松属、青冈属乔木侧根的强度在防护林固土护坡作用中的意义

 乔木根系的土壤加强作用是防护林稳定土壤和保护坡面的最有效的机械途径,其中侧根的牵引效应在林地的固土护坡过程中具有重要作用,其潜能与侧根的抗张强度呈正相关关系。本研究构建了侧根抗张强度与其牵引效应的数学模型,对云南山地以云南松林和滇青冈林为代表的松属和青冈属乔木群落进行了分析。结果表明：青冈属和松属乔木侧根的抗张强度分别在40一10MPa和30～5 MPa范围内,量值的高低随侧根直径的增加而降低。两种乔木的侧根在0～60cm的土壤深处有较高的分布密度,由于具有一定的强度,通过它们的牵引效应,侧根使这一深度的根际土层的抗张强度提高了6.85～12.41 kPa。在各个土层,青冈属乔木固土护坡能力明显高于松属,说明松属侧根在浅层土体加固方面具有局限性。     

云南松侧根对浅层土体的水平牵引效应的初步研究

植物的侧根对周围土壤具有机械牵引作用。一般来讲 ,垂直根可以通过增加根际土层的抗剪强度来加固土体 ,斜向侧根则能够在对周围土体进行牵引固持的过程中 ,通过提高土体的水平抗张强度实现对土体的增强加固 ,这一作用即侧根的水平牵引效应。为了检验高山峡谷区云南松林是否也有这种效应 ,并调查其量值 ,我们在金沙江中上游的虎跳峡地区对云南松根际土层进行了直接剪土测试。结果表明 ,在表层土体中 ( 0～ 2 0 cm)松树侧根能在 1 0 0 0 cm2 的垂直横截面上提供 42 1 .1 9～ 561 .0 5N的水平牵引力 ,使土层的抗滑力提高 33.2 %～ 37.58%。受该牵引力的影响 ,侧根把根际土层的抗张强度提高了4.2～ 5.6k Pa。测试结果预示 ,只要云南松垂直根可以把浅层土体锚固到较深层稳定的土体上 ,通过水平牵引效应 ,云南松侧根可在一定程度上与垂直根共同克服林地浅层坡面的不稳定性 ,如浅层滑动和蠕移。     

胡杨根系水力提升作用的证据及其生态学意义

生长在塔里木河流域的荒漠河岸林植被虽长期忍受着高温和干旱的威胁, 然而它们却能够一直延续并保存至今。除了植物深根系吸水作用外, 另一个更主要的原因可能就是荒漠河岸林植被存在水力提升的效应。该文采用HRM热比率法茎流仪对3株胡杨(Populus euphratica)主根和侧根的液流速率分别进行了为期4 d的连续监测; 利用自动气象站对微气象因子：风速、空气相对湿度、叶面温度和地表温度进行连续监测; 同时采用了烘干法对不同深度土层在不同时刻的土壤含水率进行了取样分析。试验结果表明：胡杨主根液流在白天和夜间均表现为正值, 相反的, 胡杨侧根液流速率则出现了明显的夜间负向流动。胡杨根系0~120 cm土层土壤水分含量具有下湿上干的变化趋势; 胡杨侧根在夜间发生负向流动后, 土壤含水率显著升高, 尤其在60~120 cm土层中, 4:00土壤含水率上升幅度达到4:00时刻土壤含水率的22%~26%。影响胡杨侧根液流速率的主要气象因子主要是叶面水汽压亏缺。     

植物根系固坡抗蚀的效应与机理研究进展

植物根系对抵抗坡体浅层滑坡和表土侵蚀起着巨大的作用.植物根系通过增强土体的抗剪强度发挥固坡效应.目前有关植物根系固坡机理的模型较多,普遍接受的是Wu-Waldron模型.该模型表明,植物根系产生的土体抗剪强度的增量与根系的平均抗拉强度和根面积比成正比,应用该模型评价根系固坡效应的2个最重要因素是根系的平均抗拉强度和根面积比.研究发现,土壤抗侵蚀性随着植物根系数量的增加而提高,但未有一致的定量函数关系.植物根系提高土壤抗侵蚀性主要通过直径小于1mm的须根起作用.须根通过增加土壤水稳性团聚体的数量与粒径等作用来提高土壤的稳定性,以抵抗水流分散;须根还能有效地增强土壤渗透性,减少径流,从而达到减少土壤冲刷的目的.     

