Responses of phytohormones and gas exchange to mycorrhizal colonization in trifoliate orange subjected to drought stress

Phytohormones have an essential ability to adapt to abiotic stresses, including drought stress (DS), by mediating physiological and molecular processes. Arbuscular mycorrhizas (AMs) can enhance tolerance of DS, but the information regarding phytohormone changes in AM plants exposed to DS is little known. Trifoliate orange (Poncirus trifoliata) seedlings colonized by an AM fungus Funneliformis mosseae were subjected to DS and well-watered for 6 weeks. Plant growth performance, gas exchange, indole-acetic acid (IAA), gibberellins (GAs), brassinosteroids (BRs), abscisic acid (ABA), methyl jasmonate (MeJA) and zeatin riboside (ZR) were determined. The 6-week DS treatment strongly restricted root mycorrhizal colonization. Mycorrhizal inoculation significantly increased plant growth parameters under DS, as compared with non-mycorrhizal treatment. Mycorrhizal treatment also induced significantly higher leaf-relative water content, net photosynthetic rate, transpiration rate and stomatal conductance but lower intercellular CO₂ concentration and leaf temperature under DS, compared with non-mycorrhizal treatment. Mycorrhizal plants under DS condition represented significantly higher leaf ABA, IAA, GAs, BRs and ZR levels than non-mycorrhizal plants. The study, hence, suggested that mycorrhizal inoculation induced the changes of gas exchange and endogenous phytohormone levels to enhance drought tolerance in trifoliate orange.     

Arbuscular mycorrhizas improve plant growth and soil structure in trifoliate orange under salt stress

Arbuscular mycorrhizal fungi (AMF) as a biostimulant enhance salt tolerance in plants, while the informations regarding AMF-induced changes in soil structure are only available to a limited degree. In this study, trifoliate orange (Poncirus trifoliata) seedlings were inoculated with Diversispora versiformis under 100 mM NaCl for 85 days. The salt stress considerably inhibited mycorrhizal colonization by 26%, compared with non-salt stress. Mycorrhizal inoculation significantly increased plant height, stem diameter, leaf number, shoot biomass, and root biomass, length, surface area, and volume in comparison to non-mycorrhizal inoculation under salt stress or non-salt stress. Mycorrhization induced significantly higher production of easily extractable glomalin-related soil protein (EE-GRSP), and total glomalin-related soil protein (T-GRSP), higher percentage of water-stable aggregates (WSAs) in 0.25–0.50, 0.50–1.00, and 1.00–2.00 mm size, and lower in 2.00–4.00 mm size, regardless of non-salt stress or salt stress. Mycorrhizal soils represented higher aggregate stability (in terms of mean weight diameter) under salt and non-salt stress, which was related with root colonization, root surface area, root volume, EE-GRSP, and T-GRSP. The better soil structure by mycorrhization provided higher leaf water potential under salt stress. It suggests that mycorrhizas had a positive contribution to improve plant growth and soil structure, thereby enhancing salt tolerance.     

Effect of arbuscular mycorrhizal fungi on rhizosphere organic acid content and microbial activity of trifoliate orange under different low P conditions

ABSTRACT

Arbuscular mycorrhizal (AM) fungi can improve plant phosphorus (P) uptake; however, information about how AM fungi affect rhizosphere organic acid and microbial activity to alleviate citrus low P stress is limited. Here, a pot experiment was conducted to evaluate the effect of AM fungi (Rhizophagus intraradices, Ri) inoculation on rhizosphere organic acid content, microbial biomass (MB) and enzyme activity of trifoliate orange (Poncirus trifoliata L. Raf.) seedlings grown under three low P conditions. The results showed that mycorrhizal seedlings all recorded higher P concentrations, plant biomass and better root morphology with more lateral and fine roots, but lower root mass ratios, irrespective of P conditions. Mycorrhizal P absorption contribution did not differ significantly among three P conditions. Mycorrhizal seedling rhizosphere soil exhibited lower organic acid content, soil organic P content and ratio of MB-carbon (C)/MB-P, but higher MB and enzyme activity. Additionally, the main organic acids showed a negative relationship with mycorrhizal colonization rate and hyphal length; however, phosphatase and phytase activity had a significantly positive relationship with MB. Therefore, the results suggest that AM fungi inoculation may help citrus to efficiently utilize organic P source by improving microbial activity under low available P conditions.     

