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。     

丛枝菌根真菌生态功能及其与共生植物互作机理

丛枝菌根真菌是陆生植物根系广泛存在的一类真菌类群,并与宿主植物形成互惠共生体,在土壤生态环境中发挥着重要的生态作用和功能。从丛枝菌根提高宿主植物非生物胁迫(水、温度、盐碱和重金属等)抗性、生物胁迫(植物病害等)抗性以及改变宿主根际微生态等方面,对丛枝菌根真菌的生态作用、互作机理和研究热点进行了综述。     

烟草与丛枝菌根真菌的共生效应研究进展

丛枝菌根(Arbuscular mycorrhiza,AM)真菌是陆地生态系统中广泛存在的一类专性共生土壤微生物,是根系土壤区域中重要的功能菌群之一。AM真菌可侵染植物根系形成丛枝菌根共生体,改变植物根系形态和改善营养状况,从而提高宿主植物的生长发育、产量、质量和抗逆性。目前从烟草根系土壤分离报道的AM真菌已达13属54种,显示出烟草(Nicotiana tobacum L.)栽培的潜在AM真菌资源较为丰富。围绕烟草与AM真菌的共生效应,总结了影响AM真菌侵染和定殖烟草根系的主要因素,阐述了AM真菌对烟草生长、抗性生理及品质的影响,并对PGPR与AM真菌的协同作用进行了简要回顾,最后讨论了该领域存在的不足及今后展望;旨在为菌根技术运用于烟草栽培提供参考。     

土壤中丛枝菌根真菌对宿主植物磷吸收作用机制综述

由于贫瘠土壤不能供给植物足够磷素,而丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)在促进植物生长和吸收利用磷方面发挥着重要的作用。评述了国内外丛枝菌根真菌吸收土壤磷、根际环境与AMF共同作用对土壤磷的影响、AMF储磷机理、磷从菌丝到根系转移和植物吸收利用磷机制的研究进展,为今后应用AMF改善土壤肥力和深刻了解接菌土壤中磷的迁移转化规律奠定基础。     

丛枝菌根真菌(Glomus caledonium)对铜污染土壤生物修复机理初探

利用盆栽试验,研究了丛枝菌根真菌(Glomus.caledonium)在不同程度铜污染土壤上对玉米苗期生长的影响。结果表明,即使在土壤施铜量达150mg/kg时,菌根真菌对玉米仍有近55%的侵染率;接种菌根真菌,能显著促进玉米根系的生长。菌根玉米的根系生物量和根系长度,平均较未接种处理分别提高108.4%和58.8%;接种处理的植株地上部生物量达到每盆(3株)10.58g,显著高于不施铜的非菌根玉米。这些结果表明,丛枝菌根真菌对铜污染具有较好的抗性;并且由于菌根的形成,使宿主植物明显地改善了对磷的吸收和运输,并能通过抑制土壤酸化、降低土壤可溶态铜的浓度等机制,增强宿主植物对铜污染的抗(耐)性。在150mg/kg施铜水平时,与非菌根玉米相比,菌根玉米地上部和根系铜浓度分别降低24.3%和24.1%,吸铜量分别提高了28.2%和60.0%,表明菌根植物对铜污染土壤具有一定的生物修复作用。     

丛枝菌根与土壤修复

菌根是真菌与植物根系所建立的互惠共生体, 其中以丛枝菌根在自然界中分布最广。近年来,随着菌根研究的发展,丛枝菌根在土壤修复中的应用日益受到人们的关注。本文综述了丛枝菌根在土壤重金属污染、有机污染、放射污染以及土壤退化修复中的作用,并对当前研究中存在的问题和未来发展前景作了探讨。     

