Variation of Germination Response to Temperature in Formosan Lily (Lilium formosanum Wall.) Collected from Different Latitudes and Elevations in Taiwan

Abstract

Deep penetration of an axile root is one of the important factors that allow crops to form deep root systems. In this study, the nodes from which the deepest penetrated roots had emerged were examined at the heading stage in upland rice and maize grown in large root boxes and in the field. Both experiments were designed to measure the direction, length, and rooting nodes of each root. In maize, the growth angles of axile roots increased with vertical elongation as rooting nodes acropetally advanced. The roots that emerged from the lower nodes, namely from coleoptilar to the second node, exhibited conspicuously horizontal elongation in the field, reaching 2.3 m in width at the maximum. The roots that emerged from higher than the fifth node were too short to penetrate deeply. Thus, these roots became the deepest root in less or no probability under field conditions. On the other hand, the fourth nodal root, which had an intermediate growth angle and length, had the highest probability. In upland rice, the deepest roots emerged from the nodes lower than the forth node on the main stem in the root boxes. In the field, however, the deepest roots emerged at later stages, that is, the roots from the middle nodes on the main stem and from the low nodes on the primary and secondary tillers were the deepest roots. Five out of nine of the deepest roots were from the prophyll nodes in three field-grown upland rice. The deepest roots from the same plant were estimated to have emerged and grown at approximately the same stage.     

Deep rooting in winter wheat: rooting nodes of deep roots in two cultivars with deep and shallow root systems

Deep rooting of wheat has been suggested that it influences the tolerance to various environmental stresses. In this study, the nodes from which the deepest penetrated roots had emerged were examined in winter wheat. The wheat was grown in long tubes with or without mechanical stress and in large root boxes. The length and growth angle of each axile root were examined to analyze the difference in the vertical distribution of the roots between the two wheat cultivars, one with a deep and one with a shallow root system. In Shiroganekomugi, a Japanese winter wheat cultivar with a shallow root system, the rooting depths of the seminal and nodal roots decreased as the rooting nodes advanced acropetally. Six out of nine deepest roots were seminal root in the non-mechanical stress conditions. In Mutsubenkei, a Japanese winter wheat cultivar with a deep root system, grown in root boxes, not only the seminal roots but also the coleoptilar and the first nodal roots penetrated to a depth of more than 1.3 m in the root box, and became the deepest roots. In both cultivars, the seminal roots became the deepest roots under the mechanical stress conditions. There were no clear tendencies in the root growth angles among the rooting nodes in the wheat root system. This indicates that the length of the axile roots can explain the differences in the rooting depths among axile roots in a wheat root system. On the other hand, the axile roots of Mutsubenkei elongated significantly more vertically than those of Shiroganekomugi. This suggests that not only seminal but also nodal roots exhibit strong positive gravitropism and penetrate deeply in a cultivar with a deep root system. In wheat cultivars, it is likely that the extent of its Root Depth Index results partly from the gravitropic responses of both seminal and nodal roots.     

田间条件下水稻根系分布及其与土壤容重的关系

 采用大田和筒栽方法研究了超高产三系杂交稻协优9308和两系杂交稻两优培九在穗分化期和开花期根系生长和分布及土壤容重对根系分布的影响。结果表明，在田间条件下，土层15 cm内水稻根系占根系总量的89%～98%，深层根系丛间比丛中比例高。不早衰的协优9308根系生长量较两优培九大。土壤容重提高，根系总生长量下降，且深层根系的量和比例下降。就深耕法对水稻根系生长和分布的影响进行了讨论。     

Genotypic variations in the plasticity of nodal root penetration through the hardpan during soil moisture fluctuations among four rice varieties

