Improved observation of colonized roots reveals the regulation of arbuscule development and senescence by drought stress in the arbuscular mycorrhizae of citrus

Citrus is the typical mycorrhizal fruit tree species establishing symbiosis with arbuscular mycorrhizal (AM) fungi. However, arbuscule development and senescence in colonized citrus roots, especially in response to drought stress, remain unclear, which is mainly due to the difficulty in clearing and staining lignified roots with the conventional method. Here, we improved the observation of colonized roots of citrus plants with the sectioning method, which enabled the clear observation of AM fungal structures. Furthermore, we investigated the effects of one week of drought stress on arbuscule development and senescence with the sectioning method. Microscopy observations indicated that drought stress significantly decreased mycorrhizal colonization (F%and M%) although it did not affect plant growth performance. Fluorescence probes (WGA 488 and/or Nile red) revealed that drought stress inhibited arbuscule development by increasing the percentage of arbuscules at the early stage and decreasing the percentages of arbuscules at the midterm and mature stages. Meanwhile, drought stress accelerated arbuscule senescence, which was characterized by the increased accumulation of neutral lipids. Overall, the sectioning method developed in this study enables the in-depth investigation of arbuscule status, and drought stress can inhibit arbuscule development but accelerate arbuscule senescence in the colonized roots of citrus plants. This study paves the way to elaborately dissecting the arbuscule dynamics in the roots of fruit tree species in response to diverse abiotic stresses.

Efficacy of Mycorrhizae Based Manure on the Vegetative Growth of Rice Grown within Bauchi State, Nigeria

Background: Rice is one of the staple crops in the African continent for its ability to give maximum yields which can help to achieve food security under the sustainable development goals (SDGs);to those effects, the incessant use of inorganic fertilizer has been employed which proved to have devastating effect in the environment and the ecosystem at large. Therefore, the thirst for an alternative method to ensure bumper production of rice cannot be overemphasized so as to prevent soil alteration and environmental damage. Objective: This study aimed at determining the efficacy of mycorrhizae-based manure on the vegetative growth of rice as compared to inorganic fertilizer and its sustainability. Methods: Soil samples were collected from seven (7) locations (M1 - M7). Mycorrhiza were isolated from the soils and mass produced, mixed with organic waste to form manure (biofertilizer) and were applied at concentrations of 50 g, 100 g and 150 g to the potted rice in tree (3) replicates. Growth parameters observed were plant height, girth diameter, leaf broadness and leaf number. Results: The result revealed mycorrhizal spore count ranging from 1.7 × 107 - to 4.1 × 107 across the locations. The mycorrhizae-based manure gives the highest plant height of 45.33 cm as compared with the least plant height of 18.5 cm from the inorganic fertilizer. Furthermore, the biofertilizer gives a positive influence on the other parameters observed in comparison with the inorganic fertilizer. Statistical analysis shows that, the means of all the parameters except for leaf numbers were significantly different at p ≤ 0.05 across the sampling locations. Conclusions: Mycorrhizae-based manure proves to be an effective replacement of inorganic fertilizer that can boost rice production at a cheaper cost.

A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy(MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal(AM) and ectomycorrhizal(ECM) trees, and established eighteen20 m×20 m plots in each rainforest. Six nitrogen(N) and phosphorus(P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon(C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall,distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily in an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECMdominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECMdominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

菌根共生体及其在生态系统中的功能概述

菌根是土壤中的菌根菌与植物根系形成的互惠共生体,在地球化学循环,特别是碳循环方面扮演着重要角色。本文综述了菌根的类型及其对植物群落多样性、生态系统生物地球化学循环的影响,尤其介绍了其对碳固定和碳排放的意义,以期为中学生物学教学中关于菌根在生态系统中的功能及其对碳中和的作用提供参考资料。

