Root architecture and wind-firmness of mature Pinus pinaster

This study aims to link three-dimensional coarse root architecture to tree stability in mature timber trees with an average of 1-m rooting depth. Undamaged and uprooted trees were sampled in a stand damaged by a storm. Root architecture was measured by three-dimensional (3-D) digitizing. The distribution of root volume by root type and in wind-oriented sectors was analysed. Mature Pinus pinaster root systems were organized in a rigid 'cage' composed of a taproot, the zone of rapid taper of horizontal surface roots and numerous sinkers and deep roots, imprisoning a large mass of soil and guyed by long horizontal surface roots. Key compartments for stability exhibited strong selective leeward or windward reinforcement. Uprooted trees showed a lower cage volume, a larger proportion of oblique and intermediate depth horizontal roots and less wind-oriented root reinforcement. Pinus pinaster stability on moderately deep soils is optimized through a typical rooting pattern and a considerable structural adaptation to the prevailing wind and soil profile.     

Root system architecture of Quercus pubescens trees growing on different sloping conditions

BACKGROUND AND AIMS: Plant roots' growth direction has important implications for plant development and survival; moreover it plays an effective and vital role in stabilizing weathered soil on a steep slope. The aim of this work was to assess the influence of slope on the architecture of woody root systems. METHODS: Five mature, single-stemmed Quercus pubescens trees growing on a steep slope and five on a shallow slope were excavated to a root diameter of 1 cm. A very precise numeric representation of the geometry and topology of structural root architecture was gained using a low-magnetic-field digitizing device (Fastrak, Polhemus). Several characteristics of root architecture were extracted by macros, including root volume, diameter, length, number, spatial position and branching order. KEY RESULTS: The diameter at breast height (dbh) was the best predictor of the root volume but had no correlation with length and number of roots. The slope affected the root volume for each branching order, and the basal cross-sectional area (CSA), number and length of the first-order roots. Number and length of the second- and third-order laterals were closely related in both conditions, although this relationship was closer in the shallow trees, suggesting the influence of a genetic control. Sloping trees showed a clustering tendency of the first- and second-order lateral roots in the up-slope direction, suggesting that the laterals rather than the taproots provide much of the anchorage. In a steep-slope condition, the taproot tapering was positively correlated with the asymmetry magnitude of first-order roots, indicating compensation between taproot and main lateral roots' clustering tendency. CONCLUSIONS: These results suggest that on a slope, on clayey soils, root asymmetry appears to be a consequence of several environmental factors such as inclination, shallow-slides and soil compactness. In addition, this adaptive growth seems to counteract the turning moment induced by the self-loading forces acting in slope conditions, and as a consequence improves the tree stability.     

丛枝菌根真菌调控根系构型与矿质元素平衡提高西瓜植株耐盐性的研究

丛枝菌根（arbuscular mycorrhiza,AM）真菌可通过多种途径或机制来增强植物的耐盐性,进而促进植株的生长发育。本研究在盆栽条件下设西瓜Citrullus lanatus品种‘京欣四号’幼苗接种变形球囊霉Glomus versiforme和不接种以及施加和不施加100mmol/L NaCl共4个处理,测定植株根系菌根侵染状况、根系构型及其根茎叶中钾（K）、钙（Ca）、磷（P）、钠（Na）含量、K⁺/Na⁺、Ca²⁺/Na和植株生长状况等。AM真菌显著增加了盐胁迫下西瓜植株总根长度、根表面积、根体积和根尖数量,改善了根系构型;促进了西瓜根系对K、Ca和P的吸收,提高了茎Ca和P含量、根系K和P含量、K⁺/Na⁺和Ca²⁺/Na⁺,而降低了根Na⁺含量;茎P和Na⁺、叶K和Ca的含量显著高于其他器官相应含量。典范对应分析表明,根系K含量、K⁺/Na⁺和Ca²⁺/Na⁺与总根长度、主根长度、根表面积、根体积、根尖数量、根平均直径呈正相关;叶K⁺/Na⁺与主根长度呈正相关;根系Na⁺含量与根系总根长、根平均直径和根尖数量呈负相关。接种AM真菌改善了矿质元素平衡及其分配状况。盐胁迫后西瓜植株对菌根的依赖性增强。结果表明,K、Ca、P是AM真菌介导植物耐盐性的关键养分;K⁺/Na⁺和Ca²⁺/Na⁺是重要的矿质元素平衡指标,接种AM真菌能调控植物根系构型和矿质元素平衡状况,从而缓解盐胁迫对西瓜生长的抑制作用,提高植株的耐盐性。     