丛枝菌根真菌对镉污染土壤中黑麦草幼苗生长的影响

通过不同浓度的镉污染土壤接种丛枝菌根真菌的黑麦草盆栽试验,研究了丛枝菌根真菌对镉污染条件下黑麦草幼苗生长的影响。结果表明:重度镉污染(Cd2+:180 mg/kg)条件下,Glomus mosseae对黑麦草根系的侵染率仍达到30.23%,对黑麦草的生长有较好的促进作用;丛枝菌根在一定程度上缓解了镉污染对黑麦草株高、根长和生物量积累的抑制;镉污染显著降低黑麦草叶片的叶绿素含量,叶绿素a在重度镉污染时下降幅度最大,不接种丛枝菌根真菌的黑麦草较对照下降37.9%,而接种的黑麦草下降26.7%,接种菌根真菌在中重度镉污染条件下显著提高了黑麦草叶片的叶绿素含量;重度镉污染下接种和不接种的黑麦草根系活力都开始显著下降,但接种植株根系活力下降的幅度小于不接种植株。     

蚯蚓菌根互作对土壤酶活、 甘薯根系生长及养分吸收的影响

【目的】蚯蚓和丛枝菌根真菌处于不同的营养级,但在促进植物生长和提高土壤肥力等方面却都发挥着积极作用。单独对土壤微生物或土壤动物的研究较多,但对土壤微生物与土壤动物之间相互作用的研究很少。因此研究它们对土壤和植物生长的作用可为挖掘土壤生物的潜力和提高土壤生物肥力提供依据。【方法】采用盆栽试验,研究了蚯蚓(Eisenia fetida)与丛枝菌根真菌(Rhizophagus irregularis)互作对甘薯生长和养分吸收的影响。试验采用两因素完全随机试验设计,分为接种和不接种菌根真菌及添加和不添加蚯蚓。试验共4个处理: 不加菌根和蚯蚓(CK); 接种菌根真菌(AM); 添加蚯蚓(E); 添加蚯蚓和菌根真菌(E+AM),每个处理4次重复。调查了甘薯养分吸收、 根系形态及土壤养分变化,采用Canoco4.5软件对土壤生物与植物对应关系进行RDA (redundancy analysis)分析。【结果】接种菌根真菌显著提高了甘薯地上和地下部生物量(P0.05),而添加蚯蚓的处理仅提高了甘薯地上部生物量。同时添加蚯蚓和菌根的处理显著提高了甘薯地上地下部生物量,并且高于其他三个处理(P0.05)。与对照相比,接种菌根真菌显著提高了土壤磷酸酶活性(P0.01),增幅近一倍; 同时提高了土壤磷的植物有效性,土壤有效磷含量下降了30%左右。添加蚯蚓后土壤脲酶活性从5.45 mg NH+4-N/g显著增加到8.71 mg NH+4-N/g,土壤碱解氮的含量从5.82 mg/kg显著增加到6.89 mg/kg (P0.05)。RDA分析表明蚯蚓菌根互作对甘薯地上和地下部氮磷含量、 根表面积、 根体积、 根平均直径和根尖数均存在显著的正交互效应。蚯蚓菌根互作通过调控土壤酶和改变土壤养分有效性促进甘薯对土壤氮磷养分的吸收。【结论】蚯蚓(Eisenia fetida)通过调控土壤脲酶和碱性磷酸酶增加了土壤中氮磷的有效性从而促进甘薯地上部生长。丛枝菌根真菌(Rhizophagus irregularis)通过调控土壤磷酸酶和增加植株地上地下部吸磷量从而促进甘薯生长。添加蚯蚓或接种菌根真菌均能增加根系吸收面积和根体积从而促进甘薯对养分的吸收。蚯蚓和菌根真菌相互作用通过调控土壤酶和改变土壤养分有效性以及促进根系发育从而互补的促进甘薯养分吸收和生长。     

AM真菌与地上草食动物的互作及其对宿主植物的影响

丛枝菌根是自然生态系统中广泛存在的一种植物根系与菌根真菌的共生体.放牧是草原生态系统的一种重要生态学功能.目前,关于AM真菌和植物的关系,以及草食动物与植物的相互作用研究已经非常深入,但有关AM真菌-植物-草食动物的多重相互作用研究尚处于发展初期.本文从揭示AM真菌-植物-草食动物三者相互作用机理的角度出发,围绕动物采食作用对AM真菌的侵染、孢子群落组成的变化及其作用机理,丛枝菌根对动物采食行为的影响,以及植物个体与群落对二者共同作用的响应等方面,对AM真菌-植物-草食动物研究领域最新的成果进行综述,并在此基础上,提出AM真菌-植物-草食动物相互作用领域未来的研究方向.     

