Selection of efficient VA mycorrhizal fungi

Summary A procedure is described for selection and screening of VA mycorrhizal fungi in pot and field trials. The VA mycorrhizal fungi from 20 farm paddocks with unexpectedly high pasture production were compared withGlomus fasciculatus for ability to stimulate plant growth. The fungi from three soils (F4, F11, and F20) which were 84–142% more effective thanG. fasciculatus at stimulating growth in sterilised soils were then tested for ability to stimulate clover growth in unsterilised soils in pots, and in the field. F4, F11 and F20 were more efficient thanG. fasciculatus and the indigenous mycorrhizal fungi in all except one field soil.     

红壤中VA菌根真菌侵染力及接种效应的研究

本文报道了丘陵地区发育于第四纪红色粘土母质的马尾松林自然植被下红壤、栽种胡枝子的两种侵蚀红壤及花生-油菜轮作的耕作红壤等3种生态条件下的土壤中VA菌根真菌繁殖体数量、种类、侵染势、施用石灰石粉改土和增施磷肥对VA菌根真菌侵染的影响以及VA菌根真菌的接种效应.试验结果表明,3种生态条件下的土壤中VA菌根真菌繁殖体数量和侵染势显然不同:马尾松林自然植被下的红壤中VA菌根真菌繁殖体数量大,侵染迅速;花生-油菜轮作的耕作红壤VA菌根真菌繁殖体数量也大,但侵染缓慢,有明显的滞后期;栽种胡枝子的侵蚀红壤VA菌根真菌繁殖体数量小,侵染力很低.对侵蚀红壤与耕作红壤接种VA菌根真菌,显著提高了VA菌根的侵染率,在适当施用磷肥及施石灰石粉改土后,都能促进VA菌根侵染,从而增加了植物的吸磷量,植物生长量显著提高.     

红壤中VA菌根真菌侵染力及接种效应的研究

本文报道了丘陵地区发育于第四纪红色粘土母质的马尾松林自然植被下红壤、栽种胡枝子的两种侵蚀红壤及花生-油菜轮作的耕作红壤等3种生态条件下的土壤中VA菌根真菌繁殖体数量、种类、侵染势、施用石灰石粉改土和增施磷肥对VA菌根真菌侵染的影响以及VA菌根真菌的接种效应。试验结果表明,3种生态条件下的土壤中VA菌根真菌繁殖体数量和侵染势显然不同:马尾松林自然植被下的红壤中VA菌根真菌繁殖体数量大,侵染迅速;花生-油菜轮作的耕作红壤VA菌根真菌繁殖体数量也大,但侵染缓慢,有明显的滞后期;栽种胡枝子的侵蚀红壤VA菌根真菌繁殖体数量小,侵染力很低。对侵蚀红壤与耕作红壤接种VA菌根真菌,显著提高了VA菌根的侵染率,在适当施用磷肥及施石灰石粉改土后,都能促进VA菌根侵染,从而增加了植物的吸磷量,植物生长量显著提高。     

Relatedness among arbuscular mycorrhizal fungi drives plant growth and intraspecific fungal coexistence

Arbuscular mycorrhizal fungi (AMF) form symbioses with most plant species. They are ecologically important determinants of plant growth and diversity. Considerable genetic variation occurs in AMF populations. Thus, plants are exposed to AMF of varying relatedness to each other. Very little is known about either the effects of coexisting AMF on plant growth or which factors influence intraspecific AMF coexistence within roots. No studies have addressed whether the genetics of coexisting AMF, and more specifically their relatedness, influences plant growth and AMF coexistence. Relatedness is expected to influence coexistence between individuals, and it has been suggested that decreasing ability of symbionts to coexist can have negative effects on the growth of the host. We tested the effect of a gradient of AMF genetic relatedness on the growth of two plant species. Increasing relatedness between AMFs lead to markedly greater plant growth (27% biomass increase with closely related compared to distantly related AMF). In one plant species, closely related AMF coexisted in fairly equal proportions but decreasing relatedness lead to a very strong disequilibrium between AMF in roots, indicating much stronger competition. Given the strength of the effects with such a shallow relatedness gradient and the fact that in the field plants are exposed to a steeper gradient, we consider that AMF relatedness can have a strong role in plant growth and the ability of AMF to coexist. We conclude that AMF relatedness is a driver of plant growth and that relatedness is also a strong driver of intraspecific coexistence of these ecologically important symbionts.     