黄土区草本植被根系与土壤垂直侵蚀产沙关系研究

为了系统揭示植被根系对径流侵蚀产沙的影响,采用土钻法对草地植被根系分布特征进行系统调查,采用分层冲刷的方法对黄土高原草地土壤不同坡度、不同流量条件下的侵蚀产沙特征进行了研究。结果表明不同立地上的植被根系都表现出了随着土层深度增加而减少的趋势。分层冲刷的试验结果表明在土壤表层,植被根系对侵蚀产沙的影响是占主导地位的;而当土层超过一定深度后,根系的分布数量减少,不同流量和坡度下的深层土壤侵蚀产沙量明显增加,根系提高土壤抵抗径流侵蚀产沙的能力受到了限制。同时随着土层深度的不断加大,坡面上径流侵蚀的形态也在发生变化,逐渐从面蚀向细沟侵蚀发展。结合对草地植被根系生物量垂直分布特征的研究,证明土壤侵蚀产沙的这种变化是与草本植被根系的分布特征密切相关的。通过进一步分析植被根系分布特征和土壤垂直侵蚀产沙之间的联系,建立了草地植被根系生物量与土壤垂直侵蚀产沙特征之间的定量关系。     

漓江水陆交错带典型立地根系分布与土壤性质的关系

研究根系与土壤关系是发掘河岸带生态退化等问题内在原因的重要途径。在漓江流域水陆交错带选取缓坡、陡坡、江心洲、人工岸坡4种典型立地类型,对不同土层深度的根长密度、根系生物量、比根长,以及根系特征与土壤有机质、全氮、有效磷的关系进行了研究,旨在为漓江流域生态修复过程中植被恢复、植被配置、快速绿化材料选取提供科学依据。结果表明:(1)同一立地类型0—10 cm土层和10—20 cm土层比根长差异性不显著。0—10 cm到10—20 cm土层,各立地类型根长密度和根系生物量密度均减小,但不同立地类型根长密度和根系生物量密度的差异程度逐渐缩小,表明地形、地表植物类型及生长状况对根长密度分布的影响也随土层深度的增加而逐渐减小。细根根长和生物量随着土壤深度的增加而减小。(2)土壤有机质含量差异性显著,分布规律为人工岸坡陡坡江心洲缓坡;土壤全氮含量从大到小依次是人工岸坡、陡坡、缓坡、江心洲,其值分别为:3.12、2.33、1.56、1.32 g/kg;土壤全氮与土壤有机质呈显著正相关。江心洲和缓坡有效磷含量远远大于人工岸坡和陡坡,原因是漓江水长期受人为洗漱影响,导致受江水干扰大的立地类型有效磷含量高。(3)根长密度、比根长、根系生物量与有机质、全氮含量呈正相关,与有效磷含量呈负相关,说明土壤根系越丰富,越有利于增加土壤有机质和全氮含量,但遏制了土壤有效磷。细根长度、生物量与根长密度在0.01水平(双侧)上显著正相关,与根系生物量密度呈负相关。     

