Effect of native and introduced arbuscular mycorrhizal fungi on growth and nutrient uptake ofLygeum spartum andAnthyllis cytisoides

The interaction between native and introduced fungi and their effect on plant growth and mineral uptake were studied. The host plants wereLygeum spartum andAnthyllis cytisoides, the introduced fungus wasGlomus fasciculatum. The four soils used were selected from disturbed and contaminated by mining activities areas. Inoculated and uninoculated plants were grown in the unsterilized and sterilized soils (with and withouth native microflora, respectively). Plants inoculated withG. fasciculatum were higher and had higher tissue P concentration than uninoculated plants, especially inA. cytisoides. However, this inoculation was not effective in unsterilized substrates, suggesting a competition between introduced and native fungi. Concentration of mineral elements other than P varied depending on the host plant and soil. Decrease in Fe, Cu, Mn, Zn and Pb was observed in mycorrhizalA. cytiosides plants and a slight increase in Zn concentration was noted in mycorrhizalL. spartum plants. The study showed that the type of soil and their populations of native endophytes have a considerable effect on plant response to mycorrhizal symbiosis, especially in disturbed soils.     

Influence of vesicular-arbuscular mycorrhizal infection and P addition on growth and P nutrition of Anthyllis cytisoides L. and Brachypodium retusum (Pers.) Beauv.

The effect of P applications and mycorrhizal inoculation on the growth and P nutrition of Anthyllis cytisoides L. (Fabaceae) and Brachypodium retusum (Pers.) Beauv. (Poaceae) was studied. Both plants are widely distributed and well adapted to semi-arid habitats in southern Spain. In all treatments, even with high P doses, mycorrhizal plants showed a higher concentration of phosphorus in their tissues than non-mycorrhizal plants. Mycorrhizal inoculation enhanced the growth of the plants when no P was applied. At high P addition, non-mycorrhizal plants showed higher growth than mycorrhizal plants. The response of each plant type to P application was somewhat different.     

Differential effects of AM fungal isolates on Medicago truncatula growth and metal uptake in a multimetallic (Cd, Zn, Pb) contaminated agricultural soil

Toxic metal accumulation in soils of agricultural interest is a serious problem needing more attention, and investigations on soil–plant metal transfer must be pursued to better understand the processes involved in metal uptake. Arbuscular mycorrhizal (AM) fungi are known to influence metal transfer in plants by increasing plant biomass and reducing metal toxicity to plants even if diverging results were reported. The effects of five AM fungi isolated from metal contaminated or non-contaminated soils on metal (Cd, Zn) uptake by plant and transfer to leachates was assessed with Medicago truncatula grown in a multimetallic contaminated agricultural soil. Fungi isolated from metal-contaminated soils were more effective to reduce shoot Cd concentration. Metal uptake capacity differed between AM fungi and depended on the origin of the isolate. Not only fungal tolerance and ability to reduce metal concentrations in plant but also interactions with rhizobacteria affected heavy metal transfer and plant growth. Indeed, thanks to association with nodulating rhizobacteria, one Glomus intraradices inoculum increased particularly plant biomass which allowed exporting twofold more Cd and Zn in shoots as compared to non-mycorrhizal treatment. Cd concentrations in leachates were variable among fungal treatments, but can be significantly influenced by AM inoculation. The differential strategies of AM fungal colonisation in metal stress conditions are also discussed.     

Influence of BA and sucrose on the competence and determination of pepper (Capsicum annuum L. var. Sweet Banana) hypocotyl cultures during shoot formation

Summary The simultaneous presence of 6-benzyladenine (BA) and sucrose in a Murashige and Skoog medium (SIM) during the initial stages of shoot initiation have been found to be obligatory for high-frequency shoot formation in the Capsicum annuum L. var. Sweet Banana upper hypocotyl explants. The explants are determined for shoot formation following a minimum of 8 days of culture on SIM. Deprivation of exogenous sucrose from day 6 to day 20 of culture had no effect on the shoot forming response of the explants. BA and sucrose appear to act independently on different aspects of the competence of explants to respond to SIM during shoot initiation.Abbreviations BA N⁶-benzyladenine - MS Murashige and Skoog medium - SIM shoot induction medium - HFM hormone free medium - SUC sucrose minus medium     

Influence of arbuscular mycorrhizae on the metabolism of maize under drought stress

