Effects of soil moisture on cotton root length density and yield under drip irrigation with plastic mulch in Aksu Oasis farmland

Effects of soil moisture on cotton root length density (total root length per unit soil volume) and yield under drip irrigation with plastic mulch were studied through field experiments. The results indicate that spatial distributions of root length density of cotton under various water treatments were basically similar. Horizontally, both root length densities of cotton in wide and narrow rows were similar, and higher than that between mulches. Vertically, root length density of cotton decreased with increasing soil depth. The distribution of root length density is different under different irrigation treatments. In conditions of over-irrigation, the root length density of cotton between mulches would increase. However, it would decrease in both the wide rows and narrow rows. The mean root length density of cotton increased with increasing irrigation water. Water stress caused the root length density to increase in lower soil layers. There is a significant correlation between root length density and yields of cotton at the flower-boll and wadding stages. The regression between irrigation amount and yield of cotton can be expressed as y = -0.0026x2+18.015x-24845 (R2 = 0.959). It showed that the irrigation volume of 3,464.4 m3/hm2 led to op-timal root length density. The yield of cotton was 6,360 .8 kg/hm2 under that amount of irrigation.

Root length density distribution and associated soil water dynamics for tomato plants under furrow irrigation in a solar greenhouse

Furrow irrigation is a traditional widely-used irrigation method in the world. Understanding the dynamics of soil water distribution is essential to developing effective furrow irrigation strategies, especially in water-limited regions. The objectives of this study are to analyze root length density distribution and to explore soil water dynamics by simulating soil water content using a HYDRUS-2D model with consideration of root water uptake for furrow irrigated tomato plants in a solar greenhouse in Northwest China. Soil water contents were also in-situ observed by the ECH_2O sensors from 4 June to 19 June and from 21 June to 4 July, 2012. Results showed that the root length density of tomato plants was concentrated in the 0–50 cm soil layers, and radiated 0–18 cm toward the furrow and 0–30 cm along the bed axis. Soil water content values simulated by the HYDRUS-2D model agreed well with those observed by the ECH_2O sensors, with regression coefficient of 0.988, coefficient of determination of 0.89, and index of agreement of 0.97. The HYDRUS-2D model with the calibrated parameters was then applied to explore the optimal irrigation scheduling. Infrequent irrigation with a large amount of water for each irrigation event could result in 10%–18% of the irrigation water losses. Thus we recommend high irrigation frequency with a low amount of water for each irrigation event in greenhouses for arid region. The maximum high irrigation amount and the suitable irrigation interval required to avoid plant water stress and drainage water were 34 mm and 6 days, respectively, for given daily average transpiration rate of 4.0 mm/d. To sum up, the HYDRUS-2D model with consideration of root water uptake can be used to improve irrigation scheduling for furrow irrigated tomato plants in greenhouses in arid regions.

Flavonoid scutellarin positively regulates root length through NUTCRACKER

Exploring approaches to regulate meristem is of special importance and broad interest.In this study,we found that the flavonoid scutellarin,which has a 6-hydroxyl and a 7-glucoside,increased root length through the transcription factor NUTCRACKER(NUC).This root lengthening disappeared in NUCknockout and reappeared in NUC-rescue plants.Scutellarin induced NUC expression and promoted the division of cortex/endodermal initials.In contrast,naringenin,which has same chemical backbone but without 6-hydroxyl and with 7-hydroxyl group,showed the opposite or no effects.Our results demonstrate that scutellarin promotes root length through NUC-mediated regulatory pathways and reveal that flavonoids with and without the 6-hydroxyl and 7-glucoside have positive and negative effects on meristem size,respectively。

Root Length Density in Maize/Cowpea Intercropping under a Basin Tillage System in a Semi-Arid Area of Zimbabwe

A study to assess the effect of intercropping maize (Zea mays L.) and cowpea (Vigna unguiculata L.) within the same basin or outside the basin on root length density (RLD) was conducted at the International Crop Research Institute for Semi-Arid Tropics (ICRISAT) Matopos Research Station from December 2009 to April 2010. The experiment was laid out in a Randomised Complete Block Design (RCBD) with four treatments replicated four times namely;sole maize, sole cowpea, maize-cowpea intercrop with cowpea and maize planted within the same basin and maize-cowpea intercrop with cowpea planted 20 cm outside the maize basin. There was significant difference (P < 0.001) in RLD, grain yield and stover yield. Maize-cowpea intercropped within the same basin achieved higher RLD, grain yield and stover yield than cowpea that was intercropped outside the basin and the sole crops. The land equivalent ratio (LER) in both intercrop designs showed that intercropping had better grain yield performance when compared to sole cropping. It can be concluded that intercropping maize and cowpeas within the same basin can result in an environment around the crop achieving higher RLD which translates to better grain yield compared to the sole cropping and intercropping cowpeas outside the basin.