多胺对共生条件下丛枝菌根真菌及宿主植物生长发育的影响

为探讨多胺对共生条件下丛枝菌根真菌及其宿主植物生长发育的影响,本研究以丛枝菌根真菌(Gigaspora margarita)为试验材料,通过施用不同浓度的多胺(Polyamine,PA)及其生物合成抑制剂[Methylglyoxal bis(guanylhydrazone),MGBG]处理接种丛枝菌根真菌的葡萄微繁苗,研究共生培养条件下外源多胺及多胺合成抑制剂对丛枝菌根真菌孢子萌发、芽管菌丝及其宿主植物生长发育的影响.试验结果表明,共生培养条件下,一定浓度的外源PA对丛枝菌根真菌及其宿主植物的生长发育具显著促进作用,丛枝菌根真菌孢子数、菌丝长度、侵染率、丛枝丰富度及菌根化葡萄幼苗生长势均显著提高.MGBG则表现较强的抑制作用.且该抑制作用可被外源PA部分解除,证明外源多胺对菌根化葡萄微繁苗生长发育的促进作用是通过活化根系土壤中丛枝菌根真菌,促进微繁苗丛枝菌根共生体的良好发育,最大程度地发挥菌根化效应得以表现的.     

Additive and interactive effects of functionally dissimilar soil organisms on a grassland plant community

The productivity and diversity of plant communities are affected by soil organisms such as arbuscular mycorrhizal fungi (AMF), root herbivores and decomposers. However, it is unknown how interactions between such functionally dissimilar soil organisms affect plant communities and whether the combined effects are additive or interactive. In a greenhouse experiment we investigated the individual and combined effects of AMF (five Glomus species), root herbivores (wireworms and nematodes) and decomposers (collembolans and enchytraeids) on the productivity and nutrient content of a model grassland plant community as well as on soil microbial biomass and community structure. The effects of the soil organisms on productivity (total plant biomass), total root biomass, grass and forb biomass, and nutrient uptake of the plant community were additive. AMF decreased, decomposers increased and root herbivores had no effect on productivity, but in combination the additive effects canceled each other out. AMF reduced total root biomass by 18%, but decomposers increased it by 25%, leading to no net effect on total root biomass in the combined treatments. Total shoot biomass was reduced by 14% by root herbivores and affected by an interaction between AMF and decomposers where decomposers had a positive impact on shoot growth only in presence of AMF. AMF increased the shoot biomass of forbs, but reduced the shoot biomass of grasses, while root herbivores only reduced the shoot biomass of grasses. Interactive effects of the soil organisms were detected on the shoot biomasses of Lotus corniculatus, Plantago lanceolata, and Agrostis capillaris. The C/N ratio of the plant community was affected by AMF.In soil, AMF promoted abundances of bacterial, actinomycete, saprophytic and AMF fatty acid markers. Decomposers alone decreased bacterial and actinomycete fatty acids abundances but when decomposers were interacting with herbivores those abundances were increased. Our results suggests that at higher resolutions, i.e. on the levels of individual plant species and the microbial community, interactive effects are common but do not affect the overall productivity and nutrient uptake of a grassland plant community, which is mainly affected by additive effects of functionally dissimilar soil organisms.     

丛枝菌根真菌促进植物摄取土壤磷的作用机制

磷在土壤中易被固定沉淀,在植物磷利用率低的情况下,过度施肥会造成磷肥浪费,可能通过地表径流、地下水溶解等方式,造成水体富营养化产生面源污染,对人类生产生活造成较大影响。丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)和植物结合所形成的共生菌根可以显著增强植株对磷的吸收利用。通过AMF可以提高宿主植株对磷的吸收转运的特性,从AMF促进植株对磷元素的摄取机制、AMF促进植物磷摄取分子机理、AMF作用下根系分泌物对植株磷利用的影响与根际微生物对AMF磷元素利用的影响4个方面的研究进展进行分析总结。AMF可以通过改变宿主植株的根系形态和菌丝网络的形成,扩大植株对养分吸收范围;释放有机酸、磷酸酶和质子等根系分泌物改变土壤结构和理化性质,与根际微生物共同作用降解土壤中难溶性磷酸盐;诱导相关磷转运蛋白基因的特异性表达,提高植株对磷的转运能力而促进其吸收。     