菌根真菌提高植物抗旱性机制的研究回顾与展望

菌根真菌与全世界约97％的维管植物具有广泛的共生关系.大量研究结果显示菌根植物相比于非菌根植物对于干旱胁迫具有更高的耐受性,说明菌根真菌在植物抗旱过程中发挥着重要作用.本文对近年来国内外在菌根真菌协助植物抵御干旱作用机制方面的研究进行了归纳和总结,主要包括在干旱胁迫下菌根真菌对植物生理学特性的影响机制、菌根真菌提高植物...     

Interaction between supernodulating or non-nodulating mutants of soybean and two arbuscular mycorrhizal fungi

 Twelve nodulation mutants (seven non-nodulating and five supernodulating) of soybean [Glycine max (L.) Mirr.] were screened for arbuscular mycorrhizal colonization in the presence of either Glomus etunicatum Becker and Gerdemann or Gigaspora margarita Becker and Hall. The cultivars showed variation in colonization parameters. The two supernodulating mutants En6500 and NOD1–3 had higher frequencies of colonization with 2.5–4.5 times higher arbuscular abundance than the respective wild types. The enhanced mycorrhization resulted in significant enhancement of P uptake by En6500. The non-nodulating mutants showed decreases in mycorrhizal parameters. Mutants En1282 and Harosoy^–exhibited aborted infection after formation of typical appressorium-like structures at some sites. However, none of these had the non-mycorrhizal phenotype. Growth and nutrient-uptake parameters should be considered while studying plant mutants for mycorrhization. Accepted: 7 July 2000     

Differential plant response to inoculation with two VA mycorrhizal fungi isolated from a low-pH soil

Sericea lespedaza and ladino clover were inoculated withAcaulospora laevis andGigaspora margarita VA mycorrhizal fungi, both isolated from a local soil having a pH of 4.4. Plants were grown in a greenhouse in fumigated (methyl bromide) soil with four rates of applied P. This soil had a pH of 5.1 for theG. margarita experiment and a 5.8 for theA. laevis experiment. Neither plant species responded to theG. margarita isolate in terms of mycorrhizal infection of roots, top growth, or elemental uptake. TheA. laevis isolate caused increased growth of Ladino clover at the lowest rate of P application and increased growth of sericea lespedeza at the two lowest P application rates. Shoot tissue concentrations of P for both plant species were greater at the two lowest rates of P application when inoculated withA. laevis. Inoculation withA. laevis also resulted in different VAM fungal root colonization patterns between the two plant species as a function of P application rate. Roots of both plants had high infection rates (near 70%) for the two lowest P application rates but sericea lespedeza declined to 40 and 6% at the next two P application rates, respectively, whereas infection in Ladino clover was 74 and 41% at the next two P application rates, respectively. The results of this study support the concept that plant host-VAM fungal endophyte interactions are extremely variable and that characterization of individual combinations must be done if types and magnitudes of responses are to be defined.     

一种改进的丛枝菌根染色方法

研究改进了Vierheilig等描述的AM菌根染色法:将根样于20%KOH溶液中60℃水浴透明40-120 min,5%醋酸酸化5min后,用5%醋酸墨水染色液(派克纯黑书写墨水Quink),于60℃水浴染色30 min,清水浸泡脱色(14h)后即可镜检。根皮层细胞内AM真菌的丛枝结构清晰可见,并且能够明确地分辨AM真菌与其它未知真菌。此外,Quink初染后,再经过SudanⅣ复染(60℃、60 min),70%乙醇脱色5min,暗隔真菌的透明菌丝内所积聚的脂类颗粒被SudanⅣ染上鲜红色,在复式显微镜下能够观察到此类透明菌丝在根皮层组织内的存在状况。采用甘油明胶为封固剂制片,根的染色效果可以保存长久。此项技术可以对同一种植物的多个根样进行同步的透明和染色处理,而且操作简便、低毒性、成本低廉、染色效果极佳,适用于野生和栽培草本植物AM菌根的染色和制片观察。     