黄土高原不同演替阶段草地植被细根垂直分布特征与土壤环境的关系

研究了黄土区不同演替阶段草地植被细根垂直分布特征与土壤环境的关系,结果表明不同演替阶段草地植被细根生物量、根长密度、表面积、直径和比根长均具有明显的垂直分布特征。细根生物量、根长密度和细根表面积一般随土层加深而逐渐减少,且集中分布于0-40cm土层;随着演替的进行,除20a弃耕地外,0—80cm土层细根生物量、根长密度和细根表面积逐渐增加;除25a弃耕地外,细根直径随演替进行逐渐减小。0～100cm土层土壤含水量随演替进行而增加,不同演替阶段深层土壤水分较表层稳定。土壤容重的变化趋势为9〈4〈15〈20〈25a弃耕地,根系对表层土壤水分和容重的影响较大,而对深层土壤水分与容重影响较少。不同演替阶段细根各参数和土壤水分、容重差异均达到显著水平。各弃耕地细根参数之间,细根参数和土壤环境因子之间存在不同程度的相关关系,土壤含水量在草本植被的不同演替阶段均是影响其细根垂直分布的关键因素。土壤容重在演替早期对草本植被根系的影响较小,随着演替进行其影响作用进一步增强。     

我国西南山地喀斯特植被的根系生物量初探

在贵州茂兰喀斯特森林国家自然保护区内,选取2种立地条件上(岩石和土壤分别占优势)的5个植被恢复阶段(草本群落、灌草群落、灌木群落、次顶极常绿落叶阔叶林和顶极常绿落叶阔叶林)共10个样地,利用平均标准木机械布点法对根系进行采集,分析了其生物量总量、不同根系径级的分配格局和地下空间的分布规律。结果表明:1)喀斯特植物群落的正向植被恢复进程极显著地增加了地下生物量(p0.001),从草本群落的2.63Mg·hm–2增加到顶极森林群落的58.15Mg·hm-2;同一恢复阶段的石生和土壤立地上根系生物量的差异不显著(p0.05),在顶极和次顶极常绿落叶阔叶林阶段,石生立地的根系生物量高于土壤立地,而灌木、灌草和草本群落阶段则相反。2)同一恢复阶段的石生立地的粗根生物量均高于土壤立地,但差异不显著(p0.05),而细根和小根生物量则从石生到土壤立地显著增加(p0.05);随着喀斯特植被的恢复,石生和土壤立地上粗根占总根系生物量的比例均逐渐增加。3)石生立地根系的分布以水平扩散和穿梭为主,无垂直层次分布;而土壤立地各恢复阶段的根系生物量主要集中在地面到地下10cm的垂直空间内;在不同的土层深度,粗根占所有根径级生物量的80%,且随土层加深,其比例降低。该研究不仅填补了喀斯特植被根系生物量观测的空白,为估算我国西南喀斯特地区植被的总生物量和生产力提供了本底数据,也为进一步研究喀斯特森林稳定性维持机制和喀斯特石漠化防治与植被适应性修复奠定了基础。     

植物功能性状对土壤保持的影响研究述评

植被对土壤保持具有重要的影响,但是从植物功能性状的角度总结评述植被对土壤保持影响的研究并不多见。总结评述了植物地上功能性状、地下功能性状对土壤保持功能的影响以及植物地上、地下功能性状的关系,认为:(1)植被地上部分功能性状对土壤保持的作用主要体现在对溅蚀、面蚀的影响及间接改变土壤理化性质等方面,其功能性状指标主要包括叶面积、叶长、叶宽、枝数、植被高度等;(2)植被地下部分功能性状对土壤保持的作用主要体现在固持土壤、提高土壤抗剪切强度、提高土壤抗侵蚀能力、增强土壤渗透性,植物根系固持土壤与根系抗拉能力密切相关,植物根系土壤的物理和水文性质,与细根比例、根长密度、根表面积等性状密切相关;(3)可以通过植物地上部分功能性状间接反映地下部分功能性状,但是现有研究多为定性认识;(4)在植物功能性状对土壤保持的研究中亟待加强植被地上地下功能性状的长期定位监测,深化植被功能性状尤其是根系特征与土壤保持的作用机理,加强植被地上部分、地下部分功能性状的定量表达,建立植被功能性状与土壤保持功能的定量关系,实现植被功能性状与土壤保持功能特征的动态链接。     