低磷胁迫下熊猫豆侧根增多的生理机制研究

采用溶液培养方法,通过外源添加生长素吲哚-3-乙酸（IAA）及生长素极性运输抑制剂2,3,5-三碘苯甲酸（TIBA）,研究了低磷胁迫下熊猫豆根系构型与生长素相关代谢酶活性之间的关系,以阐明生长素在低磷胁迫下塑造植物根系构型的作用。结果表明,熊猫豆在低磷胁迫下形成特定根系构型,具体表现为侧根增多。IAA在侧根发生过程中起重要作用,外源IAA可以在一定程度上模拟低磷信号引导的侧根发生,而生长素极性运输抑制剂TIBA则显著抑制侧根发生。根系中生长素代谢相关酶生长素氧化酶（IAAO）和过氧化物酶（POD）活性在根构型形成过程中呈现规律性变化。低磷环境下熊猫豆根系中的IAAO、 POD酶活性均高于正常施磷的处理。外源IAA可以增加这两种酶的活性,而TIBA则能够逆转低磷诱导的IAAO、 POD活性的增加。     

Effects of arbuscular mycorrhizal fungi on the growth of two turfgrasses grown under greenhouse conditions

ABSTRACT

The need for salinity resistance in turfgrass is increasing because of the enhanced use of effluent and other low-quality water for turfgrass irrigation. Although most turfgrasses form an arbuscular mycorrhizal fungus (AMF) symbiosis, there is little information on the mycorrhization of turfgrass species. Therefore, the aim of this study was to determine the effects of three AMF species, Glomus intraradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, and Glomus deserticola Trappe & John, and a mixture thereof on the growth, productivity, and nutrient uptake of two species of cool-season turfgrasses, Challenger Kentucky bluegrass (Poa pratensis L.) and Arid tall fescue (Festuca arundinacea Schreb.), and to relate the effects to colonization of the roots by mycorrhiza to assess the dependency of the plants (mycorrhizal dependency [MD]). Following the experimental period (4 months) and measurements, the mycorrhizal inoculated plants had significantly greater biomass production compared to that of non-inoculated plants. MD and shoot mineral contents (particularly P) differed among turfgrass hosting AMF, and the highest value (13%) occurred for P. pratensis and F. arundinacea seedlings colonized with G. intraradices and G. deserticola, respectively. The P content was highest for the F. arundinacea/mixed AMF combination compared to other treatments. We confirmed that mycorrhizal inoculation (P. pratensis/G. intraradices and F. arundinacea/mixed AMF combinations) enhanced plant productivity and nutrient uptake (especially P) even under non-optimum conditions.     

Effects of arbuscular mycorrhizal fungi on the growth and zinc uptake of trifoliate orange (Poncirus trifoliata) seedlings grown in low-zinc soil

The effects of the arbuscular mycorrhizal (AM) fungi, Glomus intraradices and G. versiforme, on growth and zinc (Zn) uptake were investigated in trifoliate orange (Poncirus trifoliata) seedlings exposed to low-Zn soil. Low-Zn decreased growth, levels of leaf chlorophyll, soluble protein and sugar, and soil enzymatic activities, and pH in 0–2 cm rhizosphere soil. Low-Zn soil also decreased mineral nutrients (including Zn) concentrations in the shoots and roots. Glomus intraradices especially, significantly enhanced plant biomass, leaf soluble protein and sugar concentrations, root viability, acid phosphatase, catalase, invertase and urease activities, and easily extractable glomalin content in 0–2 cm and 2–4 cm rhizosphere soil. It also increased concentrations of Zn, phosphorus, potassium and magnesium in the shoots and roots, while decreased the soil pH. Arbuscular mycorrhizal fungi, especially G. intraradices, has the potential to improve growth and Zn uptake of triofoliate orange seedlings grown in low-Zn soil.     