A greenhouse experiment was carried out to investigate the influence of the arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on metabolic changes in tropical maize (Zea mays L.) under drought. Two cultivars, Tuxpeno sequia CO (drought sensitive) and C8 (drought resistant), were subjected for 3 weeks to water stress following tasselling (75–95 days after sowing). Fully expanded 7th or 8th leaves were sampled and assessed for levels of chlorophyll, sugars, proteins, and amino acids. Chlorophyll content was not altered either by water stress or the presence of mycorrhizae. Mycorrhizal plants (M+) had higher total and reducing sugars than nonmycorrhizal plants (M-) at the end of 3 weeks of the drought cycle. An increase in protein content was observed with drought stress in M + plants of the cultivar C0. Most of the amino acids showed a linear increase during the period of water stress in M+ and M- plants for both cultivars. Total amino acids increased by 40.6% and 43.7% in M- plants of C0 and C8, respectively. With the presence of AM fungus, amino acid levels increased by only 10.7% and 19.2% of leaf dry mass in C0 and C8, respectively. Alanine, asparagine, glutamine, and glycine accounted for 70% of the amino acid pool. Under drought, AM inoculation enabled the plants to retain considerable amounts of sugars and proteins, especially in the drought-sensitive cultivar C0. This may be of physiological importance in helping the plant to withstand moderate drought.     

Vesicular arbuscular mycorrhizal mediation of grass response to acidic and heavy metal depositions

Summary The perennial bunchgrassEhrharta calycina was grown with and without V.A.M. fungal infection (Glomus fasciculatum) in a sandy loam exposed to a range of acidic and heavy metal depositions. Heavy metals (Cu, Ni, Pb, Zn, Fe, and Co) were applied in simulated rain (pH 3.0, 4.0, and 5.6) at deposition rates approximating those observed to result from smelter efluents. Metal concentrations in the roots and shoots of mycorrhizal plants were greater than those of non-mycorrhizal plants. Mycorrhizal enhancement of plant metal uptake increased with greater acidity and higher heavy metal content of treatment. The growth of mycorrhizal plants was reduced compared to non-mycorrhizal plants when metal depostion was combined with simulated acid rain. We propose that mycorrhizal enhancement of heavy metal uptake caused reduced growth in plants exposed to acidic and heavy metal depositions.     

Efficient Zn and Pb uptake by filamentous fungus Paecilomyces marquandii with engagement of metal hydrocarbonates precipitation

Zinc and lead biosorption by living non-growing filamentous fungus Paecilomyces marquandii was examined for its potential application in heavy metals elimination from contaminated areas. Metal uptake by the studied fungus was pH dependent and reached the level of 308 mg of Zn²⁺ g⁻¹ and 505 mg of Pb²⁺ g⁻¹ at pH of 7.5 caused by microprecipitation in slightly alkaline environment. All other metal studies were cultivated with unregulated pH yielding the maximum of 186.2 mg of Zn²⁺ g⁻¹ and 305.8 mg of Pb²⁺ g⁻¹. Interestingly, zinc binding by mycelium increased intensively after 15 h of incubation, whereas the lead concentration in biomass extended gradually and proportionally to the initial concentration and the time of contact. The study showed that thermal pretreatment of mycelium led to a decline in metal uptake, especially in the case of zinc. The mycelium slightly digested by the cell wall lytic enzyme complex, could adsorb lead twice as well after 2 h of exposure whereas zinc loading did not differ from the metal uptake by mycelia without any digestion procedure. The release of potassium ions from the mycelium, concomitant with lead uptake was observed suggesting ion exchange participation in lead binding. Energy-dispersive X-ray analysis, X-ray diffraction and FTIR spectroscopy revealed the presence of both metals hydrocarbonates on the mycelium surface. Additionally, the contribution of carboxyl and amide groups, originating from the mycelium, in metal binding was confirmed by FTIR analysis.The obtained results suggest that the effective metals uptake by P. marquandii was due to a combined mechanism with a dominant role of metabolism dependent microprecipitation.     

The use of seed protein electrophoresis in the study of phylogenetic relationships in Chili pepper (Capsicum L.)

Summary The seed protein profile of eight taxa of Chili peppers obtained by disc electrophoresis was found to be a diagnostic character in the study of phylogenetic relationships. The distinctness of each species and the wild and cultivated nature of concerned taxa has been confirmed. While the clustering of wildC. annuum var. glabriusculum withC. baccatum types indicated that the former is the progenitor of the latter group, the marked differences discernible in the seed protein profile of all other taxa suggest a polyphyletic origin for the genusCapsicum.     

