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.     

Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability

Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.     

The influence of plant diversity on slope stability in a moist evergreen deciduous forest

The influence of plant diversity on slope stability was investigated at early phases of succession in a mixed forest in Sichuan, China. The first phase comprised big node bamboo (Phyllostachys nidularia Munro) only. In the second phase, bamboo co-existed with deciduous tree species and in the third phase, deciduous species existed alone. Root density at different depths and root tensile strength were determined for each species. The factor of safety (FOS) was calculated for slopes with and without vegetation for each succession phase. For phase 2, FOS was determined for different species mixtures and positions. In phase 3, simulations were performed with a single tree at the top, middle or toe of the slope. Due to its shallow root system, bamboo contributed little to slope stability. In simulations with the tree at the top or middle of the slope, FOS decreased because tree weight added a surcharge to the slope. FOS increased with the tree at the bottom of the slope. Different mixtures of species along the slope had no influence on FOS. Differences in root tensile strength between species played a small role in FOS calculations, and tree size and density were the most important factors affecting slope stability, excluding hydrological factors.     

华北山地6个外生菌根树种的根属性及其与菌根侵染率的关系

该研究以共存于同一暖温带森林的6个外生菌根(ECM)树种为研究对象,测定分析不同根序(1～5级)和功能根系(吸收细根和运输细根)的主要形态和构型属性及ECM侵染率,探究不同外生菌根树种的根属性变异模式及其与菌根真菌侵染程度的关系。结果表明:(1)随着根序的增加,不同树种根直径和单根长度均增加,而比根长和根分支强度均降低;根属性在同一根序下均存在显著的种间差异,尤其是2个裸子植物(落叶松和油松)的根直径较其他4个被子植物大。(2)同一树种的所有根属性在吸收细根和运输细根之间均有显著差异;吸收细根和运输细根的根直径、比根长和根组织密度在树种间均存在显著差异,而其单根长度和根分支强度在树种间无显著差异。(3)ECM侵染率以落叶松最高,千金榆和白桦最低,且与根尖直径呈显著正相关关系,与根尖比根长呈显著负相关关系。研究发现,基于根序或者功能根系,根属性在种间的变异模式不完全一致,单根长度和根分支强度在两个功能根系中均没有表现出显著的种间差异;吸收细根的比根长和根分支强度的变异系数较大,对环境变化有较敏感的响应;古老树种的根直径相对较粗,对菌根真菌的依赖性更高。     

隔沟交替灌溉条件下玉米根系形态性状及结构分布

为揭示根系对土壤环境的适应机制,研究了隔沟交替灌溉条件下玉米根系形态性状及结构分布。以垄位和坡位的玉米根系为研究对象,利用Minirhizotrons法研究了根系（活/死根）的长度、直径、体积、表面积、根尖数和径级变化及其与土壤水分、土温和水分利用效率（WUE）的相关关系。结果表明,对于活根,在坡位非灌水区域复水后根系平均直径减小,而根系日均生长速率、单位面积土壤根系体积密度、根尖数和表面积均增大,并随灌水区域土壤水分的消退逐渐减小;对于死根,在坡位非灌水区域复水后根系日均死亡速率、根系体积密度、根尖数和表面积变化均减小,其中根系死亡速率和死根直径随土壤水分的消退逐渐降低,而死根体积密度、根尖数和表面积分布随土壤水分降低呈增大趋势;在垄位,根系形态分布趋势与坡位一致,除根系直径与与坡位比较接近外,其他根系形态值均小于坡位。将根系分成4个径级区间分析根系的形态特征,结果表明在根系长度和体积密度分布中以2.5－4.5 mm径级的根系所占比例最大,在根尖数和根系表面积分布中以0.0－2.5 mm径级的根系为主。通过显著性相关分析,死根直径、体积密度、活根表面积等根系形态与土壤含水率、土壤温度和WUE间均存在显著或极显著的正相关关系,部分根系形态指标（如根系的生长速率、活根体积密度）只与坡位土壤含水量、土壤温度具有明显的相关性,表明隔沟交替灌溉对坡位根系形态的调控作用比垄位显著。     

