The presence of aluminum in arbuscular mycorrhizas of Clusia multiflora exposed to increased acidity

In this work, we present the results obtained after 9 months of watering with acidic solutions seedlings of Clusia multiflora, inoculated with arbuscular mycorrhizal fungi (AMF). The fungi were isolated from acid and neutral soil. C.multiflora is a tropical woody species that naturally grows on acid soils high in soluble Al. The research evaluated if arbuscular mycorrhizas (AM) could be responsible at least partially for the tolerance to acidity and to aluminum of C.multiflora and if an inoculum of AM fungi (AMF) coming from acid soils contributes more to the tolerance of acidity of C. multiflora than one coming from neutral soils. Results showed that in the absence of AMF (control treatment), the seedlings of C. multiflora did not grow, indicating that this species is highly dependent on AMF. When C. multiflora was exposed to a very acidic solution (pH 3), plants inoculated with AMF from acid soils were taller than those inoculated with AMF from neutral soils. Acidity affected root growth and root length. Plants inoculated with AMF from neutral soils showed thicker roots and lower shoot-root relationships than those inoculated with AMF from acid soils. Acidity did not affect root growth of C. multiflora inoculated with AMF from acid soils even when they were watered with solutions of pH 3. All plants accumulated high quantities of Al in roots (>10000 mg.kg ^–1), but plants inoculated with AMF from acid soils, accumulated less aluminum in roots than plants from the other treatments. A histochemical study of the distribution of Al in roots showed that in mycorrhizal plants, the aluminum was bound to the cell walls in the mycelium of the fungus, mainly in the vesicles or in auxiliary cells, a fact showed for the first time in this work.     

Mycorrhizal response of <Emphasis Type="Italic">Clusia pusilla</Emphasis> growing in two different soils in the field

Arbuscular mycorrhizas (AM) are important for promoting the mineral nutrition, growth and survival of plants used to rehabilitate degraded areas. Clusia pusilla is an evergreen shrub which is tolerant of high irradiance, germinates readily and can be easily reproduced by cuttings. All these characteristics make this species useful in the recovery of deforested areas. The aim of this work was to explore the response of C. pusilla to AM in the field, in two types of soil: the shrubland soil in which the species naturally grows and in a soil of a riparian forest. Eight treatments were performed in each type of soil. The treatments consisted of a non-mycorrhizal control and mycorrhizal plants colonized by one of the three AM inocula tested in the presence or absence of triple superphosphate (150 kg ha^-1). After 11 months of growth in the shrubland soil, C. pusilla seedlings showed an increase in height and dry weight in response to the fertilizer but not to mycorrhizas. In contrast, in the forest soil the arbuscular mycorrhizal fungi (AMF) effect was equivalent to the fertilizer effect, and the two effects interacted positively. The lack of response to AM in shrubland soil was caused by its high sand content, which hinders the retention of the inocula. Due to a higher clay content, the forest soil binds inocula more tightly than shrubland soil. In conclusion, C. pusilla appears to benefit greatly from the addition of AMF in forest soil, though it requires an additional P source for such benefits in shrubland soil. This P source must be organic so that phosphorus is not lost by leaching. Although the growth rate of this species is very low, its survival can be guaranteed with the application of AMF inocula together with P-fertilizer applied at a low rate.     

Establishment and effectiveness of inoculated arbuscular mycorrhizal fungi in agricultural soils