不同供铵水平对番茄根系生长的影响

植物根系对各种养分供应高度敏感。本文以番茄为研究材料,采用整株和根部琼脂培养方法,研究不同浓度NH4+对根系生长的影响。结果表明：当整体供NH4+ 浓度大于0.5 mmol/L,主根长、侧根数和株高均随着NH4+ 的增加而变小,10 mmol/L NH4+ 几乎完全抑制了侧根形成。整体供NH4+ 对番茄生长的抑制效应大于相等浓度的NH4+ 仅供应于根部。而低浓度的NH4+ （10 ~ 100 mmol/L）供应于根部,在基本不影响主根长度的情况下,能显著增加侧根数量。依据所使用的NH4+ 浓度及不同的供NH4+方式,NH4+对番茄生长特别是侧根形成具有显著的抑制作用或促进效应。     

大气氮沉降提高低磷土壤条件下马尾松菌根共生和磷效率的原因

【目的】菌根共生是提高植物磷(P)营养高效利用的重要机制之一。近年来大气氮(N)沉降的增加,导致森林土壤有效氮含量增加、 N/P比发生改变,将影响菌根共生植物的生长和磷效率。【方法】以马尾松优良家系作为试验材料,NH4NO3作为外加氮源,设置模拟氮沉降与同质低磷(介质表层与深层均缺磷)、 异质低磷 (介质表层磷丰富、 深层缺磷)耦合条件下马尾松外生菌根共生的盆栽实验,系统研究模拟氮沉降对低磷胁迫下马尾松家系菌根化苗生长和磷效率的影响。【结果】 1)模拟氮沉降对马尾松菌根共生的影响与土壤磷素环境有关。在表层和深层磷素均极为匮乏的同质低磷条件下,氮沉降降低了苗木菌根侵染率和侵染程度,然而提高了菌根共生对马尾松生长和磷效率作用的有效性,马尾松的生长量和生物量均显著增加。在表层磷丰富、 深层缺磷的异质低磷条件下,菌根共生对马尾松苗木生长有抑制作用,然而氮沉降降低了其抑制程度,高氮较低氮处理对菌根侵染苗木和菌根化苗生物量积累的抑制程度小; 2)同质低磷下,模拟氮沉降显著降低了菌根化苗的根系生长,但增加了根系APase活性和有机酸分泌量,尤其是有机酸分泌量增加了近3倍。相关性分析表明,有机酸分泌对菌根化苗生长的贡献显著高于APase,这是氮沉降促进马尾松生长的主要原因之一。异质低磷下,模拟氮沉降处理后苗木深层菌根的生长发育程度较表层好,深层根的根尖数显著增加。有机酸分泌的增加提高了苗木的磷效率,促进了菌根化苗木的生长; 3)不同低磷环境下,氮沉降的增加均降低了土壤磷的相对有效性,菌根通过增加马尾松苗木对土壤磷的吸收和利用, 从而改善磷素营养促进马尾松生长发育。两种磷素环境下,马尾松菌根化苗生长对模拟氮沉降均较敏感; 4)马尾松菌根化苗生长对模拟氮沉降的响应存在显著的家系差异。【结论】大气氮沉降可改善马尾松的氮素营养,增加菌根作用的有效性,从而促进马尾松对磷的吸收,进而促进了林木的生长。不同马尾松品种对氮沉降的反应有差异,筛选高氮-低磷环境下菌根共生能力强的马尾松基因型,将成为提高土壤磷素生物学利用效率的重要途径。     