Rainfed lowland rice fields are characterized by soil moisture fluctuations (SMF) and the presence of hardpan that impedes deep rooting and thus limits water extraction from deep soil layer during the periods of drought. In this study, we used rootboxes with three layers; shallow layer, artificial hardpan, and deep and wet layer below the hardpan, to evaluate differences in the plasticity of nodal roots elongation through the hardpan and promote root branching below the hardpan in response to SMF among four rice varieties; Sasanishiki, Habataki, Nipponbare, and Kasalath. Experiments were conducted during the summer and autumn seasons. Plasticity was computed as the difference in root traits within each variety between the SMF and continuously well-watered treatments. In both experiments, Habataki consistently tended to exhibit higher root plasticity than the other three varieties by increasing number of nodal roots that penetrated the hardpan during rewatering period in SMF, when the soil moisture increased and penetration resistance decreased. This root plasticity then contributed to greater water use at the deeper soil during the subsequent drought period and overall shoot dry matter production. Habataki had significantly higher δ¹³C value in roots at deep layer than roots at the shallow and hardpan layers under SMF, which may indicate that these were relatively newly grown roots as a consequence of root plasticity. This study also indicates that CSSLs derived from Sasanishiki and Habataki varieties may be suitable for the analysis of QTLs associated with root plasticity expression in rainfed lowland with hardpan and experiencing SMF.     

耕作方式与玉米根系功能及其保护酶活性关系研究

采用根箱模拟方法,研究3种耕作方式(苗带耕作、行间耕作和全层耕作)和两种耕作深度(10 cm、30 cm)对玉米根系空间分布和保护酶活性的影响。结果表明,耕作方式显著影响玉米根系空间分布状况,深耕可延长行间耕作和全层耕作的根系功能期。根系超氧化物歧化酶(SOD)和过氧化物酶(POD)活性在耕作方式间表现为全层耕作行间耕作苗带耕作,深耕可增加玉米生育后期(乳熟期)深层土壤中根系SOD活性。行间耕作和全层深耕均延长玉米深层根系功能期和保护酶活性,实现增产(无显著差异)。因此,从节约成本和提高经济效益考虑,行间深耕是一种更适宜推广的玉米耕作栽培方式。     

Dynamics of Root Border Cells in Rhizosphere Soil of Zea mays L.: Crushed Cells during Root Penetration,Survival in Soil,and Long Term Soil Compaction Effect

Abstract

Plant roots release mucilage and root border cells (RBCs) into rhizosphere, which function as a complex at the root–soil interface. The dynamics of RBCs in rhizosphere soil, however, remains unknown. In this study, the ratio of crushed root cap cells during root penetration into soil and survival of the RBCs after the release from the root cap were estimated in maize seminal root. In addition, the effects of long term soil compaction on RBCs release were investigated. During the root penetration into rhizosphere soil, 78, 56, and 45% of sloughed root cap cells were estimated to be crushed at the first, second, and third day after planting, respectively. The number of surviving RBCs decreased with time, but 6% of the RBCs in the rhizosphere still retained their cell walls at one month after planting. These cells were estimated to remain in the soil for at least 10 d after the release from lateral roots. Furthermore, RBCs release from newly emerged nodal root increased with aging of plants, and the cell release was significantly increased by soil compaction only at the seedling stage. In conclusion, significant number of RBCs were crushed during root penetration into soil, however many RBCs remained in the rhizosphere soil for a relatively longer period. Soil compaction significantly increased cell release only at the seedling stage.     

Development and Distribution of Root System in Two GrainSorghum Cultivars Originated from Sudan under Drought Stress

Abstract

The difference in rooting pattern between two grain sorghum cultivars differing in drought tolerance was investigated under drought stress. The cultivars, Gadambalia (drought-tolerant) and Tabat (droughtsusceptible), were grown in bottomless wooden or acrylic root boxes to examine root parameters. Gadambalia consistently exhibited higher dry matter production and leaf water potential than Tabat under drought stress in both root boxes. In the experiment with wooden root boxes, under a drought condition, Gadambalia extracted more water from deep soil layers (1.1-1.5 m), which was estimated from the reduction in soil water content, than Tabat. This was because Gadambalia had a significantly higher root length density in these soil layers. The high root length density was due to enhanced lateral root development in Gadambalia. In the other experiment with acrylic root boxes, though total root length in the upper soil layer (0-0.5 m) was declined by limited irrigation in both cultivars, the reduction in Gadambalia was moderate compared with that in Tabat owing to the maintenance of fine root growth. Unlike Tabat, Gadambalia had an ability to produce the nodal roots from higher internodes even under drought, which resulted in the high nodal root length of Gadambalia. The growth angle of nodal roots was significantly correlated with root diameter, and the nodal roots from the higher internodes had large diameters and penetrated into the soil more vertically. These results indicate that the responses of roots (i.e. branching and/or growth of lateral root, and nodal root emergence from higher internodes) to soil dryness could be associated with the drought tolerance of Gadambalia.     

