Nitrogen and genotype effects on root growth and root survivorship of spring wheat

The nitrogen (N) fertilization of wheat (Triticum aestivum L.) is important for stable and high grain yield. However, the effect of N on root growth and survivorship is poorly understood. The objectives of this study were (1) to determine the effect of varying N availability on the growth and survivorship of roots and (2) to determine whether genotypic variation in N‐related traits are linked to root growth and survivorship. In a two‐year study, two spring wheat cultivars (Albis and Toronit) and an experimental line (L94491) were grown under low (20 kg N ha^–1) and high N supply (270 kg N ha^–1) in lysimeters equipped with minirhizotrons. The genotypes showed significant differences in N‐related traits: total shoot N content, grain N yield, N harvest index, and rate of decline in flag‐leaf greenness. However, there were relatively weak and inconsistent genotypic effects on the time course of root density, root growth during grain filling, and root survivorship. The level of N supply was the factor that most influenced the establishment, growth, and survivorship of roots; the high N supply, depending on the year and genotype, increased growth and survivorship of roots from 0% to 68% and 24% to 34%, respectively.     

Soil sterilization effects on root growth and formation of rhizosheaths in wheat seedlings

Sterilized soils are frequently used in experiments related to soil biology. Soil sterilization is known to alter physicochemical characteristics of soil, plant growth and community structure of the newly developed bacterial population. However, little information exists regarding soil sterilization effects on belowground processes mediated through root–microbe–soil interactions, e.g., development of rhizosheaths which significantly promote the plant growth under stress environments. The present study was conducted to elucidate effects of soil sterilization on wheat root growth and formation of rhizosheaths in relation to chemical changes caused by soil sterilization and the proportion of expolysaccharide (EPS)-producers in bacterial population recolonizing the sterilized soils. Wheat plants were grown for two weeks under greenhouse conditions either in the unsterilized soil or in soils sterilized by autoclaving (121 °C, 1 h) or by gamma (γ)-irradiation (50 kGy). While soil sterilization had no effect on the release of macronutrients, both sterilization procedures significantly increased the electrical conductivity, water-soluble carbon and DTPA-extractable Mn. Seedlings grown in sterilized soils produced higher root biomass and the rhizosheath soil (RS) mass as compared to those grown in the unsterilized soil. Soil sterilization also increased the root length, surface area, volume and number of tips. In bulk soil, RS and on roots, the proportion of EPS-producers in the total bacterial population was higher in sterilized treatments than in the unsterilized. Amending the unsterilized soil with glucose-C increased the root biomass, whereas adding Mn II increased the RS mass. The results showed that soil sterilization by autoclaving or γ-irradiation increases the root growth and RS mass of wheat seedlings. The water-soluble C and DTPA-extractable Mn released upon sterilization, and the increased proportion of EPS-producers in the bacterial population recolonizing the sterilized soils were involved in the observed effects. The results may have implications in studies using autoclaved or γ-irradiated soils to investigate soil–plant–microbe interactions and signify the need to account for intrinsic stimulatory effects of soil sterilization.     

The effects of simultaneous root colonisation by three Glomus species on soil pore characteristics

The spatial and temporal nature of the precise interactions between soil fungi and roots and their subsequent role in developing soil structure is still a subject where our understanding is limited. This research examines the relationship between three species of arbuscular mycorrhizal fungus (AMF) and soil structural characteristics. Plantago lanceolata was inoculated with one of: Glomus geosporum, Glomus mosseae or Glomus intraradices, and every combination of the fungal species. Infectivity was similar for each individual species, but G. mosseae and G. intraradices together resulted in the lowest per cent root length colonised. Despite the lower percentage colonisation, this combination induced the greatest mycorrhizal growth response. Aggregate stability and aggregate size distribution were unaffected by AMF but were increased by the presence of roots. Microbial biomass-C was also enhanced by roots. Pore size, pore size distribution and nearest neighbour distance were all reduced by G. mosseae and increased by G. intraradices. All AMF inocula containing G. intraradices resulted in greater distances between pores within the experimental soils. Porosity (%) was increased by G. mosseae suggesting that more, smaller pores with less distance between them enhanced overall porosity.     