Arbuscular mycorrhizal fungi (AMF) are promoted as biofertilizers for sustainable agriculture. So far, most researchers have investigated the effects of AMF on plant growth under highly controlled conditions with sterilized soil, soil substrates or soils with low available P or low inoculum potential. However, it is still poorly documented whether inoculated AMF can successfully establish in field soils with native AMF communities and enhance plant growth. We inoculated grassland microcosms planted with a grass–clover mixture (Lolium multiflorum and Trifolium pratense) with the arbuscular mycorrhizal fungus Rhizoglomus irregulare. The microcosms were filled with eight different unsterilized field soils that varied greatly in soil type and chemical characteristics and indigenous AMF communities. We tested whether inoculation with AMF enhanced plant biomass and R. irregulare abundance using a species specific qPCR. Inoculation increased the abundance of R. irregulare in all soils, irrespective of soil P availability, the initial abundance of R. irregulare or the abundance of native AM fungal communities. AMF inoculation had no effect on the grass but significantly enhanced clover yield in five out of eight field soils. The results demonstrate that AMF inoculation can be successful, even when soil P availability is high and native AMF communities are abundant.     

Mycorrhization and phosphorus nutrition affect water relations and CAM induction by drought in seedlings of Clusia minor

Background and Aims

Crassulacean acid metabolism (CAM) is currently viewed as an adaptation to water deficit. In plants of Clusia minor, which grow mostly on acidic, P-deficient soils, CAM is induced by water deficit. The symbiosis between plants and mycorrhizal fungi alleviates the symptoms of P deficiency and may influence drought resistance. Therefore, the effect of P supply, modified by three different experimental treatments, on the induction of CAM by drought in C. minor was investigated to test the hypothesis that P deficiency will produce greater CAM activity and, in addition, that treatment will modify drought tolerance.

Methods

Seedlings were grown in forest soil sterilized and inoculated with Scutellospora fulgida (SF treatment), sterilized and supplemented with P (Ph treatment) or non-sterilized and containing native mycorrhizae (Nat treatment). Leaf turgor potential (ψ_T) was determined psychrometrically, and CAM activity as nocturnal acid accumulation (ΔH⁺) by titration of dawn and dusk leaf sap.

Key Results

Plant mass and P content were higher in SF and Ph than in Nat seedlings. After 21 d of water deficit, ψ_T increased in SF, decreased in Ph and remained unchanged in Nat, and, after 7 and 14 d of water deficit, ΔH⁺ in Nat was three times higher than at the beginning of drought, whereas in SF and Ph ΔH⁺ was lower than on day 0.

Conclusions

P deficiency in Nat seedlings was ameliorated by inoculation or P addition. The SF and Nat seedlings showed greater tolerance of drought than Ph. P deficiency promoted the induction of CAM by drought in Nat seedlings, whereas P fertilization and mycorrhization did not. Nocturnal acid accumulation was highly and negatively correlated with plant P and N contents, indicating that P and N deficiencies are promoters of CAM in droughted plants of C. minor.Key words: Clusia minor, crassulacean acid metabolism, CAM, mycorrhiza, drought, phosphorus deficiency, nitrogen–water relations     

Local soil,but not commercial AMF inoculum,increases native and non‐native grass growth at a mine restoration site

Soil communities are often degraded in mined sites, and facilitating the recovery of soil mutualists such as arbuscular mycorrhizal fungi (AMF) may assist with the restoration of native plants. At a grassland mine restoration site, I compared a commercial AMF inoculum with soil collected from beneath native grasses as a source of inoculum, as well as a control treatment. Field plots were broadcast‐inoculated and seeded with native grasses, and biomass of native and non‐native species was measured in three consecutive years. In addition, greenhouse‐grown seedlings of a native bunchgrass (Stipa pulchra) were inoculated with similar treatments, transplanted into the field, and assessed after 18 months. When broadcast inoculation was used, the local soil inoculum tended to increase non‐native grass biomass, and marginally decreased non‐native forb biomass in the second year of study, but did not significantly affect native grass biomass. Broadcast commercial inoculum had no detectable effects on biomass of any plant group. Stipa pulchra transplants had greater N content and mycorrhizal colonization, and marginally higher shoot mass and K content, when pre‐inoculated with local soil (relative to controls). Pre‐inoculation with commercial AMF increased AMF colonization of the S. pulchra transplants, but did not significantly affect biomass or nutrient content. The findings indicate that at this site, the use of local soil as an inoculum had greater effects on native and non‐native plants than the commercial product used. In order to substantially increase native grass performance, inoculation of transplanted plugs may be one potential strategy.     