蚯蚓与菌根提高玉米生长和氮磷吸收的互补效应

【目的】蚯蚓和丛枝菌根真菌处于不同的营养级,但在促进植物生长和提高土壤肥力等方面却都发挥着积极作用。研究蚯蚓菌根互作及其对玉米吸收土壤中的氮、磷养分的影响,可为提升土壤生物肥力及促进农业的可持续发展提供理论依据。【方法】本研究采用田间盆栽方式,以玉米为供试作物,研究蚯蚓(Eisenia fetida)与丛枝菌根真菌(Glomus intraradices)互作及其对玉米养分吸收的影响。试验设置P 25和175 mg/kg两个水平。每个磷水平进行接种与不接种菌根真菌以及添加与不添加蚯蚓,共8个处理。调查了玉米生长、养分吸收以及真菌浸染和土壤养分的有效性。【结果】两个磷水平下,蚯蚓和菌根在增加玉米地上部和根系生物量方面有显著正交互作用(P0.05)。接种菌根真菌的各处理显著增加了玉米的侵染率及泡囊丰度、根内菌丝丰度等菌根指标。同时添加蚯蚓和接种菌根真菌的处理(AM+E)显著提高了菌根的侵染率、菌丝密度、丛枝丰度和根内菌丝丰度但是泡囊丰度有所下降。两种磷水平下,AM+E处理玉米地上部和地下部含氮量和含磷量均显著高于其他三个处理。在低磷条件下,地上部氮磷总量的增加分别是添加蚯蚓和接菌的作用;而地下部磷总量的增加主要是菌根真菌的作用。在高磷条件下,单加蚯蚓显著增加玉米氮磷的总量,而接种菌根真菌对玉米氮磷吸收的影响未达显著性水平。在高磷条件下,单加蚯蚓的处理显著提高玉米地上地下部生物量(P0.05),而单接菌的处理效应不显著,蚯蚓菌根互作通过提高土壤微生物量碳、氮实现对玉米生长和养分吸收的调控。在低磷条件下,单接菌显著提高了玉米的生物量(P0.05),单加蚯蚓的处理具有增加玉米生物量的趋势。菌根真菌主要促进玉米对磷的吸收,蚯蚓主要矿化秸秆和土壤中的氮磷养分增加土壤养分的有效性,蚯蚓菌根互作促进了玉米根系对土壤养分的吸收并形成氮磷互补效应。【结论】无论在高磷还是低磷水平下,蚯蚓菌根相互作用都提高了玉米地上地下部生物量、氮磷吸收量同时提高了土壤微生物量碳、氮。蚯蚓菌根相互作用对植物生长的影响取决于土壤养分条件。在高磷条件下(氮相对不足),蚯蚓菌根互作通过调控土壤微生物量碳、氮调控玉米生长和养分吸收。低磷条件下,菌根主要发挥解磷作用,蚯蚓主要矿化秸秆和土壤中的氮素,蚯蚓和菌根互补调控土壤中氮、磷,从而促进植物的生长和养分吸收。     

Ring nematodes (Mesocriconema xenoplax) alter root colonization and function of arbuscular mycorrhizal fungi in grape roots in a low P soil