广西金花茶根系丛枝菌根真菌染色方法探讨

金花茶(Camellia nitidissima)为山茶科山茶属植物,属于国家一级保护植物,具有很高的观赏价值及药用价值。但目前金花茶野生资源少,因此寻找高效的人工种植方法快速繁殖金花茶优良种苗,进而大幅度提高规模化种植金花茶的产量十分必要。丛枝菌根(arbuscular mycorrhiza,AM)真菌能显著促进植物生长发育、提高作物产量、增强植物抗逆性和抗病性,金花茶接种AM真菌,对金花茶有积极的影响。由于几乎所有的AM真菌接种试验均涉及菌根发育状况观察与侵染率测定,而目前AM侵染状况的观察测定方法种类繁多,良莠不齐,因此本研究探究一种金花茶根系AM真菌检测的最佳染色方法,以便更好地观察AM真菌对金花茶根系的侵染情况。本研究以金花茶健康植株根系为试验材料,探讨5种染色剂(苏丹红Ⅳ、酸性品红、苯胺蓝、台酚蓝、醋酸墨水)对金花茶根系AM真菌的染色效果。研究表明:5%醋酸墨水染色液的染色效果最佳,根皮层细胞内AM真菌的菌丝、泡囊、孢子等结构清晰可见,且能够明确分辨AM真菌与其他未知真菌,根的染色效果可以长久保存;利用苏丹红Ⅳ和酸性品红染色的AM真菌菌丝、泡囊与背景反差不明显,而且酸性品红的染色效果保存时间短,不利于观察;苯胺蓝和台酚蓝的染色效果略次于醋酸墨水,且价格昂贵,成本高。除醋酸墨水外,其他4种染色剂均是疑似致癌物,长期使用对操作人员的健康产生非常大的安全隐患。醋酸墨水染色操作简便、毒性低、成本低廉、染色效果极佳,适用于金花茶根系AM真菌的染色和制片观察。本研究结果可为今后金花茶菌根种苗的应用提供新的思路。

设施蔬菜土壤丛枝菌根真菌多样性及群落构建的季相变化

为研究设施生态系统丛枝菌根(Arbuscularmycorrhiza,AM)真菌群落变化的关键驱动过程,采集设施番茄不同生长季(休耕、花期、果期)土壤样品,利用IlluminaMiSeq高通量测序技术分析AM真菌物种和谱系多样性及群落结构变化特征,并结合群落谱系分析方法探讨不同生长季随机性过程和确定性过程之间的相对贡献。结果表明,不同生长季AM真菌的物种多样性和谱系多样性均发生显著改变:相比于休耕期,番茄生育期(花期、果期)土壤中AM真菌丰富度、Shannon多样性、Pielou均匀度、谱系多样性(PD)和平均成对谱系距离(MPD)分别显著下降了42.82%~59.18%、43.25%~48.31%、17.46%~25.40%、57.14%~67.86%和50.00%;除球囊霉属相对多度显著增加,近明球囊霉属和类球囊霉属相对多度均显著下降,原囊霉属相对多度先增加后降低。置换多元方差分析(PERMANOVA)和非度量多维度分析(NMDS)结果表明休耕期基于物种组成和谱系组成的AM真菌群落结构显著差别于番茄生育期,但花期和果期之间差异不显著。谱系分析结果显示,休耕期净亲缘关系指数NRI=0,表明AM真菌在谱系结构上是随机的,花期和果期NRI>0,表明谱系聚集,暗示了AM真菌群落构建由随机性过程主导向确定性过程主导的转变,中性群落模型(NCM)结果也支持该推断。Mantel检验结果显示,土壤pH、养分(有机碳、全量氮磷钾和有效磷)、盐分含量以及土壤温湿度作为确定性因素显著影响AM真菌群落的季相变化。综上所述,设施生态系统高集约化生产方式促进了AM真菌群落构建从随机性过程主导向确定性过程主导转变,导致多样性降低和群落结构变化,研究结果对揭示设施蔬菜栽培条件引起的土壤质量退化及其过程中的微生物组演变规律具有重要意义。

