Direct assessment of mineral phosphorus availability to tropical crops using 32P labelled compounds

The availability to plants of phosphorus (P) derived from sparingly soluble iron and aluminium phosphates was directly assessed with ³²P labelled compounds in two glasshouse trials.In the first experiment, the comparative availability of all mineral phosphate (P) compounds to maize increased with time (14 to 42 days post emergence) and plant total P uptake, but P source did not affect the growth or total plant uptake of P. The comparative availability of the amorphous AlPO₄ (Al-P), crystalline AlPO₄ (variscite), amorphous FePO₄ (Fe-P), and crystalline FePO₄ (strengite) compared to KH₂PO₄ (=100) was 53.1, 3.4, 38.9, and 1.9%, respectively. In the second experiment, the availability of Fe-P, strengite, and KH₂PO₄ to several topical crop species was examined. There was no difference between maize, sorghum, mungbean, cowpea or soybean in their ability to utilise Fe-P or KH₂PO₄, although maize utilised strengite more than the other species. The major difference between these species in their ability to acquire P appears to be a difference in ability to locate soluble soil P rather than differences in their ability to access different pools of soil P.The advantages of using neutron irradiation to directly measure P absorption from mineral P compounds over traditional methodologies is discussed.     

Fungal endophyte presence and genotype affect plant diversity and soil-to-atmosphere trace gas fluxes

Aims

Novel fungal endophyte (Neotyphodium coenophialum; Latch, Christensen and Samuels; Glenn, Bacon, and Hanlin) genotypes in symbiosis with tall fescue (Lolium arundinaceum; Schreb. Darbysh.) have been recently introduced to agricultural seed markets. These novel endophytes do not produce the full suite of toxins that the ‘common toxic’ form does, and therefore, may not have the same consequences on plant and soil processes. Here, we evaluated the effects of endophyte presence and genotype on ecosystem processes of tall fescue stands.

Methods

We quantified the effects of the presence of the common toxic endophyte (CT), two novel endophyte genotypes (AR-542, AR-584), no endophyte (endophyte free, E-), and a mixture of all endophyte statuses (mix) within a single genotype of tall fescue (PDF) on various soil and plant parameters.

Results

Endophyte presence and genotype affected tall fescue cover and plant species diversity: cover—CT, AR-542, AR -584, mix > E- and species diversity—E- > AR-542, AR -584 > CT, mix. Most measured soil parameters had significant endophyte effects. For example, higher fluxes of soil CO₂ and N₂O were measured from stands of AR-542 than from the other endophyte treatments.

Conclusions

These results indicate that endophyte presence and genetic identity are important in understanding the ecosystem-scale effects of this agronomically important grass-fungal symbiosis.     

Endophytes inconsistently affect plant communities across Schedonorus arundinaceus hosts

Fungal endophytes in cool-season grasses may affect communities at multiple trophic levels. However, it is unclear whether community-scale endophyte effects arise due to the endophyte itself or as a result of unique, endophyte–host interactions. We used a long-term field experiment to test whether common-toxic (CT) and non-ergot alkaloid-producing (novel) endophytes in Schedonorus arundinaceus (tall fescue) forage cultivars consistently affect communities across tall fescue hosts. Tilled plots (2 × 2 m; Guelph, ON) were seeded with Georgia 5 and Jesup cultivars containing either the CT or AR542 (novel) endophyte and allowed to be re-colonized by plant species from the local propagule pool. Non-seeded control plots were included to assess effects of seeding the non-native grass. We assessed plant, invertebrate, soil moisture, and soil nutrient responses to the endophyte–cultivar treatments after four growing seasons. Seeding tall fescue affected plant species abundances, but not richness, and did not consistently alter soil moisture and nutrient pools. Endophyte identity in the tall fescue cultivars affected the communities, but effects were not consistent between cultivars. Within Georgia 5, the AR542 endophyte reduced tall fescue abundance and altered the invertebrate community relative to CT plots. Within Jesup, the AR542 endophyte reduced species evenness and decreased soil moisture during dry periods relative to CT plots. Endophyte effects were not consistent between cultivars, and it is probable that the community-scale effects of endophyte infection in tall fescue cultivars arise due to unique interactions between cultivar and endophyte.     