不同强度盐胁迫下AM真菌对羊草生长的影响

不同浓度NaCl盐处理下,AM真菌对羊草(Leymus chinensis)的侵染能力和对植物生长的影响,从植物形态和离子含量角度探讨了AM真菌提高羊草耐盐性的作用机理。结果表明,在高盐胁迫下,AM真菌显著降低了盐胁迫效应,提高了羊草生物量,菌根效应明显。菌根化羊草的根茎比显著增加,并且N、P浓度较高,Na~+和Cl~-离子浓度较低,表明AM真菌即促进羊草对营养元素的吸收,又减少了离子毒害。菌根化羊草的Ca~(2+)和K~+离子浓度,以及P/Na~+和K~+/Na~+比高于非菌根化羊草,表明AM真菌可通过调节渗透势以避免或减缓盐胁迫造成的生理缺水。随着盐胁迫的增加,菌根化羊草对磷的依赖性逐渐转换为对钾的依赖性。研究结果有助于揭示AM真菌提高植物耐盐能力的作用机理,并对应用菌根技术修复盐化草地具有理论指导意义。     

The role of arbuscular mycorrhizal fungi in plant community establishment at Samphire Hoe, Kent, UK – the reclamation platform created during the building of the Channel tunnel between France and UK

Samphire Hoe is a newly-created land platform comprising the sub-seabed material excavated during the construction of the Channel tunnel. It represents a unique resource where the arrival and establishment of arbuscular mycorrhizal fungi (AMF) within a sown plant community on a low nutrient substrate can be monitored. Arbuscular mycorrhizal fungi invasion was monitored in a number of ways: by assessing the degree of root colonisation within the roots of plants on the site, by using a successive trap culture technique to determine AMF species richness, and by using sterile substrate bins to determine the extent of wind-borne and rain-dispersed immigration of AMF propagules into the site. Levels of colonisation of indigenous plants by AMF were high in May–June (the pre-flowering phase of growth for many plants) reflecting the important role of the mycorrhizal symbiosis in dry, low nutrient soils. Twelve species of AMF were identified, representing a relatively high diversity for a recently deposited subsoil. An on-site experiment indicated that inoculum of AMF could enter the site within 8 months and that wind dispersal and/or rain were possible vectors. A field experiment compared the outplanting performance of commercially-produced Elymus pycnanthus seedlings (in a commercial compost with added nutrients) with seedlings produced in a low nutrient substrate and inoculated with AMF isolated from the site (a mixture of 5 species of Glomus) or left uninoculated. After 14 months in the field seedlings, inoculated with the indigenous AMF, had the same tiller production as commercially-produced plants, despite slower initial growth. In contrast, non-mycorrhizal controls grew very poorly with a greater frequency of plant mortality compared with the other treatments. Elymus seedlings inoculated with the indigenous AMF ultimately produced approximately seven times the mean number of seed spikes per surviving plant as commercially-produced seedlings and five times greater weight of seed spike. A phyto-microbial approach to the revegetation of nutrient-poor soils is proposed to stimulate plant successional processes as a economically-viable sustainable input for landscaping anthropogenic sites.     