丛枝菌根真菌对入侵植物南美蟛蜞菊生长及竞争力的影响

【背景】丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)能促进植物的养分吸收及生长发育。入侵中国华南地区的外来入侵植物南美蟛蜞菊(Wedelia trilobata)常分布于养分匮乏的荒地,却能迅速生长并排挤本地植物而快速扩张领地。【目的】探究丛枝菌根真菌是否促进南美蟛蜞菊的生长与竞争能力。【方法】采用南美蟛蜞菊及其同属本地植物蟛蜞菊(Wedelia chinensis)的盆栽对比控制试验,并设置接种及不接种AMF变形球囊霉(Glomus versiforme)、不同磷营养水平以及单种或混种的种植方式3种处理对两种植物的生长及竞争能力进行比较。【结果】AMF均能侵染上述两种植物,并且AMF对南美蟛蜞菊根系的侵染率显著高于其对蟛蜞菊根系的侵染,尤其是在低磷水平下南美蟛蜞菊的菌根侵染率更高,而且AMF的侵染显著促进了低磷水平下南美蟛蜞菊的生长及其对蟛蜞菊的竞争能力。【结论】丛枝菌根真菌能够促进南美蟛蜞菊的生长,增强其对本地植物的竞争优势,该效应很可能对外来植物南美蟛蜞菊的成功入侵产生一定的作用。     

Modelling the contribution of arbuscular mycorrhizal fungi to plant phosphate uptake

In this paper, we investigate the role of arbuscular mycorrhizal fungi in plant phosphorus nutrition. We develop a mathematical model which quantitatively assesses the contribution of external fungal hyphae to plant phosphate uptake.We derive an equation for solute uptake by a growing fungal mycelium which we couple with a model for root uptake. We analyse the model using nondimensionalization and numerical simulations.Simulations predict that removal of phosphate from soil is dominated by hyphal uptake as opposed to root uptake. Model analysis shows that the depletion zones around hyphae overlap within 8 h and that the transfer between fungus and root is a critical step for the behaviour of phosphorus within the mycelial phase. We also show that the volume fraction of mycelium is negligibly small in comparison to other soil phases.This is the first model to quantify the contribution of mycorrhizal fungi to plant phosphate uptake. A full data set for model parametrization and validation is not currently available. Therefore, more complete sets of experimental measurements are necessary to make this model more applicable.     

Interactions between arbuscular mycorrhizal fungi and the hemiparasitic angiosperm Rhinanthus minor during co-infection of a host

The outcome of dual infection of the grass Lolium perenne L. by arbuscular mycorrhizal (AM) fungi and the parasitic angiosperm Rhinanthus minor L. was investigated in a glasshouse study. Colonization of L. perenne roots by AM fungi was significantly reduced by the presence of R. minor , as was host growth which fell by 44–51%. It was concluded that these two responses were linked, with AM colonization declining in response to the reduction in availability of host carbon. Parasite growth and reproductive output rose by 58% and 47% respectively when the hosts were mycorrhizal. These trends were unrelated to the attachment success of the parasite, but were accompanied by a significant increase in the formation of secondary haustoria. The benefits afforded the parasite when the hosts were mycorrhizal were attributed to increased carbon and nutrient flux resulting from alternations in sink strength. Host responses to parasitism and mycorrhizal colonization were not affected by the interaction between the two symbionts. However, the suggestion is made that the interaction between the AM fungi and parasite might have long-term ecological implications for the host species via its impact on parasite fecundity.     

Can orchid mycorrhizal fungi be persistently harbored by the plant host?

The environmental distribution of non-obligate orchid mycorrhizal (OM) symbionts belonging to the ‘rhizoctonia’ complex remains elusive. Some of these fungi, indeed, are undetectable in soil outside the host rhizosphere. A manipulation experiment was performed to assess the importance of neighbouring non-orchid plants and soil as possible reservoirs of OM fungi for Spiranthes spiralis, a widespread photosynthetic European terrestrial orchid species. Fungi of S. spiralis roots were identified by DNA metabarcoding before and 4 months after the removal of the surrounding vegetation and soil. Although such a treatment significantly affected fungal colonization of newly-formed orchid roots, most OM fungi were consistently associated with the host roots. Frequency patterns in differently aged roots suggest that these fungi colonize new orchid roots from either older roots or other parts of the same plant, which may thus represent an environmental source for the subsequent establishment of the OM symbiosis.     