Genotypic Variations in Response of Lateral Root Development to Fluctuating Soil Moisture in Rice

Abstract

Developmental plasticity in lateral roots may be one of the key traits for the growth of rice plants under soil moisture fluctuations. We aimed to examine responses in seminal root system development to changing soil moisture for diverse rice cultivars. Special attention was paid to the two different types of lateral roots ; the generally long, thick L type capable of branching into higher orders, and the non-branching S type. Plants were grown in half-split polyvinyl chloride tubes fixed with transparent acrylic plate for root observation under glasshouse conditions. When plants were grown first under drought conditions, then rewatered, the seminal root system development in terms of dry weight and total length was promoted as compared with plants grown under continuously well-watered conditions in IR AT 109 and Dular, drought tolerant cultivars. Promoted production of L type lateral roots mainly contributed to the development of the longer seminal root system. Plants exposed to soil submergence before they were grown under drought conditions did not show such promoted responses in these two cultivars. However, in KDML 105, a drought tolerant cultivar, the production of especially L type laterals was substantially promoted under drought and rewatered conditions. Honenwase was characterized by the shallow root system and great reduction in root system length when soil moisture becomes limited. These facts show that genotypic variations exist in the plastic response of rice seminal root system and that the L type lateral root plays a key role in manifestation of this plasticity.     

Drought-induced root plasticity of two upland NERICA varieties under conditions with contrasting soil depth characteristics

To identify differences in root plasticity patterns of two upland New Rice for Africa (NERICA) varieties, NERICA 1 and 4, in response to drought under conditions with contrasting soil profile characteristics, soil moisture gradients were imposed using a sloping bed system with depths ranging 30–65 cm and a line-source sprinkler system with a uniformly shallow soil layer of 20 cm depth. Varietal differences in shoot and root growths were identified only under moderate drought conditions, 11–18% v/v soil moisture content. Further, under moderate drought soil conditions where roots could penetrate into the deep soil layer, deep root development was greater in NERICA 4 than in NERICA 1, which contributed to maintaining dry matter production. However, under soil conditions with underground impediment to deep root development, higher shoot dry weight was noted for NERICA 1 than for NERICA 4 at 11–18% v/v soil moisture content, which was attributed to increased lateral root development in the shallow soil layer in NERICA 1. Enhanced lateral root development in the 0–20-cm soil layer was identified in NERICA 1 even under soil conditions without an impediment to deep root development; however, this did not contribute to maintaining dry matter production in upland rice. Thus, we show different root developmental traits associated with drought avoidance in the two NERICA varieties, and that desirable root traits for upland rice cultivation vary depending on the target soil environment, such as the distribution of soil moisture and root penetration resistance.     

垄作栽培对寒地水稻根系生长的影响

 以黑龙江省早熟高产优质粳稻品种空育131为材料,通过垄作栽培与平作栽培方式对比试验,研究垄作栽培对寒地水稻根系生长的影响。结果表明，水稻根系的生长和分布在不同栽培方式间有较大差异，供试品种在不同的栽培方式下其根系体积、干质量、根长及活力均存在明显不同。与对照（平作）相比，水稻（空育131）在垄作栽培条件下根系发达，表现为根长增加、根系干质量增大，根量尤其下层根量增多，根系吸收面积增大，根冠比增大，产量提高。     