Modification of root architecture in woody plants is possible for the presence of two different mechanisms of lateral root production: The effect of slope in Spartium junceum L. seedlings

Abstract

This paper investigates the modification of root architecture of Spartium junceum L. seedlings grown in slope condition. It is reported that 50% of the total number of lateral roots are concentrated in few centimetres of the taproot near the collar. The anatomical analysis of transverse sections along the taproot axis reveals that this taproot zone is characterised by two types of lateral roots: one with a trace extending to the centre of the vascular cylinder by following the path of a medullar ray; one with a trace which ends in the vascular cambium. The first type may be lateral roots originated from the taproot primary structure; the second type seems to be lateral roots developing later when a secondary structure has completely substituted the primary structure. The emission of this second type of lateral roots seems to be strongly controlled by environmental conditions with considerable consequences upon the overall root architecture. In the example reported in this paper, young plants growing under mechanical stress due to a slope develop asymmetric root architecture with lateral roots elongating in two prevalent directions: up-slope or down-slope. This asymmetric architecture is produced in the zone of the taproot where a secondary structure is present and represents the plant response to the need of increasing its anchorage strength.     

A comparison of root architecture and shoot morphology between naturally regenerated and container-grown seedlings of Quercus ilex

We explored the different mechanisms developed by naturally regenerated seedlings of Quercus ilex L. (Holm oak) under Mediterranean conditions compared to container-seedlings commonly used in plantations. We examined the differences in root architecture (including topology and morphology) and shoot parameters. The results showed that there are many differences in the architecture of the root system as well as in the shoot morphology between the two types of seedlings. The naturally regenerated seedlings were smaller with regard to most of the shoot and root parameters, but they developed a longer taproot, only first order lateral roots, and presented a more herringbone-like root system compared to the container seedlings. Conversely, all types of container seedlings, were larger and had a more extended root system with many orders of lateral roots, while their taproot length was restricted within the container’s depth. The quotient log (α)/ log (μ) for all seedlings, showed a tendency to decrease with plant size. A strict herringbone root system with an elongated taproot may be the optimal root architecture for Quercus ilex L. seedlings in order to survive under Mediterranean conditions.     

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。     

Photosynthate Partitioning and Enzymes of Sucrose Metabolism in Sugarbeet Roots

Populations of sugarbeet (Beta vulgaris L.) plants that differed in taproot/leaf weight ratio and in photosynthate partitioning between taproots and fibrous roots did not differ in root/shoot ratio as indicated by relative dry weight distribution. Based on the hypothesis that dry weight distribution is influenced by the metabolism of imported sucrose, we examined the relationships between the activity of the enzymes of sucrose metabolism and dry weight distribution as a function of genotype and ontogeny. A decreased specific activity of acid invertase in taproots was associated with increased taproot/fibrous root weight ratio at 21 and at 28 days post-emergence. Alkaline invertase activity was negatively correlated with taproot/fibrous root weight ratio at 28 days. Sucrose synthetase specific activities of taproots were not correlated with dry matter distribution. Acid invertase may influence photosynthate partitioning between the taproot and fibrous roots via regulation of sucrose levels in the region of fibrous root initiation.     