Influence of vesicular-arbuscular mycorrhiza fungi on growth and uptake of various nutrients as well as uptake ratio of fertilizer P for lucerne (Medicago sativa)

Summary Lucerne plants were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus caledonius andRhizobium meliloti and grown in pots in voliére. Treatments were 0,1 and 2 mg P added to 100 g of a soil with low P-fertility. Plants were harvested after 6, 9, 13 and 18 weeks, allowing shoots to regrow between harvests. VAM-infection was determined after 6 and 18 weeks, dry weight, concentration and uptake of P and concentrations of N, K, Ca, Mg, Cu and Zn were determined at all harvests. VAM-inoculation increased growth of shoots, P-concentration and P-uptake at all soil-P levels and the increase was most pronounced at the lowest soil-P level. P-fertilization also increased growth, P-concentration and P-uptake. VAM-inoculation showed tendency to increase N-and K-uptake and decreased Ca-, Mg- and Zn-concentrations in shoots. The uptake ratio of fertilizer-P was increased by VAM.     

Effect of vesicular-arbuscular mycorrhizae on the growth and yield of rice-stubble cultured soybeans

Summary Inoculation with vesicular-arbuscular (VA) mycorrhizal fungiGlomus fasciculatus, G. mosseae, G. etunicatus orAcaulospora scrobiculatus, increased plant dry weight and seed yields of pot-grown soybean plants in sterilized soil. Inoculation with a mixture ofG. fasciculatus, G. mosseae andG. etunicatus, orG. fasciculatus alone, increased seed yields and other agronomic traits of soybean plants grown in a no-tillage, rice-stubble field.     

The rediscovery of Capsicum lanceolatum (Solanaceae), and the importance of nature reserves in preserving cryptic biodiversity

After more than 50 years, the rare autochthonous species, Capsicum lanceolatum, of Mesoamerica was rediscovered in a virgin remnant of the Guatemala cloud forest, Mario D'Arcy Avila Biotopo el Quetzal, a nature reserve for the resplendent quetzal. At all previous known locations C. lanceolatum was extirpated. Specific variation in flower and seed traits of the C. lanceolatum from the Biotopo el Quetzal population suggests it is a heretofore undiscovered population of this species. The usefulness of nature preserves in saving designated and cryptic species is illustrated.     

Arbuscular mycorrhizal fungi can contribute to maintain antioxidant and carbon metabolism in nodules of Anthyllis cytisoides L. subjected to drought

The symbiosis legume-arbuscular mycorrhizal fungi-nitrogen fixing bacteria is of relevant interest in Mediterranean regions where Anthyllis cytisoides L. grows. In these areas, nitrogen is one of the nutrients that most limits plant growth. In addition, the long periods of water deficit decrease the diffusion rate of phosphorus and, consequently, also decrease the biological nitrogen fixation. It is well known that mycorrhizal fungi can improve phosphorus uptake and, recently, some authors have found that antioxidant activities in mycorrhizal plants can delay drought-induced nodule senescence. The objective of our work was to evaluate weather mycorrhizal fungi could preserve the nodule metabolism in A. cytisoides subjected to drought. Results showed that a low soil water content associated with an enhancement of soil compaction accelerated the senescence of nodules in both non-mycorrhizal and mycorrhizal plants. However, while total soluble protein, leghaemoglobin (Lb) content, as well as carbon and antioxidant metabolism significantly decreased in nodules from non-mycorrhizal A. cytisoides subjected to drought, nodules from stressed mycorrhizal plants maintained Lb levels, showed greater rates of carbon metabolism, and exhibited higher enzymatic activities related to the removal of reactive oxygen species. In addition to the greater activity of antioxidant enzymes, other mechanisms related or unrelated to enhanced nodule water status could also be implied in the better nodule functioning observed in mycorrhizal plants under stressful conditions.     

Seed phosphorus (P) content affects growth,and P uptake of wheat plants and their association with arbuscular mycorrhizal (AM) fungi

Two experiments were carried out in a growth chamber and a naturally lit glasshouse to investigate the influence of seed phosphorus (P) reserves on growth and P uptake by wheat plants (Triticum aestivum cv Krichauff), and their association with arbuscular mycorrhizal (AM) fungi. Increased seed P reserves improved plant growth at a range of P supply up to over 100 mg P kg^–1 soil. Plants grown from seeds with high P reserves tended to accumulate more P from soil, which was mainly attributed to better root system development. Mycorrhizal colonisation did not significantly affect P uptake of plants grown with low irradiance (in growth chamber). However, in the naturally lit glasshouse, mycorrhizal plants had significantly higher P concentrations than non-mycorrhizal plants. Furthermore, mycorrhizal plants grown from seeds low in P accumulated similar amounts of P compared with those grown from seeds with high P, indicating that mycorrhizal colonisation may overcome the disadvantage of having low seed P reserves in the field.     