我国超级稻根系特性及根际生态研究现状与趋势

以超级稻为代表的一批超高产水稻研发成功使水稻单产获得大幅度提高。较大的根系生物量、根重密度、根长、根长密度和根直径,根系偏向纵深分布且土壤深层根系生物量增大是超级稻根系生物学主要特征;高的单株根系氧化力、总吸收表面积、活跃吸收表面积、根系细胞分裂素(玉米素与玉米素核苷)含量是超级稻扩库增产的重要根系生理基础。生产中的施肥管理、水分管理、种植方式和根际土壤生态环境pH、氧、微生物、氮素形态等均可显著影响水稻根系的生长发育。通过适当的技术措施调控水稻根际生态环境向有利于水稻生长生理需求方向发展,以促进水稻根系健壮生长,实现水稻增产。水稻高产群体根系构型的形成与根际土壤生态因子匹配原理与调控,高产水稻地下根系、根际生态因子与地上群体的互作机制与调控路径,水稻根系定量化等方面是今后水稻根系深入研究的主要方向。     

Root plasticity under fluctuating soil moisture stress exhibited by backcross inbred line of a rice variety,Nipponbare carrying introgressed segments from KDML105 and detection of the associated QTLs

In rainfed lowland rice ecosystem, rice plants are often exposed to alternating recurrences of waterlogging and drought due to erratic rainfall. Such soil moisture fluctuation (SMF) which is completely different from simple or progressive drought could be stressful for plant growth, thereby causing reduction in yield. Root plasticity is one of the key traits that play important roles for plant adaptation under such conditions. This study aimed to evaluate root plasticity expression and its functional roles in dry matter production and yield under SMF using Nipponbare, KDML 105 and three backcross inbred lines (BILs) and to identify QTL(s) associated with root traits in response to SMF at two growth stages using Nipponbare/KDML105 F₂ plants. A BIL, G3-3 showed higher shoot dry matter production and yield than Nipponbare due to its greater ability to maintain stomatal conductance concomitant with greater root system development caused by promoted production of nodal and lateral roots under SMF. QTLs were identified for total nodal root length, total lateral root length, total root length, number of nodal roots, and branching index under SMF at vegetative and reproductive stages. The QTLs detected at vegetative and reproductive stages were different. We discuss here that relationship between root system of G3-3 and the detected QTLs. Therefore, G3-3 and the identified QTLs could be useful genetic materials in breeding program for improving the adaptation of rice plants in target rainfed lowland areas.     

不同耕作方式对辽西褐土物理性状及玉米根系分布的影响

通过连续3年大田试验,对旋耕、翻耕、深松3种耕作方式下的土壤物理性质、玉米根系分布和产量进行测定。结果表明,与翻耕和旋耕相比,深松显著增加了玉米田土壤耕层厚度和降低了犁底层厚度。在中下层土壤,深松还降低了土壤紧实度和容重,改善了土壤的孔隙状况,有利于玉米根系向下生长,使得中下层土壤的玉米根系不仅更丰富,而且占总根系量的比例也更高,最终提高了玉米产量。本研究表明,深松耕作有利于改善辽西褐土区土壤结构和促进玉米生长。     

机械化播栽对杂交籼稻根系性状的影响

以杂交籼稻宜香优2115和F优498为材料,手栽为对照,采用二因素裂区设计,使用新设计加工的取样工具,研究机直播和机插对杂交籼稻根系性状的影响。结果表明:1) 创新设计的水稻根系取土器能够便捷而准确地进行根系取样甚至根系的分层取样;2)移栽前及返青后总根长、根体积、根尖数均表现为直播>手栽>机插,返青期间,机插和手栽秧苗的根系生长快速,根冠比呈增大趋势,同期的直播稻地上部的生长快于根系,根冠比减小。3)直播稻根系早期生长迅速,抽穗期根多而细,根尖数大于机插和手栽,根冠比最大;机插根系具有后发优势,分蘖盛期后快速生长,抽穗期总根长、根体积最大;手栽根系少而粗,根冠比最小。4)与手插相比,抽穗期直播和机插根系分布浅,0~10 cm土层直播、机插、手栽根干质量分别占植株根系总干质量的76.9%、76.5%、67.9%,10~20 cm及20 cm以上土层直播和机插根干质量所占比例均低于手栽;横向分布上,直播在植株正下方0~12 cm直径范围内根干质量所占比例较机插和手栽分别高3.5%和3.3%,根系更加集中分布在植株正下方。5)移栽前,根活性表现为直播>机插>手栽,差异极显著;移栽后,机插和手栽根活性快速提高,返青后无显著差异;至抽穗后35 d,直播、机插和手栽方式下,宜香优2115根系伤流强度较抽穗0d分别降低84.7%、75.4%和74.3%,F优498分别降低79.3%、75.9%和74.3%,直播的根系衰老快于机插和手栽。总的来看,机械化播栽对杂交籼稻根系性状有显著影响,抽穗期机插根系分布浅,根粗而多;直播根系分布浅,根直径最小,根尖数最多,抽穗后衰老快;手栽根系分布深,根粗而少。     