干旱胁迫条件下AMF促进小马鞍羊蹄甲幼苗生长的机理研究

采用温室水分控制试验,在干旱胁迫条件下,定量化研究优势丛枝菌根真菌(AMF)影响优势乡土植物小马鞍羊蹄甲(Bauhinia faberi var.microphylla)幼苗生长的机理,主要通过研究干旱胁迫条件下摩西球囊霉菌(Funneliformis mosseae)与小马鞍羊蹄甲的共生关系,阐明AMF在植物生长初期的作用。结果表明,干旱胁迫条件下,摩西球囊霉菌能够很好地侵染幼苗,侵染率高达89%—97%,并且不受水分条件影响。接种的幼苗最大光合速率、水分利用效率随着干旱胁迫程度从重度到轻度(水分从低到高)逐渐增大,相反地,叶片脯氨酸含量逐渐减小。接种显著地促进幼苗株高、叶片数、叶面积、根长、根面积等生长指标,提高幼苗各部分生物量、地上地下磷(P)含量。当含水量为60%田间持水量时,AMF促进小马鞍羊蹄甲幼苗吸收P的效果最好。接种还显著影响幼苗的生物量分配,在重度干旱胁迫时影响P分配,水分条件也显著影响幼苗的生物量分配。此外,接种和水分的交互作用对叶生物量、总生物量、生长指标以及地上部氮(N)总量影响显著。结果表明干旱胁迫条件下菌根效应显著,并在干旱条件下显著促进了小马鞍羊蹄甲幼苗的生长,这为进一步干旱河谷植被恢复提供了理论依据。     

接种AM真菌对玉米和油菜种间竞争及土壤无机磷组分的影响

在温室盆栽条件下,分别模拟单作、间作和尼龙网分隔种植,比较接种丛枝菌根(arbuscular mycorrhizal, AM)真菌Glomus intraradices和Glomus mosseae对菌根植物玉米和非菌根植物油菜生长和磷吸收状况的影响,并分析土壤中各无机磷组分的变化。结果发现,接种AM真菌可以促进土壤中难溶性磷(Ca₁₀-P和O-P)向有效态磷转化,并显著降低总无机磷含量 (P<0.05),显著提高菌根植物玉米的生物量和磷吸收量(P<0.05),特别是在间作体系中使玉米的磷营养竞争比率显著提高了45.0%-104.1% (P<0.05),显著降低了油菜的生物量和磷吸收量(P<0.05),从而增强了了菌根植物的竞争优势,降低了非菌根植物与菌根植物的共存能力。揭示了石灰性土壤中AM真菌对植物物种多样性的影响,有助于更加全面地理解AM真菌在农业生态系统中的作用。     

Soil fumigation and phosphorus supply affect the formation of Pisolithus-Eucalyptus urophylla ectomycorrhizas in two acid Philippine soils

To examine the effects of microbial populations and external phosphorus supply of two Philippine soils on mycorrhizal formation, Eucalyptus urophylla seedlings were inoculated with two Pisolithus isolates and grown in fumigated, reinfested and unfumigated soil fertilized with four rates of phosphorus. The Pisolithus isolates used were collected from under eucalypts in Australia and in the Philippines. Soils were infertile acid silty loams collected from field sites in Pangasinan, Luzon and Surigao, Mindanao.Significant interaction was observed between inoculation, soil fumigation and phosphorus supply on mycorrhizal formation by the Australian isolate in Surigao soil but not in Pangasinan soil. Soil fumigation enhanced mycorrhizal formation by the Australian isolate but did not affect root colonization by the Philippine isolate. Root colonization by the Australian isolate was highest in the reinfested soil while for the Philippine isolate it was highest in the unfumigated soil. The Australian isolate was more effective than the Philippine isolate in promoting growth and P uptake of E. urophylla seedlings in both soils. Total dry weight and P uptake of E. urophylla seedlings inoculated with the Australian isolate were maximum in fumigated and in the reinfested Pangasinan and Surigao soils supplied with 8 mg P kg^-1 soil. In the unfumigated soil, growth of seedlings inoculated with the Australian isolate was significantly reduced. Seedlings inoculated with the Philippine isolate had the largest dry weights and P contents in unfumigated Pangasinan and Surigao soils supplied with 8 mg P kg^-1 soil.These results indicate that the performance of the Australian Pisolithus isolate was markedly affected by biological factors in unfumigated soil. Thus, its potential use in the Philippines needs to be thoroughly tested in a variety of unfumigated soils before its widespread use in any inoculation programme.     