Leaf endophyte Neotyphodium coenophialum modifies mineral uptake in tall fescue

Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon and Hanlin, a fungal endophyte found primarily in shoots of tall fescue (Festuca arundinacea Shreb.), can modify rhizosphere activity in response to phosphorus (P) deficiency. In a controlled environment experiment, two cloned tall fescue genotypes (DN2 and DN4) free (E-) and infected (E+) with their naturally occurring endophyte strains were grown in nutrient solutions at low P (3.1 ppm) or high P (31 ppm) concentrations for 21 d. Endophyte infection increased root dry matter (DM) of DN4 by 21% but did not affect root DM of DN2. Under P deficiency, shoot and total DM were not affected by endophyte but relative growth rate was greater in E+ than E- plants. In high P nutrient solution, E+ plants produced 13% less (DN2) or 29% more (DN4) shoot DM than E- plants. Endophyte affected mineral concentrations in roots more than in shoots. Regardless of P concentration in nutrient solution, E+ DN2 accumulated more P, Ca, Zn and Cu but less K in roots than E- plants. When grown in high P nutrient solution, concentrations of Fe and B in roots of E+ DN2 plants were reduced compared with those of E- plants. Concentrations of P, Ca and Cu in roots of DN4 were less, but K was greater in E+ than E- plants. In shoots, E+ DN2 had greater concentrations of Fe and Cu than E- DN2, regardless of P concentration in nutrient solution. Genotype DN4 responded to endophyte infection by reducing B concentration in shoots. Nutrient uptake rates were affected by endophyte infection in plants grown in low P nutrient solution. A greater uptake rate of most nutrients and their transport to shoots was observed in DN2, but responses of DN4 were not consistent. Results suggest that endophyte may elicit different modes of tall fescue adaptation to P deficiency. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization of the Mineral Phosphate-Solubilizing Activity of <Emphasis Type="Italic">Pantoea aglomerans</Emphasis> MMB051 Isolated from an Iron-Rich Soil in Southeastern Venezuela (Bolívar State)

The mineral phosphate-solubilizing (MPS) activity of a Pantoea agglomerans strain, namely MMB051, isolated from an iron-rich, acidic soil near Ciudad Piar (Bolívar State, Venezuela), was characterized on a chemically defined medium (NBRIP). Various insoluble inorganic phosphates, including tri-calcium phosphate [Ca₃(PO₄)₂], iron phosphate (FePO₄), aluminum phosphate (AlPO₄), and Rock Phosphate (RP) were tested as sole sources of P for bacterial growth. Solubilization of Ca₃(PO₄)₂ was very efficient and depended on acidification of the external milieu when MMB051 cells were grown in the presence of glucose. This was also the case when RP was used as the sole P source. On the other hand, the solubilization efficiency toward more insoluble mineral phosphates (FePO₄ and AlPO₄) was shown to be very low. Even though gluconic acid (GA) was detected on culture supernatants of strain MMB051, a consequence of the direct oxidation pathway of glucose, inorganic-P solubilization seemed also to be related to other processes dependent on active cell growth. Among these, proton release by ammonium (NH₄⁺) fixation appeared to be of paramount importance to explain inorganic-P solubilization mediated by strain MMB051. On the contrary, the presence of nitrate (NO₃^–) salts as the sole N source affected negatively the ability of MMB051 cells to solubilize inorganic P.     