Influence of sodium polyacrylate on the water-holding capacity of three different soils and effects on growth of wheat

Abstract. The effectiveness of sodium polyacrylate to increase soil water retention and to enhance growth of wheat under water deficit was evaluated. Water-holding capacity of the soils was considerably increased only when the soil was amended with the polymer at a rate 3 g L⁻¹. The effect on plant-available water was greater at soil matric potentials up to −1000 hPa. The biomass and grain yield of plants without water deficit were increased by the polymer amendment, but decreased under severe water deficit stress. The polymer had no significant affect on plant N, grain N or grain Na content.     

根区限制及氮营养对杂交小麦生长的影响

To study the physiological effects of small root zone, plants of a hybrid wheat variety (Triticum aestivum L. cv. Meiyou 4) were grown in small pots (1 litre) or large pots (8 litre) with low nitrogen (50 mg kg^-1 soil) and high nitrogen (200 mg kg^-1 soil). Restricting root zone decreased dry weight of plants at the stages of stem elongation and flowering, compared to those of control plants grown in the large pots (P<0.01). Spraying of 6-benzylaminopurine (50 μmol L^-1) increased dry weight of plants and chlorophyll concentration in leaves. Restriction of root zone decreased the concentrations of total nitrogen, chlorophyll and soluble protein in the flag leaf and accelerated senescence of the leaves. Supply of high nitrogen delayed senescence of the flag leaf. The results suggested that the shortage of nutrients, especially nitrogen deficiency, was the primary reason for the decreased growth of plant in the treatment of root zone restriction.     

小麦生长期土壤养分与根系活力变化及其相关性研究

研究了小麦生长期内土壤氮、钾与小麦根系活力变化及其相关性。结果表明,土壤碱解氮、速效钾和非交换性钾含量随小麦生育进程呈现有规律的变化;小麦根系活力呈现先增加,孕穗期峰值出现后迅速下降,成熟时根系活力下降到最低值的变化规律,不同施肥处理小麦整个生育期内根系活力大小顺序为:MNPK、NPK>NK>N、NP>CK、M。土壤碱解氮、速效钾、非交换性钾含量与小麦根系活力呈显著或极显著正相关,说明土壤N、K养分有效性的高低是影响小麦根系活力的重要因素。     

Compensatory root growth in winter wheat: Effects of copper exposure on root geometry and nutrient distribution

Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown for seven days in split‐root chambers containing nutrient solutions with various copper chloride (CuCl₂) concentrations [0.5/0.5 (controls), 0.5/2, 0.5/5, 0.5/7 and 0.5/10 μM]. At harvest (day 11), shoot dry weights were about the same in the different copper (Cu) treatments. Dry weights of the root parts exposed to 2–10 μM Cu (Cu‐fed) decreased while they increased for the control roots. A Cu exposure of 2–10 μM severely retarded lateral root initiation and average lateral root length. Average seminal root length was also reduced. The control roots compensated for the retarded growth of the Cu‐fed roots by increasing chiefly in lateral root number, but their average length remained similiar. Phosphorus (P) concentration decreased gradually in all determined plant parts (shoots, Cu‐control and Cu‐fed roots) with increased external Cu concentration. The potassium (K) concentration in the shoots was similarly affected, but it did not decrease in the Cu‐fed roots until the external Cu concentration reached 10 μM. The Cu concentration in the Cu‐fed roots increased proportionally to the external Cu concentration, but Cu was not exported to the other plant parts. The reasons for changes in root geometry and nutrient balance are discussed.     

田菁茎瘤固氮根瘤菌对小麦种子侵染的促生作用及其在根系内的定殖

选取8个常见小麦品种,通过室内限菌试验筛选出对于田菁茎瘤固氮根瘤菌Azorhizobium caulinodans ORS571 (A.caulinodans) 侵染响应敏感的品种,研究了浸种侵染、菌液浓度和添加葡萄糖对接菌小麦幼苗生长的影响,并结合荧光显微镜检测绿色荧光蛋白（GFP）标记A.caulinodans在小麦幼苗根系内的分布与定殖规律。结果表明:小偃22为响应敏感品种;在室内限菌条件下,浸种侵染小偃22幼苗平均根长和平均株高分别较对照增加了17.04%和8.37%;最适菌液浓度为1.0108个/mL;在菌液中添加1g/L葡萄糖有助于A.caulinodans浸种侵染和定殖。荧光显微镜检测结果显示,GFP标记A.caulinodans从小麦幼苗根毛和侧根裂隙处进入,定殖于根维管组织等部位。田间试验结果进一步表明A.caulinodans浸种侵染对不同小麦品种均具较明显的促生作用。     