氮沉降对4个树种外生菌根群落结构和酶活性功能的影响

【目的】氮沉降水平不断上升对森林生态系统产生了不同程度的影响。过量的有效氮输入导致植物根系对养分获取策略发生变化,从而改变了土壤重要微生物,如树木根系外生菌根ECM群落的结构和生态功能。了解和确定森林主要树种根系微生物群落活动受氮沉降影响的变化阈值,对于研究森林养分循环特征和可持续经营管理具有重要的指导意义。【方法】采用室内盆栽试验,选取马尾松、华山松、湿地松和火炬松4个树种进行5个梯度的氮施加(0、15、30、60、150 kg·hm^(-2)·a^(-1)),通过检测树苗的养分含量、ECM根尖酶活性,以及提取鉴定DNA,分析不同松树在氮沉降水平下外生菌根群落结构和酶活性功能的动态变化。【结果】1)大多数松科树苗的菌根胞外酶活性在氮浓度30 kg·hm^(-2)·a^(-1)时达到了阈值;以分解纤维素为主的G酶在华山松、湿地松和火炬松中随着N浓度增加而持续提高,即便施氮水平达到当地氮沉降水平的10倍(150 kg·hm^(-2)·a^(-1)),酶活性仍未达到阈值;2)对菌根群落进行分析得出,棉革菌属Tomentella在4个树种中都为优势物种,而须腹菌属Rhizopogon、深色内隔菌Phialocephala会因宿主不同呈现不同的侵染丰度;3)华山松和火炬松的ECM菌根群落酶活性在不同氮浓度间无明显差异,即呈现生态冗余。【结论】在长期氮输入水平升高的情况下,ECM群落组成会因宿主植物和氮沉降水平的变化发生调整,而这一过程中会以变化阈值作为判断标准,该过程对于土壤养分循环中碳氮磷循环以及森林经营管理具有重要的指导意义。

两种丛枝菌根真菌定殖青山杨后对舞毒蛾的抗性研究

【目的】研究丛枝菌根真菌(AMF)对青山杨抗虫性的影响以及舞毒蛾对AMF定殖青山杨的适应能力,为AMF定殖青山杨后抗虫性的研究提供科学依据。【方法】分别以对照(CK,无AMF定殖)、根内根孢囊霉(GI)或摩西管柄囊霉(GM)定殖的青山杨叶片饲喂舞毒蛾幼虫,统计3、4、5龄幼虫的体重、体长、头壳宽和食物利用率,测定4、5龄幼虫解毒酶酸性磷酸酯酶(ACP)和碱性磷酸酯酶(AKP)的活性。【结果】GI组3、4龄幼虫的体重显著高于对照组(P<0.05),5龄与对照组差异不显著,GM组5龄幼虫的体长、体重、头壳宽、食物利用率均显著高于对照组。GI组3龄幼虫取食量显著高于对照组(P<0.05),4、5龄显著低于对照组,GM组5龄显著高于对照组,3、4龄与对照组差异不显著。GI组ACP显著低于对照组(P<0.05),AKP在4龄显著高于对照组,5龄AKP活性显著低于对照组。GM组两种解毒酶活性均显著高于对照组。【结论】GI定殖的青山杨能促进舞毒蛾低龄幼虫的生长,对舞毒蛾老熟幼虫的生长影响不显著。GM定殖青山杨叶片促进了舞毒蛾幼虫的生长发育,提高了食物的利用效率,激发了幼虫体内磷酸酯酶活性,表明舞毒蛾对GM定植的青山杨有更好的适应性。AMF对树木及植食性昆虫的影响具有种类特异性,GI定殖对青山杨的抗虫性的影响呈中性,GM定殖对青山杨的抗舞毒蛾产生负效应。

不同AMF菌肥对桑树“嘉陵30”生长和叶品质的影响

“嘉陵30”是我国西南地区大面积推广种植的优质果叶两用桑树(Morus alba)品种,为了研究不同丛枝菌根真菌(AMF)菌肥对其生长和桑叶品质的影响,实验添施了5种AMF菌肥,并比较桑树植株的色素含量、生长发育和叶片品质在施加前后的差异,以此筛选出适合“嘉陵30”的最佳菌肥。结果显示:(1)色素含量方面,与对照相比,施加隐类球囊霉(Paraglom occultum)菌肥的植株叶绿素b、总叶绿素和类胡萝卜素含量均显著增加,分别提高30.00%、21.96%和21.35%。(2)生长发育方面,与对照相比,施加隐类球囊霉菌肥的植株株高、基径、叶面积、叶干重、茎干重、总干重均显著增加,分别提高50.32%、21.06%、31.68%、27.25%、98.39%和39.01%。(3)叶片品质方面,与对照组相比,施加根内球囊霉(Glomus intraradices)的植株叶C、N、粗蛋白以及总氨基酸含量均显著增加,分别提高4.07%、3.94%、4.51%和7.14%,而生物碱显著降低64.30%。上述结果表明,施加隐类球囊霉菌肥在促进植株生长发育和增加生物量的积累方面效果最佳,而施加根内球囊霉菌肥在提高桑叶品质方面效果更好。

