Mycorrhizal colonization and distribution of arbuscular mycorrhizal fungi associated with Michelia champaca L.under plantation system in northeast India

Arbuscular mycorrhizal fungi（AMF） and dark septate endophyte（DSE） colonization were investigated in three different plantation sites（Umdihar,Umsaw and Mawlein） of Meghalaya,northeast India.Isolation and identification of the AMF spore were conducted to evaluate the AMF diversity and host preference in terms of AMF species distribution and abundance in the plantation sites.Results showed that AMF colonization was significantly higher than dark septate endophyte colonization（p〉0.05）.AMF and DSE colonization had a narrow range of colonization,varying from 50.91%-58.95% and 1.84%-4.11%,respectively.Spore density varied significantly in all the sites（p〉0.05）.Out of 29 species identified from 7 genera,the species from Glomus was found to be highly abundant.Sorenson coefficient（Cs） ranged from 0.35-7.0.Species richness varied from 2.0-2.9 in the sites.Total species richness was significantly correlated with total relative abundance（p=0.001）.The distribution,abundance and principal component analysis plot suggest that Glomus macrocarpum,G.multicaulis,G.constrictum and Acaulospora sp 1 were the most host preferred species which possibly may favour the host with proper nutrient acquisition and growth.

Influence of Long-Term Fixed Fertilization on Diversity of Arbuscular Mycorrhizal Fungi

Diversity of arbuscular mycorrhizal fungi(AMF) was investigated in a field that had received long-term fixed ferti-lization(LFF) for 26 years.There were a total of 12 treatments in triplicates with different amounts of manure,urea,calcium phosphate,and potassium chloride.Rhizosphere soil samples of maize and wheat grown in the experimental field in Shandong Province,China,were collected in September 2003 and May 2004,respectively.Arbuscular mycorrhizal fungal spores were isolated and identified using morphological characters.Mycorrhizal colonization percentage,spore density(SD),species richness(SR),relative abundance(RA),and Shannon-Weiner index(SWI) were determined.Nineteen recognized species of AMF belonging to 5 genera were identified.Long-term fixed fertilization significantly influenced colonization percentage,SR,SD,and species diversity of AMF.The adaptability of AMF to soil fertility was different among species.Species richness and SD of AMF in maize and wheat rhizosphere soils were the highest in the nonferti-lization treatment(control) and lowest in the high manure + high nitrogen treatment(M2N2).The SWI decreased as the fertilization level increased except in the low manure treatment(M1) on maize.Compared with the other treatments,Treatment M2N2 significantly reduced SD of Glomus,and the high manure + low nitrogen treatment(M2N1) significantly retarded sporulation of Scutellospora.Manure treatments stimulated sporulation of Glomus mosseae.Spore density of G.mosseae was higher in the high nitrogen + phosphorus + potassium treatment(N2PK) than in the high nitrogen + phosphorus treatment(N2P) and the high nitrogen + potassium treatment(N2K).The SD of S.pellucida was higher in Treatment N2K than Treatments N2PK and N2P.In conclusion,long-term fixed fertilization,especially with high levels of manure and N,decreased SR,SD,and colonization and changed the species composition of AMF.

Dynamics of arbuscular mycorrhizal fungi associated with desert ephemeral plants in Gurbantunggut Desert

Previous studies documented that most desert plants can be colonized by arbuscular mycorrhizal （AM） fungi, however, little is known about how the dynamics of AM fungi are related to ephemerals in desert ecosystems. The dynamics of AM fungi with desert ephemerals were examined to determine the effects of host plant life stages on the development of AM fungi. Mean colonization of ephemeral annual plants was 45% lower than that of ephemeral perennial plants. The colonizations were much higher in the early part of the growing season than in later parts, peaking at flowering times. The phenology of AM fungi in root systems varied among different ephem- erals. The density of AM fungal spores increased with the development of ephemeral annual plants, reached its maximum at flowering times, and then plateaued about 20 days after the aboveground senescence. A significant positive correlation was found between AM fungi spore density and biomass of ephemeral annual plants. The life cycles of AM fungi associated with desert ephemerals were very shod, being about 60-70 days. Soil temperature and water content had no direct influence on the development of AM fungal spores. We concluded that the development of AM fungi was in response to desert ephemeral phenology and life history strategy.