Effect of arbuscular mycorrhizal fungi inoculation of rice seedlings at the nursery stage upon performance in the paddy field and greenhouse

We examined the effect of arbuscular mycorrhizal fungi inoculation at the nursery stage on the growth and nutrient acquisition of wetland rice (t Oryza sativa L.) under field and pot conditions. Seedlings were grown on -ray sterilized paddy soil in two types of nurseries, namely dry nursery and wet nursery, with or without arbuscular mycorrhizal fungi (AMF) inoculation which was a mixture of indigenous AMF (t Glomus spp.) spores collected from the paddy field. Five-to-six week old seedlings were transplanted to the unsterilized soil under field and pot, respectively. Mycorrhizal seedlings had higher shoot biomass under both nursery conditions 5 weeks after sowing. Mycorrhizal colonization and sporulation were 2 to 3 times higher in the dry nursery than the wet nursery at the transplanting stage. Mycorrhizal colonization of plants inoculated in the nursery remained higher than those not inoculated under both field and pot conditions. Sporulation after transplanting to field conditions was about 10 times higher than in the pot. Inoculated plants produced higher biomass at maturity under field conditions, and the grain yield was 14-21% higher than those not inoculated. Conversely, grain yield and shoot biomass were not significantly influenced by AMF colonization under pot conditions. For plants originating from the dry nursery, N, P, Zn and Cu concentrations of field-grown plants at harvest were significantly increased by preinoculation with AMF over those left uninoculated. We conclude that the AMF inoculation at the nursery stage under both dry and wet conditions increased growth, grain yield and nutrient acquisition of wetland rice under field conditions.     

Interactions between arbuscular mycorrhizae and Fusarium oxysporum f. sp. ciceris: effects on fungal development,seedling growth and wilt disease suppression in Cicer arietinum L.

The purpose of present study was to develop a management strategy based on a time effective inoculation of arbuscular mycorrhizal fungi (AMF) to mitigate the yield losses of Cicer arietinum L. due to Fusarium oxysporum f. sp. ciceris (Foc). The interactions between AMF (mycorrhizal consortium; Myc) and Foc were studied in three separate experiments in two successive years (2011 and 2012). In particular, we investigated: the effect of Myc on population density of Foc, the effect of Foc on mycorrhisation (root colonisation index and AMF spore density/50?g sand) and the interactive effects of Myc and Foc on growth, phosphorus (P) content and disease severity index of C. arietinum. Results suggested that pre-inoculating plants with AMF (Myc?+?Foc) considerably reduced Foc population density, while combined (Myc/Foc) and early inoculation of AMF (Myc?+?Foc) increased mycorrhisation, growth and P content of plants. Combined and early inoculation of AMF reduced disease severity index up to 68 and 89.5%, respectively. Thus, the results suggested that soil pretreated with AMF acted as bioprotectant against the Fusarium. In conclusion, Myc should be inoculated before transplantation of crop seedlings to the fields. However, extrapolation of the results to the real field conditions should be done with caution because of differences in growth conditions and substrate used in present study i.e. net house and sand, respectively.     

Arbuscular mycorrhizal fungi influence life history traits of a lepidopteran herbivore