Effect of salinity and inoculation on growth,nitrogen fixation and nutrient uptake ofVigna radiata (L.) Wilczek

This study reports the effect of salinity and inoculation on growth, ion uptake and nitrogen fixation byVigna radiata. A soil EC_e level of 7.5 dS m⁻¹ was quite detrimental causing about 60% decline in dry matter and grain yield of mungbean plants whereas a soil EC_e level of 10.0 dS m⁻¹ was almost toxic. In contrast most of the studied strains of Rhizobium were salt tolerant. Nevertheless, nodulation, nitrogen fixation and total nitrogen concentration in the plant was drastically affected at high salt concentration. A noticeable decline in acetylene reduction activity occurred when salinity level increased to 7.5 dS m⁻¹.     

海马齿对重金属Pb、Zn胁迫的生长及生理生化响应

重金属污染是当前生态环境保护话题的一个热点,当环境污染后,重金属容易被植物体吸收、富集,阻碍植物的生长发育。海马齿(Sesuvium portulacastrum)是一种生长在海边沙地及河流入海口两岸滩涂地带的多年生肉质草本植物,拥有一套有别于淡土植物的遗传背景和耐盐碱生理机制。为了讨论其抗重金属逆境能力,用1/10的Hoagland营养液配制不同浓度的Zn2+、Pb2+溶液,浓度梯度为0、5、10、25、50μmol·L-1(0μmol·L-1为对照组),在Pb、Zn单因子处理下对海马齿的生物量指标节间长度、鲜重、干重和海马齿生理生化指标叶绿素、丙二醛、脯氨酸、可溶性糖、可溶性蛋白和根系活力进行测定,研究其生理活动和生长动态。结果表明:叶片叶绿素含量下降,根系活力降低;同时,高浓度的Pb、Zn离子对海马齿的相对生长率和节间长度存在明显的抑制作用;蛋白质含量显著下降;脯氨酸、可溶性糖、丙二醛能够被诱导且显著升高;但同时,海马齿鲜重和干重并没有显著的变化。说明海马齿对重金属Pb、Zn具有一定的耐受性,为研究海马齿是否可以作为一种净化水源的植物提供理论参考依据。     

Heavy metal uptake by arbuscular mycorrhizas of Elsholtzia splendens and the potential for phytoremediation of contaminated soil

A pot culture experiment and a field experiment were carried out separately to study heavy metal (HM) uptake from soil contaminated with Cu, Zn, Pb and Cd by Elsholtzia splendens Nakai ex F. Maekawa inoculated with arbuscular mycorrhizal (AM) fungi and the potential for phytoremediation. The HM-contaminated soil in the pot experiment was collected from the field experiment site. Two AM fungal inocula, MI containing only one AM fungal strain, Glomus caledonium 90036, and M II consisting of Gigaspora margarita ZJ37, Gigaspora decipens ZJ38, Scutellospora gilmori ZJ39, Acaulospora spp. andGlomus spp., were applied to the soil under unsterilized conditions. In the pot experiment, the plants were harvested after 24 weeks of growth. Mycorrhizal colonization rate, plant dry weight (DW) and P, Cu, Zn, Pb, Cd concentrations were determined. MI-treated plants had higher mycorrhizal colonization rates than MII-treated plants. Both MI and MII increased shoot and root DW, and MII was more effective than MI. In shoots, the highest P, Cu, Zn and Pb concentrations were all observed in the plants treated with MII, while MI decreased Zn and Pb concentrations and increased P but did not alter Cu, and Cd concentrations were not affected by either of two inocula. In roots, MII increased P, Zn, Pb concentrations but did not alter Cu and Cd, and MI did not affect P, Cu, Zn, Pb, Cd concentrations. Cu, Zn, Pb, Cd uptake into shoots and roots all increased in MII-treated plants, while in MI-treated plants, Cu and Zn uptake into shoots and Cu, Zn, Pb, Cd into roots increased but Pb and Cd uptake into shoots decreased. In general, MII was more effective than MI in promoting plant growth and HM uptake. The field experiment following the pot experiment was carried out to investigate the effects of MII under field conditions. The 45-day-old nonmycorrhizal and MII-colonized seedlings of E. splendens were transplanted to HM-contaminated plots and harvested after 5 months. MII-inoculation increased shoot DW and shoot P, Cu, Zn, Pb concentrations significantly but did not alter shoot Cd concentrations, which led to higher uptake of Cu, Zn, Pb, Cd by E. splendens shoots. These results indicate that the AM fungal consortium represented by MII can benefit phytoextraction of HMs and therefore play a role in phytoremediation of HM-contaminated soils.     

