The influence of inorganic nutrient fertilization on the growth,nutrient composition and vesicular-arbuscular mycorrhizal colonization of pretransplant rice (Oryza sativa L.) plants

Summary The effects of P, N and Ca+Mg fertilization on biomass production, leaf area, root length, vesiculararbuscular mycorrhizal (VAM) colonization, and shoot and root nutrient concentrations of pretransplant rice (Oryza sativa L.) plants were investigated. Mycorrhizal plants generally had a higher biomass and P, N, K, Ca, Mn, Fe, Cu, Na, B, Zn, Al, Mg, and S shoot-tissue nutrient concentrations than non-mycorrhizal plants. Although mycorrhizal plants always had higher root-tissue nutrient concentrations than non-mycorrhizal plants, they were not significantly different, except for Mn. N fertilization stimulated colonization of the root system (colonized root length), and increased biomass production and nutrient concentrations of mycorrhizal plants. Biomass increases due to N were larger when the plants were not fertilized with additional P. P fertilization reduced the colonized root length and biomass production of mycorrhizal plants. The base treatment (Ca+Mg) did not significantly affect biomass production but increased the colonized root length. These results stress the importance of evaluating the VAM rice symbiosis under various fertilization regimes. The results of this study suggest that pretransplant mycorrhizal rice plants may have a potential for better field establishment than non-mycorrhizal plants.     

The effect of vesicular-arbuscular mycorrhizae in decreasing Ca acquisition by alfalfa plants in calcareous soils

Summary The legume Medicago sativa L. was grown in three calcareous soils supplied with increasing amounts of soluble phosphate, or a vesicular-arbuscular mycorrhizal (VAM) inoculum. The three test soils had high concentrations of extractable Ca. Analyses of dry-matter production and of the concentrations and content of the nutrients N, P, K, Ca, and Mg in plant tissues showed that, for each soil, a particular level of P application was able to match the VAM effects on N, P, and K levels. The Ca concentration and content in the VAM inoculated plants were, however, significantly lower than those in the P-supplied non-mycorrhizal treatments that matched the VAM effects. The N:P and the K:P ratios were about the same for mycorrhizal and non-mycorrhizal P-supplied control plants in all the three soils, but VAM inoculation lowered the Ca:P ratio in all soils. The mycorrhizae decreased Mg uptake in one of the soils, where non-mycorrhizal plants had high Mg concentrations in tissues. It is concluded that VAM depress the excessive acquisition of Ca by plants in calcareous soils.     

Interactions between drought stress and vesicular-arbuscular mycorrhiza on the growth of Faidherbia albida (syn. Acacia albida) and Acacia nilotica in sterile and non-sterile soils

Summary Faidherbia albida (syn. Acacia albida) (Del.) A. Chev. and Acacia nilotica (L.) Willd. were grown for 18 weeks in sterile and non-sterile soils inoculated with Glomus clarum (Nicolson and Schenck). During this period, drought stress was imposed for the last 10 (F. albida) or 12 weeks (A. nilotica) at 2-week intervals. A greater number of leaves abscissed in drought-stressed mycorrhizal plants of A. nilotica than drought-stressed non-mycorrhizal and unstressed plants. In F. albida, the number of abscissed leaves was few and similar for all treatments. At the end of the drought stress, inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi in sterile soil increased the plant biomass of the two tree species compared to the control plants. In non-sterile soil, the mycorrhizal growth response of introduced G. clarum equalled the effect of indigenous VAM fungi. There were significant interactions between the mycorrhizal and drought stress treatments and between the mycorrhizal and soil treatments for plant biomass and P uptake in F. albida. The absence of these interactions except for that between the mycorrhizal and soil treatments in A. nilotica indicates that the increased plant biomass and nutrient uptake cannot be attributed directly to a mycorrhizal contribution to drought tolerance. F. albida tolerated the drought stress by producing long tap roots and similar weights of dry matter in shoots and roots. Whereas A. nilotica tolerated the drought stress by developing larger root systems able to explore a greater volume of soil, in addition to leaf abscission, for a favourable internal water status. The introduction of G. clarum increased nodulation by A. nilotica under unstressed conditions, but at the expense of a reduced P uptake in sterile soil.     