Results from pot and microcosm studies in the greenhouse have shown that plant growth and foliar chemistry is altered by the presence and species composition of arbuscular mycorrhizal fungi (AMF). The growth and survival of herbivores which feed on plants could, as a consequence, also be affected by these mutualistic soil fungi. Consequently, interactions between AMF, plants and herbivores could occur. To test this, larvae of the common blue butterfly, Polyommatus icarus (Lycaenidae), were fed with sprigs of Lotus corniculatus (Fabaceae) plants which were inoculated with one of two different AMF species, with a mixture of these AMF species or with sprigs of plants which were not inoculated with AMF. Survival and larval weight of third instar larvae fed with plants colonised by AMF were greater than those of larvae fed with non-mycorrhizal plants. Survival of larvae feeding on non-mycorrhizal plants was 1.6 times lower than that of larvae feeding on plants inoculated with a mixture of AMF species and 3.8 times lower than that of larvae feeding on plants inoculated with single AMF species. Furthermore, larvae fed with non-mycorrhizal plants attained only about half the weight of larvae fed with mycorrhizal plants after 11 days of growth. These differences in larval performance might be explained by differences in leaf chemistry, since mycorrhizal plants had a 3 times higher leaf P concentration and a higher C/N-ratio. Our results, thus, show that the presence of belowground mutualistic soil fungi influences the performance of aboveground herbivores by altering their food quality. Larval consumption, larval food use and adult lipid concentrations of the common blue butterfly differed between larvae which were fed with plants inoculated with different AMF species. This suggests that the performance of herbivores is not only influenced by the presence of AMF but also depends on the identity of the AMF species colonising the host plants. Moreover, a significant interaction term between AMF species and maternal identity of the larvae occurred for adult dry weight, indicating that the performance of offspring from different females was differently influenced by AMF species composition. To our knowledge, these results show for the first time that the species composition of AMF communities can influence life-history traits of butterfly larvae and possibly herbivores in general.     

Chemical alteration of the rhizosphere of the mycorrhizal-colonized wheat root

Plexiglass pot growth chamber experiments were conducted to evaluate the chemical alterations in the rhizosphere of mycorrhizal wheat roots after inoculation with Glomus intraradices [arbuscular mycorrhizal fungus (AMF)]. Exchange resins were used as sinks for nutrients to determine whether the inoculated plant can increase the solubility and the uptake of P and micronutrients. Treatments included: (1) soil (bulk soil); (2) AMF inoculation no P addition (I–P); (3) no inoculation with no P addition (NI–P); (4) AMF inoculation with addition of 50 mg P (kg soil)^–1 (I+P), and (5) no inoculation with addition of 50 mg P (kg soil)^–1 (NI+P). The AMF inoculum was added at a rate of four spores of G. intraradices (g soil)^–1. The exchange resin membranes were inserted vertically 5 cm apart in the middle of Plexiglass pots. Spring wheat (Triticum aestivum cv. Len) was planted in each Plexiglass pot and grown for 2 weeks in a growth chamber where water was maintained at field capacity. Rhizosphere pH and redox potential (Eh), nutrient bioavailability indices and mycorrhizal colonization were determined. Mycorrhizal inoculation increased the colonization more when P was not added, but did not increase the shoot dry weight at either P level. The rhizosphere pH was lower in the inoculated plants compared to the noninoculated plants in the absence of added P, while the Eh did not change. The decrease in pH in the rhizosphere of inoculated plants could be responsible for the increased P and Zn uptake observed with inoculation. In contrast, Mn uptake was decreased by inoculation. The resin-adsorbed P was increased by inoculation, which, along with the bioavailability index data, may indicate that mycorrhizal roots were able to increase the solubility of soil P.     

Mechanism of application nursery cultivation arbuscular mycorrhizal seedling in watermelon in the field