The root system architecture of young Greek fir (Abies cephalonica Loudon) trees

Abstract

The root system architecture of young Greek fir (Abies cephalonica Loudon) trees was studied in Evritania, Central Greece. A sample of naturally regenerated fir plants were uprooted and divided into three age groups of 5 (5–6 years), 10 (9–11 years) and 15 (15–16 years) years old. Root architectural data (e.g. root length and volume, topology, branching structure) were obtained with a 3D digitizer (3SPACE Fastrak, Polhemus). In all nine trees the largest vertical root originating from the stump was selected, measured and coded as a taproot. The topological and geometrical information from the data file was analysed by computing the characteristics of each root segment. The AMAPmod software was used, providing the user with various tools for encoding, exploring and modelling plants. The findings showed that the age of fir trees is an important parameter that affects root architecture. Topological analysis revealed that the root system of Greek fir have almost a typical herringbone pattern during the first 10 years of tree life, and then the root systems changes to a less herringbone pattern. The root system is expanded with the tree age; however, the total root length and the total number of roots seems to increase in a linear trend, while the root volume appears to increase in a geometric way.     

The biomechanics of Pachycereus pringlei root systems

We report on the root system of the large columnar cactus species Pachycereus pringlei to explore the hypothesis that increasing plant size decreases the ability to resist wind-throw but increases the capacity to absorb and store nutrients in roots (i.e., plant size limits the performance of these functions and may shift the performance of one function in favor of another as size increases). Based on 18 plants differing in size, the root system is characterized by a broad and deep bayonet-like root central to a shallow and extensive lateral system of root elements bearing sinker roots near the stem base. All root types have a living secondary cortex and contain wood with a large volume fraction of ray tissues that increases toward the stem base. Wood stiffness and tensile strength are correlated negatively with the ray tissue volume fraction and thus decrease toward the stem base in lateral and bayonet roots. Calculations show that the ability of the bayonet and proximal lateral root elements to resist wind-throw decreases with increasing plant size, whereas the nutrient absorption/storage capacity of the total root system increases with plant size (i.e., a size-dependent shift between these two root functions occurs).     

Control of soil physical properties and response ofBrassica rapa L. seedling roots

A system was designed, constructed, tested, and used to growBrassica rapa L. seedling roots which were exposed to O₂ concentrations from 0 to 0.21 mol mol⁻¹, water potentials from 0 to −80 kPa, temperatures from 10 to 34°C, and mechanical impedance from 0 to 20.8 kPa. The experimental design was a central composite rotatable design with seven replications of the center point. Measurements were taken of taproot length, taproot diameter at the point of initiation of root hairs (diameter 1), and one cm above the first measurement (diameter 2), and total length and number of first-order laterals. Temperature had the greatest effect on seedling root growth, with linear and quadratic temperature effects significant for all root measurements except taproot diameter 2 which just had a significant linear effect. Water potential had a significant linear effect on lateral length and number of laterals and a significant quadratic effect on taproot diameter 1. Mechanical impedance had a significant effect only on taproot diameter 2. Oxygen was not significant for any root measurement. The mechanical impedance by water potential interaction was significant for taproot length and taproot diameter 1. A temperature optimum was found for taproot length, taproot diameter 1, lateral length, and lateral number, at 26.0, 42.5, 26.5, and 26.4°C, respectively. Taproot diameter 1 had a water potential optimum at −36.5 kPa, whereas taproot diameter 2 had a mechanical impedance optimum at 12.5 kPa. A growth cell designed for this study allows independent control of soil strength, water potential, oxygen concentration, and temperature. Thus, the cell provides the capability which was demonstrated forBrassica rapa L. to grow seedling roots under complete control of the soil physical properties.     

Deep Phenotyping of Coarse Root Architecture in R. pseudoacacia Reveals That Tree Root System Plasticity Is Confined within Its Architectural Model

This study aims at assessing the influence of slope angle and multi-directional flexing and their interaction on the root architecture of Robinia pseudoacacia seedlings, with a particular focus on architectural model and trait plasticity. 36 trees were grown from seed in containers inclined at 0° (control) or 45° (slope) in a glasshouse. The shoots of half the plants were gently flexed for 5 minutes a day. After 6 months, root systems were excavated and digitized in 3D, and biomass measured. Over 100 root architectural traits were determined. Both slope and flexing increased significantly plant size. Non-flexed trees on 45° slopes developed shallow roots which were largely aligned perpendicular to the slope. Compared to the controls, flexed trees on 0° slopes possessed a shorter and thicker taproot held in place by regularly distributed long and thin lateral roots. Flexed trees on the 45° slope also developed a thick vertically aligned taproot, with more volume allocated to upslope surface lateral roots, due to the greater soil volume uphill. We show that there is an inherent root system architectural model, but that a certain number of traits are highly plastic. This plasticity will permit root architectural design to be modified depending on external mechanical signals perceived by young trees.     