Structure and histochemistry of mycorrhizae synthesized between Arbutus menziesii (Ericaceae) and two basidiomycetes,Pisolithus tinctorius (Pisolithaceae) and Piloderma bicolor (Corticiaceae)

Arbutoid mycorrhizae were synthesized in growth pouches between Arbutus menziesii Pursch. (Pacific madrone) and two broad host range basidiomycete fungi, Pisolithus tinctorius (Pers.) Coker and Couch and Piloderma bicolor (Peck) Jülich. P. tinctorius induced the formation of dense, pinnate mycorrhizal root clusters enveloped by a thick fungal mantle. P. bicolor mycorrhizae were usually unbranched, and had a thin or non-existent mantle. Both associations had the well-developed para-epidermal Hartig nets and intracellular penetration of host epidermal cells by hyphae typical of arbutoid interactions. A. menziesii roots developed a suberized exodermis which acted as a barrier to cortical cell penetration by the fungi. Ultrastructurally, the suberin appeared non-lamellar, but this may have been due to the imbedding resin. Histochemical analyses indicated that phenolic substances present in epidermal cells may be an important factor in mycorrhiza establishment. Analyses with X-ray energy dispersive spectroscopy showed that some of the granular inclusions present in fungal hyphae of the mantle and Hartig net were polyphosphate. Other inclusions were either protein or polysaccharides.     

Effect of arbuscular mycorrhizae on soil microbial populations and associated plant performance of the salt marsh grass Spartina patens

The effect of arbuscular mycorrhizae (AM) on soil microbial populations and on growth performance of the high salt marsh plant Spartina patens was investigated in a AM suppression study on field-collected soil cores with S. patens. The application of benomyl resulted in a significant reduction of AM colonization on roots of S. patens, but did not completely suppress AM. Non-treated cores had significantly greater colonization (26 ± 6%) than either benomyl- (12 ± 7%) or benomyl-phosphorus-treated (7 ± 3%) cores at a depth of 2.5 cm. Colonization differences between cores declined with depth (5.0 and 7.5 cm), however, so that at 7.5 cm there was no difference between treatments. This decline was attributed to a reduction in oxygen availability with depth as evidenced by decreasing redox potential. Basic environmental conditions generally resembled those found at the field site. There were no environmental differences between treatments at the depths examined. Cell numbers and specific biomass of DAPI-stained organisms as well as members of the Domain Bacteria were significantly higher when AM colonization was suppressed, while those of the Domains Eucarya and Archaea were not significantly influenced. The increase in both microbial and bacterial population size and biomass in the presence of lower levels of AM colonization is most likely due to increases in carbon exudation to soil and rhizosphere populations that accompany AM suppression. PCR-RFLP analysis of nifH amplicons in bulk soil and rhizosphere at varying depths through the soil cores showed differences in banding patterns between rhizosphere and soil material in the presence of AM. The lack of such strong differences in the benomyl-treated cores suggests that AM colonization more strongly affects the nitrogen-fixing population than do physicochemical conditions (e.g. redox potential) alone. Plant growth performance assessed by analyzing root and leaf biomass, as well as excitation transfer efficiency of open photosynthesis system II (PS II) reaction centers (Fv/Fm) was not significantly influenced by AM. Significant differences were found between treatments for C/N ratios and nitrogen content in leaf tissue, indicating that suppression of AM increased plant nitrogen acquisition.     

Influence of Azospirillum inoculation on the mineral uptake and growth of rice under hydroponic conditions

Seedlings of rice (Oryza sativa L. var. IR42) were inoculated with nitrogen-fixingAzospirillum lipoferum (strain 34H) by immersing the roots in the inoculum for 6 h. The plants were grown in the prescence of NH₄ ⁺-N for 47 days in a hydroponic system under greenhouse conditions. Inoculation significantly enhanced PO₄-ion uptake of the plants in 4 of the 7 samplings tested while the uptake of NH₄-ion was significantly increased in two samplings and was decreased in one sampling. Inoculation reduced root length significantly and caused significant increases in shoot fresh and dry weights. Root surface area was not affected by inoculation. Bacterial population counts suggested thatA. lipoferum survived on the roots till the end of the experiment.