Dual inoculation of pretransplant stage Oryza sativa L. plants with indigenous vesicular-arbuscular mycorrhizal fungi and fluorescent Pseudomonas spp.

Summary This study examined the response of rice (Oryza sativa L.) plants at the pretransplant/nursery stage to inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi and fluorescent Pseudomonas spp., singly or in combination. The VAM fungi and fluorescent Pseudomonas spp. were isolated from the rhizosphere of rice plants. In the plants grown in soil inoculated with fluorescent Pseudomonas spp. alone, I found increases in shoot growth, and in root length and fine roots, and decreases in root growth, and P and N concentrations. In contrast, in the plants colonized by VAM fungi alone, the results were the reverse of those of the pseudomonad treatment. Dual inoculation of soil with VAM fungi and fluorescent Pseudomonas spp. yielded plants with the highest biomass and nutrient acquisition. In contrast, the plants of the control treatment had the lowest biomass and nutrient levels. The dual-inoculated plants had intermediate root and specific root lengths. The precentages of mycorrhizal colonization and colonized root lengths were significantly lower in the dual-inoculated treatment than the VAM fungal treatment. Inoculation of plants with fluorescent Pseudomonas spp. suppressed VAM fungal colonization and apparently reduced photosynthate loss to the mycorrhizal associates, which led to greater biomass and nutrient levels in dual-inoculated plants compared with plants inoculated with VAM fungi alone. Dual inoculation of seedlings with fluorescent Pseudomonas spp. and VAM fungi may be preferable to inoculation with VAM alone and may contribute to the successful establishment of these plants in the field.     

Use of nutrient: phosphorus ratios to evaluate the effects of vesicular arbuscular mycorrhiza on nutrient uptake in unsterilized soils

Summary Red clover was grown in soil previously treated with P at various rates, and growth, nutrient uptake, nutrient uptake in relation to phosphorus values, and levels of vesicular-arbuscular mycorrhizal (VAM) infection were determined. The soil was a silty clay loam and Glomus lacteum was the only fungus colonizing the plant roots. An examination of the effects of various rates of P application and of VAM colonization on nutrient (P, K, Ca, Mg, Mn, Fe, and Zn) uptake showed that the Mg : P ratio significantly increased and the Mn : P ratio significantly decreased with increasing VAM infection. It is concluded that in the Trifolium pratense-Glomus lacteum symbiosis, mycorrhizae improve Mg uptake and depress Mn uptake.     

Linking sorghum nutrition and production with arbuscular mycorrhizal fungi and alternative soil amendments

Mounting fertilizer costs are disproportionally affecting farmers in developing countries. Alternative soil fertility amendments [worm compost, pyrolyzed carbon (biochar)] and arbuscular mycorrhizal fungi have the potential to reduce these costs while promoting soil health. Our greenhouse study investigated the role of mycorrhizal associations and alternative fertility amendments on the productivity and plant nutrition of grain sorghum. We assessed sorghum (Sorghum bicolor cv. Macia) grown with ten different treatments (combinations of biochar, worm compost, and commercial N and P fertilizers) plus a non‐amended control. An amendment blend containing worm compost, biochar, and 50% of the typically recommended commercial fertilizer rate produced similar plant biomass and protein, similar total tissue mineral contents (Ca, Fe, K, Mg, P, and Zn), and supported ≈ 60% more mycorrhizal fungi in the host plant's roots, compared to sorghum grown with the recommended rate of commercial fertilizer (N and P). Our results indicate the potential of biochar and worm compost to enhance the benefits of mycorrhizal fungi for grain sorghum production and plant nutrition while reducing commercial fertilizer applications.     