关帝山云杉次生林树木径向生长的空间关联及其影响因子

以关帝山4 hm²云杉次生林样地为研究对象,按照CTFS(Center for Tropical Forest Science)技术规范对样地树木进行连续定位监测。利用2010至2015年间样地主要树种生长量观测数据,结合地形、土壤等环境因子调查及采样测定数据,分析了树木种群径向生长的空间关联性及其随生境的变化,并探讨了树木种群径向生长的影响因素。结果表明,青杄、华北落叶松、红桦、白桦和辽东栎为云杉次生林主要树种,在样地4个生境型(山脊生境、低海拔缓坡生境、高海拔缓坡生境、低洼地陡坡生境)中均有分布且呈现不同的径级结构。标记相关函数分析显示,同一生境型中,5树种径向生长的空间关联性各异;对于同一树种,径向生长的空间自相关性不仅具有尺度依赖性,同时生境型的不同导致树木径向生长的空间关联性发生变化。线性混合效应模型分析显示,初始胸径对树木径向生长的显著正效应在样地各类生境型的所有种群中普遍存在;生物因子对树木径向生长的显著影响只在特定生境型的青杄种群中被检测到,表明树木径向生长受同种邻体影响,但其影响显著性因树种而异;环境因子中,海拔和凹凸度对树木径向生长呈显著负效应...     

长白山白桦山杨次生林细根形态特征和解剖结构对氮沉降的响应

根系作为植物与土壤物质交换和养分循环的桥梁,长期以来一直是生态学研究的热点。于2017年7月植物生长季,对长白山模拟11年氮(N)沉降控制试验样地的白桦(Betula platyphylla)山杨(Populus davidiana)天然次生林进行了根系采样,并利用根序法研究了根系形态特征和解剖结构对不同梯度N添加处理的响应,旨在探求两物种根系之间潜在生态联系。本试验共设置了三个N添加梯度,分别为对照(CK,0 g N m~(-2 )a~(-1))、低N处理(T_L,2.5 g N m~(-2 )a~(-1))和高N处理(T_H,5.0 g N m~(-2 )a~(-1))。研究结果如下:1)T_L显著抑制白桦和山杨前三级细根皮层厚度的生长。白桦通过增加皮层细胞直径(一级根增加了72.77%,二级根增加了53.22%,三级根增加了39.96%)但减少皮层层数来降低皮层厚度,而山杨主要通过皮层细胞直径的减少(一级根下降了40.80%,二级根下降了28.17%)来降低其皮层厚度。2)T_H显著抑制山杨前三级细根生长。主要通过增加皮层厚度(一级根增加了68.78%,二级根增加了50.81%,三级根增加了88.53%)以及降低导管横截面积来抑制吸收养分,从而达到影响生长的目的。3)白桦T_H相比于T_L细根直径呈抑制生长状态。其主要通过抑制中柱直径(一级根下降了17.61%,二级根下降了16.89%,三级根下降了20.62%)的生长来实现。以上结果表明,在同一立地条件下,白桦和山杨的细根对不同浓度N沉降的响应方式不同。     

Soil microbial properties under different vegetation types on Mountain Han

This study investigated the influence of broadleaf and conifer vegetation on soil microbial communities in a distinct vertical distribution belt in Northeast China.Soil samples were taken at 0-5,5-10 and 10-20 cm depths from four vegetation types at different altitudes,which were characterized by poplar(Populus davidiana)(1250-1300 m),poplar(P.davidiana) mixed with birch(Betula platyphylla)(1370-1550 m),birch(B.platyphylla)(1550-1720 m),and larch(Larix principis-rupprechtii)(1840-1890 m).Microbial biomass and community structure were determined using the fumigation-extraction method and phospholipid fatty acid(PLFA) analysis,and soil fungal community level physiological profiles(CLPP) were characterized using Biolog FF Microplates.It was found that soil properties,especially soil organic carbon and water content,contributed significantly to the variations in soil microbes.With increasing soil depth,the soil microbial biomass,fungal biomass,and fungal catabolic ability diminished;however,the ratio of fungi to bacteria increased.The fungal ratio was higher under larch forests compared to that under poplar,birch,and their mixed forests,although the soil microbial biomass was lower.The direct contribution of vegetation types to the soil microbial community variation was 12%.If the indirect contribution through soil organic carbon was included,variations in the vegetation type had substantial influences on soil microbial composition and diversity.     