Arbuscular mycorrhizal fungi (AMF) colonisation of plant root facilitates the absorption of nutrients such as phosphorus (P) and enhances plant biotic and abiotic resistance generally. However, arbuscular mycorrhiza (AM) colonisation decreases with application of chemical fertiliser. Here, we investigated whether AMF inoculation in nurseries would facilitate AM colonisation and take physiological and ecological functions in watermelon (Citrullus lanatus) in the field. Pot experiments were carried out to study the change of AMF colonised seedling on physiology and gene expression in nursery site. Field experiments were performed to investigate the effect of nursery AMF inoculation on yield, quality and disease resistance of watermelon in the field. The results showed that nursery‐inoculated seedlings produced more dry matter and root surface area than non‐inoculated seedlings. Expression of the secretory purple acid phosphatase (PAP) genes ClaPAP10 and ClaPAP26 was up‐regulated following AMF colonisation. Accordingly, acid phosphatase activities at the root surface and P concentrations in seedling were enhanced. After transplantation to the field, the shoot dry matter and P concentration in old stem were higher in the nursery AMF inoculated seedlings than that in non‐AMF inoculated seedling. AMF inoculation also induced increase of yields and decrease of wilt disease indexes and soluble sugar content. In addition, acid phosphatase activities and AMF spore densities were increased by nursery‐inoculation in watermelon rhizosphere soil in the field. In conclusion, nursery colonisation AMF seedling enhanced watermelon growth and yield by improving the root growth and P acquisition in nursery cultivating stage, as well as optimised soil properties in the field. Nursery cultivation of watermelon seedling with AMF was an effective technique to reduce wilt disease in continuous cropped management in watermelon.     

Differential host plant performance as a function of soil arbuscular mycorrhizal fungal communities: experimentally manipulating co-occurring Glomus species

In order to evaluate host plant performance relative to different soil arbuscular mycorrhizal fungal (AMF) communities, Andropogon gerardii seedlings were grown with nine different AMF communities. The communities consisted of 0, 10, or 20 spores of Glomus etunicatum and 0, 10, or 20 spores of Glomus intraradices in all possible combinations. Spores were produced by fungal cultures originating on A. gerardii in a serpentine plant community; seeds of A. gerardii were collected at the same site. The experiment was performed in the greenhouse using a mixture of sterilized serpentine soil and sand to which naturally occurring non-mycorrhizal microbes were added. There was no difference in root AMF colonization rates between single species communities of either G. etunicatum or G. intraradices, but G. intraradices enhanced plant growth and G. etunicatum did not. However, plants grew larger with some combinations of G.␣intraradices plus G. etunicatum than with the same quantity of G. intraradices alone. These results suggest the potential for niche complementarity in the mycorrhizal fungi. That G. etunicatum only increased plant growth in the presence of G. intraradices could be illustrative of why AMF that appear to be parasitic or benign when examined in isolation are maintained within multi-species mycorrhizal communities in nature.     

Synergistic effect of colonization with arbuscular mycorrhizal fungi improves growth and drought tolerance of Plukenetia volubilis seedlings

The objective of this study was to investigate the effects of arbuscular mycorrhizal fungus (AMF) inoculation on plant growth and drought tolerance in seedlings of a promising oilseed crop, Sacha Inchi (Plukenetia volubilis L.), under well-watered or drought conditions. AMF inoculation was applied in four treatments: without AMF inoculation, Glomus versiforme, Paraglomus occultum, or combination of both microorganism inoculations. The results showed that AMF colonization significantly enhanced the growth of Sacha Inchi seedlings regardless of soil water conditions, and the greatest development was reached in plants dually inoculated under well-watered conditions. G. versiforme was more efficient than P. occultum. Plants inoculated with both symbionts had significantly greater specific leaf area, leaf area ratio and root volume when compared with the uninoculated control, G. versiforme, and P. occultum treatments alone, indicating a synergistic effect in the two AMF inoculation. Photosynthetic rate and water-use efficiency were stimulated by AMF, but not stomatal conductance. Inoculation with AM fungus increased antioxidant enzymes activities including guaiacol peroxidase and catalase, thus lowering hydrogen peroxide accumulation and oxidative damage, especially under drought stress conditions. However, proline content showed little change during drought stress and AMF colonization conditions, which suggested that proline accumulation might not serve as the main compound for osmotic adjustment of the studied species. These results indicate that AMF inoculation stimulated growth and enhanced drought tolerance of Sacha Inchi seedlings, through alterations in morphological, physiological and biochemical traits. This microbial symbiosis might be an effective cultivation practice in improving the performance and development for Sacha Inchi plants.     