Arbuscular mycorrhizal fungi regulate plant mineral nutrient uptake and partitioning in iron ore tailings undergoing eco-engineered pedogenesis

Excess available K and Fe in Fe ore tailings with organic matter amendment and water-deficiencies may restrain plant colonization and growth,which hinders the formation of eco-engineered soil from these tailings for sustainable and cost-effective mine site rehabilitation.Arbuscular mycorrhizal(AM)fungi are widely demonstrated to assist plant growth under various unfavorable environments.However,it is still unclear whether AM symbiosis in tailings amended with different types of plant biomass and under different water conditions could overcome the surplus K and Fe stress for plants in Fe ore tailings,and if so,by what mechanisms.Here,host plants(Sorghum sp.Hybrid cv.Silk),either colonized or noncolonized by the AM fungi(Glomus spp.),were cultivated in lucerne hay(LH,C:N ratio of 18)-or sugarcane mulch(SM,C:N ratio of 78)-amended Fe ore tailings under well-watered(55%water-holding capacity(WHC)of tailings)or water-deficient(30%WHC of tailings)conditions.Root mycorrhizal colonization,plant growth,and mineral elemental uptake and partitioning were examined.Results indicated that AM fungal colonization improved plant growth in tailings amended with plant biomass under water-deficient conditions.Arbuscular mycorrhizal fungal colonization enhanced plant mineral element uptake,especially P,both in the LH-and SM-amended tailings regardless of water condition.Additionally,AM symbiosis development restrained the translocation of excess elements(i.e.,K and Fe)from plant roots to shoots,thereby relieving their phytotoxicity.The AM fungal roles in P uptake and excess elemental partitioning were greater in LH-amended tailings than in SM-amended tailings.Water deficiency weakened AM fungal colonization and functions in terms of mineral element uptake and partitioning.These findings highlighted the vital role AM fungi played in regulating plant growth and nutrition status in Fe ore tailings technosol,providing an important basis for involvement of AM fungi in the eco-engineered pedogenesis of Fe ore tailings.

Screening of Streptomyces strains helping arbuscular mycorrhizal symbiosis against pepper(Capsicum annuum L.)Phytophthora blight

Mycorrhiza helper bacteria(MHB)can promote the formation and functioning of arbuscular mycorrhizal(AM)symbiosis,but their role and application potential in coping with soil-borne diseases are still unclear.A 14-week greenhouse pot experiment was conducted to obtain several actinomycete strains helping AM symbiosis in suppressing the Phytophthora blight of pepper(Capsicum annuum L.),using a soil inoculated with Phytophthora capsici after sterilization.Five Streptomyces strains,including S.pseudogriseolus,S.albogriseolus,S.griseoaurantiacus,S.tricolor,and S.tendae,as well as the AM fungus(Funneliformis caledonium)were tested.The Phytophthora blight severity reached 66%at full productive stage in the uninoculated control,and inoculation of F.caledonium,S.griseoaurantiacus,and S.tricolor alone significantly decreased(P<0.05)it to 47%,40%,and 35%,respectively.Compared to F.caledonium alone,additional inoculation of S.tricolor or S.tendae,which were isolated from the rhizosphere of a healthy individual in an infected field,significantly elevated(P<0.05)root mycorrhizal colonization,root biomass,fruit yield,and total K acquisitions of pepper and further significantly decreased(P<0.05)blight severity.According to the feature of enhancing disease-suppression by AM symbiosis,both S.tricolor and S.tendae were confirmed as MHB strains here.Specifically,S.tendae had a stronger performance in directly accelerating mycorrhization,while S.tricolor was also an antagonist to the pathogenic P.capsici.Furthermore,S.griseoaurantiacus with the independent disease-suppression function was not an MHB strain here.The redundancy analyses demonstrated that when AM fungus was present,root mycorrhizal colonization replaced soil pH becoming the main factor affecting pepper Phytophthora blight.Thus,S.tricolor and S.tendae seemed to have the value of preparation and application in the future to help AM symbiosis against pepper Phytophthora blight.