The Influence of Phosphate Uptake on Cation Uptake in Fusarium oxysporum f. sp. vasinfectum

Fusarium oxysporum grown in a low phosphate medium was found to take up several times as much K from KH₂PO₄ as from KCI solutions. Large amounts of phosphate also were taken up from KH₂PO₄. Similar large uptakes of Na and phosphate took place from solutions of NaH₂PO₄. Substantial quanties of phosphate were taken up from solutions of Ca(H₂PO₄)₂ in the absence of any appreciable Ca uptake. When the fungus was grown in a medium containing high phosphate, little or no uptake of phosphate from KH₂PO₄ solutions occured and the K Uptake was at the same level as from KCI solutions. During large phosphate uptake sizable reductions in the organic acid content of the fungal cells were observed. Much, but not all, of the data could be explained on the basis of maintenance of charge balance within the cells. – The respiratory rate of fungus, grown in a low P medium, was markedly increased in KH₂PO₄ solution. Fungus, grown in a medium with high phosphate, had a higher respiratory rate which showed only a slight response to KH₂PO₄ solution. Fungus, grown in a medium with high phosphate, had a higher respiratory rate which showed only a slight response to KH₂PO₄.     

Mechanisms of phosphate solubilization by fungal isolates when exposed to different P sources

The use of phosphate-solubilizing fungi is a promising biotechnological strategy in the management of phosphorus (P) fertilization, as it enables the utilization of rock phosphates (RP) or the recovery of P fixed in soil particles. The objective of our study was to evaluate fungal isolates for mechanisms of solubilization of P-bearing compounds, such as AlPO₄, FePO₄, Ca₃(PO₄)₂, Araxá RP, and Catalão RP. Four fungal isolates obtained from Brazilian soils were characterized in liquid media: Aspergillus niger FS1, Penicillium canescens FS23, Eupenicillium ludwigii FS27, and Penicillium islandicum FS30. A. niger FS1 was the only isolate able to solubilize all of the P sources, solubilizing 71, 36, 100, and 14 % of the P from AlPO₄, FePO₄, Ca₃(PO₄)₂, and RPs, respectively. Medium acidification was an effective solubilization mechanism, particularly for Ca₃(PO₄)₂. The other P sources were mainly solubilized through organic acids produced by the fungi. Oxalic acid, produced exclusively by A. niger FS1, and citric acid were decisive factors in the solubilization of AlPO₄ and FePO₄. Penicillium isolates produced more gluconic acid than A. niger FS1 in all treatments. However, this higher production did not result in higher solubilization for any of the P sources, showing that gluconic acid contributes little to the solubilization of the P sources evaluated. The higher capacity of medium acidification and the production of organic acids with stronger metal-complexation activity are characteristics that confer to A. niger FS1 a wider action on insoluble P sources. Consequently, this isolate qualifies as a promising candidate for application in the management of P fertilization.     

Temporal and spatial patterns of soil water following wildfire-induced changes in plant communities in the Great Basin in Nevada,USA

Infection of tall fescue (Festuca arundinacea Schreb.) with its endemicNeotyphodium coenophialum-endophyte (Morgan-Jones and Gams) Glenn, Bacon and Hanlin appears to reduce copper (Cu) concentrations in forage and serum of grazing animals, contributing to a range of immune-related disorders. A greenhouse experiment was conducted to identify effects of novel endophyte strains on Cu acquisition by tall fescue (Festuca arundinacea Schreb.) varieties Grasslands Flecha and Jesup infected with a novel, non ergot producing endophyte strain AR542, and two perennial ryegrass (Lolium perenne L.) varieties Aries and Quartet infected with a novel, non lolitrem B producing strain AR1, and their noninfected (E−) forms. Individual endophyte/grass associations were cultivated in nutrient solutions at 1.0 (P+) and 0.0 mM (P−) phosphorus concentrations. The Cu²⁺-binding activity of extracellular root exudates, and concentrations of Cu and other heavy metals in roots and shoots were measured. Extracellular root exudates of AR542-infected vs. E− tall fescue had higher Cu²⁺-binding activity only in P− nutrient solution as shown by lower concentration of free Cu²⁺ (0.096 vs. 0.188 mmol Cu²⁺ g⁻¹ root DM, respectively). The Cu²⁺-binding activity by root exudates of perennial ryegrass was not affected by endophyte infection, but was higher (i.e., lower concentration of free Cu²⁺) in P− vs. P+ nutrient solution (0.068 vs. 0.114 mmol Cu²⁺ g⁻¹ root DM). In this hydroponic experiment, Cu concentrations in shoots of both grasses were not a function of Cu²⁺-binding activity and endophyte effects on heavy metal concentrations in shoots and roots were specific for each variety. The Cu²⁺-binding activity of extracellular root exudates may affect Cu accumulation by field-grown, endophyte-infected tall fescue under P-limiting growth conditions and warrants verification by more specific methods.     