模拟矿区复垦接种丛枝菌根缓解伤根对玉米生长影响

针对煤炭开采过程中地表塌陷造成植物根系损伤问题,通过人为伤根模拟煤炭开采造成植物根系受损的盆栽试验,以玉米为宿主植物,矿区退化土壤为供试基质,研究接种丛枝菌根真菌对根系受损玉米生长的缓解作用。结果表明,玉米根系受损条件下,接种丛枝菌根真菌缓解了伤根对玉米生长造成的不利影响,促进了玉米的生长,接菌组玉米干质量平均每株要比对照组高出9.74 g。强化接种菌根真菌提高了玉米对土壤中矿质元素的吸收,增加了受损玉米根际土壤中球囊霉素和有机质含量,接菌组玉米根际土壤中总球囊霉素和有机质含量分别比对照组高出48.1%和24.5%。接种菌根改善了玉米根际微环境,有利于矿区退化土壤改良和培肥。通过研究菌根真菌对根系受损植物生长效应,为采煤塌陷区土地复垦与生态重建提供技术支撑。     

干旱胁迫下丛枝菌根对大豆抗氧化代谢及根围微生物的影响

丛枝菌根真菌(AMF)可促进作物营养吸收和提高抗逆性,成为寄主抵御干旱胁迫的有效途径。为探明AMF提高大豆抗旱性的机制,以‘桂春豆103’为材料接种幼套近明囊霉(Claroideoglomus etunicatum,简写为C.e),研究干旱条件下C.e对田间大豆叶抗氧化酶及根围土中C/N/P循环相关酶活性等的影响,并用变性梯度凝胶电泳等方法探索土壤微生物群落结构的变化。结果表明:干旱处理前,接种C.e(+AM)处理大豆SOD、POD活性及游离脯氨酸(FP)含量,磷酸酶、蔗糖酶和脲酶活性,土壤细菌、真菌和放线菌数量及物种多样性、丰富度和群落均匀度指数,大豆生物量和株高均显著高于(-AM)处理(P0.05),MDA含量显著降低(P0.05)。干旱(D)处理后,+AM+D处理的上述各项指标,除MDA含量比-AM+D或+AM处理分别显著降低或升高(P0.05),FP含量比两处理显著提高(P0.05)外,其余指标值及细菌和真菌r DNA条带数均比-AM+D处理显著升高,比+AM处理显著下降(P0.05)。-AM+D与-AM处理的细菌和真菌群落均分别聚类于两不同分支,+AM与+AM+D处理聚于同一分支。可见,+AM+D处理能显著促进大豆抗氧化酶系统活性,维持较强的活性氧清除和渗透调节能力,缓解干旱对土壤酶活性的抑制,保持较高的细胞膜稳定性、土壤微生物数量和群落多样性,有利于C/N/P循环转化,提高抗旱性,最终促进大豆生长。本研究可为促进农业生态系统可持续发展奠定基础。     