黄土塬沟壑区典型植被沟头土壤渗透性和抗剪强度特征

沟头是沟蚀的主要活跃部位,严重影响沟头溯源侵蚀发生。为明确典型植被沟头根系分布及土壤物理和力学特征,本研究以自然植被恢复沟头和人工植被恢复沟头为对象,分析0～1 m不同土层土壤入渗、根系分布以及根-土复合体物理和力学性质特征。结果表明：不同植被沟头土壤容重和总孔隙变异较小,容重在1.10～1.37 g·cm^-3,土壤总孔隙在48.3%～58.4%;各入渗指标总体随土层增加呈减小趋势,自然植被恢复沟头不同土层入渗速率在20～30 min趋于稳定,人工植被恢复沟头在40 min趋于稳定,人工植被恢复沟头的稳定入渗速率、平均入渗速率总体大于自然植被恢复沟头;根长密度、根表面积密度、平均直径均随土层的增加呈降低趋势,除20～40 cm土层,自然植被恢复沟头的根长密度、根表面积密度、平均直径皆小于人工植被恢复沟头,两种植被沟头根系主要由0～0.5 mm根系构成,占总根长的84.2%～93.6%;在垂直深度上,随着含水率的增加,黏聚力随土层由上至下迅速线性衰减,变化范围为0.42～22.67 kPa,在相同含水率条件下,人工植被恢复沟头平均黏聚力总体大于自然植被恢复沟头。本研...     

The traction effect of lateral roots of Pinus yunnanensis on soil reinforcement: a direct in situ test

A traction effect by lateral roots is one way in which roots can contribute to lateral in-plane reinforcement of a shallow soil mass. ln contrast to the effect of vertically-extending roots, whereby soil is reinforced by an increase in its shear strength, the traction effect reinforces the soil by enhancing the tensile strength of the rooted soil zone. To verify whether or not a traction effect exists in the root system of a pine forest (Pinus yunnanensis French) in the Hutiaoxia Gorge, SW China, and to investigate the magnitude of this effect, a direct in situ test was conducted at two sites in the gorge. The results from the two sites showed that, in the topmost soil (020cm), the lateral roots are able to provide a tractive force of up to 421.19561.05 N over a vertical cross-section area of 20×50 cm², or an increase in the pulling resistance of the rooted soil by 33.237.58%.This is equivalent to a tensile strength increase of the shallow rooted soil by 4.25.6 KPa. The test results imply that, together with the pine's vertical roots, which anchor the shallow rooted soil zone to the deep and more stable soil mass, the lateral roots of the pine trees, through their traction effect, are able to mitigate against shallow instability in the forested slopes, such as shallow slide and creep, to a certain degree.     

The influence of slope on <Emphasis Type="Italic">Spartium junceum</Emphasis> root system: morphological,anatomical and biomechanical adaptation

Root systems have a pivotal role in plant anchorage and their mechanical interactions with the soil may contribute to soil reinforcement and stabilization of slide-prone slopes. In order to understand the responses of root system to mechanical stress induced by slope, samples of Spartium junceum L., growing in slope and in plane natural conditions, were compared in their morphology, biomechanical properties and anatomical features. Soils sampled in slope and plane revealed similar characteristics, with the exception of organic matter content and penetrometer resistance, both higher in slope. Slope significantly influenced root morphology and in particular the distribution of lateral roots along the soil depth. Indeed, first-order lateral roots of plants growing on slope condition showed an asymmetric distribution between up- and down-slope. Contrarily, this asymmetric distribution was not observed in plants growing in plane. The tensile strength was higher in lateral roots growing up-slope and in plane conditions than in those growing down-slope. Anatomical investigations revealed that, while roots grown up-slope had higher area covered by xylem fibers, the ratio of xylem and phloem fibers to root diameter did not differ among the three conditions, as also, no differences were found for xylem fiber cell wall thickness. Roots growing up-slope were the main contributors to anchorage properties, which included higher strength and higher number of fibers in the xylematic tissues. Results suggested that a combination of root-specific morphological, anatomical and biomechanical traits, determines anchorage functions in slope conditions.     