Responses of arbuscular mycorrhizal fungi to straw return and nitrogen fertilizer reduction in a rainfed maize field

Straw return can be used to reduce fertilizer input and improve agricultural sustainability and soil health.However,how straw return and reduced fertilizer application affect beneficial soil microbes,particularly arbuscular mycorrhizal fungi(AMF),remains poorly understood.Here,we conducted a five-year field experiment in a rainfed maize field on the Loess Plateau of northwestern China.We tested four treatments with straw return combined with four nitrogen(N)application rates,i.e.,100%,80%,60%,and 0%of the common N application rate(225 kg N ha^(-1)year^(-1))in this region,and two reference treatments(full or no N application),with three replicates for each treatment.Mycorrhizal colonization was quantified and AMF communities colonizing maize roots were characterized using Illumina sequencing.Forty virtual taxa(VTs)of AMF were identified in root samples,among which VT113(related to Rhizophagus fasciculatus)and VT156(related to Dominikia gansuensis)were the predominant taxa.Both root length colonization and AMF VT richness were sensitive to N fertilization,but not to straw return;furthermore,both gradually increased with decreasing N application rate.The VT composition of the AMF community was also affected by N fertilization,but not by straw return,and the community variation could be well explained by soil available N and phosphorus concentrations.Additionally,60%,80%,and full N fertilization produced similar maize yields.Thus,our study revealed the response patterns of AMF to straw return and N fertilizer reduction and showed that straw return combined with N fertilizer reduction may be a promising practice to maintain mycorrhizal symbiosis concomitantly with crop productivity.

Selection experiments for the optimum combination of AMF-plant-substrate for the restoration of coal mines

A complex substrate consisting of fly ash, coal gangue and excess sludge was used as an experimental soil in pot culture experiments. Different soil compositions were tested by observing the growth of arbuscular mycorrhizal （AM） fungi inoculated white clover, rye grass or com. The biomass of the host plants, the mycorrhizal colonization （MC） rate and the mycorrhizal depen- dency （MD） were measured. The research addresses the preferable AMF-plant-substrate combination appropriate for restoration of coal mines. We used two inoculation methods： single-inoculation with Glomus versiforme or Glomus mosseae and a dual inocula- tion with both Ctv and Gm. The results show that G^m is the preferable fungi and that dual inoculation does not show advantages for the restoration of coal mines. White clover inoculated with AM fungi is the most suitable condition for restoration of coal mines. The best weight ratio of fly ash, coal gangue and excess sludge was found to be 20：60：20. The optimum treatment conditions of AMF-plant-activated-substrate are described.

Arbuscular mycorrhizal fungi alter the response of growth and nutrient uptake of snap bean(Phaseolus vulgaris L.) to O_3

The effects of arbuscular mycorrhizal fungi（AMF） Glomus mosseae on the responses to elevated O3 in growth and nutrition of snap bean（Phaseolus vulgaris L.cv Guangzhouyuan） were investigated.Exposure was conducted in growth chambers by using three O3 concentrations（20（CF）,80（CFO1） and 120 nL/L（CFO2）;8 hr/day for 75 days）.Results showed that elevated O3 slightly impacted overall mycorrhizal colonization,but significantly decreased the proportional frequency of hypha and increased the proportional frequency of spores and vesicles,suggesting that O3 had significant effects on mycorrhizal structure.Elevated O3 significantly decreased yield,dry mass and nutrient contents（N,P,K,Ca and Mg） in both non-mycorrhizal and mycorrhizal plants.However,significant interactive effects were found in most variables due to that the reduction by O3 in the mycorrhizal plants was less than that in the non-mycorrhizal plants.Additionally,AMF increased the concentrations of N,P,Ca,and Mg in shoot and root.It can be concluded that AMF alleviated detrimental effects of increasing O3 on host plant through improving plant nutrition and growth.