不同种植年限苜蓿地球囊霉素相关土壤蛋白含量及其影响因素

球囊霉素相关土壤蛋白(GRSP)是丛枝菌根真菌(AMF)分泌的一种糖蛋白,有利于土壤团聚体形成。本研究借助于黄土高原半干旱区的长期定位试验,以不同建植年限(L2019、L2012、L2003)紫花苜蓿(Medicago sativa)草地为研究对象,玉米(Zea mays)田为对照,研究GRSP含量的主要调控因子及其与土壤有机碳和团聚体结构特征的关系。结果表明,随苜蓿种植年限增加,AMF丰度(侵染率、菌丝密度)和GRSP含量显著提高(P<0.05),线性回归分析结果表明,总提取球囊霉素相关土壤蛋白(T-GRSP)含量与土壤有机碳和微生物生物量碳之间显著正相关(P<0.05),而易提取球囊霉素相关土壤蛋白(EE-GRSP)和总提取球囊霉素土壤蛋白含量均与水稳性团粒特征平均重量直径(MWD)和大于0.25 mm的团聚体含量(R0.25)之间显著正相关(P<0.05),冗余分析(RDA)结果表明,影响土壤AMF丰度和GRSP含量的主要环境因子是土壤速效磷(P=0.002)和微生物量碳(P=0.002)。与农田相比,T-GRSP含量在土壤有机碳中的比例随苜蓿种植年限的增加而提高,说明持续多年种植苜蓿引起GRSP含量增加,促进GRSP含量在土壤有机碳中的积累,提高了GRSP含量对土壤团聚体稳定性和有机碳的贡献。该研究结果可为黄绵土GRSP研究及紫花苜蓿栽培草地可持续利用提供理论依据。

基于Meta分析菌根菌对植物叶片生理的影响

叶片作为植物的重要器官,其养分、光合色素、可溶性糖、可溶性蛋白等含量,以及各种酶活性都是表征其生理的重要参数;而光合作用、蒸腾作用则是叶片重要的生理活动指标。菌根菌是一类与绝大多数植物形成共生的土壤微生物,能够影响叶片生理。本研究选择分布最广泛的丛枝菌根菌(arbuscular mycorrhizal fungi, AMF),针对以往大多数研究只关注单一植物接种AMF探究其生理功能的问题,采用Meta分析(Meta-analysis)的定量研究方法,对152篇相关文献整理建库,评估了AMF对植物叶片生理的影响,探究了不同分类水平上AMF的效应。结果表明:AMF显著提高了叶片氮、磷、钾、钙、镁和锌含量,提高了12.6%~26.3%;增加了叶绿素、叶绿素a和叶绿素b含量,分别增加了16.3%、12.1%和11.1%;对可溶性糖和可溶性蛋白则分别提升了34.8%和18.4%;同时,AMF提高了叶片各种酶活性,分别为过氧化物酶31.3%、超氧化物歧化酶17.8%、过氧化氢酶23.3%、多酚氧化酶59.1%、苯丙氨酸解氨酶65.3%;AMF提高了叶片的净光合速率(27.7%)和蒸腾速率(31.1%)。表明AMF因分类(科、属、种)不同,对叶片生理的影响也存在差异。本研究系统评价了AMF对叶片生理的影响,丰富了AMF的功能多样性理论,为筛选改善叶片生理的高效AMF提供了切实的依据。

铝对马尾松菌根化幼苗抗逆生理和根尖细胞超微结构的影响

[目的]不同Al^(3+)水平下,研究马尾松菌根/非菌根幼苗的生理、根尖细胞超微结构的变化以及Al的亚细胞分布,分析菌根化苗木对铝的响应及其耐铝性,为外生菌根真菌提高寄主植物耐铝性和育苗造林应用提供理论依据。[方法]以半年生菌根和非菌根马尾松苗为材料,采用砂培盆栽浇铝法,分别设置0、0.2、0.4、0.8mmol·L^(-1) Al^(3+)(AlCl_(3))处理,分析其根系抗氧化酶活性和MDA含量等生理指标变化,Al的亚细胞分布,通过组织染色观察根尖ROS和MDA分布,并观察根尖超微结构变化。[结果](1)随外源[Al^(3+)]的升高,马尾松菌根/非菌根苗根系SOD、CAT、POD活性和MDA含量均呈总体上升趋势,在高铝(0.8 mmol·L^(-1))水平时,抗氧化酶活性和MDA含量最大,且非菌根苗受到铝的影响程度更大;(2)随外源[Al^(3+)]的升高,马尾松根尖吸收的铝含量显著增加,且菌根苗吸收的铝含量显著高于非菌根苗;(3)从细胞超微结构和Al的亚细胞分布看,大量Al^(3+)首先与细胞壁结合,细胞内的Al^(3+)与生物膜强烈结合,使细胞器物质向外渗漏作用加强,干扰细胞核和线粒体等的各种调节过程。而由于菌根对铝的吸附作用,降低了侵入细胞内的铝离子含量,保护亚细胞器结构的同时也维持了细胞的基本功能,从而缓解铝毒性。[结论]铝处理使马尾松根系抗氧化酶活性和MDA含量增加,0.4 mmol·L^(-1)以上的铝浓度产生明显铝毒害症状。而菌根可以通过吸收更多的铝降低铝毒害,并提高植物耐铝能力,这很可能是马尾松菌根苗的一个重要外部抗性机制。