Root morphology and effects on soil reinforcement and slope stability of young vetiver (Vetiveria zizanioides) plants grown in semi-arid climate

Currently used in many countries in the world, vetiver grass (Vetiveria zizanioides) applications include soil and water conservation systems in agricultural environment, slope stabilization, mine rehabilitation, contaminated soil and saline land remediation, as well as wastewater treatment. The root system morphology of vetiver was investigated in a small plantation growing on abandoned marl terraces in southern Spain. Root distribution with depth, laterally from the plant, as well as root parameters such as root diameter and tensile strength were also investigated. The profile wall method combined with the block excavation showed that the vetiver grass grows numerous positively gravitropic roots of more or less uniform diameter. These were generally distributed in the uppermost soil horizon closer to the culm base. In situ shear test on blocks of soil permeated with vetiver roots were carried out and showed a greater shear strength resistance than the samples of non vegetated soil. The root reinforcement measured in situ was comparable to the one predicted by the perpendicular root reinforcement model. The stability of a modelled terraced slope planted with vetiver was marginally greater than the one of a non-vegetated slope. A local instability on one terrace can have a detrimental effect on the overall stability of the terraced slope.     

Different biomass-allocation patterns among four tree species in heavily disturbed sites on a volcanic mountain in Hokkaido,northern Japan

We have compared biomass-allocation patterns and frequency of sprouting among saplings of four tree species (Larix kaempferi, Betula platyphylla var. japonica, Populus maximowiczii, and Populus sieboldii) growing on a volcanic mountain in Hokkaido, northern Japan. Growing conditions were very harsh on the mountainside. Leaf mass and fine root mass relative to root mass were larger in L. kaempferi, and L. kaempferi root mass was less than for the other species. Sprouting ratios were high for the broadleaved species. Different allometries and sprouting ratios among species suggest that survival strategies for L. kaempferi were different from those for the broadleaved species. L. kaempferi has greater ability to increase leaf mass under harsh growing conditions; this probably results in large photosynthetic production by L. kaempferi on the volcano. In contrast, the two Populus species and Betula platyphylla seem to maintain populations through their ability to produce sprouts from large root systems.     

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.     

Growth characteristics of root-shoot relations of three birch seedlings raised under different water regimes

Three birch species (Betula ermanii, B. maximowicziana, B. platyphylla var. japonica) widespread in northern Japan were raised under different water regimes (ca. 23, 35, and 60%) to study root-shoot increment and gas exchange traits in relation to their habitat preferences in natural conditions. Total biomass of all birches was larger for medium, wet and dry treatment. Maximum root length of B. platyphylla raised at dry or wet condition was higher than other species. Root growth rate of three birches peaked around mid July to early September while shoot growth rate was found maximum between late June and mid August. Root growth of three birches was suppressed under dry and wet treatment, especially for B. ermanii. Allocation percentage of biomass to roots of three birches ranged from 30 to 40% but it mainly allocated to elongate the root length under dry and wet condition. Fine roots of B. ermanii and B. maximowicziana under wet condition were distributed mainly on soil surface. In the dry treatment, B. platyphylla allocated photosynthates to elongate the root length and fine root production (<2 mm) and had highest plasticity of roots to different water conditions among the three birches. Specific leaf area (SLA) of three birches decreased with decreasing soil moisture content. Plasticity in SLA of B. platyphylla was found largest. Net photosynthetic rate (Pn) and water use efficiency (WUE) of B. platyphyllashowed highest among all the treatments. Leaf nitrogen content of B. platyphyllawas also relatively higher under different water conditions as compared to the other two birch species, suggesting B. platyphylla may enable to invade to various growing conditions with different water regimes.     