Spatial mapping of phosphorus influx in bean root systems using digital autoradiography

A novel technique was developed to spatially map the phosphorus net influx capacity in intact root systems. The method is based on digital autoradiography and permits the quantification of phosphorus influx at high spatial resolution (2 mm). Roots of 18-d-old common bean plants were exposed to (32)P-labelled orthophosphate, quickly frozen, excised, lyophilized, scanned, and exposed to a storage phosphor screen. Plots of (32)P content versus root length (distance from the root tip or from the base of the root) were obtained for three different root classes: basal, basal laterals, and taproot laterals. Radioactivity detected by filmless autoradiography correlated well (r(2)=0.99) with measurements made by scintillation counting. Basal roots absorbed 2.5 times and 1.9 times more phosphorus than the taproot lateral and basal lateral root classes, respectively, in the first 20 mm from the root apex. External phosphorus markedly affected influx: roots averaged 5, 16, and 34 pmol P min(-1) in the apical 20 mm when exposed to 1, 5, and 10 microM P solutions, respectively. The spatial pattern of phosphorus influx along the root axes of the different root classes was rather homogeneous when measured on a root surface area basis. Phosphorus influx in the older segments of basal roots (those next to the hypocotyl) did not differ from the newer segments close to the root apex. However, a heterogeneous pattern was detected for basal roots when measured on a length basis, indicating that both root class and diameter constitute main factors controlling the spatial pattern of net influx.     

Effects of Soil Compaction and Meloidogyne incognita on Cotton Root Architecture and Plant Growth

The effects of a soil hardpan and Meloidogyne incognita on cotton root architecture and plant growth were evaluated in microplots in 2010 and 2011. Soil was infested with M. incognita at four different levels with or without a hardpan. The presence of a hardpan resulted in increased plant height, number of main stem nodes, and root fresh weight for cotton seedlings both years. Meloidogyne incognita decreased height and number of nodes for seedlings in 2010. Nematode infestation increased seedling root length and enhanced root magnitude, altitude, and exterior path length in 2010. This was also the case for root length and magnitude in 2011 at lower infestation levels suggesting compensatory growth. A hardpan had no consistent effect on these root parameters but increased root volume in both years. A hardpan hastened crop maturity and increased the number of fruiting branches that were produced, while M. incognita infection delayed crop development and reduced plant height and number of bolls. Both M. incognita infection and a hardpan reduced taproot length and root dry weight below the hardpan in both years. Root topological indices under all the treatments ranged from 1.71 to 1.83 both years indicating that root branching followed a herringbone pattern. The techniques for characterizing root architecture that were used in this study provide a greater understanding of changes that result from disease and soil abiotic parameters affecting root function and crop productivity.     

Modelling applicability of fractal analysis to efficiency of soil exploration by roots