Effects of gauge length and strain rate on the tensile strength of tree roots

Root tensile strength plays an important role in soil stabilization and fixation. Testing and separating the different factors that affect root tensile strength are important. In the present study, the effects of four factors, namely, gauge length, strain rate, species, and root diameter, on root tensile strength were studied. Uniaxial tensile tests were conducted to acquire the root tensile strength of five tree species commonly growing in the mountains of northern China, namely, Chinese pine (Pinus tabulaeformis Carr.), Larch (Larix principis-rupprechtii Mayr.), White birch (Betula platyphylla Suk.), Mongolian oak (Quercus mongolicus Fisch.), and Elm (Ulmus pumila L.). Based on the results, Elm and White birch roots were the most resistant to tension, followed by Mongolian oak and Chinese pine roots. Larch roots were found to be the least resistant to tension. A power relationship was established between root diameter and root tensile strength. Based on linear regression analysis, gauge length was negatively correlated with root tensile strength. Tensile strength decreased with increasing gauge length. In addition, an unexpected variation of tensile strength was observed between two strain rates (10 and 400?mm?min^?1). The present study can serve as a basis for further studies on mechanical properties of root system and root reinforcement under different test circumstances, although this should be done with caution.     

Resin Production and Susceptibility to Heterobasidion annosum in Corsican Pine

The vertical resin ducts in Corsican pine sapwood made the majorcontribution to resin yields as assessed by sampling tubes.Resin yields from roots appeared to be influenced by soil physicalfactors which affect vertical duct frequency. Yields from stemswere not affected by soil pH, as had been suggested previously,and the greater resistance of pines to Heterobasidion annosumattack on acidic soils does not seem to be due to an effectof soil pH on the resin response. Considerations of the infectionhabit suggested that the tube sampling method did not measurethe most relevant parameters of resin production in the contextof host resistance.     

Long-Term Effects of Liming on Health and Growth of a Masson Pine Stand Damaged by Soil Acidification in Chongqing,China

In the last decades, the Masson pine (Pinus massoniana) forests in Chongqing, southwest China, have increasingly declined. Soil acidification was believed to be an important cause. Liming is widely used as a measure to alleviate soil acidification and its damage to trees, but little is known about long-term effects of liming on the health and growth of declining Masson pine forests. Soil chemical properties, health condition (defoliation and discoloration), and growth were evaluated following application of limestone powder (0 (unlimed control), 1, 2, 3, and 4 t ha⁻¹) in an acidified and declining Masson pine stand at Tieshanping (TSP) of Chongqing. Eight years after liming, in the 0–20 cm and 20–40 cm mineral soil layers, soil pH values, exchangeable calcium (Ca) contents, and Ca/Al molar ratios increased, but exchangeable aluminum (Al) levels decreased, and as a result, length densities of living fine roots of Masson pine increased, with increasing dose. Mean crown defoliation of Masson pines (dominant, codominant and subdominant pines, according to Kraft classes 1–3) decreased with increasing dose, and it linearly decreased with length densities of living fine roots. However, Masson pines (Kraft classes 1–3) in all treatments showed no symptoms of discoloration. Mean current-year twig length, twig dry weight, needle number per twig, needle length per twig, and needle dry weight per twig increased with increasing dose. Over 8 years, mean height increment of Masson pines (Kraft classes 1–3) increased from 5.5 m in the control to 5.8, 6.9, 8.3, and 9.5 m in the 1, 2, 3, and 4 t ha⁻¹ lime treatments, and their mean DBH (diameter at breast height) increment increased from 3.1 to 3.2, 3.8, 4.9, and 6.2 cm, respectively. The values of all aboveground growth parameters linearly increased with length densities of living fine roots. Our results show that liming improved tree health and growth, and these effects increased with increasing dose.     