Fitting plants to soil through mycorrhizal fungi: plant nutrition in host-endophyte combinations evaluated by the diagnosis and recommendation integrated system

Summary Vesicular-arbuscular mycorrhizal (VAM) fungi improve plant growth in marginal soils. This study was conducted to determine the effects of three species of VAM fungi on plant nutrition in two cultivars of corn (Zea mays L.) and one of sunflower (Helianthus annus L.). Plants were grown in pot cultures under controlled (greenhouse) conditions in a soil high in K, Mg, and P, and low in Ca and N, and were supplied with amounts of VAM-fungal inocula in which equal numbers of infective propagules had previously been determined. Analysis of variance showed highly significant main effects and interactions due to both factors (plant and fungus) for N, P, Ca, and Mg. For K, only plant effects were significant (P<0.043). The uptake of nutrients was selectively enhanced or inhibited by one or the other VAM fungus relative to non-VAM control plants. In sunflower, N concentration was markedly enhanced (73%) by the mixed inoculum of the three fungi, even though individual effects were not significant. Evaluation of leaf nutrient analyses by the Diagnosis and Recommendation Integrated System (DRIS) revealed the utility of this system to rank nutritional effects by VAM fungi in an order of relative nutrient deficiency. The DRIS therefore is seen as a useful tool in evaluating and selecting VAM fungi for the alleviation of specific nutrient disorders.Work was funded by the Program in Science and Technology Cooperation, Office of the Science Advisor, Agency for International Development, as Project No. 8.055, and was conducted in collaboration at the Colegio de Postgraduados and the Western Regional Research Center     

The influence of chemical soil factors on the development of VA mycorrhizas of ash (Fraxinus excelsior L.) and sycamore(Acer pseudoplatanus L.) in pot experiments

The objectives of this study were (1) to investigate effects of soil acidity on the formation of mycorrhizas in ash and sycamore, and (2) to elucidate if mycorrhization can improve the acquisition of Ca, Mg, and P by these tree species. Soil substrates with different Ca, Mg, and Al saturation were used in pot experiments with mycorrhizal ash and sycamore seedlings and various Ca and Mg fertilization treatments. The development of vesicular‐arbuscular‐mycorrhizas (VAM) in both species was considerably affected by the chemical soil properties and by the nutritional status of the plants. Mycorrhizal fungi developed well only in plants growing on basalt‐derived, Ca and Mg rich loam and in substrates fertilized with Ca and Mg carbonate. In these substrates, the pH value, Ca and Mg supply and growth of the plants were optimal. The mycorrhizas degenerated in an acid loam derived from phyllite, in tertiary sand and in all treatments receiving Ca and Mg sulfate. Ash and sycamore suffered from Ca and Mg (P) deficiency, and partly from Al antagonism against Ca and Mg uptake (sycamore) or Al toxicity (ash). The symbiosis between fungi and the plants was disrupted since the tree species and the VAM fungi (from fertile nursery soils) did not adapt to the acidic experimental soil substrates with high Al activity. Consequently, the fungi lost their function of supporting the plants by improved nutrient uptake and the plants likely did not produce enough organic substances for the fungi. In addition, N fertilization possibly suppressed the development of VA mycorrhizas and inhibited new colonization in acid substrates.     

Soil temperature,mycorrhizal infection and nodulation of Medicago truncatula and Trifolium subterraneum

Establishment of vesicular-arbuscular mycorrhizal fungi in plant roots involves a pre-infection phase of propagule germination, hyphal growth and appressorium formation, followed by growth of the fungus within the root. The effect of soil temperature on the pre-infection stage was examined by counting the numbers of fungal “entry-points” on the main roots of Medicago truncatula and Trifolium subterraneum, grown at soil temperatures of 12°, 16°, 20° and 25°C for periods up to 12 days. Increased root temperature was positively associated with increased numbers of “entry-points”. This effect was more marked between 12° and 16°C than at higher temperatures, as shown by comparing plants at the same stage of development (emergence of spade leaf) and by calculating the results as entry points per cm root.The first root nodules appeared sooner at higher temperatures (20° and 25°), but subsequent development of nodules (measured as nodule number and aggregate volume of nodules per plant, up to 21 days) was best at 16°C for both host Rhizobium combinations in non-sterile and autoclaved soil. There was no evidence that competition between mycorrhizal fungi and Rhizobium for infection sites occurred.A method of obtaining numbers of infective propagules of vesicular-arbuscular mycorrhizal fungi in soil is described.     

