Using radius frequency distribution functions as a metric for quantifying root systems

Root radius frequency distributions have been measured to quantify the effect of plant type, environment and methodology on root systems, however, to date the results of such studies have not been synthesised. We propose that cumulative frequency distribution functions can be used as a metric to describe root systems because (1) statistical properties of the frequency distribution can be determined, (2) the parameters for these can be used as a means of comparison, and (3) the analytical expressions can be easily incorporated into models that are dependent upon root geometry. We collated a database of 96 root radii frequency distributions and botanical and methodology traits for each distribution. To determine if there was a frequency distribution function that was best suited to root radii measurements we fitted the exponential, Rayleigh, normal, log-normal, logistic and Weibull cumulative distribution functions to each distribution in our database. We found that the log-normal function provided the best fit to these distributions and that none of the distribution functions was better or worse suited to particular shapes. We derived analytical expressions for root surface and volume and found that they are a valid, and simpler method for incorporating root architectural traits into analytical models. We also found that growth habit and growth media had a significant effect on mean root radius.     

Evolving technologies for growing,imaging and analyzing 3D root system architecture of crop plants

A plant's ability to maintain or improve its yield under limiting conditions,such as nutrient de ficiency or drought,can be strongly in fluenced by root system architecture(RSA),the three-dimensional distribution of the different root types in the soil. The ability to image,track and quantify these root system attributes in a dynamic fashion is a useful tool in assessing desirable genetic and physiological root traits. Recent advances in imaging technology and phenotyping software have resulted in substantive progress in describing and quantifying RSA. We have designed a hydroponic growth system which retains the three-dimensional RSA of the plant root system,while allowing for aeration,solution replenishment and the imposition of nutrient treatments,as well as high-quality imaging of the root system. The simplicity and flexibility of the system allows for modi fications tailored to the RSA of different crop species and improved throughput. This paper details the recent improvements and innovations in our root growth and imaging system which allows for greater image sensitivity(detection of fine roots and other root details),higher ef ficiency,and a broad array of growing conditions for plants that more closely mimic those found under field conditions.     

不同穗型冬小麦品种根系时空分布特征及其碳氮代谢的研究

在大田柱栽试验条件下,对2种穗型冬小麦品种根系的时空变化及其碳氮代谢进行了研究。结果表明,2种穗型冬小麦品种的单株根系干重、根重密度随生育时期逐渐增加,均在抽穗期达到最大值;不同土壤深度的根系活力随生育时期的变化不一致,2品种0～20 cm根系活力的变化趋势从越冬期逐渐下降,在抽穗期达到较低值后缓慢上升,并于灌浆期出现一个小的峰值;根系中可溶性糖含量、含氮量均从越冬期开始下降,在抽穗期达到最低值, 随后在开花期又出现一个峰值后缓慢下降。2种穗型冬小麦品种相比,重穗型小麦品种的根系各项指标略高于多穗型品种;在不同土层深度之间,各项指标总体趋势为随着土层深度加深逐渐下降,但是在不同生育时期,各土层之间出现有个别波动现象。     

Growth direction of nodal roots in rice: its variation and contribution to root system formation

The root system of a rice plant (Oryza sativa L.) consists of numerous nodal roots and their laterals. The growth direction of these nodal roots affects the spatial distribution of the root system in soil, which seems to relate to yield and lodging resistance. The growth angle of a nodal root varies with the type and timing of emergence of the nodal root. The body of a rice plant can be recognized as an integrated set of shoot units, each unit consisting of an internode with a leaf and several roots. Nodal roots formed at the apical part of a shoot unit often elongate horizontally, whereas those formed at the basal part of the shoot unit show various growth directions depending on both the growth stages of the plant and the environmental conditions. Moreover, nodal roots that emerge from the most basal shoot unit of a tiller are usually thick and grow downwards. External factors such as planting density and nitrogen application affect the growth direction of nodal roots, probably partly because of the changing tillering pattern of the shoot. In addition to the growth angle of nodal roots, size of nodal roots may be another important factor determining the spatial distribution of the root system in soil.     