Human intervened post-fire forest restoration in the Northern Great Hing’an Mountains: a review

The devastating fire in May 1987 in the northern Great Hing’an Mountains created a mosaic of burned severity. Subsequent log harvesting and tree planting complicated the restoration process. Based on intensive field work and GIS analysis for the burned area, we studied the landscape pattern change in relation with its influencing factors, the restoration of some ecosystem functions and the long-term effect of human planting on vegetation restoration. A post-fire vegetation restoration process was also established using spatial series instead of temporal series. The results indicated that coniferous forest, broad-leaved forest and mixed forest increased obviously in the burned area. Factors influencing the restoration process are ranked as the burned severity, way of restoration (planting, promoted restoration or natural restoration) and topographical factors. The latter was further ranked as the slope, elevation, slope position and aspect. Primary productivity, hydrological functions, habitats for wild animals and permanent frozen soil of the area have all largely been restored to the pre-fire level after more than 15 years. Parameters demonstrated a transitional character of the forest from the early succession stage to middle stage. LANDIS simulation for the long-term forest succession under pure natural restoration and human-intervened restoration indicated that post-fire tree planting largely influenced the age structure, spatial pattern and timber stock of dominant species such as Larix gmelini, Betula platyphylla and Pinus sylvestris var. mongolica. In general, the influence of post-fire human planting can remain for more than 200 years.     

Spatial Characteristics and Change for Tree Species along the North East China Transect (NECT)

Spatial characteristics of sixteen tree species were analyzed by theinformation from 287 permanent plots in 1986 and 1994 on North East ChinaTransect (NECT). Some species expanded and some retracted theirdistribution extents. Betula costata andPhellodendron amurense spread most fast toward west andeast, respectively. All tolerant tree species extended their frontiers and allintolerant tree species retracted their frontiers except Betulaplatyphylla. The distribution area decreased for all species exceptBetula costata, Juglans mandshurica,Ulmus spp. and Fraxinusrhynchophylla.The patch sizes of Pinus koraiensis, Populusdavidiana, Phellodendron amurense,Juglans mandshurica, Fraxinusmandshurica, Betula dahurica,Picea spp., Abies nephrolepis andLarixolgensis decreased, however, the patch sizes of Quercusmongolica, Betula costata, Acermono, Tilia spp., Ulmusspp., Betula platyphylla and Fraxinusrhynchophylla increased. The frequency pattern of Populusdavidiana, Betula platyphylla,Fraxinus rhynchophylla and Betuladahurica changed significantly(p< 0.05). The dominance pattern ofPopulus davidiana, Tilia spp.,Juglans mandshurica, Betulaplatyphylla, Betula dahurica andAbiesnephrolepis changed significantly(p < 0.05). The spatial correlation betweenspecies changed, such as the spatial correlation between Larixolgensis and Betula platyphylla, Acermono and Ulmus spp. increased. The possiblecause of these changes might be climate change, disturbances and habitat loss.     

乌拉山自然保护区白桦种群的年龄结构和点格局分析

白桦群落是乌拉山森林植被的主要类型之一,在高海拔阴坡、半阴坡以纯林形式分布.根据乌拉山自然保护区白桦林不同林龄结构设置3个典型样地,采用种群径级结构代替年龄结构、点格局分析(Ripley's K-Function)方法探讨了乌拉山白桦种群年龄结构、空间分布规律和种群动态.结果表明:(1)乌拉山自然保护区白桦种群径级结构呈典型的“金字塔”型,种群自然更新良好,属增长型种群;(2)由于种内不同个体间为争夺空间和资源,种群在第Ⅲ、Ⅳ径级死亡率较高,自疏作用明显;(3)白桦种群的存活曲线接近于Deevey Ⅰ型曲线;(4)在研究尺度内白桦种群以幼树、中龄树为主时呈聚集分布,而成龄树或老龄树占多数时呈随机分布,即随着种群年龄的增加,其分布格局逐渐由集群分布向随机分布转变.乌拉山白桦种群在小于1.5m的尺度呈聚集分布,即具有2株以上个体“丛生”现象.在环境条件相似的情况下,白桦种群自身的生物、生态学特性是影响其分布格局的最主要因素.     