Nutrient availability and corn growth in a poultry litter biochar‐amended loam soil in a greenhouse experiment

Nutrient‐rich biochar produced from animal wastes, such as poultry litter, may increase plant growth and nutrient uptake although the role of direct and indirect mechanisms, such as stimulation of the activity of mycorrhizal fungi and plant infection, remains unclear. The effects of poultry litter biochar in combination with fertilizer on mycorrhizal infection, soil nutrient availability and corn (Zea mays L.) growth were investigated by growing corn in a loam soil in a greenhouse with biochar (0, 5 and 10 Mg/ha) and nitrogen (N) and phosphorus (P) fertilizer (0, half and full rates). Biochar did not affect microbial biomass C or N, mycorrhizal infection, or alkaline phosphomonoesterase activities, but acid phosphomonoesterase activities, water‐soluble P, Mehlich‐3 Mg, plant height, aboveground and root biomass, and root diameter were greater with 10 Mg/ha than with no biochar. Root length, volume, root tips and surface area were greatest in the fully fertilized soil receiving 10 Mg/ha biochar compared to all other treatments. The 10 Mg/ha biochar application may have improved plant access to soil nutrients by promoting plant growth and root structural features, rather than by enhancing mycorrhizal infection rates.     

Influence of soil on the interactions between endomycorrhizae and Azospirillum in sorghum

Sorghum (S. bicolor L. Moench cv. Bok 8) plants were grown in soil or sand-perlite low in plant-available N and P. Plants were inoculated with a vesicular-arbuscular mycorrhizal (VAM) fungus, or a strain of Azospirillum brasilense or both endophytes together. Plants received a nutrient solution which did not contain N or P. Increases in plant dry weight, shoot-to-root ratios, and the N content of dually-infected plants could be accounted for by summing the VAM and Azospirillum effects. For sorghum inoculated with both endophytes, the presence of A. brasilense in the rhizosphere increased VAM colonization and biomass, while the N input due to Azospirillum decreased, possibly due to competition for carbohydrates.Comparisons between sorghum grown with or without VAM-fungal infection in four growth media showed that edaphic factors other than P availability determined the host response to VAM infection. The P-fixing capacity of the soil, rather than the amount of available (NaHCO₃-extractable) P, influenced the balance between mutualistic and parasitic VAM-fungal growth.     