种植方式和菌根类型对吸收根性状的影响

[目的]通过分析种植方式对两种菌根类型树种吸收根性状的影响,揭示物种共存的适应条件。[方法]本研究选择8个树种(5个AM树种和3个EM树种)的单种和所有树种混种的样地,分析不同种植方式(单种vs混种)下两类型菌根(AM vs EM)树种吸收根(1~2级根)的主要形态性状(根直径、比根长、根组织密度、单根长)和构型性状(根分支强度、根分支比)及菌根侵染率的差异。[结果]菌根类型极显著影响吸收根的形态和构型性状(p<0.001),显著影响菌根侵染率(p<0.05);种植方式仅显著影响吸收根的组织密度和根构型性状(p<0.05);菌根类型和种植方式对所有性状均无交互影响(p>0.05)。AM树种根性状间的相关程度高于EM树种,混种大幅度降低AM树种根性状间的相关性。混种降低AM树种根形态性状的可塑性(比根长除外),增大其构型性状的可塑性;混种降低EM树种根组织密度的可塑性,增大根直径、构型性状及侵染率的可塑性。[结论]AM和EM树种的根形态和构型性状均有显著差异。混种对AM和EM树种根性状的可塑性有不同程度的影响,主要增大AM树种的分支强度,降低EM树种的根组织密度。可见,不同菌根树种可以通过调节不同根性状变化来实现物种共存。

丛枝菌根对植物叶片δ^(15) N含量影响的数据挖掘分析

为明确丛枝菌根(AM)对植物叶片稳定氮同位素(δ^(15)N)含量的影响,探索丛枝菌根在调控植物应对全球变化方面的重要功能,通过数据挖掘,建立了AM植物和非AM(non-AM)植物叶片δ^(15)N含量数据库,探究了AM对植物叶片δ^(15)N含量的影响。结果表明:AM植物叶片δ^(15)N含量为0.86‰,显著高于non-AM植物叶片的0.50‰。丛枝菌根针对不同植物功能群而言,将植物的AM状况与植物的固氮状况和生长周期结合作为影响因素时,AM都显著影响着植物叶片的δ^(15)N含量。虽然AM没有显著提高固氮植物叶片δ^(15)N含量,但却把非固氮植物叶片δ^(15)N的含量从0.58‰提高到了0.99‰。AM使多年生植物叶片δ^(15)N含量的增加最显著,从0.49‰增加到了0.82‰。可见,丛枝菌根作为与植物长期共生进化的最广泛共生体,对植物叶片δ^(15)N含量有不同程度的影响。