High‐throughput two‐dimensional root system phenotyping platform facilitates genetic analysis of root growth and development

High‐throughput phenotyping of root systems requires a combination of specialized techniques and adaptable plant growth, root imaging and software tools. A custom phenotyping platform was designed to capture images of whole root systems, and novel software tools were developed to process and analyse these images. The platform and its components are adaptable to a wide range root phenotyping studies using diverse growth systems (hydroponics, paper pouches, gel and soil) involving several plant species, including, but not limited to, rice, maize, sorghum, tomato and Arabidopsis. The RootReader2D software tool is free and publicly available and was designed with both user‐guided and automated features that increase flexibility and enhance efficiency when measuring root growth traits from specific roots or entire root systems during large‐scale phenotyping studies. To demonstrate the unique capabilities and high‐throughput capacity of this phenotyping platform for studying root systems, genome‐wide association studies on rice (Oryza sativa) and maize (Zea mays) root growth were performed and root traits related to aluminium (Al) tolerance were analysed on the parents of the maize nested association mapping (NAM) population.     

Early growth of Brazilian pine (Araucaria angustifolia[Bertol.] Kuntze) in response to soil compaction and drought

Soil compaction leads to changes in soil physical properties such as density, penetration resistance and porosity, and, by consequence, affects root and plant growth. The initial growth of Brazilian pine is considered as being more affected by soil physical than chemical conditions, and the presence of a well-developed tap root system has been associated with this fact. A greenhouse experiment was conducted in order to evaluate the impact of soil compaction on the growth of Brazilian pine seedlings and on their susceptibility to a simulated drought period. In the first phase of the experiment, the effects of three levels of soil compaction on root morphology and plant growth were examined. Soil cylinders were artificially compacted in PVC tubes. Pre-germinated seeds were planted, and 147 days later 10 plants from each treatment were harvested for analysis. Higher values of soil density were associated with a shorter and thicker tap root. Growth of lateral roots and shoots remained unaffected at this stage. In the second phase, half of the plants (12) in each compaction treatment were drought-stressed by withholding water for a period of 77 days. Increased soil compaction again resulted in reduced length and increased diameter of the main tap root. This time, the effects were also extended to the lateral roots. Shoot extension growth and overall plant mass, however, increased with soil compaction. This greater mass accumulation in plants growing under increased soil compaction may be attributed to a more intimate contact between roots and soil particles. Drought stress reduced both root and shoot growth, but root mass was more negatively affected by drought stress in plants growing under high levels of soil compaction. Future investigations on the effects of soil compaction on the initial growth of Brazilian pine should include a wider range of compaction levels to better establish the relationship between soil physical parameters and plant growth.     

Modelling the influence of assimilate availability on root growth and architecture

A model has been designed to simulate rubber seedling root development as related to assimilate availability. Each root of the system is defined both as an element of a network of axes, characterized by its order, position and connections and as an individual sink competing for assimilates. At each time step, the growth of each root is calculated as a function of its own growth potential and of assimilate availability calculated within the whole plant. The potential elongation rate of a root is estimated by its apical diameter, which reflects the size of the meristem. When a root is initiated, the apical diameter depends on root type, but it varies thereafter according to assimilate availability. Thus, the latter controls both current and potential elongation. The model was able to simulate periodicity in root development as related to shoot growth and to reproduce differences in sensitivity to assimilate availability related to root type. It thereby validated the hypothesis that root growth but also root system architecture depend on assimilate allocation and that apical diameter is a good indicator of root growth potential. Provided that specific calibration is done, this model may be used for other species.     