Root growth dynamics and stomatal behaviour of rice (Oryza sativa L.) grown under aerobic and flooded conditions

Aerobic rice culture is a new technology designed to reduce water use, but the vulnerability of rice to aerobic condition has limited its development. The objective of this study was to characterize the root growth and stomatal behaviour of four rice cultivars grown in flooded and aerobic culture for 2 years. In aerobic culture, where the soil water potential at 20-cm depth averaged between −15 and −30 kPa, total root biomass was significantly lower than in flooded culture for the whole growth period, owing to a reduction in root biomass in the surface layer. Dry-matter partitioning to roots decreased, but the ratio of deep root biomass to total root biomass tended to be higher in aerobic culture than in flooded culture. The low root-to-shoot ratio and poor root growth in the surface layer in aerobic culture are attributable to the considerable reduction in adventitious root number. As a result, the varietal difference in total root biomass was due largely to individual root growth in aerobic culture. Stomatal closure was distinct at the vegetative stage in aerobic culture, even when the soil water potential was near field capacity, partly because of the poor rooting vigour. When the soil water potential at 20-cm depth was below −50 kPa, the stomatal behaviour reflected the root growth in the subsurface layer. These results suggest the role of vigorous root growth in soil water uptake and hence, in maintaining transpiration in aerobic rice culture.     

Phytochromes are Involved in Elongation of Seminal Roots and Accumulation of Dry Substances in Rice Seedlings

Phytochromes have been reported to play important roles in seedling de-etiolation and flowering in rice.To identify the roles of phytochromes in regulating root growth and accumulation of dry substances,the lengths of seminal roots and the dry weights of seedlings were measured in the wild type as well as the phytochrome A(phyA) and phytochrome B(phyB) mutants grown under different conditions.When the whole seedlings were exposed to white light,the elongation of the seminal roots was significantly photoinhibited in the wild type,whereas this inhibitory effect was clearly reduced in the phyA and phyB mutants.When the roots of the seedlings were blocked from white light,the phyA and phyB mutants exhibited significantly longer seminal roots than the wild type.These results suggest that both the root-localized and shoot-localized PHYA and PHYB are involved in the photoinhibition of seminal root elongation in rice seedlings.By measuring the dry weights of roots and shoots,it is revealed that PHYB positively regulates the accumulation of dry substances in shoots,however,PHYA exerts the contrary effects on the accumulation of dry substances in roots and shoots of rice seedlings.     

Shoot growth potential drives N uptake in maize plants and correlates with root growth in the soil