旱作区农田土壤AM真菌对长期有机无机施肥的响应

AM真菌群落动态变化对于长期有效的土壤生态系统管理非常重要。为揭示旱作区农田土壤丛枝菌根(AM)真菌对长期有机、无机培肥管理的响应机制,利用单因素随机区组设计,基于连续11年的定位试验及高通量测序方法,研究了不施肥(T0)、长期单施化肥(T1)、长期化肥与牛粪有机肥(T2)和长期化肥与羊粪有机肥(T3)对土壤的影响,比较了土壤AM真菌群落组成及多样性间的差异,探究了驱动土壤AM真菌群落组成及多样性变化的土壤环境因子及其相互作用效应。结果表明:随培肥时间延长,与T0处理相比,T2、T3处理的土壤全氮、有机质含量显著增加,pH显著下降(P<0.05);与2018年相比,2021年的T0、T1和T3处理土壤全磷和速效钾含量显著下降。有机无机肥配施下,球囊霉属(Glomus)和类球囊霉属(Paraglomus)是土壤AM真菌的优势属,但近明球囊霉属(Claroideoglomus)的相对丰度显著下降,从优势属变为非优势属。近明球囊霉属较球囊霉属和类球囊霉属相对丰度而言,更容易受长期培肥影响而发生显著改变。连续有机无机肥配施到2018年后,T2、T3处理的土壤近明球囊霉属和两性球囊霉属(Ambispora)的相对丰度与T0间有显著差异(P<0.05);培肥至2021年后,T2、T3处理土壤近明球囊霉属和两性球囊霉属的相对丰度与T0处理间无显著差异。随培肥时间延长,不同处理间土壤AM真菌群落的α多样性差异消失。NMDS分析结果表明:长期培肥改变了土壤AM真菌群落的β多样性,但T2与T3处理间土壤AM真菌群落相似性较一致。连续培肥改变了土壤AM真菌群落结构组成和多样性,驱动AM真菌群落变化的土壤环境因子由土壤全氮、pH转变为土壤全磷。长期有机无机培肥没有同步提升土壤全磷、速效钾等主要理化性状。随培肥年限增加,驱动土壤AM真菌群落结构和多样性变化的土壤因子发生了显著改变,AM真菌群落会随土壤环境因子的变化倾向于更加敏感的驱动因子。

Arsenic uptake by arbuscular mycorrhizal maize (Zea mays L.) grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal （AM） fungus （Glomus mosseae） and phosphorus （P） addition （100 mg/kg soil） on arsenic （As） uptake by maize plants （Zea mays L.） from an As-contaminated soil were examined in a glasshouse experiment. Non-mycorrhizal and zero-P addition controls were included. Plant biomass and concentrations and uptake of As, P, and other nutrients, AM colonization, root lengths, and hyphal length densities were determined. The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium. Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments, but shoot and root biomass of AM plants was depressed by P application. AM fungal inoculation decreased shoot As concentrations when no P was added, and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition, respectively. Shoot and root uptake of P, Mn, Cu, and Zn increased, but shoot Fe uptake decreased by 44.6%, with inoculation, when P was added. P addition reduced shoot P, Fe, Mn, Cu, and Zn uptake of AM plants, but increased root Fe and Mn uptake of the nonmycorrhizal ones. AM colonization therefore appeared to enhance plant tolerance to As in low P soil, and have some potential for the phytostabilization of As-contaminated soil, however, P application may introduce additional environmental risk by increasing soil As mobility.

Effects of metal lead on growth and mycorrhizae of an invasive plant species (Solidago canadensis L.)

It is less known whether and how soil metal lead （Pb） impacts the invasion of exotic plants. A greenhouse experiment was conducted to estimate the effects of lead on the growth and mycorrhizae of an invasive species （Solidago canadensis L.） in a microcosm system. Each microcosm unit was separated into HOST and TEST compartments by a replaceable mesh screen that allowed arbuscular mycorrhizal （AM） fungal hyphae rather than plant roots to grow into the TEST compartments. Three Pb levels （control, 300, and 600 mg/kg soil） were used in this study to simulate ambient soil and two pollution sites where S. canadensis grows. Mycorrhizal inoculum comprised five indigenous arbuscular mycorrhizal fungal species （ Glomus mosseae, Glomus versiform, Glomus diaphanum, Glomus geosporum, and Glomus etunicatum）. The ^15N isotope tracer was used to quantify the mycorrhizally mediated nitrogen acquisition of plants. The results showed that S. canadensis was highly dependent on mycorrhizae. The Pb additions significantly decreased biomass and arbuscular mycorrhizal colonization （root length colonized, RLC%） but did not affect spore numbers, N （including total N and ^15N） and P uptake. The facilitating efficiency of mycorrhizae on nutrient acquisition was promoted by Pb treatments. The Pb was mostly sequestered in belowground of plant （root and rhizome）. The results suggest that the high efficiency of mycorrhizae on nutrient uptake might give S. canadensis a great advantage over native species in Pb polluted soils.