蚯蚓菌根互作对土壤酶活、 甘薯根系生长及养分吸收的影响

【目的】蚯蚓和丛枝菌根真菌处于不同的营养级,但在促进植物生长和提高土壤肥力等方面却都发挥着积极作用。单独对土壤微生物或土壤动物的研究较多,但对土壤微生物与土壤动物之间相互作用的研究很少。因此研究它们对土壤和植物生长的作用可为挖掘土壤生物的潜力和提高土壤生物肥力提供依据。【方法】采用盆栽试验,研究了蚯蚓(Eisenia fetida)与丛枝菌根真菌(Rhizophagus irregularis)互作对甘薯生长和养分吸收的影响。试验采用两因素完全随机试验设计,分为接种和不接种菌根真菌及添加和不添加蚯蚓。试验共4个处理: 不加菌根和蚯蚓(CK); 接种菌根真菌(AM); 添加蚯蚓(E); 添加蚯蚓和菌根真菌(E+AM),每个处理4次重复。调查了甘薯养分吸收、 根系形态及土壤养分变化,采用Canoco4.5软件对土壤生物与植物对应关系进行RDA (redundancy analysis)分析。【结果】接种菌根真菌显著提高了甘薯地上和地下部生物量(P0.05),而添加蚯蚓的处理仅提高了甘薯地上部生物量。同时添加蚯蚓和菌根的处理显著提高了甘薯地上地下部生物量,并且高于其他三个处理(P0.05)。与对照相比,接种菌根真菌显著提高了土壤磷酸酶活性(P0.01),增幅近一倍; 同时提高了土壤磷的植物有效性,土壤有效磷含量下降了30%左右。添加蚯蚓后土壤脲酶活性从5.45 mg NH+4-N/g显著增加到8.71 mg NH+4-N/g,土壤碱解氮的含量从5.82 mg/kg显著增加到6.89 mg/kg (P0.05)。RDA分析表明蚯蚓菌根互作对甘薯地上和地下部氮磷含量、 根表面积、 根体积、 根平均直径和根尖数均存在显著的正交互效应。蚯蚓菌根互作通过调控土壤酶和改变土壤养分有效性促进甘薯对土壤氮磷养分的吸收。【结论】蚯蚓(Eisenia fetida)通过调控土壤脲酶和碱性磷酸酶增加了土壤中氮磷的有效性从而促进甘薯地上部生长。丛枝菌根真菌(Rhizophagus irregularis)通过调控土壤磷酸酶和增加植株地上地下部吸磷量从而促进甘薯生长。添加蚯蚓或接种菌根真菌均能增加根系吸收面积和根体积从而促进甘薯对养分的吸收。蚯蚓和菌根真菌相互作用通过调控土壤酶和改变土壤养分有效性以及促进根系发育从而互补的促进甘薯养分吸收和生长。     

Influence of mycorrhiza vs. soluble phosphate on growth,nodulation, and N2 fixation (15N) in alfalfa under different levels of water potential

Summary The legume Medicago sativa (+Rhizobium melilott) was grown under controlled conditions to study the interactions between soluble P in soil (four levels), or a mycorrhizal inoculum, and the degree of water potential (four levels) in relation to plant development and N₂ fixation. ¹⁵N-labelled ammonium sulphate was added to each pot for a qualitative estimate of N₂ fixation, in order to rank the effects of the different treatments.Dry-matter yield, nutrient content and nodulation increased with the amount of plant-available P in the soil, and decreased as the water stress increased, for each P-level. The mycorrhizal effect on dry matter, N yield, and on nodulation was little affected by the water potential. Since P uptake was affected by the water content in mycorrhizal plants, additional mechanisms, other than those mediated by P, must be involved in the mycorrhizal activity.There was a positive correlation between N yield and nodulation for the different P levels and the mycorrhizal treatment at all water levels. A high correlation between plant unlabelled N content and atom% ¹⁵N excess was also found for all levels of P. In mycorrhizal plants, however, the correlation between unlabelled N yield and ¹⁵N was lower. This suggests that mycorrhiza supply plants with other N sources in addition to those derived from the improvement on N₂ fixation.     

Defoliation effects on Plantago lanceolata resource allocation and soil decomposers in relation to AM symbiosis and fertilization

Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.     

Mitigation of alkaline stress by arbuscular mycorrhiza in zucchini plants grown under mineral and organic fertilization