The effects of vegetation types and microhabitats on carabid beetle community composition in cool temperate Japan

The effects of vegetation types and environmental factors on carabid beetle (Coleoptera: Carabidae) communities were studied. Carabid beetles were collected using pitfall traps (total 2844 trapping days) and seven microenvironmental factors were measured in four vegetation types: grassland, natural evergreen coniferous forest (Pinus densiflora), deciduous broad-leaved natural forest (Quercus crispula, Betula platyphylla, Alnus japonica, or Fagus crenata), and deciduous coniferous plantation (Larix kaempferi) in cool temperate Japan. These four vegetation types provided a novel comparison between natural forests and plantations because the vast majority of related studies have investigated only deciduous broad-leaved natural forests and evergreen coniferous plantations. PERMANOVA indicated that vegetation types affected carabid community composition. Ordination plots showed that community composition differed greatly between grassland and forest vegetation types, but that community composition in the plantation forest overlapped with that of natural forest types. Characteristics differentiating the grassland included a high proportion of winged species and a low mean carabid body weight. Among the examined environmental factors, litter depth, soil water content, and depth of the soil A-horizon had large effects on carabid communities. These results suggest that the effect of afforestation on carabid communities in cool temperate Japan might be insignificant compared with the effects of cover types (deciduous vs. evergreen) and microenvironmental factors.     

小兴安岭不同耐荫性树种枝叶性状变异及权衡

随着植株生长,不同耐荫性树种枝叶性状对资源的响应策略存在差异。探究不同耐荫性树种在不同径级间枝叶性状变异及其相关关系,对理解植物功能性状种内和种间变异以及植物对资源的响应策略具有重要意义。以黑龙江凉水国家级自然保护区阔叶红松（Pinus koraiensis）林中不同径级（小树、中等树和大树）的喜光树种（白桦Betula platyphylla、枫桦Betula costata）和耐荫树种（春榆Ulmus japonica、紫椴Tilia amurensis、色木槭Acer mono）为研究对象,测定其出叶强度、枝横截面积、枝干重、单叶面积、总叶面积、总叶干重共6个枝叶性状。利用单因素方差（LSD）分析检验不同耐荫性树种在不同径级间其枝、叶性状是否存在显著差异;以标准化主轴估计（SMA）对不同耐荫性树种枝叶性状间相关关系进行分析。结果表明：除枝干重外,耐荫树种枝叶性状均大于喜光树种;不同耐荫性树种大树枝横截面积均最大,中等树叶面积均最小;喜光树种不同径级间枝干重、总叶干重和出叶强度无显著差异,而耐荫树种均存在显著差异。随径级增大,不同耐荫性树种枝横截面积与叶面积均呈正异速生长关系,且除耐荫树种枝横截面积与单叶面积外,均存在共同斜率;不同耐荫性树种出叶强度与单叶面积存在共同斜率为-0.51和0.47,小树和中等树枝横截面积与总叶面积和总叶干重的异速生长指数均与1存在显著差异,而大树与1无显著差异。结果表明：不同耐荫性树种在不同径级间对资源的获取策略存在差异,不同耐荫性树种小树阶段均表现出资源获取策略,大树阶段则表现出资源保守型策略。与耐荫树种相比,喜光树种表现为快速生长策略,而随着径级增大不同耐荫性树种这种差异逐渐消失,本研究结果为森林演替过程中种内和种间的相互作用提供了一个新的视角。     

Quantifying the effects of root reinforcement of Persian Ironwood (Parrotia persica) on slope stability; a case study: Hillslope of Hyrcanian forests,northern Iran