Characterization of alpine meadow surface crack and its correlation with root-soil properties

Quantifying surface cracks in alpine meadows is a prerequisite and a key aspect in the study of grassland crack development.Crack characterization indices are crucial for the quantitative characterization of complex cracks,serving as vital factors in assessing the degree of cracking and the development morphology.So far,research on evaluating the degree of grassland degradation through crack characterization indices is rare,especially the quantitative analysis of the development of surface cracks in alpine meadows is relatively scarce.Therefore,based on the phenomenon of surface cracking during the degradation of alpine meadows in some regions of the Qinghai-Tibet Plateau,we selected the alpine meadow in the Huangcheng Mongolian Township,Menyuan Hui Autonomous County,Qinghai Province,China as the study area,used unmanned aerial vehicle(UAV)sensing technology to acquire low-altitude images of alpine meadow surface cracks at different degrees of degradation(light,medium,and heavy degradation),and analyzed the representative metrics characterizing the degree of crack development by interpreting the crack length,length density,branch angle,and burrow(rat hole)distribution density and combining them with in situ crack width and depth measurements.Finally,the correlations between the crack characterization indices and the soil and root parameters of sample plots at different degrees of degradation in the study area were analyzed using the grey relation analysis.The results revealed that with the increase of degradation,the physical and chemical properties of soil and the mechanical properties of root-soil composite changed significantly,the vegetation coverage reduced,and the root system aggregated in the surface layer of alpine meadow.As the degree of degradation increased,the fracture morphology developed from"linear"to"dendritic",and eventually to a complex and irregular"polygonal"pattern.The crack length,width,depth,and length density were identified as the crack characterization indices via analysis of variance.The results of grey relation analysis also revealed that the crack length,width,depth,and length density were all highly correlated with root length density,and as the degradation of alpine meadows intensified,the underground biomass increased dramatically,forming a dense layer of grass felt,which has a significant impact on the formation and expansion of cracks.

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors.Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past,our understanding of it remains limited.This is because the dynamics processes associated with soil resources availability are still poorly understood.Soil moisture,temperature,and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level.In temperate forest ecosystems,seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground.Therefore,fine root biomass,root length density(RLD)and specific root length(SRL)vary during the growing season.Studying seasonal changes of fine root biomass,RLD,and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover.The objective of this study was to understand whether seasonal variations of fine root biomass,RLD and SRL were associated with soil resource availability,such as moisture,temperature,and nitrogen,and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation.We used a soil coring method to obtain fine root samples(≤2 mm in diameter)every month from May to October in 2002 from a 17-year-old L.gmelinii plantation in Maoershan Experiment Station,Northeast Forestry University,China.Seventy-two soil cores(inside diameter 60 mm;depth intervals:0-10 cm,10-20 cm,20-30 cm)were sampled randomly from three replicates 25 m×30 m plots to estimate fine root biomass(live and dead),and calculate RLD and SRL.Soil moisture,temperature,and nitrogen(ammonia and nitrates)at three depth intervals were also analyzed in these plots.Results showed that the average standing fine root biomass(live and dead)was 189.1 g·m^(-2)·a^(-1),50%(95.4 g·m^(-2)·a^(-1))in the surface soil layer(0-10 cm),33%(61.5 g·m^(-2)·a^(-1)),17%(32.2 g·m^(-2)·a^(-1))in the middle(10-20 cm)and deep layer(20-30cm),respectively.Live and dead fine root biomass was the highest from May to July and in September,but lower in August and October.The live fine root biomass decreased and dead biomass increased during the growing season.Mean RLD(7,411.56 m·m^(-3)·a^(-1))and SRL(10.83 m·g^(-1)·a^(-1))in the surface layer were higher than RLD(1474.68 m·m^(-3)·a^(-1))and SRL(8.56 m·g^(-1)·a^(-1))in the deep soil layer.RLD and SRL in May were the highest(10621.45 m·m^(-3) and 14.83m·g^(-1))compared with those in the other months,and RLD was the lowest in September(2198.20 m·m^(-3))and SRL in October(3.77 m·g^(-1)).Seasonal dynamics of fine root biomass,RLD,and SRL showed a close relationship with changes in soil moisture,temperature,and nitrogen availability.To a lesser extent,the temperature could be determined by regression analysis.Fine roots in the upper soil layer have a function of absorbing moisture and nutrients,while the main function of deeper soil may be moisture uptake rather than nutrient acquisition.Therefore,carbon allocation to roots in the upper soil layer and deeper soil layer was different.Multiple regression analysis showed that variation in soil resource availability could explain 71-73%of the seasonal variation of RLD and SRL and 58%of the variation in fine root biomass.These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability,which resulted in an increased allocation of carbohydrate to these roots,but a lower allocation of carbohydrate to those in soil with lower resource availability.

