氢酶显著高于单作花生。根系分泌的酚酸与土壤有机质呈显著负相关,总糖与蔗糖酶呈显著正相关,氨基酸与脲酶呈显著正相关;根系浸提液中的有机酸与pH呈显著正相关,氨基酸与SOM呈显著负相关、与AK呈极显著负相关。脲酶与AK呈显著负相关,蔗糖酶与SOM呈极显著负相关。综上,甘蔗/花生间作主要影响根系分泌氨基酸、总糖和酚酸的代谢活动,且可显著提高甘蔗的土壤有效养分。

干旱条件下淮北平原夏玉米根系水分来源研究

为探究干旱胁迫条件下淮北平原夏玉米生长期水分利用特征,分析农田降水-土壤水-作物水之间的转化规律。通过野外实验和室内分析,测定分析不同生长期内降水、土壤水、植物水、地下水的稳定氢氧同位素值。采用稳定氢氧同位素技术分析了各水体的同位素分布特征,利用直接对比法和多元线性混合模型法分析夏玉米对土壤水分的主要吸水深度及贡献率,进而研究其水分来源。结果表明,五道沟实验站夏季大气降水线方程为δD=7.26×δ^(18)O+3.11(R^(2)=0.98),其斜率和截距均小于全球大气降水线方程,表明降水在降落过程存在蒸发富集过程。土壤水氢氧同位素在垂直方向剖面呈现明显的梯度分布。干旱胁迫条件下,夏玉米拔节-抽雄期主要吸收0~20、20~40、40~60 cm处的土壤水,贡献率分别为21.8±13.6%、25.5±20%和25.1±18.2%;抽雄-灌浆期主要吸收0~20 cm处的土壤水,贡献率为68.6±3.6%;灌浆-成熟期主要吸收0~20 cm处的土壤水,贡献率为72.0±0.9%。夏玉米根系优先利用浅层土壤水,土壤水主要来自大气降水。地下水埋深较浅地区,干旱条件下夏玉米在整个生长期内根系吸水深度较浅,由此考虑生长期改变灌溉方式来提高灌溉水利用率。

阴山北麓武川地区藜麦根-土复合体抗剪特性研究

在阴山北麓武川地区选择了的G28、WD9、WD12、W7高产藜麦作为研究对象,通过素土与藜麦根-土复合体直剪试验,探究了藜麦根系在不同径级和不同土壤含水率条件下的抗剪强度特性。研究结果表明,藜麦根-土复合体的抗剪强度与根系径级存在明显的正相关关系,即随着根系径级的增大,其抗剪强度也显著提升。同时,较大的根系径级不仅增强了复合体的抗剪强度,还促进了黏聚力和内摩擦角的增加。直剪试验结果显示在6.25 kPa、12.5 kPa垂直荷载(藜麦根系集中区)下,藜麦根-土复合体的黏聚力增长率均高于27%,最高值达到了32%,相比之下,内摩擦角的增长率较为稳定,平均约为4%。种植藜麦后,其根系显著增强了土体的抗剪强度,其中黏聚力起到了主导作用。此外,随着土壤含水率的上升,藜麦根-土复合体的抗剪强度与黏聚力也呈现出增大的趋势,当土壤含水率达到11.54%时,二者均达到最大值。然而,内摩擦角却随着含水率的增加而减小。自然条件下藜麦根-土复合体抗剪强度、黏聚力在6.25 kPa、12.5 kPa垂直荷载(藜麦根系集中区)时相对于素土的增长率,得出固着水土能力最优的品种为G28。

降雨条件下草本植物根系对残积土边坡渗流稳定性的影响

为研究紫穗槐和胡枝子两种植被根系对残积土边坡的渗流稳定性影响,本实验研究设计采用数值模拟的方法进行研究,以Geo-studio软件为平台,计算分析不同降雨强度作用下,裸坡与指数形根系和均布形根系对边坡渗流及稳定性的影响规律,计算的内容包括孔隙水压力、饱和度和安全系数。研究结果表明:植被边坡的孔隙水压力的上升速度大于裸坡,指数形根系边坡的敏感性高于均布形根系边坡;植被边坡比裸坡易达到饱和,指数形根系边坡对饱和度的变化同样具有较高的敏感性,饱和度变化幅度与降雨强度呈负相关的关系;对残积土边坡稳定性影响效果,指数形根系对边坡稳定性表现得更有利,降雨强度较小时均布形根系提高作用稳定,降雨强度增大时其安全系数向裸坡靠拢,而指数形根系在四种降雨强度下对边坡仍可稳定发挥提高作用,且安全系数一直位于均布形根系之上,对提高残积土边坡稳定性的积极性更高。