A greenhouse experiment was carried out during the spring–summer 2009 to test the hypotheses that: (1) arbuscular‐mycorrhizal (AM) inoculation with a biofertilizer containing Glomus intraradices gives an advantage to overcome alkalinity problems, (2) mineral fertilization is more detrimental to AM development than organic fertilization on an equivalent nutrient basis. Arbuscular mycorrhizal (AM) and non‐AM of zucchini (Cucurbita pepo L.) plants were grown in sand culture with two pH levels in the nutrient solution (6.0 or 8.1) and two fertilization regimes (organic or mineral). The high‐pH nutrient solution had the same basic composition as the low‐pH solution, plus an additional 10 mM NaHCO₃ and 0.5 g L^–1 CaCO₃. Increasing the concentration of NaHCO₃ from 0 to 10 mM in the nutrient solution significantly decreased yield, plant growth, SPAD index, net assimilation of CO₂ (A_CO2), N, P, Ca, Mg, Fe, Mn, and Zn concentration in leaf tissue. The +AM plants under alkaline conditions had higher total, marketable yield and total biomass compared to –AM plants. The higher yield and biomass production in +AM plants seems to be related to the capacity of maintaining higher SPAD index, net A_CO2, and to a better nutritional status (high P, K, Fe, Mn, and Zn and low Na accumulation) in response to bicarbonate stress with respect to –AM plants. The percentage root colonization was significantly higher in organic‐fertilized (35.7%) than in mineral‐fertilized plants (11.7%). Even though the AM root colonization was higher in organic‐fertilized plants, the highest yield and biomass production were observed in mineral‐fertilized plants due to the better nutritional status (higher N, P, Ca, and Mg), higher leaf area, SPAD index, and A_CO2.     

Vesicular-arbuscular mycorrhizal infection of “host” and “non-host” plants: Effect on the growth responses of the plants and competition between them

The effect of host plant infection on the mycorrhizal response of non-host plants was examined in a double pot system. The absence of nutrient transfer from a mature host (sorghum) to a young-non-host (cabbage) indicates the inability of the atypical infection of non-host plants to take up nutrients. However, nutrient transfer between mature and young sorghum plants, possibly through mycelial connections, was observed. The direction of this nutrient transfer seemed to depend on the nutrient status of the nurse plant. Because the nurse plants were grown in P-deficient soil, mature sorghum competed with young sorghum plants. Sorghum infected with vesicular-arbuscular (VA) mycorrhiza was better equipped than non-infected sorghum to compete with young cabbage for soil nutrients.     

Influence of O3, rainfall acidity,and soil Mg status on growth and ectomycorrhizal colonization of loblolly pine roots

Root biomass, length, and branching frequency, and number and type of mycorrhizal short roots were determined for loblolly pine seedlings grown at two levels of soil Mg and exposed to chronic levels of O₃ and simulated acidic rainfall. Seedlings were planted in a sandy loam soil having approximately 15 or 35 mg kg^?1 Mg and were exposed to subambient; ambient, or twice ambient concentrations of O₃ in open top chambers from May through October. Seedlings also received ambient amounts of simulated rainfall at pH 3.8 or 5.2. Root biomass, length, and branching frequency were not significantly affected by O₃, rainfall acidity, or soil Mg treatments. Seedlings grown in the subambient O₃ treatment had a greater number of short roots infected with mycorrhizae than seedlings grown in ambient or twice ambient O₃ treatments, but trends were not statistically significant. Increasing rainfall acidity and soil Mg concentration resulted in a significantly (P = 0.07) greater number of mycorrhizal short roots, due primarily to an increased occurrence of one corraloid mycorrhizal type. Results suggest that mycorrhizal fungi differ in their response to O₃, rainfall acidity, and soil Mg status, and suggest that mycorrhizal infection is more sensitive than seedling root growth to O₃, acidic rainfall, and soil Mg status.     

Effects of weathering state of coarse‐soil fragments on tree‐seedling nutrient uptake