Freeze-thaw process induced by increased precipitation affects root growth of alpine steppe on the Tibetan Plateau

The response of vegetation productivity to precipitation is becoming a worldwide concern.Most reports on responses of vegetation to precipitation trends are based on the growth season.In the soil freeze/thaw process,the soil water phase and heat transport change can affect root growth,especially during the thawing process in early spring.A field experiment with increased precipitation(control,increased 25%and increased 50%)was conducted to measure the effects of soil water in early spring on above-and below-ground productivity in an alpine steppe over two growing seasons from June 2017 to September 2018.The increased 50%treatment significantly increased the soil moisture at the 10 cm depth,there was no difference in soil moisture between the increased 25%treatment and the control in the growing season,which was not consistent in the freeze/thaw process.Increased soil moisture during the non-growing season retarded root growth.Increased precipitation in the freezing-thawing period can partially offset the difference between the control and increased precipitation plots in both above-and below-ground biomass.

Tooth anatomy risk factors influencing root canal working length accessibility

The aim of this study was to analyze the specific influence of root canal anatomy on the accessibility of working length during root canal therapy. Four hundred seventy-six root canal therapy cases （amounting to a total of 1 005 root canals） were examined. The anatomy risk factors assessed in each case included： tooth type （tooth location）, root canal curvature, and root canal calcification, as well as endodontic retreatment. The investigation examined the correlation between each of these anatomic factors and the working length, with statistical analysis consisting of Chi-square tests and multiple logistic regression analysis. In an independent factor analysis, tooth type （tooth iocation）, root canal curvature, canal calcification, and endodontic retreatment were determined to be the primary risk factors. In a multiple-factor regression model, root curvature and canal calcification were found to most significantly influence root canal working length accessibility （P〈0.05）. Root canal anatomy increases the difficulty of root canal preparation. Appropriate consideration of tooth anatomy will assist in accurate determination of preparation difficulty before instrumentation. This study alerts clinical therapists to anatomical factors influencing the working length accessibility, and allows for a direct estimate of success rate given in situ measurements of tooth factors during the root canal treatment procedure.

Determination of the Root Canal Length of Teeth of Bantu Patients Attending the Teaching Hospital of Kinshasa University

Background: There is paucity of literature on the determination of the root canal length of Bantu subjects in dental professional practicing in Africa and Democratic Republic of Congo in particular. Aims: The aim of the present study was to determine the root canal length of teeth of Bantu patients extracts attending the Teaching Hospital of Kinshasa University. Methods and Material: Prospective cross-sectional study was carried out in the service of Conservative Dentistry. The patients suffering with pulpitis of permanent teeth which were selected for root canal treatment during the period of January 2014 to December 2016 were included. All patients whose main root canals were inaccessible, teeth carrying prosthesis, teeth with large coronal decay, teeth having periapical periodontitis, supernumerary teeth, wisdom and primary teeth were excluded. Results: The upper canines presented some significant longer canals compared to the lower canine (23.4 ± 2.3 mm and 21.6 ± 1.8 mm). Palatal canals of the first and second molar were respectively longer as compared to the superior teeth canals (21.5 ± 1 mm, 21.3 ± 2 mm). The distal canals of the first and second molar were the longest in the mandibular arch respectively measuring 20.7 ± 2.0 mm and 21.5 ± 1.7 mm. Conclusion: Data obtained from Bantu patients show slightly shorter roots compared to some European populations, but longer than some Asian populations.