不同水氮条件下水稻根系超微结构及根系活力差异

【目的】探讨不同水氮耦合对水稻根系超微结构及根系代谢特性的影响,从根尖细胞超微结构及根系活力方面阐明不同水氮组合处理在根际环境间的差异。 【方法】以新稻 20 号为材料,进行盆栽试验,设置浅水层灌溉、轻度水分胁迫 (灌 1～2 cm 水层,至土壤水势降到 –20 kPa 再灌浅水层,如此反复) 和重度水分胁迫 (灌 1～2 cm 水层,至土壤水势降到 –40 kPa 再灌浅水层,如此反复) 3 种灌溉方式及不施氮肥,适量氮 (N 240 kg/hm2) 和高量氮 (N 360 kg/hm2) 3 种氮肥水平,测定了不同处理水稻根系氧化力、根系伤流量及根系分泌有机酸总量,并观测了根系细胞超微结构。 【结果】随着生育进程,根系氧化力表现为先增加后降低的趋势,在幼穗分化期达到峰值,根系伤流液及根系分泌物中有机酸总量先增加后降低,在抽穗期达到峰值。在同一氮肥水平下,轻度水分胁迫后根系细胞完整,核膜界限清晰,结构特征典型;与保持水层相比,根系氧化力及根系伤流量在分蘖盛期分别增加 25.6%～32.0% 及 9.1%～18.8%,根系分泌有机酸总量在抽穗期前平均增加 16.4%。重度水分胁迫后嗜锇体和淀粉体较多,后期细胞完全扭曲变形,细胞间隙明显增多增大、细胞器出现断裂降解,细胞基质中仅存细胞器碎片,细胞壁较完整,未出现断裂情况;与保持水层相比较,根系氧化力及根系伤流量在幼穗分化始期平均降低 8.8% 及 25.6%,根系分泌有机酸总量平均降低 22.8%。在同一灌溉方式下,适量氮处理根系细胞结构较完整,核膜较清楚,有利于根系活力的提高及根系有机酸的分泌;重施氮处理根系细胞壁和核膜降解加速。与适量氮相比,高氮处理下根系氧化力及根系伤流量在分蘖盛期至幼穗分化始期分别降低了 6.6%～9.8% 及 7.7%～15.4%,根系分泌物中有机酸总量在抽穗前平均降低 11.6%,整体上根系活力降低、有机酸的分泌量显著减少。 【结论】轻度水分胁迫耦合适量氮处理的水稻根系超微结构最优,细胞结构特征典型,核膜最为清晰,细胞完整,根系代谢能力最强。表明通过适宜的水氮耦合调控,能够提高根尖细胞的生理功能,增强根系活力、促进根系有机酸的分泌,能为水稻的生长创造良好的根际环境。     

不同施肥量条件下AM真菌对烟苗生长及营养状况的影响

试验设置不同施肥量,于播种期分别接种根内球囊霉菌(Glomus intraradices Smith和Schenck,BEG193)和幼套球囊霉菌(Glomuse etunicatum Becker和Gerdemann,BEG168),探索了利用烤烟漂浮育苗技术生产菌根化烟苗和培育壮苗的可能性。结果表明:随着养分供应量的减少,AM真菌的侵染率提高,BEG193的侵染率高于BEG168。减施肥料总体上抑制烟苗生长,使烟苗生物量降低;但接种AM真菌显著促进烟苗生长,烟苗平均生物量比不接种的处理增加了74.38%(BEG168)和48.32%(BEG193)。接种BEG168使烟苗氮、磷、钾含量显著增加;接种BEG193主要是提高了烟苗含磷量。在施肥量减少75%辅以少量追肥的情况下,接种BEG168之后,烟苗生长状况和磷、钾含量超过或与常规施肥的非菌根苗相似。因此,在集约化烤烟漂浮育苗过程中,可采用接种AM真菌BEG168的方式培育壮苗,同时降低施肥量,减轻废弃营养液产生的环境污染。此外,接种AM真菌显著提高基质中的酸性磷酸酶活性,菌根苗基质中的磷酸酶活性随施肥量的降低而逐渐升高。因此,接种AM真菌有益于基质中有机磷的吸收利用,这可能是菌根烟苗含磷量提高的重要原因之一。     

9种丛枝菌根真菌对柑橘砧木枳和资阳香橙生长发育的影响

丛枝菌根（Arbuscular mycorrhizal,AM）真菌能有效促进宿主植物对土壤中水分和养分的吸收以及对有机物质的分解,从而促进植物的生长。柑橘是菌根依赖型植物。丛枝菌根真菌对宿主植物没有严格的专一性,但有选择性,因此有必要筛选出不同砧木适宜的菌株。以柑橘砧木资阳香橙（Citrus Junos Sieb. ex Tanaka）和枳壳（Poncirus trifoliate L. Raf）幼苗进行盆栽试验,通过对不同砧木接种不同AM真菌后测定其生长性状,运用隶属函数法对各指标求其隶属函数值并累加计算综合分数并排名,筛选出促进香橙和枳壳生长的优势菌株。研究表明,接种不同AM真菌对不同砧木的生长发育存在显著差异,表现为促生和抑制两个效应。根据综合评价系数,香橙中隶属函数平均值较高的菌株为G.r(Glomus reticulatum)、R.c(Rhizophagus clarus)和R.i(Rhizophagus intraradices),分别为0.71、0.66和0.63;枳壳中隶属函数平均值较高的菌株为R.c(Rhizophagus clarus)、G.v(Glomus ver...     