Fine earth accumulated within the weathering fissures of the coarse‐soil fraction (particles > 2 mm), so called “stone‐protected fine earth”, can provide a high short‐term nutrient release by cation exchange. It is thus hypothesized that unweathered gneiss particles cannot provide plants with exchangeable‐cation nutrients and that biological weathering is needed to include silicate‐bound nutrients into biochemical cycles. In a microcosm experiment, ectomycorrhizal Norway spruce (Picea abies) seedlings were grown on either weathered or unweathered paragneiss coarse‐soil fragments under natural hydraulic and climatic boundary conditions. A nutrient solution containing N, P, and K was added, however Mg and Ca could only be taken up from the coarse‐soil substrate. Solutes in drainage were analyzed during the experiment; plant nutrient uptake was determined after the experiment ended. Solute dynamics depended on the weathering state of the substrates: unweathered gneiss showed high initial Mg and Ca fluxes that diminished strongly afterwards, whereas weathered gneiss showed a much more gradual and sustainable release of these cations. Patterns in dissolved organic C and sulfate drainage indicated that the internal pores of weathered gneiss fragments contained organic material most likely as a result of living spaces from microorganisms. Plant biomass did not differ between treatments, however Mg content was higher in seedlings grown on weathered gneiss. Nutrient budgets demonstrated that the “stonesphere” of weathered gneiss can act as a quasi‐constant nutrient source whereas unweathered gneiss only provided high initial nutrients fluxes. In nutrient‐depleted, acidified fine‐earth environments, the coarse‐soil fraction may therefore act as a retreat for nutrient‐adsorbing tissues and as a buffer for nutrient shortages.     

Mycorrhizai associations with some plant species in a soil strip of different successional stages in Egypt

In this study, soil and plant samples were collected from a strip of soil comprising four successional stages from the eastern desert plateau to the Nile Valley, Egypt. On one hand, some essential elements [i.e., potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S)] and water contents decreased on transition from the desert soil to the Nile Valley. Soil nitrite content was the highest in Nile Valley soil and decreased toward desert soil. pH values of the soils did not strongly differ and were moderately alkaline. Root colonization with arbuscular‐mycorrhizae (AM) fungi of 33 plant species (11 cultivated and 22 wild) collected from the study area was highest in eastern desert plateau and decreased toward the Nile Valley. Mycorrhizai spore counts reflected the root colonization data. The decrease in mycorrhizai colonization was explained on the basis of difference in soil porosity, soil water contents, and toxicity of nitrite. Contents of K, Ca or Mg in some species were increased by increasing the colonization percentage of roots by AM fungi. Increasing the infection percentage of roots decreased or maintained the ratio of Na K+Ca+Mg (in meq) in the shoots of investigated plants. The contents of chlorophyll, soluble sugars, and protein significantly increased as a result of increasing colonization value. Also, mycorrhizal root colonization improved the water status of most plant species. These results suggest that increasing infection by AM fungi in the newly reclaimed soil may enable the plants to maintains its internal water status and mineral balance through decreasing the ratio of distressing ions to the nutrient ones.     

Arbuscular mycorrhizal fungi mitigates heavy metal toxicity adverse effects in sewage water contaminated soil on Tagetes erecta L

The aim of this experiment was to evaluate the impact of colonization with arbuscular mycorrhizal (AM) fungus Glomus constrictum on the biomass production, flower quality, chlorophyll content, macronutrients and heavy metals content of marigold (Tagetes erecta L.) planted under uncontaminated soil and watered with various rates of sewage water. Sewage water utilization significantly decreased biomass production, characters of flower, nutrient concentration and rates of mycorrhizal colonization of mycorrhizal (M) and non-mycorrhizal (NM) marigold as compared to control untreated plants especially at the higher rates, but the reduction rate was proportionally higher in non-AM treatments. Mycorrhizal plants had significantly greater yield, relative chlorophyll content, leaf area, flower quality and element (P, N, K and Mg) content compared to non-inoculated marigold plants irrigated with or without sewage water. Furthermore, AM inoculation had highly decreased heavy metal (Zn, Co, Mn, Cu) content in tissues as compared to equivalent non-inoculated plants grown under sewage water application. Growing marigold with AM inoculum can reduce toxicity of heavy metals and enhance biomass production and P uptake. The results support the view that AM have a protective function for the host plant, hence playing a potential function in soil polluted immobilization processes, and thus are of assessing the potential of phytoremediation of heavy metals in sewage water contaminated soil.