土壤养分空间异质性与植物根系的觅食反应

植物在长期进化过程中,为了最大限度地获取土壤资源,对养分的空间异质性产生各种可塑性反应．包括形态可塑性、生理可塑性、菌根可塑性等．许多植物种的根系在养分丰富的斑块中大量增生,增生程度种间差异较大,并受斑块属性(斑块大小、养分浓度)、营养元素种类和养分总体供应状况的影响．植物还通过调整富养斑块中细根的直径、分枝角、节问距以及空间构型来实现斑块养分的高效利用．根系的生理可塑性及菌根可塑性可能在一定程度上影响其形态可塑性．生理可塑性表现为处于不同养分斑块上的根系迅速调整其养分吸收速率,从而增加单位根系的养分吸收,对在时间上和空间上变化频繁的空间异质性土壤养分的利用具有重要意义,可在一定程度上弥补根系增生反应的不足．菌根可塑性目前研究较少,一些植物种的菌根代替细根实现在富养斑块中的增生．菌根增生的碳投入养分吸收效率较高、根系增生对增加养分吸收的作用较复杂,取决于养分离子在土壤中的移动性能以及是否存在竞争植物;对植物生长(竞争能力)的作用因种而异,一些敏感种由此获得生长效益,而其它一些植物种受影响较小．植物个体对土壤养分空间异质性反应能力和生长差异,影响其在群落中的地位和命运,最终影响群落组成及其结构．     

两种不同根系类型湿地植物的根系生长

实验设计了一个水培系统,利用生活污水培养,对4种“须根型”植物美人蕉、风车草、象草和香根草和4种根茎型植物菖蒲、水鬼蕉、芦苇和水烛的根系生长进行比较研究。该系统由用于盛污水的塑料桶（顶部直径36．5cm,底部直径30．Ocm,高34．5cm）和用于固定植物于水面的泡沫板构成。每桶种植1株植物,每种种5株。水培至10周时,须根型植物的平均根数达到1349条／株,而根茎型植物的平均根数只有549条／株。实验结束（水培第21周）时,须根型植物的平均根生物量为11．3g／株,根茎型植物的平均根生物量为7．4g／株。须根型植物根系中,d〈1mm的细根生物量占根系总生物量的51．9％,而根茎型植物d〈1mm的细根的生物量只占25．1％。根茎型植物的根生物量与地上生物量的比值为0．2,显著高于须根型湿地植物（0．1）。须根型湿地植物的根系表面积（6933cm^2／株）极显著地高于根茎型湿地植物（1897cm^2／株）。根茎型湿地植物根的平均寿命（46．6d）较须根型湿地植物根的平均寿命（34．8d）长。美人蕉的平均根数达1871条／株,根表面积达到22832cm^2／株,远较其他种高。     

Mutation of a chitinase-like gene causes ectopic deposition of lignin, aberrant cell shapes, and overproduction of ethylene

Chitinase-like proteins have long been proposed to play roles in normal plant growth and development, but no mutations in chitinase-like genes have been obtained previously to support this hypothesis. In this study, we have shown that the gene responsible for the elp1 mutation in Arabidopsis encodes a chitinase-like protein (AtCTL1). Mutation of this chitinase-like gene caused ectopic deposition of lignin and aberrant shapes of cells with incomplete cell walls in the pith of inflorescence stems. The AtCTL1 gene was expressed in all organs during normal plant growth and development, but it was not induced by wounding, salicylic acid, pectin fragments, or ethylene. Consistent with its ubiquitous expression pattern, mutation of the AtCTL1 gene affected many aspects of plant growth and development, including exaggerated hook curvature, reduced length and increased diameter of hypocotyls in dark-grown seedlings, and reduced root length and increased number of root hairs in light-grown seedlings. The mutant phenotypes could be rescued partially by ethylene inhibitors, and ethylene production in the mutant was significantly greater than in the wild type. Together, these results suggest that AtCTL1, a chitinase-like gene, is essential for normal plant growth and development in Arabidopsis.     