The impact of arbuscular mycorrhizal fungi on strawberry tolerance to root damage and drought stress

Individually, arbuscular mycorrhizal fungi (AMF), drought stress, and root damage can alter terrestrial plant performance but the joint effects of these three factors have not been explored. Because AMF can improve water relations, colonization by these root symbionts may increase the host’s tolerance of drought especially when roots have been compromised by herbivory. This full factorial study examined effects of AMF, water deficit, and artificial root herbivory in three genotypes of wild strawberry, Fragaria virginiana Duchesne that originated from the same restored tallgrass prairie as the AMF inoculum. Drought stress and root damage altered allocation to roots vs. shoots but the effects were not additive and the interaction did not depend on AMF treatment. Effects of AMF were absent with one exception: root damage significantly reduced belowground mass only in plants inoculated with AMF. Although drought stress did not interact with the AMF treatment, both drought stress and root damage reduced the abundance of arbuscules, and especially vesicles, and colonization varied among genotypes. Failure to detect strong effects of AMF on host growth could be due to variable responses of individual AMF species summing to no net effects. Functionally, AMF were primarily commensals of strawberry in this study.     

Arbuscular mycorrhizal fungi regulate plant mineral nutrient uptake and partitioning in iron ore tailings undergoing eco-engineered pedogenesis

Excess available K and Fe in Fe ore tailings with organic matter amendment and water-deficiencies may restrain plant colonization and growth, which hinders the formation of eco-engineered soil from these tailings for sustainable and cost-effective mine site rehabilitation. Arbuscular mycorrhizal (AM) fungi are widely demonstrated to assist plant growth under various unfavorable environments. However, it is still unclear whether AM symbiosis in tailings amended with different types of plant biomass and under different water conditions could overcome the surplus K and Fe stress for plants in Fe ore tailings, and if so, by what mechanisms. Here, host plants (Sorghum sp. Hybrid cv. Silk), either colonized or noncolonized by the AM fungi (Glomus spp.), were cultivated in lucerne hay (LH, C:N ratio of 18)- or sugarcane mulch (SM, C:N ratio of 78)-amended Fe ore tailings under well-watered (55% water-holding capacity (WHC) of tailings) or water-deficient (30% WHC of tailings) conditions. Root mycorrhizal colonization, plant growth, and mineral elemental uptake and partitioning were examined. Results indicated that AM fungal colonization improved plant growth in tailings amended with plant biomass under water-deficient conditions. Arbuscular mycorrhizal fungal colonization enhanced plant mineral element uptake, especially P, both in the LH- and SM-amended tailings regardless of water condition. Additionally, AM symbiosis development restrained the translocation of excess elements (i.e., K and Fe) from plant roots to shoots, thereby relieving their phytotoxicity. The AM fungal roles in P uptake and excess elemental partitioning were greater in LH-amended tailings than in SM-amended tailings. Water deficiency weakened AM fungal colonization and functions in terms of mineral element uptake and partitioning. These findings highlighted the vital role AM fungi played in regulating plant growth and nutrition status in Fe ore tailings technosol, providing an important basis for involvement of AM fungi in the eco-engineered pedogenesis of Fe ore tailings.     