Root Growth of the Annual Tillering Grass Panicum miliaceum in Heterogeneous Nutrient Environments

To study growth responses of the roots of Panicum miliaceum L. to heterogeneous supply of nutrients. The authors analyzed the effects of the nutrient levels in both original patches (O) and destination patches (D) on the root growth of P. miliaceum when its roots were allowed to extend from original patch into destination patch. When the nutrient levels in the original patches were low, coarse root biomass ratio (coarse root biomass in the D/total coarse root biomass), coarse root length ratio (coarse root length in the D/total coarse root length), coarse root surface area ratio (coarse root surface area in the D/total coarse root surface area) and fine root length ratio (fine root length in the D/total fine root length) were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, while fine root length, fine root length density, fine root surface index, and fine root surface area density were smaller in the former than in the latter. When the nutrient levels in the original patches were high, fine root length, fine root length density, fine root surface area index and fine root surface density were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, coarse roots did not respond to the nutrient levels in the destination patches significantly. When the roots extended from the original patches with the same nutrient level into the destination patches with contrasting nutrient levels, fine root biomass and its percentage allocation did not respond to the nutrient levels in the destination patches significantly, whereas both root length and root surface area did. This indicates that the fine roots of P. miliaceum responded to difference in nutrient supply by plasticity in their length and surface area, rather than in their root biomass.

Effects of Pb on Growth and Development of Broad Bean Roots

[Objective] This study aimed to investigate the influence of Pb2＋ on the growth and development of broad bean roots. [Method] The effects of Pb2＋ solution of different concentrations on root length, color, bending and mitotic index frequency of root tip cells of broad bean were measured and observed. [Result] Pb2＋ at concentration lower than 20 mg/L promoted the growth and development of roots, increased the cell mitotic indexes, but had little influence on root color and bending. When the Pb2＋ concentration was higher than 20 mg/L, the root growth was inhibited; the root color gradually turned deeper; the roots bended, but the cell mitotic index was decreased. [Conclusion] Pb2＋ promoted the growth of broad bean at low concentration but inhibited the growth at high concentration, and the influence was related to Pb2＋ concentration and time.

口腔临床诊疗中数字牙片影像技术的应用价值

目的探讨口腔临床诊疗中数字牙片影像技术的应用价值。方法选择2022年1月至2023年5月期间在本院口腔科就诊且需要拔牙治疗的50例正畸患者作为研究对象。患者在治疗前,完成数字化牙片摄影和传统牙片摄影。记录投照上、下颌牙齿X线倾斜的垂直平均角度,并统计牙齿根尖片的曝光时间,对比两种摄影技术对牙齿长度的测量结果。结果传统牙片摄影时,上颌和下颌切牙位、单尖牙、双尖牙位、第一磨牙位、第二及三磨牙位(足侧倾斜)选择投射角度低于数字化牙片摄影(P<0.05)。数字化牙片摄影投照上颌和下颌切牙位、单尖牙位、双尖牙位、第三磨牙位及第一、二磨牙位牙齿根尖片的曝光时间低于传统牙片摄影(P<0.05)。数字化牙片摄影对待拔除牙齿单根、双根颊和双根腭测量结果与游标卡尺测量结果相比,差异无统计学意义(P>0.05);传统牙片摄影对待拔除牙齿单根、双根颊和双根腭测量结果低于游标卡尺测量结果,差异具有统计学意义(P<0.05);以游标卡尺测量结果为依据,数字化牙片摄影和传统牙片摄影对待拔除牙齿单根、双根颊和双根腭测量结果相比,差异具有统计学意义(P<0.05)。结论数字牙片影像技术投照条件宽容度相对较大,投射时曝光时间短,对牙齿根尖的测量准确度较高,便于细致观察牙齿,应用于口腔临床诊疗的价值较高。

岷江上游干旱河谷地区油松和岷江柏细根生物量和根长密度

了解岷江上游干旱河谷地区12年生油松(Pinus tabulaeformis)和岷江柏(Cupressus chengiana)人工林细根(直径≤2 mm)生物量和根长密度在土层中的垂直分布状况,分析不同土层中细根系统的碳分配策略,为岷江上游干旱河谷地区植被恢复提供理论依据。以岷江上游干旱河谷地区的油松和岷江柏人工林为研究对象,采用土钻法进行取样,测定2种林分不同土层深度(h)(0 cm<h≤15 cm和15 cm<h≤30 cm)中吸收根(1~3级)和运输根(≥4级的细根)生物量和根长密度,以及吸收根占总细根生物量和根长密度比例。结果显示:油松和岷江柏吸收根生物量和根长密度在0 cm<h≤15 cm土层均显著高于15 cm<h≤30 cm土层,而运输根生物量和根长密度在土层间差异均不显著;油松和岷江柏吸收根占总细根生物量和根长密度比例在0 cm<h≤15 cm土层均显著高于15 cm<h≤30 cm土层(P<0.05);岷江柏吸收根占总细根生物量和根长密度比例在2个土层中均显著高于油松(P<0.05)。研究结果表明,在养分有效性最高的土壤表层,油松和岷江柏细根系统内将更多的碳分配到吸收根。