Auxin transport inhibitors act through ethylene to regulate dichotomous branching of lateral root meristems in pine

Many soil fungi colonize the roots of pines to form symbiotic organs known as ectomycorrhizas. Dichotomous branching of short lateral roots and the formation of coralloid organs are diagnostic of ectomycorrhizas in many pine species, although the regulation of these changes in root morphology is not well understood. We used axenic root cultures of six pine species to examine the role of auxin, cytokinin, ethylene and nutrients in the regulation of root architecture. Surprisingly, extensive dichotomous and coralloid branching of lateral roots occurred spontaneously in Pinus taeda , P. halepensis and P. muricata . In P. sylvestris , P. ponderosa and P. nigra , treatment with auxin transport inhibitors (ATIs), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) or the ethylene-releasing compound 2-chloroethylphosphonic acid (CEPA or ethephon) induced extensive dichotomous branching and coralloid organ formation. Formation of both spontaneous and ATI-induced coralloid structures was blocked by treatment with an ethylene synthesis inhibitor L-α-(2-aminoethoxyvinyl)glycine; this inhibition was reversed by either ACC or CEPA. In addition, the induction of this unique morphogenetic pattern in pine root cultures was regulated by nutrient levels. The morphology and anatomical organization of the chemically induced dichotomous and coralloid structures, as well as the regulation of their formation by nutrient levels, show a striking similarity to those of ectomycorrhizas.     

The Pines and Pine Forests of Xizang

Six species of pines are distributed in Xizang. They are: Pinus griffithii McClell., P. armandi Franch. and P. gerardiana Wall. of haploxylon pines and P. densata Mast., P. yttnnanensis French. and P. roxburghii Sarg. of diploxylon pines. According to the relation of these pines with water-temperature conditions, 4 ecological types may be divided: the warm-temp erate and wet type (P. griffithii), the warm-temperate and dry type (P. yunnanensis, P. roxburghii), the temperate-cold and moist type (P. armandi) and the temperate-cold and dry type (P. densata). The composition and structure of every pine community reflect the ecological environments of the given pine in the region. The main pine comnmnity in Xizang are P. griffithii forest and P. densata forest. The P. griffithii forest is distributed on the southern side of Himalayas, while the P. densata forest on the northern side of Himalayas and the southern part of Hengtuan mountains. This indicates that the Himalaya range is a clear boundary and there is difference in water-temperature condition between southern and northern parts. They belong different vegetation regions. The different distribution of other several pine forests reflects the difference of environmental conditions within these two regions. These facts have significance in the investigation of the regularity of vegetation distribution and vegetation division in Xizang. Besides, the vertical distribution of pines cannot be used as a marker to divide the altitudinal belts due to the wide range of adaptation of pines, though there must be regularity of vertical distribution too.     

Nine Years of Irrigation Cause Vegetation and Fine Root Shifts in a Water-Limited Pine Forest

Scots pines (Pinus sylvestris L.) in the inner-Alpine dry valleys of Switzerland have suffered from increased mortality during the past decades, which has been caused by longer and more frequent dry periods. In addition, a proceeding replacement of Scots pines by pubescent oaks (Quercus pubescens Willd.) has been observed. In 2003, an irrigation experiment was performed to track changes by reducing drought pressure on the natural pine forest. After nine years of irrigation, we observed major adaptations in the vegetation and shifts in Scots pine fine root abundance and structure. Irrigation permitted new plant species to assemble and promote canopy closure with a subsequent loss of herb and moss coverage. Fine root dry weight increased under irrigation and fine roots had a tendency to elongate. Structural composition of fine roots remained unaffected by irrigation, expressing preserved proportions of cellulose, lignin and phenolic substances. A shift to a more negative δ¹³C signal in the fine root C indicates an increased photosynthetic activity in irrigated pine trees. Using radiocarbon (¹⁴C) measurement, a reduced mean age of the fine roots in irrigated plots was revealed. The reason for this is either an increase in newly produced fine roots, supported by the increase in fine root biomass, or a reduced lifespan of fine roots which corresponds to an enhanced turnover rate. Overall, the responses belowground to irrigation are less conspicuous than the more rapid adaptations aboveground. Lagged and conservative adaptations of tree roots with decadal lifespans are challenging to detect, hence demanding for long-term surveys. Investigations concerning fine root turnover rate and degradation processes under a changing climate are crucial for a complete understanding of C cycling.