BACKGROUND AND AIMS: Fractal analysis allows calculation of fractal dimension, fractal abundance and lacunarity. Fractal analysis of plant roots has revealed correlations of fractal dimension with age, topology or genotypic variation, while fractal abundance has been associated with root length. Lacunarity is associated with heterogeneity of distribution, and has yet to be utilized in analysis of roots. In this study, fractal analysis was applied to the study of root architecture and acquisition of diffusion-limited nutrients. The hypothesis that soil depletion and root competition are more closely correlated with a combination of fractal parameters than by any one alone was tested. MODEL: The geometric simulation model SimRoot was used to dynamically model roots of various architectures growing for up to 16 d in three soil types with contrasting nutrient mobility. Fractal parameters were calculated for whole roots, projections of roots and vertical slices of roots taken at 0, 2.5 and 5 cm from the root origin. Nutrient depletion volumes, competition volumes, and relative competition were regressed against fractal parameters and root length. KEY RESULTS: Root length was correlated with depletion volume, competition volume and relative competition at all times. In analysis of three-dimensional, projected roots and 0 cm slices, log(fractal abundance) was highly correlated with log(depletion volume) when times were pooled. Other than this, multiple regression yielded better correlations than regression with single fractal parameters. Correlations decreased with age of roots and distance of vertical slices from the root origin. Field data were also examined to see if fractal dimension, fractal abundance and lacunarity can be used to distinguish common bean genotypes in field situations. There were significant differences in fractal dimension and fractal abundance, but not in lacunarity. CONCLUSIONS: These results suggest that applying fractal analysis to research of soil exploration by root systems should include fractal abundance, and possibly lacunarity, along with fractal dimension.     

Differences in root and shoot development of tomato (Lycopersicon esculentum L.) varieties across contrasting soil environments

Summary The root and shoot growth of three tomato (Lycopersicon esculentum L.) varieties, VF-10, VF-1908 and Paste 56 were compared in either a river-washed sand or an alluvial silty loam, with or without added nutrients, to determine factors influencing root growth and development. VF-10 had consistently higher shoot weights than the other two varieties, particularly by 45 days from germination. Although the root-to-shoot ratio varied with soil treatment, no significant differences in this ratio occurred among varieties. The roots were characterised by a taproot, thickened in the uppermost 3 to 5 cm, with 86 to 190 secondary roots when harvested 30 days after germination. The variety VF-1908 had a higher proportion of fine roots than the other two varieties over all treatments. On the basis of root weight and length, VF-1908 was also more stable across the imposed environmental gradient than the varieties VF-10 or Paste 56. This arose from less variability across soil treatments in secondary branching in VF-1908; over the four soil treatments the number of secondary roots varied from 104 to 131 in VF-1908 compared to 86 to 139 in VF-10 and 95 to 190 in Paste 56. VF-1908 and Paste 56 also had less variation in tertiary branching than VF-10, which had a consistently greater number of major tertiary roots than the other two varieties over all soil treatments. With the exception of Paste 56 in the fertilized silt, shoot growth was correlated with root length.     

指数施肥对楸树无性系生物量分配和根系形态的影响

为探求楸树不同无性系生物量分配和根系形态的差异,2011年3-8月在甘肃省天水市小陇山林科所,以2年生楸树无性系1-4、7080和015-1组培苗为试验材料,设置了CK、6、10、14 g尿素/株4个处理,研究指数施肥对楸树无性系生物量分配和根系形态的影响.结果表明:(1)同一无性系中,10 g尿素/株的根、茎、叶生物量及总生物量、根长、根表面积、根体积和根平均直径均高于其它处理.无性系015-1的生物量和根系形态参数整体上高于无性系1-4和7080.无性系015-1在10 g尿素/株的根、茎、叶生物量及总生物量分别为89.44 g、61.30 g、79.97 g、230.71 g,是CK的1.48、1.52、2.09、1.66倍;根长、根表面积和根体积为22667 cm、6260 cm2、578.14 cm3,是CK的1.94、1.54、2.43倍.(2)指数施肥和无性系的遗传差异明显影响楸树不同无性系生物量的分配格局.适量施氮明显促进3个楸树无性系生物量的积累,而氮素缺乏或过量均不利于生物量的积累.8月同一无性系的根冠比均随施氮量的增加而降低;同一处理下无性系7080的根冠比高于无性系1-4和015-l.无性系1-4和7080的生物量主要向叶和茎分配,而无性系015-1主要向叶分配.(3)指数施肥在6月和7月主要促进细根根长和根表面积的增加;指数施肥在8月主要促进细根、中等根和粗根体积的急剧增加,分别比7月高达36.88％、124.96％、154.79％.这利于根系在中后期吸收更多养分,从而引起生物量分配格局的变化.(4)生物量参数和根系形态参数关系密切.根生物量、地上生物量、总生物量分别和根长、根表面积、根体积、根平均直径极显著正相关;根冠比和根长、根表面积、根体积、根平均直径极显著负相关;比根长和地上生物量、总生物量显著正相关,和根冠比极显著负相关.     

Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root:shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.     

Assessing variability in root traits of wild Lupinus angustifolius germplasm: basis for modelling root system structure

Background and aims

Intra-specific variation in root system architecture and consequent efficiency of resource capture by major crops has received recent attention. The aim of this study was to assess variability in a number of root traits among wild genotypes of narrow-leafed lupin (Lupinus angustifolius L.), to provide a basis for modelling of root structure.

Methods

A subset of 111 genotypes of L. angustifolius was selected from a large germplasm pool based on similarity matrices calculated using Diversity Array Technology markers. Plants were grown for 6?weeks in the established semi-hydroponic phenotyping systems to measure the fine-scale features of the root systems.

Results

Root morphology of wild L. angustifolius was primarily dominated by the taproot and first-order branches, with the presence of densely or sparsely distributed second-order branches in the late growth stage. Large variation in most root traits was identified among the tested genotypes. Total root length, branch length and branch number in the entire root system and in the upper roots were the most varied traits (coefficient of variation CV >0.50). Over 94% of the root system architectural variation determined from the principal components analysis was captured by six components (eigenvalue >1). Five relatively homogeneous groups of genotypes with distinguished patterns of root architecture were separated by k-means clustering analysis.

Conclusions

Variability in the fine-scale features of root systems such as branching behaviour and taproot growth rates provides a basis for modelling root system structure, which is a promising path for selecting desirable root traits in breeding and domestication of wild and exotic resources of L. angustifolius for stressful or poor soil environments.     

Mapping QTLs for root morphological traits inBrassica rapa L. based on AFLP and RAPD markers

Root growth and thickening plays a key role in the final productivity and even the quality of storage roots in root crops. This study was conducted to identify and map quantitative trait loci (QTLs) affecting root morphological traits in Brassica rapa by using molecular markers. An F2 population was developed from a cross between Chinese cabbage (Brassica rapa ssp. chinensis) and turnip (B. rapa ssp. rapifera), which differed greatly in root characters. A genetic map covering 1837.1 cM, with 192 marker loci and 11 linkage groups, was constructed by using this F2 population. The F3 families derived from F2 plants were grown in the field and evaluated for taproot traits (thickness, length, and weight). QTL analysis via simple interval mapping detected 18 QTLs for the 3 root traits, including 7 QTLs for taproot thickness, 5 QTLs for taproot length, and 6 QTLs for taproot weight. Individually, the QTLs accounted for 8.4-27.4% of the phenotypic variation. The 2 major QTLs, qTRT4b for taproot thickness and qTRW4 for taproot weight, explained 27.4% and 24.8% of the total phenotypic variance, respectively. The QTLs for root traits, firstly detected in Brassica crops, may provide a basis for marker-assisted selection to improve productivity in root-crop breeding.     

星毛委陵菜根系构型对草原退化的生态适应

对轻度、中度、重度和极度退化的草原群落中星毛委陵菜(Potentilla acaulis)根系构型参数及相应的土壤水分、容重和硬度等指标进行了分析, 以研究星毛委陵菜根系构型对草原退化的生态适应性。结果表明: 1)在以大针茅(Stipa grandis)为建群种的典型草原中, 随着退化程度的加剧, 星毛委陵菜在群落中的作用逐渐增强, 其根幅、根深、一级垂向根数、分蘖子株数和水平分蘖根长度显著增加; 2)根表面积、二级侧根长度、总根长和根分叉数4个根系构型参数是解释星毛委陵菜根系构型对草原退化生态适应的首选指标, 解释力依次减小, 累计贡献率为92.34%; 3)直径2 mm以下的根系对单株系星毛委陵菜的根表面积和总根长影响显著; 4)阔腰倒锥体三维根系构型是星毛委陵菜适应草原退化并使之成为建群种的优势构型。