Encroachment of Endophyte-infected on Endophyte-free Tall Fescue

Persistence of endophyte-free (E-) tall fescue (Festuca arundinaceaSchreb.)is erratic. Little information exists as to how fast endophyte(Neotyphodium coenophialum)-infected (E+) tall fescue mightencroach on E- tall fescue and whether specific conditions mightinfluence the speed of encroachment. Plots of E+ and E- tallfescue genotypes 7 and 17 were established using a modifiedNelder's design to compare performance of the E+ forms of theplants in pure and mixed communities at different populationdensities. The plots were planted at the USDA Southern PiedmontConservation Research Laboratory in Watkinsville, Georgia, andthe University of Georgia Plant Sciences Farm in Bogart, Georgia.Plants were grown over a 5 year period and dry matter yieldmonitored 1, 3, and 5 years after establishment. Relative crowdingcoefficients were calculated for each to establish trends ofencroachment of the E+ on the E- plants in the mixed communities.Generally, dry matter yields of E+ tall fescue were greaterthan E- tall fescue regardless of whether they were grown inpure or mixed communities. As time progressed, the differencein dry matter yield between E+ and E- tall fescue grown in mixedcommunities was greater than that of the pure communities. Relativecrowding coefficients increased as time progressed. Relativecrowding coefficients at the Watkinsville location were greaterafter 5 years than those at the Plant Sciences Farm. Therefore,site specific conditions exist which affect the competitivenessof E- tall fescue and degree of encroachment by E+ tall fescue.Research is needed to identify which biotic, abiotic and managementvariables exacerbate encroachment of E+ tall fescue to betterdefine the conditions which best suit E- tall fescue.Copyright1998 Annals of Botany Company tall fescue, endophyte,Neotyphodium coenophialum,Festuca arundinacea, competition, population density     

Host Status of Endophyte-Infected and Noninfected Tall Fescue Grass to Meloidogyne spp

Tall fescue grass cultivars with or without endophytes were evaluated for their susceptibility to Meloidogyne incognita in the greenhouse. Tall fescue cultivars evaluated included, i) wild-type Jesup (E+, ergot-producing endophyte present), ii) endophyte-free Jesup (E-, no endophyte present), iii) Jesup (Max-Q, non-ergot producing endophyte) and iv) Georgia 5 (E+). Peach was included as the control. Peach supported greater (P ≤ 0.05) reproduction of M. incognita than all tall fescue cultivars. Differences in reproduction were not detected among the tall fescue cultivars and all cultivars were rated as either poor or nonhosts for M. incognita. Suppression of M. incognita reproduction was not influenced by endophyte status. In two other greenhouse experiments, host susceptibility of tall fescue grasses to two M. incognita isolates (BY-peach isolate and GA-peach isolate) did not appear to be related to fungal endophyte strain [i.e., Jesup (Max-Q; nontoxic endophyte strain) vs. Bulldog 51 (toxic endophyte strain)]. Host status of tall fescue varied with species of root-knot nematode. Jesup (Max-Q) was rated as a nonhost for M. incognita (BY-peach isolate and GA-peach isolate) and M. hapla, a poor host for M. javanica and a good host for M. arenaria. Bulldog 51 tall fescue was also a good host for M. arenaria and M. javanica, but not M. incognita. Jesup (Max-Q) tall fescue may have potential as a preplant control strategy for M. incognita and M. hapla in southeastern and northeastern United States, respectively.     