缺锌对玉米根系发育、生长素含量及生长素转运基因表达的影响

【目的】研究缺锌对玉米根系生长及根系中生长素含量与生长素运输关键基因表达的影响,揭示缺锌胁迫下玉米根系生长与生长素响应特征。【方法】以郑单958玉米为材料,进行营养液培养试验,设置Zn 0缺锌 (0 μmol/L) 和正常供锌 (1 μmol/L) 两个处理。植株干样经硝酸–过氧化氢消煮,利用原子吸收分光光度计测定消煮液锌浓度。保存于FAA溶液 (70% 乙醇︰38% 甲醛︰乙酸 = 90︰5︰5,体积比) 中的根系样品,经洗涤扫描获得数字图像,利用WinRHIZO软件分析得到根长、根表面积、根体积等指标;采用气相色谱-质谱联用仪检测根系中生长素吲哚乙酸含量;采用实时荧光定量PCR技术对玉米根系生长素转运基因ZmAUX1和ZmPIN1c表达进行定量分析。【结果】缺锌胁迫下,植株地上部锌含量低于20 μg/g,生物量显著降低;缺锌根系表面积与体积变小,总根长、侧根总长度与侧根平均长度变短,侧根密度增大,直径变细。缺锌条件下,距根尖2 cm的区域中生长素较正常供锌处理降低近30%。缺锌根系中ZmAUX1和ZmPIN1c基因表达明显受抑。【结论】缺锌胁迫下玉米根系中生长素转运关键基因表达降低,生长素含量下降,生长素分布改变,影响根系生长发育。     

Wood biochar produces different rates of root growth and transpiration in two maize hybrids (Zea mays L.) under drought stress

This study investigated the effects of wood-derived biochar (BC) applied at 1% to a C-poor silty-loam soil in the drought-tolerant (D24) and in the drought-sensitive (P1921) Pioneer Hi-Bred maize hybrids in pot and field trials (NE Italy). D24 had better growth than P1921 under rain-fed conditions without irrigation and soil amendment. The addition of biochar increased root growth in D24 (+38% root area) and decreases it in P1921 (?9%) at the silking stage, while the fraction of finer roots (<250 µm diam.) was reduced in D24 and increased in P1921. This led both hybrids to maintain the maximum transpiration at a lower fraction of transpirable soil water (from 82% to 45% in D24, and from 46% to 22% in P1921). There were no significant variations in plant nutrient contents, productivity and in the protein and starch contents of the grains, whereas the lipid content was reduced by biochar, particularly in P1921 (2.6% vs. 3% DW, ?13%).

We conclude that biochar can be profitably used to enhance drought tolerance in maize, possibly due to improvements in the physicochemical characteristics and the water content of treated soils, although maximum benefits are expected in drought-tolerant hybrids through increased root elongation and transpiration.     

Responses of arbuscular mycorrhizal fungi to straw return and nitrogen fertilizer reduction in a rainfed maize field

Straw return can be used to reduce fertilizer input and improve agricultural sustainability and soil health. However, how straw return and reduced fertilizer application affect beneficial soil microbes, particularly arbuscular mycorrhizal fungi (AMF), remains poorly understood. Here, we conducted a five-year field experiment in a rainfed maize field on the Loess Plateau of northwestern China. We tested four treatments with straw return combined with four nitrogen (N) application rates, i.e., 100%, 80%, 60%, and 0% of the common N application rate (225 kg N ha^-1 year^-1) in this region, and two reference treatments (full or no N application), with three replicates for each treatment. Mycorrhizal colonization was quantified and AMF communities colonizing maize roots were characterized using Illumina sequencing. Forty virtual taxa (VTs) of AMF were identified in root samples, among which VT113 (related to Rhizophagus fasciculatus) and VT156 (related to Dominikia gansuensis) were the predominant taxa. Both root length colonization and AMF VT richness were sensitive to N fertilization, but not to straw return; furthermore, both gradually increased with decreasing N application rate. The VT composition of the AMF community was also affected by N fertilization, but not by straw return, and the community variation could be well explained by soil available N and phosphorus concentrations. Additionally, 60%, 80%, and full N fertilization produced similar maize yields. Thus, our study revealed the response patterns of AMF to straw return and N fertilizer reduction and showed that straw return combined with N fertilizer reduction may be a promising practice to maintain mycorrhizal symbiosis concomitantly with crop productivity.     