Nutrient Supply and the Growth of the Seminal Root System in Barley: II. LOCALIZED, COMPENSATORY INCREASES IN LATERAL ROOT GROWTH AND RATES OP NITRATE UPTAKE WHEN NITRATE SUPPLY IS RESTRICTED TO ONLY PART OF THE ROOT SYSTEM

The development of the seminal root system, its ability to absorbnitrate, and effects on shoot growth were studied in barleyplants in nutrient solution. The roots received either a uniformsupply of 1.0 mM nitrate (controls), or a supply of the samesolution restricted to a 4-cm length of only one of the mainseminal roots (axes) on each plant, the remainder of the rootsystem receiving a solution containing a low concentration (0.01mM). Marked increases took place in both the growth of lateralroots and the absorption and transport of ¹⁵N-labelled nitrate(per unit root weight) from the zone locally supplied with 1.0mM nitrate. These effects appear largely to compensate for thedeficient supply of nitrate to the remainder of the root system,since after 14 d the relative growth rate (g g^–1d^–1)of the total plant equals that of the controls. Rates of ¹⁵N-nitrateuptake (per unit root weight) remain relatively uniform throughoutthe 29-d experiment, during which root axes develop from theirinitial unbranched form to a complex system of laterals. Theresults are discussed in relation to possible mechanisms bywhich coordination is maintained between root growth, ion uptake,and shoot growth.     

Root growth of wetland plants with different root types

A wastewater culture system was designed to study the root growth of eight species of wetland plants with two different root types. The system included a plastic barrel for holding the wastewater and a foam plate for holding the plant. The results indicated that the root growth of the plants with fibril roots was faster than that of the plants with rhizomatic roots. The species with fibril roots had higher root number (1349 per plant) than species with rhizomatic roots (549 per plant) after ten weeks of cultivation. The average root biomass of plants with fibril roots was 11.3 g per plant, whereas that of plants with rhizomatic roots was 7.4 g per plant. Fine root biomass of diameter ≤ 1 mm constituted 51.9% of the total root biomass in plants with fibril roots, whereas it accounted for only 25.1% in plants with rhizomatic roots. The root surface area of the plants with fibril roots (6933 cm² per plant) was markedly larger than that of the species with rhizomatic roots (1897 cm² per plant). The species with rhizomatic roots showed a longer root lifespan (46.6 days) than those with fibril roots (34.8 days).     

Root Development and Nutrient Uptake

Root system formation proceeds in close coordination with shoot growth. Accordingly, root growth and its functions are regulated tightly by the shoot through materials cycling between roots and shoots. A plant root system consists of different kinds of roots that differ in morphology and functions. The spatial configuration and distribution of these roots determine root system architecture in the soil, which in turn primarily regulates the acquisition of soil resources like nutrients and water. Morphological and physiological properties of each root and the concomitant tissues further affect nutrient uptake and transport, while the root traits that are related to such acquisition also depend on the kinds of nutrients and their mobility in the soil. In addition, mechanisms involved in the uptake and transport of mineral nutrients recently have been elucidated at the molecular level. A number of genes for acquisition and transport of various mineral nutrients have been identified in model plant systems such as Arabidopsis thaliana, and rice, and in other plant species. An integration of studies on nutrient behavior in soils and the morphological and physiological functions of root systems will further elucidate the mechanism of plant nutrient uptake and transport by roots, and offer a real possibility of genetically improving crop productivity in problem soils.

     

模拟喀斯特异质性小生境下三叶鬼针草地上地下协同生长对策

模拟在喀斯特异质生境下,通过随机区组实验,研究三叶鬼针草（Bidens pilosa L.）在两种土壤生境（浅而宽、深而窄）和3种水分处理（对照、减水50%、减水70%）下植物的地上和地下生长关系及生物量分配格局。结果显示：（1）两种生境中三叶鬼针草的地上生长（株高、地径、叶面积、叶生物量）与地下根系生长（根长、根表面积、根体积、根生物量）均随着施水量的减少而降低;叶面积比率随着施水量的减少而增加;根质量比在浅而宽土壤生境中呈先增后减的趋势,而在深而窄土壤生境中呈增加趋势。（2）两种生境中三叶鬼针草的地上生物量与地下根系生物量、叶面积与根长、叶面积与各层根系生长均呈显著正相关关系。但在浅而宽土壤生境中,三叶鬼针草的地上生物量与各土层根系生物量均呈显著正相关,而在深而窄土壤生境中,地上生物量仅与中上土层根系生物量呈显著正相关。研究表明三叶鬼针草在不同生境中均具有较好的地上地下协同生长对策,在增强对地下资源获取的同时也增强了对地上资源的获取。在浅而宽土壤生境中,三叶鬼针草通过协调根系的横向拓展能力与植物叶片的生长来应对快速的干旱缺水;在深而窄土壤生境中,植株能较好地协调根系向下拓展能力与地上叶面积的生长,更好地利用土壤深层的水分资源。     