Enhanced stability of a rumen-derived xylanase using SpyTag/SpyCatcher cyclization

A phosphate solubilizing bacterium ZB was isolated from the rhizosphere soil of Araucaria, which falls into the species Pantoea agglomerans. Optimization for phosphate solubilization by strain ZB was performed. At optimum culture conditions, the isolate showed great ability of solubilizing different insoluble inorganic phosphate sources viz. Ca₃(PO₄)₂ (TCP), Hydroxyapatite (HP), CaHPO₄, AlPO₄, FePO₄ along with rock phosphates (RPs). Inoculation with planktonic cells was found to enhance dissolved phosphorous as compared to that achieved by symplasma inoculation. Besides inoculation with different status of cells, pre-incubation could also exert a great effect on phosphate solubilization ability of P. agglomerans. When isolate ZB was cultured with glucose as carbon sources, phosphorous was more efficiently dissolved from HP and RP without pre-incubation in comparison to that obtained with pre-cultivation. Pre-cultivation, however, was more suitable for P solubilization than no pre-cultivation when bacteria were grown with xylose. A positive correlation was detected between the production of organic acids and phosphate solubilization. P. agglomerans ZB possessed many plant growth promotion traits such as N₂ fixation and production of indole 3-acetic acid, phytase, alkaline phosphatase. Pot experiment showed inoculation with single isolate ZB or biofertilizer prepared from semi-solid fermentation of isolate ZB with spent mushroom substrate (SMS) compost could enhance plant growth with respect to number of leaves, plant leave area, stem diameter, root length, root dry mass, shoot dry mass and biomass when compared to the abiotic control, revealing strain ZB could be a promising environmental-friendly biofertilizer to apply for agricultural field.

     

Retention of added K,Ca and P by Pseudoscleropodium purum growing under an oak canopy

Abstract

Retention of K, Ca and Pby Pseudoscleropodium purum growing under oak in Windsor Forest was examined following treatment, over 9 days, with 10 mol m^?3 CaCl₂ or KH₂PO₄ Concentrations of the added elements and Mg were determined in the intercellular, exchangeable (cell wall) and intracellular fractions of the green tissues before nutrient addition and at intervals (0–205 days) afterwards.

Increases of cations in the intercellular fraction of treated shoots were transient. Addition of K and Ca markedly increased levels of these cations in the exchangeable fraction and significantly reduced the concentration of exchangeable Mg. The changes in exchangeable cations were progressively reversed under field conditions indicating that their levels are in dynamic equilibrium with element concentrations in precipitation and/or throughfall rather than the result of a continuousaccumulation process.

Net uptake of K and Ca into the protoplasts of treated P. purum was slight but substantial net gain (+178%) of P occurred in KH₂PO₄ treated plants. One-third of the additional P was lost within 15 days due, either, to redistribution within the shoot, or, to leakage. Intracellular Mg fell significantly below controls 2 weeks after treatment with CaCl₂ suggesting that Mg uptake involves prior adsorption onto the cell wall exchange sites. Fluctuations in K, Ca and Mg levels of untreated P. purum indicated that appreciable net uptake of natural inputs occurred, particularly during autumn when leachates from the senescing tree canopy may be received.

Element concentrations, including Mg, were highest at a shaded site where the moss remained moist for long periods suggesting that either ion absorption is favoured by protracted contact times or that metabolic nutrient requirement increases with increasingly mesic conditions.     

Microsite conditions influence nutritive value characteristics of a tall fescue cultivar devoid of,or infected with a native,or a novel non-ergogenic endophyte

Tall fescue [Lolium arundinaceum, Schreb., S.J. Darbysh.] productivity and persistence often benefits from association with Neotyphodium coenophialum [Morgan-Jones and Gams], Glenn, Bacon, and Hanlin) endophyte. The influence of novel, non-ergogenic endophytes on nutritive value is unclear, especially when simultaneous stresses (e.g., defoliation and shading) are imposed on the association. We conducted a field experiment using Jesup tall fescue that had either a native or novel non-ergogenic fungal endophyte (AR542; referred to as MaxQ?), or that was endophyte free. Dry matter production and nutritive value including crude protein (CP), non-structural carbohydrates (TNC), ergo- and loline alkaloids, and phenolics were determined for plants stockpiled or clipped repeatedly in sites differing in the amount of light. Productivity varied less among sites when plants were infected with a native endophyte compared to novel or no endophyte. The trend suggests that native endophyte contributed to resilience of the host in this experiment. Leaf dry matter content was affected by host–endophyte association interacting with light availability suggesting differences in leaf composition could occur. Herbage CP increased, whereas TNC decreased with increasing shade. The concentration of loline alkaloids, irrespective of host–endophyte association, tended to increase in leaves with decreasing light availability and could be related to the relatively greater N concentrations in shade-grown leaves. Phenolics decreased in leaves, but increased in stembases as light availability decreased. The combination of increased loline alkaloids in leaves and phenolics in stembases, suggests that shade-grown tall fescue might have some competitive advantage based on the known anti-herbivory attributes of loline alkaloids and phenolic compounds.     