Growth of mycorrhizal tomato and mineral acquisition under salt stress

 High salt levels in soil and water can limit agricultural production and land development in arid and semiarid regions. Arbuscular mycorrhizal fungi (AMF) have been shown to decrease plant yield losses in saline soils. The objective of this study was to examine the growth and mineral acquisition responses of greenhouse-grown tomato to colonization by the AMF Glomus mosseae [(Nicol. And Gerd.) Gerd. and Trappe] under varied levels of salt. NaCl was added to soil in the irrigation water to give an EC_e of 1.4 (control), 4.7 (medium) and 7.4 dS m^–1 (high salt stress). Plants were grown in a sterilized, low P (silty clay) soil-sand mix. Mycorrhizal colonization was higher in the control than in saline soil conditions. Shoot and root dry matter yields and leaf area were higher in mycorrhizal than in nonmycorrhizal plants. Total accumulation of P, Zn, Cu, and Fe was higher in mycorrhizal than in nonmycorrhizal plants under both control and medium salt stress conditions. Shoot Na concentrations were lower in mycorrhizal than in nonmycorrhizal plants grown under saline soil conditions. The improved growth and nutrient acquisition in tomato demonstrate the potential of AMF colonization for protecting plants against salt stress in arid and semiarid areas. Accepted: 21 February 2000     

Mycorrhizal Fungal Effects on Growth,Antioxidant Capacity,and Medicine Quality of <i>Paris polyphylla</i> var. <i>yunnanensis</i>

A field experiment was conducted to determine the effects of two commercial strains composed of mulple arbuscular mycorrhizal fungi (AMF) species on plant growth, antioxidant capacity, and medicine quality of Paris polyphylla var. yunnanensis in three subtropical soils from Wanzhou, Anshun and Baoshan in fields. The results showed that AMF inoculation enhanced the fungal colonization rate and activities of both succinate dehydrogenase and alkaline phosphatase, thereby, enhancing the mycorrhizal viability of P. polyphylla var. yunnanensis. The concentrations of photosynthetic pigments (chlorophyll a, b, a+b and carotenoids), soluble sugar, soluble protein and photosynthetic capacity were higher in AMF-inoculated plants than in non-AMF-treated plants in field. AMFtreated plants recorded higher activities of catalase, peroxidase and superoxide dismutase, and caused the reduction in malondialdehyde content, indicating lower oxidative damage, compared with non-AMF plants. Polyphyllin I, Polyphyllin II, Polyphyllin III, Polyphyllin IV and total polyphyllin contents were increased by AMF treatment. In conclusion, AMF improved the plant growth, antioxidant capacity and medicinal quality of P. polyphylla var. yunnanensis seedlings. Hereinto, AMF effects on the soil from Wanzhou was relatively greater than on other soils.     

Investigation of the effects of Vesicular Arbuscular Mycorrhiza on mineral nutrition and growth of <Emphasis Type="Italic">Carthamus tinctorius</Emphasis> under salt stress conditions

Salt stress is considered as one of the most important abiotic factors limiting plant growth and yield in many areas of the world. It has been shown that Vesicular Arbuscular Mycorrhizal Fungi (AMF) can alleviate this deficiency. The effects of AMF inoculation on growth variables and mineral nutrition of Carthamus tinctorius L. under salt stress condition were studied. Plants were grown in a sterilized, low-P sandy soil with Glomus etunicatum inoculum (10–12 spore/g soil) in a greenhouse. RLC (Root Length Colonized) percent was higher in control plants than treated ones with different salt concentrations. Shoot and root weights, height, the number of leaves, the number of lateral branches, and also leaf area of mycorrhizal (M) plants were higher than nonmycorrhizal (NM) ones in both controlled and salt-treated plants. P, Zn, Fe, Ca, K, Cu, and N contents in M plants were higher than in NM plants in control, low and medium salinity conditions, but Na content was lower in aerial parts of the M plants. The results showed a higher tolerance of inoculated M plants toward salt stress and their better growth.