Gibberellin regulates infection and colonization of host roots by arbuscular mycorrhizal fungi

Arbuscular mycorrhiza (AM) is established by the entry of AM fungi into the host plant roots and the formation of symbiotic structures called arbuscules. The host plant supplies photosynthetic products to the AM fungi, which in return provide phosphate and other minerals to the host through the arbuscules. Both partners gain great advantages from this symbiotic interaction, and both regulate AM development. Our recent work revealed that gibberellic acids (GAs) are required for AM development in the legume Lotus japonicus. GA signaling interact with symbiosis signaling pathways, directing AM fungal colonization in host roots. Expression analysis showed that genes for GA biosynthesis and metabolism were induced in host roots around AM fungal hyphae, suggesting that the GA signaling changes with both location and time during AM development. The fluctuating GA concentrations sometimes positively and sometimes negatively affect the expression of AM-induced genes that regulate AM fungal infection and colonization.     

Competitive exclusion of a worldwide invasive pest by a native. Quantifying competition between two phytophagous insects on two host plant species

1. High competitive ability is believed to be an important characteristic of invasive species. Many animal studies have compared the competitive ability of invasive species with a native species that is being displaced, but few have looked at systems where an invasive species has failed to establish itself. These types of studies are important to determine if competition is relevant not only to invading species but also to the biotic resistance of a community. 2. The thrips species F. occidentalis is a highly invasive pest that has spread from its original range (the western states of the USA) to a worldwide distribution. Despite this, F. occidentalis is largely absent or occurs in low numbers in the eastern states of the USA, where the native F. tritici dominates. It is possible that F. tritici is competitively excluding F. occidentalis from this region. 3. Larval competition between these two thrips species was tested on two known plant hosts, Capsicum annuum (a crop plant), and Raphanus raphanistrum (an invasive weed), using a response surface design with number of larvae surviving as the response variable. The response surface design allowed competition models to be fit to data using maximum likelihood estimation, thus generating quantitative values for interspecific competition. 4. On both plant hosts, the native F. tritici did not experience significant interspecific competition from the invasive F. occidentalis. In contrast, F. occidentalis did experience significant interspecific competition from F. tritici. Competition from F. tritici larvae on F. occidentalis larvae was estimated to be 1.72 times (on C. annuum) and 1.76 times (on R. raphanistrum) the effect of intraspecific competition. The invasive F. occidentalis appears to be competitively excluded by the native F. tritici. 5. This study confirms the importance of competition in the biotic resistance of a community and is one of the few animal studies to not only test for competition in an apparently resistant ecosystem but also to quantify the level of interspecific competition between two animal species.     

Preinoculation of lettuce and onion with VA mycorrhizal fungi reduces deleterious effects of soil salinity

The hypothesis that inoculation of transplants with vesicular-arbuscular mycorrhizal (VAM) fungi before planting into saline soils alleviates salt effects on growth and yield was tested on lettuce (Lactuca sativa L.) and onion (Allium cepa L.). A second hypothesis was that fungi isolated from saline soil are more effective in counteracting salt effects than those from nonsaline soil. VAM fungi from high- and low-salt soils were trap-cultured, their propagules quantified and adjusted to a like number, and added to a pasteurized soil mix in which seedlings were grown for 3–4 weeks. Once the seedlings were colonized by VAM fungi, they were transplanted into salinized (NaCl) soil. Preinoculated lettuce transplants grown for 11 weeks in the saline soils had greater shoot mass compared with nonVAM plants at all salt levels [2 (control), 4, 8 and 12 dS m^–1] tested. Leaves of VAM lettuce at the highest salt level were significantly greener (more chlorophyll) than those of the nonVAM lettuce. NonVAM onions were stunted due to P deficiency in the soil, but inoculation with VAM fungi alleviated P deficiency and salinity effects; VAM onions were significantly larger at all salt levels than nonVAM onions. In a separate experiment, addition of P to salinized soil reduced the salt stress effect on nonVAM onions but to a lesser extent than by VAM inoculation. VAM fungi from the saline soil were not more effective in reducing growth inhibition by salt than those from the nonsaline site. Colonization of roots and length of soil hyphae produced by the VAM fungi decreased with increasing soil salt concentration. Results indicate that preinoculation of transplants with VAM fungi can help alleviate deleterious effects of saline soils on crop yield.