Influence of phosphorus nutrition on growth and metabolism of Duo grass (Duo festulolium)

Use of suitable plants that can extract and concentrate excess P from contaminated soil serves as an attractive method of phytoremediation. Plants vary in their potential to assimilate different organic and inorganic P-substrates. In this study, the response of Duo grass (Duo festulolium) to variable rates of soil-applied potassium dihydrogen phosphate (KH₂PO₄) on biomass yield and P uptake were studied. Duo grown for 5 weeks in soil with 2.5, 5 and 7.5 g KH₂PO₄ kg^?1 soil showed a significantly higher biomass and shoot P content of 8.3, 11.4 and 12.3 g P kg^?1 dry weight respectively compared to plants that received no soil added P. Also, the ability of Duo to metabolize different forms of P-substrates was determined by growing them in sterile Hoagland's agar media with different organic and inorganic P-substrates, viz. KH₂PO₄, glucose-1-phosphate (G1P), inositiol hexaphosphate (IHP), adenosine triphosphate (ATP) and adenosine monophosphate (AMP) for 2 weeks. Plants on agar media with different P-substrates also showed enhanced biomass yield and shoot P relative to no P control and the P uptake was in the order of ATP > KH₂PO₄ > G1P > IHP = AMP > no P control. The activities of both phytase (E.C.3.1.3.26) and acid phosphatases (E.C.3.1.3.2) were higher in all the P received plants than the control. Duo grass is capable of extracting P from the soil and also from the agar media and thus it can serve as possible candidate for phytoextraction of high P-soil.     

Soil organic carbon fractions differ in two contrasting tall fescue systems

The value of tall fescue (Festuca arundinacea Schreb.) for C sequestration in addition to forage production and soil conservation is of current interest. However, studies relating to the impacts of endophyte infected (E+) and endophyte free (E?) tall fescue on soil organic matter fractions are few. This study examined how E+ and E? growth affected soil C fractions 4 years after establishment. The study site was at the University of Kentucky research farm, Lexington, Kentucky, USA. From soil cores in replicated fields we measured total C, particulate organic matter C (POM C), microbial biomass C (MBC), mineralizable C (Min C), C in aggregates, and aggregate distribution at depths of 0 to 15 and 15 to 30 cm. Significant effects between E+ and E- fescue were sometimes observed for MBC, Min C, C in micro-aggregates, and aggregate distribution, but not for total C, and POM C. At 0?C15 cm MBC (E+ 26% greater than E?), Min C (E+ 43% lower than E?), C associated with micro-aggregates (E+ 15% lower than E?), and micro-aggregates (46% more micro-aggregates in E+ than E?), were affected by endophyte infection, confirming hypotheses that early changes in soil properties were reflected in labile C fractions and soil structure. Endophyte infection status in tall fescue has quantifiable effects on C sequestration and soil structure, achievable in a relatively short period that can be used to monitor conservation efforts and the consequences of pasture renovation strategies.     