钾对冬小麦根系生理性状及地上部生长的影响

本试验采用盆栽土培试验和液培试验相结合的方式研究了施钾对小麦根系生理性状及地上部生长的影响。结果表明:在缺钾的土壤上施钾可以促进根系生长,提高全生育期的根系活力和根中可溶糖含量,提高了根系在衰老过程中氮、钾养分的含量;施钾还能增大旗叶叶面积,提高小麦灌浆后期旗叶的叶绿素含量,有利于旗叶的光合和籽粒的灌浆。施钾能显著提高小麦成穗数、穗粒数和粒重,增加产量。     

土壤干旱对冬小麦幼苗根系生长及生理特性的影响

盆栽试验研究了土壤干旱对冬小麦幼苗根系生长及生理特性的影响。结果表明,随干旱胁迫的加剧,幼苗总根数、根系总长、根系体积、根系干重、根水势、根相对含水率、根系脱水速率和根系活力均降低,根冠比、饱和亏、可溶性糖含量、脯氨酸含量、质膜透性、MDA含量以及SOD、POD活性均呈增加趋势。表明干旱胁迫下冬小麦幼苗可通过改变生物量分配策略而提高根比重,并通过改变根系内部的生理变化以提高其抗旱性。     

有机肥对小麦根系生长及根系衰老进程的影响

采用土柱栽培与室内分析相结合的方法,研究了有机肥对小麦根系生长及根系衰老进程的影响。结果表明,有机肥可促进小麦根系的生长和根系在深层土壤中的分布,使小麦根系的总鲜重和深层土壤根系鲜重明显增加;提高不同土层、特别是深层土壤中根系的活力,使小麦生长后期保持较高的根系吸收养分的能力。有机肥可促进根系对氮、磷、钾的吸收和向子粒中的转移,使氮、磷、钾在子粒中的分配量增加;而且能抑制根系的膜脂过氧化作用,使不同土层小麦根系SOD活性提高、MDA含量降低,从而延缓了根系的衰老。     

小麦免耕播种机开沟器对作物生长的试验研究

为了研究具有不同开沟器的免耕播种机对动力消耗以及作物生长的影响,该文利用3种典型开沟器即短翼尖角、单圆盘和旋耕刀式在一年两熟区玉米收获地的壤土中进行了田间免耕播种试验研究,分别从土壤扰动量、返青期小麦根系状况以及单株干重和产量等方面进行了测定与分析。结果表明,3种开沟器对小麦产量影响不大,但对土壤扰动和耗油量以及返青期的小麦生长影响较大。旋耕刀开沟器土壤扰动较大,高达40%～60％,动力消耗多,返青期小麦的次生根数也最多;单圆盘开沟器播种后土壤扰动较小,仅为10%～15％,动力消耗较小,返青期小麦的次生根数和单株干重也最小;尖角开沟器土壤扰动、耗油量以及小麦根系情况居于其间。因此,可以看出不同的开沟器适应于不同的地区和需要,在保护性耕作实施过程中,可根据当地的气候环境等实际情况来设计或选用。     

Selection for root colonising bacteria stimulating wheat growth in saline soils

High salinity of soils in arid and semi-arid regions results in desertification and decreased crop yield. One possibility to circumvent this problem is to use root colonising salt tolerant bacterial inoculants which can alleviate salt stress in plants. In the present work, the best five enhanced wheat root tip coloniser bacteria were selected from the rhizosphere of wheat grown in saline soil and were identified by the 16S rRNA gene sequence as Pseudomonas putida, Pseudomonas extremorientalis, Pseudomonas chlororaphis and Pseudomonas aurantiaca. The isolates tolerated salt of 5% NaCl and produced indole acetic acid under saline conditions. Four isolates proved to be very efficient in promoting a significant increase in the shoot, root and dry matter of wheat and were able to survive in saline soil. Four of the isolated strains appeared to be better competitive colonisers than reference strains and probably outcompeted with indigenous microorganisms of the rhizosphere. These results are promising for the application of selected environmentally save microbes in saline agricultural soils.     