The role of arbuscular mycorrhiza on change of heavy metal speciation in rhizosphere of maize in wastewater irrigated agriculture soil

To understand the roles of mycorrhiza in metal speciation in the rhizosphere and the impact on increasing host plant tolerance against excessive heavy metals in soil, maize(Zea mays L.) inoculated with arbuscular mycorrhizal fungus(Glomus mosseae) was cultivated in heavy metal contaminated soil. Speciations of copper, zinc and lead in the soil were analyzed with the technique of sequential extraction. The results showed that,in comparison to the bolked soil, the exchangeable copper increased from 26% to 43% in non-infected and AM-infected rhizoshpere respectively; while other speciation (organic, carbonate and Fe-Mn oxide copper) remained constant and the organic bound zinc and lead also increased but the exchangeable zinc and lead were undetectable. The organic bound copper, zinc and lead were higher by 15%, 40% and 20%, respectively, in the rhizosphere of arbuscular mycorrhiza infected maize in comparison to the non-infected maize. The results might indicate that mycorrhiza could protect its host plants from the phytotoxicity of excessive copper, zinc and lead by changing the speciation from bio-available to the non-bio-available form. The fact that copper and zinc accumulation in the roots and shoots of mycorrhia infected plants were significantly lower than those in the non-infected plants might also suggest that mycorrhiza efficiently restricted excessive copper and zinc absorptions into the host plants. Compared to the non-infected seedlings, the lead content of infected seedlings was 60% higher in shoots. This might illustrate that mycorrhiza have a different mechanism for protecting its host from excessive lead phytotoxicity by chelating lead in the shoots.

Interacted Effect of Arbuscular Mycorrhizal Fungi and Polyamines on Root System Architecture of Citrus Seedlings

Either arbuscular mycorrhizal fungi （AMF） or polyamines （PAs） may change root system architecture （RSA） of plants, whereas the interaction of AMF and PAs on RSA remains unclear. In the present study, we studied the interaction between AMF （Paraglomus occultum） and exogenous PAs, including putrescine （Put）, spermidine （Spd） and spermine （Spin） on mycorrhizal development of different parts of root system, plant growth, RSA and carbohydrate concentrations of 6-m-old citrus （Citrus tangerine Hort. ex Tanaka） seedlings. After 14 wk of PAs application, PA-treated mycorrhizal seedlings exhibited better mycorrhizal colonization and numbers of vesicles, arbuscules, and entry points, and the best mycorrhizal status of taproot, first-, second-, and third-order lateral roots was respectively found in mycorrhizal seedlings supplied with Put, Spd and Spm, suggesting that PAs might act as a regulated factor of mycorrhizal development through transformation of root sucrose more into glucose for sustaining mycorrhizal development. AMF usually notably increases RSA traits （taproot length, total length, average diameter, projected area, surface area, volume, and number of first-, second-, and third-order lateral roots） of only PA-treated seedlings. Among the three PA species, greater positive effects on RSA change and plant biomass increment of the seedlings generally rank as Spd〉Spm〉Put, irrespective of whether or not AMF colonization. PAs significantly changed the RSA traits in mycorrhizal but not in non-mycorrhizal seedlings. It suggests that the application of PAs （especially Spd） to AMF plants would optimize RSA of citrus seedlings, thus increasing plant growth （shoot and root dry weight）.

Effect of Humic Acid, Mycorrhiza Inoculation, and Biochar on Yield and Water Use Efficiency of Flax under Newly Reclaimed Sandy Soil

In order to examine the application of different soil and foliar organic fertilizers as well as biofertilizing flax under sandy soil conditions, two field experiments were carried out at the Research and Production Station of the National Research Centre (NRC), Al Nubaria district, El-Behaira Governorate, Egypt during 2012/2013 and 2013/2014 winter seasons. The trials aimed to study the effect of humic acid (HA) as low cost natural fertilizer, inoculation with mycorrhiza, and biocharcoal on on yield, quality and water use efficiency of flax variety (Amon) under newly reclaimed sandy soil. The treatments consisted of HA (25 kg/feddan), inoculation with mycorrhiza (1 kg/ feddan), and biochar (4 tons/feddan) and all the combinations among the treatments. Results showed that the treatment combination of (humic acid + mycorrhiza + biochar) was significantly superior compared to all the other treatments in number of capsules/plant, biological yield/plant (g), seed yield/plant (g), seed yield (kg/feddan), straw yield (tons/feddan), oil percent (%), and oil yield (kg/feddan). However, it gave the highest fruiting zone length (cm) but not significantly different from (mycorrhiza + biochar) and (humic acid + biochar), also it gave the highest seed index (g) but not significantly different from humic acid and (humic acid + mycorrhiza). The treatment combination of (humic acid + biochar) gave the highest plant height (cm), technical stem length (cm), and number of branches/plant.