A reduction of arbuscules in roots of grapevines (Vitis vinifera) observed when ring nematodes were added to field microplots led to the hypothesis that nematode feeding suppresses arbuscules by competing for root carbohydrates. Support for this hypothesis was tested by growing ‘Pinot noir’ grapevines in a factorial experiment with three levels of initial nematode densities (0, 0.1, 1.0 nematodes g^?1 soil), two levels of light (full sun, 50% sun), and two levels of AMF (nonAMF, +AMF). Effects on plant growth were primarily driven by a light and AMF treatment interaction, such that low light increased stem dry matter accumulation at the expense of roots in +AMF vines only. Nematodes had only a minor influence on plant growth (leaf mass was reduced at the highest nematode density), but nematodes did not affect overall plant dry matter accumulation. Since nonAMF vines were severely limited by P and their growth was so poor, the impact of nematode and light treatments was further analyzed in +AMF plants only. Nematode populations, AMF colonization, and root carbohydrates were differentially affected by initial nematode density or light levels. Root biomass, and reducing sugar and starch concentrations in fine roots were reduced by low light, but the final nematode populations and arbuscule frequencies in roots were unaffected by light. Nematodes reduced arbuscules and starch concentrations in fine roots, but did not affect total colonization by AMF (hyphae, vesicles or arbuscules). Nematodes reduced plant P and K uptake at the highest density, and low light reduced Mg uptake. These findings are consistent with the hypothesis that ring nematodes suppress arbuscules in roots via competition for root carbohydrates. However, the lack of a treatment interaction between light and nematodes in our study suggests that ring nematode–AMF interactions in grape roots are controlled by more than competition for photosynthate.     

Root trait plasticity and plant nutrient acquisition in phosphorus limited soil

To overcome soil nutrient limitation, many plants have developed complex nutrient acquisition strategies including altering root morphology, root hair formation or colonization by arbuscular mycorrhizal fungi (AMF). The interactions of these strategies and their plasticity are, however, affected by soil nutrient status throughout plant growth. Such plasticity is decisive for plant phosphorus (P) acquisition in P‐limited soils. We investigated the P acquisition strategies and their plasticity of two maize genotypes characterized by the presence or absence of root hairs. We hypothesized that in the absence of root hairs plant growth is facilitated by traits with complementary functions, e.g., by higher root mycorrhizal colonization. This dependence on complementary traits will decrease in P fertilized soils. At early growth stages, root hairs are of little benefit for nutrient uptake. Regardless of the presence or absence of root hairs, plants produced average root biomass of 0.14 g per plant and exhibited 23% root mycorrhizal colonization. At later growth stages of maize, contrasting mechanisms with functional complementarity explained similar plant biomass production under P limitation: the presence of root hairs versus higher root mycorrhizal colonization (67%) favored by increased fine root diameter in absence of root hairs. P fertilization decreased the dependence of plant on specific root traits for nutrient acquisition. Through root trait plasticity, plants can minimize trade‐offs for developing and maintaining functional traits, while increasing the benefit in terms of nutrient acquisition and plant growth. The present study highlights the plasticity of functional root traits for efficient nutrient acquisition strategies in agricultural systems with low nutrient availability.     

Defoliation effects on Plantago lanceolata resource allocation and soil decomposers in relation to AM symbiosis and fertilization

Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.     

Earthworm (Aporrectodea trapezoides)–mycorrhiza (Glomus intraradices) interaction and nitrogen and phosphorus uptake by maize

The interactive impacts of arbuscular mycorrhizal fungi (AMF, Glomus intraradices) and earthworms (Aporrectodea trapezoides) on maize (Zea mays L.) growth and nutrient uptake were studied under near natural conditions with pots buried in the soil of a maize field. Treatments included maize plants inoculated vs. not inoculated with AMF, treated or not treated with earthworms, at low (25 mg kg⁻¹) or high (175 mg kg⁻¹) P fertilization rate. Wheat straw was added as feed for earthworms. Root colonization, mycorrhiza structure, plant biomass and N and P contents of shoots and roots, soil available P and NO₃⁻–N concentrations, and soil microbial biomass C and N were measured at harvest. Results indicated that mycorrhizal colonization increased markedly in maize inoculated with AMF especially at low P rate, which was further enhanced by the addition of earthworms. AMF and earthworms interactively increased maize shoot and root biomass as well as N and P uptake but decreased soil NO₃⁻–N and available P concentrations at harvest. Earthworm and AMF interaction also increased soil microbial biomass C, which probably improved root N and P contents and indirectly increased the shoot N and P uptake. At low P rate, soil N mobilization by earthworms might have reduced potential N competition by arbuscular mycorrhizal hyphae, resulting in greater plant shoot and root biomass. Earthworms and AMF interactively enhanced soil N and P availability, leading to greater nutrient uptake and plant growth.     