Increasing phosphorus concentration in the extraradical hyphae of <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> DAOM 197198 leads to a concomitant increase in metal minerals

Plants associated with arbuscular mycorrhizal fungi (AMF) acquire phosphorus via roots and extraradical hyphae. How soil P level affects P accumulation within hyphae and how P in hyphae influences the accumulation of metal minerals remains little explored. A bi-compartmented in vitro cultivation system separating a root compartment (RC), containing a Ri T-DNA transformed carrot root associated to the AMF Rhizophagus irregularis DAOM 197198, from a hyphal compartment (HC), containing only the extraradical hyphae, was used. The HC contained a liquid growth medium (i.e., the modified Strullu-Romand medium containing P in the form of KH₂PO₄) without (0 μM) or adjusted to 35, 100, and 700 μM of KH₂PO₄. The accumulation of P and metal minerals (Ca, Mg, K, Na, Fe, Cu, Mn) within extraradical hyphae and AMF-colonized roots, and the expression of the phosphate transporter gene GintPT were assessed. The expression of GintPT in the extraradical hyphae did not differ in absence of KH₂PO₄ or in presence of 35 and 100 μM KH₂PO₄ in the HC but was markedly reduced in presence of 700 μM KH₂PO₄. Hyphal P concentration was significantly lowest in absence of KH₂PO₄, intermediate at 35 and 100 μM KH₂PO₄ and significantly highest in presence of 700 μM KH₂PO₄ in the HC. The concentrations of K, Mg, and Na were positively associated with the concentration of P in the extraradical hyphae developing in the HC. Similarly, P concentration in extraradical hyphae in the HC was related to P concentration in the growth medium and influenced the concentration of K, Mg, and Na. The accumulation of the metal mineral K, Mg, and Na in the extraradical hyphae developing in the HC was possibly related to their function in neutralizing the negative charges of PolyP accumulated in the hyphae.     

一株耐盐日本曲霉的筛选及其溶磷促生作用

【目的】从内蒙古种植葵花的盐碱地中筛选高效溶磷真菌,为盐碱地增产节肥开发生物肥料提供溶磷菌种资源。【方法】利用ITS r DNA序列鉴定菌株、固体培养基测定耐盐性,液体摇床培养与盆栽试验结合分析菌株溶磷能力,盆栽和田间试验明确菌株M1促进作物生长和增产作用;LC-MS技术测定菌株M1在液体培养基中分泌有机酸和植物激素含量,明确菌株M1的溶磷和促生机理。【结果】溶磷菌株M1鉴定为日本曲霉(Aspergillus japonicus)。液体培养基接种菌株M1培养6 d,以Ca_3(PO_4)_2为磷源时上清液有效磷达1020.89 mg/L,溶解率为63.30%;以AlPO_4为磷源时有效磷达995.69 mg/L,溶解率为48.59%;以贵州开阳磷矿粉、江苏锦屏磷矿粉、云南晋宁磷矿粉、河北钒山磷矿粉和云南昆阳磷矿粉为磷源接种菌株M1,从晋宁磷矿粉释放的有效磷浓度最高,达到363.64 mg/L。菌株M1可耐受10%NaCl。将M1制备的菌剂分别接种于施用Ca_3(PO_4)_2、AlPO_4和开阳磷矿粉3种磷源的4种盆栽试验土壤包括北京石灰性潮土、安徽黏性潮土、安徽水稻土和山东沿海盐潮土。结果显示,菌株M1对玉米植株促生效果显著,玉米植株鲜重比对照提高2.14%–90.91%、干重增加22.15%–268.28%;土壤有效磷提高21.81–24.27 mg/kg。菌株M1与4种土壤的适配性均高于对照菌株DSM 821。田间小区花生产量结果显示,接种溶磷菌剂M1增产效果最好,花生果实产量达4.46 t/hm~2,比不接种菌剂的对照处理增加0.81 t/hm~2,增产22.19%。菌株M1在含有磷酸三钙、磷酸铝和开阳磷矿粉3种难溶磷培养液中经过6 d培养,均产生7种有机酸,其中草酸和柠檬酸含量最高,分别为616.16 mg/L和413.69 mg/L;培养液均能检测到吲哚乙酸(IAA)和玉米素,IAA含量为15.45–77.58 mg/L,玉米素浓度为0.06–0.11 mg/L。【结论】获得了一株高效溶解多种难溶磷的日本曲霉菌M1,它能显著增加土壤有效磷、促进玉米生长和花生增产,与4种典型土壤适配性好,具有良好的农业应用前景。     

Influence of genetic variation in the fungal endophyte of a grass on an herbivore and its parasitoid