播期推迟对棉花根系生长发育特征及产量的影响

【目的】研究推迟播期对棉花根系生长发育特征和产量的影响,为黄河流域棉区棉花适期播种提供依据。【方法】2022―2023年在河北农业大学威县试验站开展田间试验,设置常规播期(4月15日)和推迟播期(5月1日)2个处理,分析推迟播期对棉花品种冀农大23号的根系分布、根系生长速率、根冠比、干物质积累量和产量等的影响。【结果】与常规播期相比,推迟播期条件下,棉花根系长度和生物量的最大增长速率分别增加2.92~5.35 cm·d^(-1)和0.40~0.76 mg·d^(-1);深层土壤中棉花根系占比提高,其中30~60 cm土层根系长度占比和根系生物量占比分别增加2.99~3.55百分点和3.94~4.42百分点;生育后期棉株地上部干物质积累量和根冠比无明显差异;根系载荷能力显著降低6.43%~17.69%;2022年籽棉产量无显著差异,2023年单位面积铃数和籽棉产量分别显著增加9.72%和7.66%。相关分析表明,0~60 cm土层根长密度、0~60 cm土层根系生物量密度、根系生物量最大增长速率和30~60 cm土层根系长度占比均与籽棉产量极显著正相关。【结论】黄河流域棉区推迟播期(5月1日)可通过提高棉花根系生长速率、深层土壤中根系长度和根系生物量的占比,增强根系吸收功能以保障地上部干物质的积累,促进棉花高产。

丁香酸对不同品种烟草苗期根系生长的影响

为探究最新发现的植物源生物硝化抑制剂丁香酸对烟草品种K326和云烟85苗期根系生长的影响,通过基质培养试验,设置0、10、25、50、100、200 μmol/L 6个丁香酸浓度,研究了不同浓度丁香酸在不同时间(3 d和5 d)对K326和云烟85主根伸长量和一级侧根发育的影响。结果表明:与对照(0 μmol/L)相比,25~100 μmol/L丁香酸能促进K326主根伸长,在3 d时促进率为13.33%~30.67%,在5 d时促进率降为8.54%~22.55%,最适浓度为50 μmol/L;10~50 μmol/L丁香酸促进云烟85主根伸长,在3 d时促进率为7.81%~18.75%,在5 d时促进率维持在4.10%~10.66%,最佳促进浓度25 μmol/L;丁香酸对两个烟草品种主根伸长的促进效果均为3 d优于5 d。在侧根发育方面,低浓度丁香酸能显著促进K326和云烟85一级侧根数,两个品种促进侧根发育的最适浓度均为25 μmol/L。相关性分析表明,丁香酸处理下两个烟草品种苗期的主根伸长变化率与侧根数变化率呈显著正相关。可见,适宜浓度的丁香酸对两个典型烟草品种苗期主根增长和侧根发育均为促进效应。生物硝化抑制剂丁香酸具有促进烟草根系生长的潜力,为研发烤烟新型专用肥提供了理论依据。

降雨集流渗灌条件下红梅杏根系分布研究

为了明确降雨集流渗灌技术在宁南山区红梅杏种植中解决缺水问题的实际效果,以5年生红梅杏果树为研究对象,设置自然条件(NAT)和覆膜安装渗灌器(RCII)两种处理,采用分层分段挖掘法挖掘根系,并对比分析根长密度分布。结果表明:通过降雨集流渗灌技术所集蓄的水量可以促进红梅杏根系更好的生长,解决缺水问题。在RCII条件下,在地表以下0~100 cm内,根长密度随深度的增加而减少。此外,在RCII条件下,沿行距方向和45°方向的根长密度的对比,证明了渗灌器集流对根系进行水分补充的有效性。通过对行距、株距、深度、根长密度进行偏相关分析和多独立样本非参数检验,发现行距(安装渗灌器)、株距(未安装渗灌器)对根长密度在水平方向的分布并未产生明显区别(显著性P>0.05);地下深度60~80 cm是影响根长密度分布的关键区间。综上,降雨集流渗灌技术对解决宁南山区红梅杏旱地种植过程中的缺水问题具有积极作用,具有较好的推广前景。