不同基因型小麦侧根生长对硝态氮的响应差异

以4个小麦品种石麦15、衡观35、H10和L14为供试作物,进行营养液培养试验,研究不同浓度硝态氮供应对小麦侧根发育的影响。结果表明:0.05~25.0 mmol/L硝态氮处理13 d,小麦生物量及侧根形态尚未受到明显影响;硝态氮处理22 d后,植株地上部生物量和氮含量明显增加,石麦15、H10和衡观35增加幅度较大,L14增幅较小;0.05 mmol/L低浓度硝态氮处理下,4个小麦品种的侧根平均长度较长。进一步研究发现,小麦侧根发育对不同浓度硝态氮供应的反应存在明显的基因型差异:0.05 mmol/L硝态氮处理下,石麦15的侧根长度和总根长增加,侧根密度无明显变化;H10的侧根总长度增加,侧根密度减少;衡观35的侧根密度减少,侧根总长度变化不大,而L14的侧根总长度和侧根密度均无明显改变。硝态氮处理浓度在2.5~20.0 mmol/L范围内,小麦侧根数量和长度均没有受到明显影响,在均匀供应硝态氮条件下,高浓度的硝态氮处理未影响小麦的侧根长度和数量。     

局部根系盐胁迫对冬小麦生长和光合特征的影响

通过分根装置设置无盐胁迫(0|0)、局部根系150 mmol-L-1NaCl胁迫(0|150)、全部根系75 mmol-L-1NaCl胁迫(75|75)、全部根系150 mmol-L-1NaCl胁迫(150|150)4种处理,研究根系局部盐胁迫对冬小麦生长及光合特征的影响。结果表明:盐胁迫显著抑制了小麦幼苗的生长,并且随着盐胁迫浓度的增加,小麦受抑制程度加重;根系盐胁迫方式对小麦幼苗生长影响显著,局部根系胁迫处理(0|150)小麦幼苗地上部干重比等浓度150 mmol-L-1NaCl全部盐胁迫处理(150|150)增加23.5%,比等浓度75 mmol-L-1NaCl全部盐胁迫处理(75|75)增加17.2%。在局部根系盐胁迫下,非盐胁迫一侧根系(0|150-0)补偿生长,其根长、侧根数、侧根长比盐胁迫一侧根系(0|150-150)分别增加195.2%、206.2%和237.8%,盐胁迫一侧根系吸收的Na+部分向非盐胁迫一侧根系运输,盐胁迫一侧根系(0|150-150)的Na+含量比全部胁迫处理(150|150)减少12.1%。与全部根系盐胁迫相比,局部根系盐胁迫减少了Na+在叶片中的积累,降低了钠/钾值。局部根系盐胁迫叶片净光合速率、气孔导度、胞间CO2浓度和叶绿素荧光参数(Fv/Fm)均高于同浓度完全盐胁迫处理的小麦幼苗,进而增加地上部和根系的生物量。因此,局部根系胁迫显著缓解了全部盐胁迫对小麦地上部和根系生长的抑制作用。     

The effect of tillage intensity on soil structure and winter wheat root/shoot growth

Despite a vast amount of data on the effect of tillage on crop productivity, surprisingly there is little detailed information available on the influence on below and aboveground crop growth dynamics. Such information is essential for developing sustainable cropping systems. The objective of this study was to investigate the effect of tillage intensity on crop growth dynamics and soil structure. A tillage experiment was established in autumn 2002 on two Danish sandy loams (Foulum and Flakkebjerg) in a cereal‐based crop rotation. The tillage systems included in this study were direct drilling (D), harrowing 8–10 cm (H_8‐10), and ploughing (P). A single‐disc drill was used in the H_8‐10 and D treatments and a traditional seed drill in the P treatment. Measurements were carried out in 2004–05 and 2005–06 and winter wheat was grown in both years (first and second year winter wheat). Shoot and root growth was followed during the growing seasons using spectral reflectance and mini‐rhizotron measurements, respectively. A range of soil physical properties were measured. We found decreased early season shoot and root growth with decreasing tillage intensity. Differences diminished later in the growing season, although significant treatment effects were observed throughout the growing season for the second year winter wheat. The formerly ploughed layer in the D and H_8‐10 treatments was noticeably compacted as indicated by increases in both penetration resistance and bulk density. Nitrate leaching increased with decreasing tillage intensity for the first year winter wheat at Foulum. In general ploughing resulted in the highest grain yields. This study highlights the important interaction between soil structure and crop growth dynamics.     