Neotyphodium coenophialum (Glenn, Bacon, Price & Hanlin) (Ascomycota: Clavicipitaceae) is an endophytic fungus that lives symbiotically within grasses and produces alkaloids that can help protect its hosts from some insect pests. We used laboratory‐based experiments to investigate whether fungal genotype influences an herbivore and its parasitoid. We tested whether variation in novel isolates, plus a control lacking fungal infection, affected preference by fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae: Amphipyrini), and growth and survival of Euplectrus comstockii Howard (Hymenoptera: Eulophidae: Euplectrini), a parasitoid of fall armyworm. Caterpillars preferred leaf blades in choice experiments from uninfected tall fescue [Lolium arundinaceum (Schreb.) Darbysh., cultivar Jesup (Poaceae)] and tended to avoid blades from plants containing fungal isolates AR502, AR542, or the most common strain from pastures in Georgia, USA, in tall fescue. However, caterpillars fed as much on leaf blades from plants containing isolate AR502 as from those lacking infection. Parasitoid pupal mass was not influenced by fungal isolate, yet fungal isolate did influence parasitoid survival. Survival was higher than expected for parasitoids reared from hosts fed plants lacking fungal infection, but was lower than expected for those reared from hosts fed plants infected with the common strain or AR542 isolates. In contrast, parasitoids reared from hosts fed plants infected with isolate AR502 did not experience higher mortality than expected by chance. Our results show that N. coenophialum can modify bottom‐up trophic cascades through direct effects on herbivores, as well as indirect effects on a natural enemy of the herbivores and that the fungus may influence the tritrophic interaction in ways that counterbalance herbivore protection provided by the symbiont. Our work also shows that these effects are influenced by fungal genotype. As attempts are made to produce forage cultivars with strains of fungal endophyte that lack negative influences on livestock, it will be prudent for investigators to assess the multi‐trophic effects of these novel associations within agroecosystems.     

Inoculation with Pseudomonas putida PCI2, a phosphate solubilizing rhizobacterium,stimulates the growth of tomato plants

The use of phosphate solubilizing plant growth-promoting microorganisms as inoculants assists in the hydrolysis of insoluble forms of phosphorus leading to increased plant growth. Pseudomonas putida PCI2 was evaluated for phosphatase activity and solubilization of AlPO₄ and FePO₄. The effect of different incubation temperatures, concentrations of NaCl and different pH on growth of PCI2 and P solubilization was studied. PCI2 proved to be positive for phosphatase activity, solubilized AlPO₄ and hydrolyzed Ca₃(PO₄)₂ even in medium with 5 % NaCl. In addition, PCI2 produced 45 % units of siderophores. The production of IAA by PCI2 was stimulated in vitro by the addition of different concentrations of L-tryptophan to the culture medium. Assays with tomato seedlings showed that the length of the root was reduced as the concentration of IAA increased. On the other hand, inoculation with PCI2 caused a clear growth-promoting effect on shoot growth in the presence of L-tryptophan. P. putida PCI2 is adapted to different environmental conditions and has potential to be developed and used as an inoculant for increasing the growth of tomato plants.     

Neotyphodium Coenophialum-Infected Tall Fescue and Its Potential Application in the Phytoremediation of Saline Soils

The growth response of endophyte-infected (EI) and endophyte-free (EF) tall fescue to salt stress was investigated under two growing systems (hydroponic and soil in pots). The hydroponic experiment showed that endophyte infection significantly increased tiller and leaf number, which led to an increase in the total biomass of the host grass. Endophyte infection enhanced Na accumulation in the host grass and improved Na transport from the roots to the shoots. With a 15 g l^?1 NaCl treatment, the phytoextraction efficiency of EI tall fescue was 2.34-fold higher than EF plants. When the plants were grown in saline soils, endophyte infection also significantly increased tiller number, shoot height and the total biomass of the host grass. Although EI tall fescue cannot accumulate Na to a level high enough for it to be termed a halophyte, the increased biomass production and stress tolerance suggested that endophyte / plant associations had the potential to be a model for endophyte-assisted phytoextraction in saline soils.