长日照下IQM3在CO的下游调控拟南芥主根长度

拟南芥(Arabidopsis thaliana)中IQM家族是含有IQ基序的钙调素结合蛋白家族,IQM3突变能增加主根长度,CO(CONSTANS)是光周期成花调控途径的重要成员,CO突变可缩短主根长度。该研究构建二者的双突变体研究IQM3与CO基因的遗传学关系。结果表明,新CO突变体co-12序列的第1个外显子上缺失了9个碱基ACTTGCTAG,其中含有限制性核酸内切酶Bfa I的酶切位点CTAG。建立了可鉴定该突变体的分子标记:利用Bfa I酶切跨编码区PCR产物时,野生型Col因有3个位点而得到4个片段,co-12因只有2个位点而得3个片段,CO/co-12杂合子得5个片段。在长日照下,co-12的主根长度比野生型Col短,iqm3-2的比野生型Col长,而双突变体co-12 iqm3-2的主根长度表型偏向于iqm3-2。因此,在长日照下,IQM3在CO的下游参与调控拟南芥主根长度。

不同草本植物根系对土壤渗透性的影响

[目的]揭示当地排土场不同草本植物根系对土壤渗透性的影响,阐明预测草本植物根系提升土壤渗透性的最优指标,并得出草本植物根系提升土壤渗透性的最佳径级,为排土场生态修复植物选择提供重要依据。[方法]以海州露天矿排土场为研究地点,以轴根型紫花地丁、根蘖型苦荬菜和根茎型水麦冬为研究对象,采用图片像素换算法量化3种根系在不同土层深度范围内的根系分布特征;并结合渗透试验获取3种草本植物原状根土复合体的渗透参数,进而探究了根土复合体根系分布参数与渗透参数的关系。[结果]3种草本植物均能提升土壤的渗透性能,轴根型、根茎型和根蘖型根土复合体的初始入渗率、稳渗率、平均渗透速率、渗透总量相较于素土分别提升82.23%~254.99%,85.59%~307.63%,72.02%~325.91%,62.93%~246.98%。3种草本植物根系的根长密度和根表面积密度与根土复合体的渗透参数均呈现线性相关,根表面积密度的相关性强于根长密度。3种根系对土壤渗透性的增强作用主要归功于0.5 mm<D≤1.5 mm径级,它们均存在提升土壤渗透性的最佳径级。[结论]草本植物根系能够提升土壤渗透性,根表面积密度是最佳预测指标,且不同根系均存在最佳径级。

Root ZX和Raypex 5两种根管长度测量仪在老年人根管治疗中的应用

比较RootZX和Raypex5两种根管长度测量仪测量老年人后牙根管工作长度(root working length,RWL)的准确性;发现二者测量准确、简便,准确性差异没有显著性;不同牙髓状态时的测量结果差异亦无显著性。

Root Physiological and Morphological Characteristics of Two Rice Cultivars with Different Nitrogen-Use Efficiency

The variation in nitrogen （N） uptake by rice has been widely studied but differences in rice root morphology that may contribute to this variation are not completely understood. Field and greenhouse experiments were carried out to study N accumulation, root dry weights, total root lengths, root surface areas, and root bleeding rates of two rice cultivars, Elio with low N-use efficiency and Nanguang with high N-use efficiency. Low （1 mmol N L^-1） and high （5 mmol N L^-1） N applications were established in the greenhouse experiment, and the N rates were 0, 120, and 240 kg ha^-1 in the field experiments at Jiangning and Jiangpu farms, Nanjing, China. The results showed that the N accumulation, root dry weight, total root length, and root surface area increased with an increase in N application. At the heading stage, N accumulation in the shoots and roots of Nanguang was greater than that of Elio in the field experiments and that of Elio at 5 mmol N L^-1 in the greenhouse experiment. After the heading stage, N accumulation was higher for Nanguang at both 1 and 5 mmol N L^-1 in the greenhouse experiment. The total root length and root surface area were significantly different between the two cultivars. Over the range of the fertilizer application rates, the root lengths of Nanguang at Jiangning Farm were 49%-6170 greater at booting and 26%-39% greater at heading than those of Elio, and at Jiangpu Farm they were 22%-42% and 26%-38% greater, respectively. Nanguang had a greater root bleeding rate than Elio. It was concluded that the N-use efficiency of the two rice cultivars studied depended to a great extent on the root morphological parameters and root physiological characteristics at different growth stages.