Forest vegetation is known to enhance the stability of slopes by reinforcing soil and increasing its shear resistance through root system. The effects of root reinforcement depend on the morphological characteristics of the root system, the tensile strength of single roots, and the spatial distribution of the roots in soil. In the present study the results of research carried out in order to evaluate the biotechnical characteristics of the root system of Persian Ironwood (Parrotia persica), in northern Iran are presented. Profile trenching method was used to obtain root area ratio (RAR) values for uphill and downhill sides of the individual trees. For each species, single root specimens were sampled and tested for their tensile strength. It was found that root density generally decreases with depth according to an exponential law. Maximum RAR values were located within the first 0.1 m, with maximum rooting depth at about 0.65 m. RAR values ranged from 0.001% at lower depths to 1.39% near the surface, at upper 0.1 m depth. Significant differences of RAR values, rooting depth and root cohesion between uphill and downhill were observed, however, the differences were not significant for number of roots (ANCOVA). Downhill profiles had higher RAR values, rooting depth and root cohesion. In general, root tensile strength tends to decrease with diameter according to a power law, as observed by other researchers. Downhill roots were significantly stronger in tensile strength than uphill ones. Inter-species variation of tensile strength in downhill roots was also observed. The resulting data were used to evaluate the reinforcing effects in terms of increased shear strength of the soil, using Wu/Waldron Model. The root reinforcement provided by Persian Ironwood is about 46.0 kPa in the upper layers and 0.3 kPa in the deeper horizons. The results of Spearman test revealed a significant correlation between RAR and c_r and that best followed by a power law. The results presented in this paper contribute to expanding the knowledge on biotechnical characteristics of Persian Ironwood on slope reinforcement.     

黄土高原子午岭林区典型树种叶片N、P再吸收特征

为揭示黄土高原子午岭林区不同演替阶段和植被类型主要树种养分再吸收特征,研究选取4种次生植被树种(白桦、山杨、辽东栎和油松)和2种人工植被树种(刺槐和侧柏),测定其成熟叶、凋落叶和林下土壤碳(C)、氮(N)、磷(P)含量,研究了叶片N、P再吸收率及其与养分指标的关系。结果表明:(1)不同树种叶片养分和林下土壤养分含量存在显著差异,土壤C、N含量和C∶N∶P计量比均表现为演替后期林地(辽东栎和油松)演替前期林地(山杨和白桦)人工林(侧柏和刺槐);(2)不同树种叶片N、P再吸收率分别为17.18%—43.34%和27.13%—58.12%,均表现为演替后期林地人工林演替前期林地,且P的再吸收率总体高于N的再吸收率;(3)不同树种叶片N、P再吸收率与叶片养分指标的关系强于土壤,与养分计量比的相关性大于养分含量的相关性。说明子午岭典型植被会通过叶片N、P再吸收来适应养分限制环境,尤其是演替后期植被再吸收能力更强,研究可为黄土高原植被恢复提供理论依据。     

祁连山北坡退化林地植被群落的自然恢复过程及土壤特征变化

采用长期定位观测的方法,研究了祁连山北坡退化林地人工抚育下2001-2008年间植被群落的自然恢复过程和土壤特征变化。结果表明:人为干扰消除后,退化林地群落环境逐渐优化,群落的科、属、种均明显增加,物种成员更替频繁;灌木和乔木物种出现后,群落垂直高度增大,群落结构出现成层现象;群落总体多样性指数呈不断增大的趋势,在空间结构上,Patrick丰富度指数、Shannon-Wiener多样性指数和Simpson优势度指数表现出:草本层>灌木层>乔木层的规律,而Pielou均匀度指数变化相反;土壤含水量、土壤有机碳和全氮含量随植被恢复均不断增加。在实施封育禁牧措施后,退化林地实现了由草本群落-灌木群落-乔木群落方向的快速演替,当恢复到早期的先锋乔灌混交阶段时,群落的物种组成、结构和多样性趋于复杂化,土壤性状也得到一定改善,显示出相对较好的适应性和恢复效果。