低钾胁迫下外源生长素对烟草根系生长及钾吸收的影响

【目的】探明生长素参与低钾胁迫下植株根系的生长发育及吸钾机制,同时为提高植物体内钾素水平提供理论依据。【方法】采用室内水培法,以模式植物烟草为试验材料,通过设置2个钾浓度(5、0.15 mmol/L)和5个外源生长素(3–吲哚乙酸)浓度(0、5、10、20、40μmol/L),对植物根系生理特征、内源生长素浓度、钾素累积及钾吸收动力学和相关钾离子通道基因转录表达进行比较研究。【结果】1)与正常钾水平相比,在低钾胁迫条件下,植株地上部干重显著降低15.6%;根系扫描8项指标中,除根平均直径外,其余7项指标值均显著降低;ATPase活性显著降低43.3%;主根尖、侧根尖及叶片内源生长素浓度显著升高;钾吸收动力学参数Vmax、Km值分别显著降低了89.2%、99.6%;植株根系、叶片钾浓度分别显著降低了93.0%、62.2%;根系中内流型钾离子通道基因Ntkc1的表达量显著降低56%。2)添加外源生长素后,正常供钾植株的根系干物质重、根系活力、主根尖及侧根尖内源生长素浓度有增加的趋势,Vmax值和内流型钾离子通道基因NKT2、NtKC1的表达量明显增加;低钾条件下,植株表现出和正常供钾相似的规律,除此之外,低钾植株的根系生长得到明显改善,ATPase活性和地上地下部钾素浓度明显增加,外流型钾离子通道基因Ntork1的表达量明显降低。3)当添加生长素浓度为10μmol/L时,与未添加生长素相比,正常供钾植株的地上地下部干重显著增加了6.05%、8.54%;根体积及根系交叠数显著增加16.5%、23.2%;根系活力显著增加了298%;Vmax值显著增加了118%;低钾植株地上地下部干重与不添加相比显著提高了5.61%、28.6%;根系活力达到113μg/(g·h), FW,为无添加生长素时的3.3倍;根系ATPase活性相对增加了87.5%;根系钾浓度显著增加250%;钾离子通道基因NKT2在根系中表达量显著增加了7.04倍,Ntork1在根系及叶片中表达量显著降低了49.5%、72.5%。【结论】低钾胁迫影响烟草根系生长及植株对钾素的吸收累积,添加适当浓度外源生长素可改善植株根系生长发育状况,增加内流型钾离子通道基因NKT2、NtKC1的表达量,降低外流型钾离子通道基因Ntork1的表达量,且提高植株钾吸收动力学参数Vmax值、降低Km值,从而提高了植株对钾离子的吸收能力与亲和力,进而增加植株钾素浓度。     

干旱胁迫及复水对豌豆根系内源激素含量的影响

采用盆栽试验方法,研究了干旱胁迫及复水对豌豆根系脱落酸(ABA)、吲哚乙酸(IAA)、赤霉素(GA)和玉米素(ZT)等4种内源激素含量的影响.结果表明:不同程度的干旱胁迫均导致各生育期豌豆根系ABA和IAA含量增加,GA和ZT含量减少,且随干旱胁迫程度的加重变化量增大.同时对各生育期豌豆根系内源激素比例产生影响,对ZT与ABA、GA与ABA、GA与IAA、ZT与IAA比例影响较大,对ZT与GA、IAA与ABA比例影响较小.旱后复水可对各生育期豌豆根系内源激素含量产生补偿效应,其补偿量决定于豌豆生育时期、干旱胁迫强度和复水历时.同时促进各生育期豌豆根系内源激素比例发生变化.