Effects of earthworms on above- and belowground herbivores

Earthworms affect plant performance and can influence plant–herbivore interactions. Both primary and secondary metabolites and the expression of stress-responsive genes of plants can be affected by earthworms. Plant-mediated effects of earthworms on aboveground herbivore performance range between positive and negative. These indirect, plant-mediated effects likely depend on the altered resource uptake of plants or changes in the soil microbial community composition in presence of earthworms. Studies on belowground interactions between earthworms and root herbivores focussed almost exclusively on root-feeding nematodes. These interactions can be either direct (e.g. ingesting of nematodes) or indirect, mediated by changes in host plant performance or biotic and abiotic soil characteristics. Earthworms were documented to counteract the negative effects of root-feeding nematodes on plants. Consistently, earthworm-worked soils (vermicompost) have been reported to reduce numbers of root-feeding nematodes and plant damage by aboveground herbivores. The results suggest context dependent impacts of earthworms on herbivore performance and an alleviation of herbivore damage of plants by earthworms, besides their well-known effects on plant growth. This knowledge is crucial for understanding the impact of earthworms on plants in natural environments, and may be applied as alternative plant protection in sustainable agriculture.     

Growth and Metal Accumulation of Mycorrhizal Sorghum Exposed to Elevated Copper and Zinc

Arbuscular mycorrhizal fungi (AMF) alter heavy metal acquisition by higher plants and may alter plant response to soil-contaminating heavy metals. Two communities comprised of Glomus intraradices and G. spurcum were investigated for their influence on copper (Cu) and zinc (Zn) resistance of Sorghum bicolor. One community was isolated from a Cu- and Zn-contaminated soil (AMF-C) and one consisted of isolates from non-contaminated soil (AMF-NC). Non-mycorrhizal (NM) sorghum plants were also included. The two community ecotypes differed in their capacity to protect sorghum from Cu and Zn toxicity and exhibited differential metal uptake into hyphae and altered heavy metal uptake by roots and translocation to plant shoots. AMF-C reduced Cu acquisition under elevated Cu conditions, but increased Cu uptake and translocation by sorghum under normal Cu conditions, patterns not exhibited by AMF-NC or NM plants. Hyphae of both fungal ecotypes accumulated high concentrations of Cu under Cu exposure. AMF-C exhibited elevated hyphal Zn accumulation and stimulated Zn uptake and translocation in sorghum plants compared to AMF-NC and NM plants. Differences in metal resistance between fungal treatments and between mycorrhizal and non-mycorrhizal plants were not related to differences in nutrient relations. The enhanced Cu resistance of sorghum and altered patterns of Cu and Zn translocation to shoots facilitated by AMF isolated from the metal-contaminated soil highlight the potential for metal-adapted AMF to increase the phytoremediation potential of mycotrophic plants on metal-contaminated environments.     

Mycorrhizal Symbioses of Cotton Grown on Sodic Soils:A Review from an Australian Perspective

The majority of terrestrial plants form some type of mycorrhizal symbiosis.This established symbiosis therefore exists in most commercially important crops, which includes cotton.Arbuscular mycorrhizal fungus(AMF) can colonise 50%–90% of cotton root length under field and controlled conditions.Mycorrhization improves growth and nutrient uptake(especially phosphorus) of cotton,particularly at the early growth stages.Mycorrhizal symbioses help plants to counter the stresses imposed by physical and chemical soil constraints; however, adverse environmental conditions may restrict the mycorrhizal associations and consequently may reduce nutrient uptake and impair plant growth.In Australia, cotton is mainly grown on sodic soils that contain more than 6% of the total cations as exchangeable sodium.High levels of sodium in the soil create adverse physical and chemical soil conditions that may negatively affect mycorrhizal symbioses of cotton.This review discusses the cotton mycorrhizal colonisation, plant growth, and disease protection effects, potential negative effects of physical and chemical properties of sodic soils, and influences of some agronomic management practices.In addition, the research gaps were identified and some practical applications of the research outcomes were suggested.