Root apical diameter and root elongation rate of rubber seedlings (Hevea brasiliensis) show parallel responses to photoassimilate availability

The hypothesis that root apical diameter may be used to evaluate root growth potential was tested. Temporal variations in the apical diameter of individual roots of rubber seedlings ( Hevea brasiliensis ) were studied together with their elongation patterns, using root observation boxes under controlled conditions. This study confirmed the overall positive correlation between apical diameter and growth rale. Moreover, the two parameters, varied in the same way during the life of a given root. For roots with short growth duration, there was a parallel quick decrease in both apical diameter and elongation rate, whereas roots that grew for longer periods showed synchronous fluctuations for both parameters. Since the mean values for the secondary roots within a root system exhibited the same trends, variations in apical diameter and elongation rates should depend on factors influencing the whole root system. When related to shoot rhythmic growth, both apical diameter and elongation rates were depressed during the periods of leaf growth. These effects were enhanced and/or prolonged by shading, hence reinforcing the hypothesis that this development depends on assimilate availability. Such results can be interpreted in terms of a source-sink relationship within the whole plant by considering the apical diameter, representing the size of the meristem related to the number of rneristematic cells, as an indicator of each root's growth potential.     

High-throughput imaging and analysis of root system architecture in Brachypodium distachyon under differential nutrient availability

Nitrogen (N) and phosphorus (P) deficiency are primary constraints for plant productivity, and root system architecture (RSA) plays a vital role in the acquisition of these nutrients. The genetic determinants of RSA are poorly understood, primarily owing to the complexity of crop genomes and the lack of sufficient RSA phenotyping methods. The objective of this study was to characterize the RSA of two Brachypodium distachyon accessions under different nutrient availability. To do so, we used a high-throughput plant growth and imaging platform, and developed software that quantified 19 different RSA traits. We found significant differences in RSA between two Brachypodium accessions grown on nutrient-rich, low-N and low-P conditions. More specifically, one accession maintained axile root growth under low N, while the other accession maintained lateral root growth under low P. These traits resemble the RSA of crops adapted to low-N and -P conditions, respectively. Furthermore, we found that a number of these traits were highly heritable. This work lays the foundation for future identification of important genetic components of RSA traits under nutrient limitation using a mapping population derived from these two accessions.     

Alkamides isolated from plants promote growth and alter root development in Arabidopsis

To date, several classes of hormones have been described that influence plant development, including auxins, cytokinins, ethylene, and, more recently, brassinosteroids. However, it is known that many fungal and bacterial species produce substances that alter plant growth that, if naturally present in plants, might represent novel classes of plant growth regulators. Alkamides are metabolites widely distributed in plants with a broad range of biological activities. In this work, we investigated the effects of affinin, an alkamide naturally occurring in plants, and its derivates, N-isobutyl-2E-decenamide and N-isobutyl-decanamide, on plant growth and early root development in Arabidopsis. We found that treatments with affinin in the range of 10(-6) to 10(-4) m alter shoot and root biomass production. This effect correlated with alteration on primary root growth, lateral root formation, and root hair elongation. Low concentrations of affinin (7 x 10(-6)-2.8 x 10(-5) m) enhanced primary root growth and root hair elongation, whereas higher concentrations inhibited primary root growth that related with a reduction in cell proliferating activity and cell elongation. N-isobutyl-2E-decenamide and N-isobutyl-decanamide were found to stimulate root hair elongation at concentrations between 10(-8) to 10(-7) m. Although the effects of alkamides were similar to those produced by auxins on root growth and cell parameters, the ability of the root system to respond to affinin was found to be independent of auxin signaling. Our results suggest that alkamides may represent a new group of plant growth promoting substances with significant impact on root development and opens the possibility of using these compounds for improved plant production.     