Evaluation of emmer wheat and other Triticeae for resistance to Russian wheat aphid

Summary During the winters of 1990/91 and 1991/92, 181 accessions of Triticum dicoccon Schrank from the CIMMYT gene-bank were screened in the field for resistance to Russian wheat aphid, Diuraphis noxia (Kurdjumov). Accessions were sown in hill plots of 10 seeds and artificially infested with D. noxia at the two-leaf growth stage. Hills were visually assessed for damage at tillering, booting and heading. Entries differed significantly in their reaction to D. noxia, and severity of symptoms increased with time. Twenty four of the entries were highly resistant to the aphid. In winter 1991/92, 807 accessions of wild and cultivated wheats (26 species) and synthetic hexaploids were screened similarly for resistance to D. noxia. A large number of A-genome species were resistant, while few D-genome species were identified as resistant. These newly discovered sources of resistance can be used to expand the genetic base of resistance to D. noxia in both bread (T. aestivum L.) and durum wheats (T. turgidum L. convar. durum (Desf.) Mackey).     

基于相关向量机的冬小麦蚜虫遥感预测

蚜虫的流行严重影响了冬小麦的产量。区域尺度上及时准确的预报冬小麦蚜害发生范围能为蚜害的有效预防提供基础信息,从而降低冬小麦产量的损失。该研究利用多时相的环境星CCD光学数据和IRS热红外数据,分别提取了冬小麦的长势因子,比值植被指数(ratio vegetation index,RVI)和归一化植被指数(normalized difference vegetation index,NDVI),以及生境因子,地表温度(land surface temperature,LST)和垂直干旱指数(perpendicular drought index,PDI),利用相关向量机(relevance vector machine,RVM)、支持向量机(support vector machine,SVM)和逻辑回归(logistic regression,LR)方法建立了北京郊区冬小麦灌浆期蚜虫发生预测模型,并对比分析了3种模型预测精度。试验结果表明,RVM总体预测精度达到87.5%,优于SVM的79.2%和LR的75.0%。另外,RVM模型计算量较小,相比于SVM和LR模型,其预测时间可分别缩短7倍和60倍。较高预测精度和较小计算量的特性扩大了RVM在实际中的应用价值。     

黄腐酸添加量对低氮胁迫下小麦生长和根系形态的影响

【目的】黄腐酸(FA)是腐植酸中分子量较小、活性最大的组分,作为一种生物刺激素,FA可以促进植物生长,提高植株的抗逆性。研究黄腐酸不同添加量对低氮胁迫下小麦生长及根系形态的影响,为小麦减氮增效提供实践和理论参考。【方法】以小麦品种‘鑫华麦818’为材料进行了水培试验。将营养液氮浓度调节为硝态氮0.1 mmol/L模拟低氮胁迫(LN),并分别设置FA添加量0、30、60、90、120 mg/L,即LN-FA0、LN-FA30、LN-FA60、LN-FA90、LN-FA120,共5个处理;以正常供氮营养液(硝态氮4 mmol/L)为对照(NN)。分析了小麦根系形态、植株生物量、植株氮浓度、氮累积量、叶片氮代谢关键酶活性等指标。【结果】与LN-FA0相比,LN-FA30、LN-FA60、LN-FA90和LN-FA120处理的地上部生物量分别提高了16.31%、23.18%、26.75%和35.16%,LN-FA120的地上部生物量与正常氮处理已无显著差异;LN-FA30、LN-FA60和LNFA90总根长增加了35.00%～44.67%,根表面积增加了39.93%～95.42%,根体积增加了...     

Tree species effects on microbial respiration from decomposing leaf and fine root litter

Tree species have an impact on decomposition processes of woody litter, but the effects of different tree species on microbial heterotrophic respiration derived from decomposing litter are still unclear. Here we used leaf and fine root litter of six tree species differing in chemical and morphological traits in a temperate forest and elucidated the effects of tree species on the relationships between litter-derived microbial respiration rates and decomposition rates and morphological traits, including specific leaf area (cm² g⁻¹) and specific root length (m g⁻¹) of litter at the same site. Litterbags set in forest soil were sequentially collected five times over the course of 18 months. During litter decomposition, microbial respiration from leaf and fine root litter differed among the six tree species. Temporal changes in the remaining mass and morphology (specific leaf area and specific root length) were observed, and the magnitude of these changes differed among species. Positive correlations were observed between respiration and mass loss or morphology across species. These results revealed that litter mass loss and morphological dynamics during decomposition jointly enhanced microbial respiration, and these carbon-based litter traits explained species differences in decomposition of leaves and fine roots. In conclusion, tree species influenced the magnitude and direction of microbial respiration during leaf/fine root litter decomposition. Tree species also affected the relationship between microbial respiration and litter decomposition through direct effects of litter traits and indirect effects mediated by regulation of heterotroph requirements.