Contribution of arbuscular mycorrhizal fungi and soil amendments to remediation of a heavy metal-contaminated soil using sweet sorghum

Owing to their potential advantages such as waste reduction,recycling,and economic attributes,fast-growing bioenergy crops have the capacity to effectively phytoremediate heavy metal-contaminated soils.However,little is known about the role of microbial and chemical amendments in phytoremediation using bioenergy crops.Here,we studied the contributions of inoculation with the arbuscular mycorrhizal fungus(AMF)Acaulospora mellea ZZ and three soil amendments,i.e.,hydroxyapatite(HAP),manure,and biochar,at doses of 0.1%and 1%(weight:weight)to heavy metal phytoremediation using sweet sorghum grown on an abandoned agricultural soil,with environmentally realistic contamination(2.6 mg kg^(-1) Cd,1796 mg kg^(-1) Pb,and 1603 mg kg^(-1) Zn),in a plant growth chamber.Mycorrhizal colonization,plant biomass and metal accumulation,metal availability,and soil pH were determined in harvested seedlings 12 weeks after sowing.The results showed that root colonization by indigenous AMF decreased by 28%-46%with HAP,but increased after manure and biochar applications as compared to the no amendment control(CK).The AMF inoculation increased root colonization rates by 16%^(-1)28%and in particular,alleviated the inhibition of HAP.The remediation effects were highly dependent on the amendment type and dose.Among the three soil amendments,HAP was the most effective in promoting plant growth and phytostabilization of Cd,Pb,and Zn and phytoextraction of Cd,particularly at a dose of 1%.Compared to CK,1%HAP decreased DTPA-extractable Cd,Pb,and Zn concentrations in soil by 31%-43%,30%-38%,and 22%-23%,respectively.Manure and biochar also exerted positive effects on heavy metal immobilization,as indicated by lower DTPA extractability,but only the 1%manure treatment showed plant growth-promoting effect.The AMF inoculation did not affect plant growth,but increased soil pH and induced synergistic interactions with amendments on the immobilization of Cd and Pb.In conclusion,soil amendments,particularly HAP,produced positive impacts and synergistic interactions with AMF on the phytostabilization of heavy metals using sweet sorghum.Accordingly,sweet sorghum combined with soil amendments and AMF may be an effective strategy for heavy metal phytoremediation.

Different canopy openings affect underground traits in herbaceous plants of a southern forest in Patagonia

Aims Forest canopy openings modify the natural environment,producing changes in light quality and intensity,precipitation and temperature.In turn,these changes promote the acclimation of understory species.However,little work has been done on underground responses to those environmental changes.The objective of this work was to determine how Osmorhiza depauperata,Phleum alpinum and Poa pratensis change its root length density and root colonization by mycorrhiza as a function of light availability in a Nothofagus pumilio(i.e.lenga)forest harvested following the variable retention prescription.Methods We selected three microenvironments in an old growth forest harvested by the variable retention prescription:aggregated retention,dispersed retention with influence of aggregated retention and dispersed retention.A non-harvested primary forest(PF),similar to the harvested one,was used as a control.Every 2 months,from October 2008 to April 2009,we took soil cores from randomly selected plants.From these soil cores,root length density and colonization percentage(CP)by arbuscular mycorrhizae were estimated.Important Findings Light availability changed significantly among the microenvironments.In general,root length density was significantly greater in P.pratensis than in P.alpinum and both species greater than in O.depauperata.Light availability increased root length density in all species,although the magnitude of these increases difference among species.Root length density was 187%greater in P.pratensis,101%in P.alpinum and 94%in O.depauperata in the disperse retention system than in the PF.Mycorrhiza CP was higher in O.depauperata than in P.alpinum and P.pratensis.Also,it was lower in the PF than in the harvested microenvironments.CPs were very low.