Split-root system optimization based on the survival,growth and development of the model Poaceae Brachypodium distachyon

Split-root system has been developed to better understand plant response to environmental factors, by exposing two separate parts of a single root system to heterogeneous situations. Surprisingly, there is no study attempting to maximize plant survival, growth and root system structure through a statistically sound comparison of different experimental protocols. Here, we aim at optimizing split-root systems on the model plant for Poaceae and cereals Brachypodium distachyon in terms of plant survival, number of roots and their equal distribution between the two compartments. We tested the effect of hydroponic or soil as growing media, with or without change of media at the transplantation step. The partial or total cutting of roots and/or shoots was also tested in different treatments as it could have an influence on plant access to energy and water and consequently on survival, growth and root development. Growing plants in soil before and after transplantation in split-root system was the best condition to get the highest survival rate, number of coleoptile node axile roots and growth. Cutting the whole root system was the best option to have a high root biomass and length at the end of the experiment. However, cutting shoots was detrimental for plant growth, especially in terms of root biomass production. In well-watered conditions, a plant submitted to a transfer in a split-root system is thus mainly lacking energy to produce new roots thanks to photosynthesis or adaptive autophagy, not water or nutrients.     

西洋参根残体对自身生长的双重作用

无论在自然生态环境还是在人工农田环境下,植株残体进入土壤后都会对土壤的物理化学性质以及后茬植物的生长产生重要影响。西洋参（Panax quinquefolium L.）为人参属多年生名贵药材,在栽培生产中存在严重的连作障碍问题。为了探明秋后残留在土壤中的须根降解产物对来年植株生长的影响,以及收获后残留在田间的根茬对连作西洋参生长的作用,本实验以3年生西洋参苗为研究对象,采用室内水培试验以及田间盆栽试验,通过添加西洋参根的粉碎物模拟根残体,测定其对西洋参生长的影响。水培试验中全营养液中分别添加0.02 mg/mL、0.1 mg/mL、0.5 mg/mL西洋参根粉碎物,处理后每隔5天测定植株叶片展开情况、株高、冠幅等生长指标。盆栽试验在土壤中添加0.1 mg/g根粉碎物,于栽种后1-2个月测定西洋参叶片展开情况、株高、冠幅等生长指标;水培及盆栽试验均于展叶期、现蕾期、结果期测定地上部及地下部生物量。采用高效液相色谱法（HPLC）测定根围土壤中8种酚酸类化合物的含量。试验结果表明,水培溶液中添加0.02-0.5 mg/mL根残体,可显著抑制西洋参自身地上部分生长,推迟展叶期,结果期生物量降低14.9%-45.0%;对地下部分的影响主要表现为在展叶期显著促进须根生长(p<0.05)。与水培试验相比,盆栽土壤中添加0.1 mg/g根残体同样导致西洋参展叶期推迟;不同的是处理组的地上、地下部及须根的平均生物量均高于对照。另外,添加根残体后盆栽西洋参根围土壤中丁香酸、香草醛、p-香豆酸、阿魏酸等酚酸类化感物质含量下降49.1%-81.4%,但作为逆境信号物质的水杨酸含量升高59.9%。以上结果可以初步确认根残体对西洋参早期生长具有自毒和促进的双重作用,表现为抑制地上部分生长,导致生物量显著下降;同时在生长早期促进须根生长;但在田间环境下,自毒作用可能受根残体降解速度以及土壤对降解产物吸附的影响有所减弱,使促进作用更为明显。