Variation in nitrogen (N) acquisition ability is known to exist among maize genotypes. Field experiments were conducted and the N-efficient maize inbred line 478 and the N-inefficient line Wu312 were employed to illustrate whether the amount of N taken up in maize plants with different N acquisition ability was determined by the shoot growth potential or by the root size. To meet the accelerated growth of the shoot from the jointing stage to the grain-filling stage, the net N gain in whole plants of both genotypes increased dramatically and accounted for 77% and 74% of the total N increment in 478 and Wu312, respectively. Similarly, the 4th to 8th nodal root whorls were initiated predominantly between 35 and 76 d after sowing, which accounted for about 90% of the total root length on 93 d after sowing. The whole plant N content of the N-efficient 478 was significantly higher than that of the N-inefficient Wu312. 478 had also longer root length, including axial and lateral roots, of the embryonic roots and each whorl of shoot-borne roots, and greater root length density (RLD) than Wu312. In spite of the smaller root size, Wu312 had higher shoot N concentration than 478 during the whole growth period, implying that N was not limited for shoot growth in Wu312. It was concluded that maize root growth, especially initiation and development of the shoot-borne roots, as well as the amount of N taken up were coordinated with shoot growth and demand for nutrients. Although a large root system and high RLD in the soil profile were beneficial for efficient N acquisition, amount of N taken up by the two maize genotypes in the presence of sufficient N supply was determined by the shoot growth potential, and not by the root size.     

耕作方式对玉米根系构型及抗根倒伏能力的影响

通过云南典型的红壤坡耕地对土壤实施深松+旋耕15 cm(SRT)、深松+免耕(SNT)、深松+翻耕20 cm(SP1)、深松+翻耕30 cm(SP2)、旋耕15 cm(RT)、免耕(NT)、翻耕20 cm(P1)和翻耕30 cm(P2)8种耕作方式,研究对玉米的根系根条数、根直径、入土角度、根幅、生物量及根系抗拔力等的影响。结果表明,深松+翻耕20 cm处理能增加玉米根条数、根系入土角度和10 cm土层处根系生长幅度,增大根系生物量,尤其是深层土壤(20～30 cm)根系生物量,同时对玉米产量也具有提高作用。深松+翻耕30 cm处理能增大根系的垂直抗拔力。因此,土壤通过深耕处理能改善玉米根系构型和分布,进而增强玉米根系抗倒伏能力。     

充足灌水条件下不同年代玉米品种根系性状比较研究

以我国20世纪50年代以来6个玉米主推品种白鹤、吉单101、中单2号、掖单13、郑单958和先玉335为材料, 在充足灌水条件下研究玉米品种更替过程中的根系性状演变特征。结果表明, 不同年代玉米品种各根系性状间存在差异, 随着品种的更替, 根系平均入土角度呈现减小的趋势, 根系分布更为紧凑。根系性状(根长、根表面积、根体积、根条数、根系干重等)随品种年代的更替表现为“先增后减”的趋势, 1950s～1970s平展型品种趋向于构建逐渐强大根系系统, 以提高根系吸收能力;1980s紧凑型品种趋向于减少高层节根, 以减少“冗余器官”的干物质消耗。与早期品种相比, 近代品种的紧凑型根系不仅增强了对土壤深层水分、养分的吸收, 也促进了干物质向子粒的高效转移和水分利用效率的提高。     

Association between root growth angle and root length density of a near-isogenic line of IR64 rice with DEEPER ROOTING 1 under different levels of soil compaction

DEEPER ROOTING 1 (DRO1) of rice controls the gravitropic response of root growth angle. In order to clarify the effects of DRO1 on root growth angle and root length density under different soil resistance to penetration, and to quantify the relationship between root growth angle and root length density, we assessed the root growth of Dro1-NIL (a near-isogenic line homozygous for the Kinandang Patong allele of DRO1 in the IR64 background) under upland Andosol field conditions in Japan in 2013 and 2014. The trial included three levels of soil compaction (none, moderate, and hard). Root length density at a depth of 30 to 60 cm was largest in Kinandang Patong, followed by Dro1-NIL, and was least in IR64 in both years and in all compaction treatments. Root length density at this depth decreased with hard compaction (to 70% of control) and increased with moderate compaction (to 135%). The number of roots with a deep angle (i.e. 45° to 90° from the horizontal) measured by the basket method was similar at maximum tillering and maturity stages, and its value as a proportion of the total number of roots was strongly correlated with the root length density at 30 to 60 cm in both years, which demonstrates the importance of a deep root angle for the development of deep roots. Dro1-NIL had a higher proportion of deep roots than IR64, but the difference was small under hard compaction, with a significant genotype × compaction interaction.