Comparative effects of vesicular-arbuscular mycorrhizal inoculation and phosphorus fertilization on growth and phosphorus uptake of maize (Zea mays L.) and sorghum (Sorghum bicolor L.) plants under drought-stressed conditions

Maize (Zea mays L.) and sorghum (Sorghum bicolor L.) Moench (local variety called Masakwat) plants were grown in a sterilized low-P soil in the greenhouse for 12 weeks. Each plant species was either mycorrhizal with vesicular-arbuscular mycorrhizal (VAM) fungi, non-mycorrhizal but minimally fertilized with soluble P, or non-mycorrhizal but highly fertilized with soluble P. Drought stress was imposed after 4 weeks at weekly intervals. Under unstressed conditions, leaf area, shoot dry weights, xylem pressure, and soil water potentials were similar for VAM and the two non-mycorrhizal P-fertilized treatments but each of the VAM-infected species had a greater total root length. Total P uptake was similar for the maize treatments but higher for VAM than non-mycorrhizal P-fertilized sorghum treatments. Under drought-stressed conditions, the growth parameters and soil water potential were similar for all maize treatments but they were reduced by mycorrhizal inoculation in sorghum. Greater water extraction occurred in drought-stressed mycorrhizal sorghum. In both plant species, total P uptake and P uptake per unit root length (including unstressed species) were significantly enhanced in non-mycorrhizal P-fertilized treatments compared with the mycorrhizal treatment. Except for the root dry weight of sorghum plants, there were no differences in the growth parameters and P uptake between minimally and highly P-fertilized non-mycorrhizal treatments for either maize or sorghum. The increased total root length in drought-stressed mycorrhizal sorghum plants and the similar infected root lengths in unstressed and drought-stressed sorghum plants may have caused high C partitioning to drought-stressed mycorrhizal roots and therefore caused the reduced growth parameters in mycorrhizal plants compared to the non-mycorrhizal P-fertilized counterparts. The results indicate that P fertilization in addition to mycorrhizal inoculation may improve the drought tolerance of maize and sorghum plants.     

Effects of ammonium and nitrate on the growth of vesicular-arbuscular mycorrhizalErythrina poeppigiana O.I. Cook seedlings

Erythrina poeppigiana, a woody tropical plant, was inoculated with vesicular-arbuscular mycorrhizal (VAM) fungiGlomus etunicatum Becker and Gerdeman,G. mosseae Nicol. and Gerd. Gerdeman and Trappe, orG. intraradices Schenk and Smith. Growth, N uptake, and nutrition were evaluated in VAM-inoculated plants and controls fertilized with two levels (3 or 6 mM) of either NH _inf4 ^sup+ -N or NO _inf3 ^sup- -N. The response by the mycorrhizal plants to N fertilization, according to N source and/or level differed significantly from that of the control plants. In general, the growth of the mycorrhizal plants was similar to that of the non-mycorrhizal plants when N was provided as NH _inf4 ^sup+ . When the N source was NO _inf3 ^sup- the control plants grew significantly less than the VAM plants. Inoculation with VAM fungi gave yield increases of 255 and 268% forG. etunicatum-colonized plants, 201 and 164% forG. mosseae-colonized plants and 286 and 218% forG. intraradices-colonized plants fertilized with 3 and 6 mM NO _inf3 ^sup- -N, respectively. The increased growth and acquisition of nutrients by plants fertilized with NO _inf3 ^sup- -N and inoculated with VAM shows that VAM mycelium has a capacity for NO _inf3 ^sup- absorption. The results also showed thatE. poeppigiana seedlings preferred NH _inf4 ^sup+ as an N source.G. etunicatum was the most effective endophyte, not only increasing N, P, Ca, Mg, and Zn uptake in the presence of NO _inf3 ^sup- fertilizer but also P and Mg in the presence of NH _inf4 ^sup+ applications. From these results we conclude that VAM symbiosis affects N metabolism inE. poeppigiana plants and that this species can overcome limitations on the use of NO _inf3 ^sup- -N by the mediation of VAM fungi.     

Response of Passiflora setacea to Mycorrhization and Phosphate Fertilization in a Semiarid Region of Brazil

The Caatinga is a unique biome that encompasses nearly 11% of Brazil's territory and contains diverse vegetation composed of trees and bushes that have been scarcely studied from the economic perspective. In this context, Passiflora setacea may constitute a strategic alternative for agriculture because it produces fruit that has commercial potential and is tolerant to some diseases. Some species of Passiflora show more robust growth when associated with arbuscular mycorrhizal fungi (AMF) and are dependent on mycorrhization. In this study, the response of P. setacea to phosphate (P) fertilization and mycorrhization with Claroideoglomus etunicatum was evaluated. The experimental design included eight replicates of four randomized treatments: non-inoculated plants (NI), plants fertilized with phosphorus (P), mycorrhized plants (AMF), and plants that were both fertilized and mycorrhized (P+AMF). The plant height, leaf number, leaf area, fresh biomass (FB), and dry biomass (DB) of the shoots and roots, nutrient content, mycorrhizal colonization (MC), and the number of glomerospores (NG) in the rhizosphere were evaluated. The MC and the NG were reduced by phosphate fertilization. The development of the mycorrhized plants was significantly better than the NI and P treated plants for all of the variables tested. Inoculation with C. etunicatum promoted the growth of P. setacea seedlings even in the absence of phosphate fertilization, reducing production costs and strengthening the potential of P. setacea as a viable agricultural alternative for the semiarid region.     

Inoculation withGlomus mosseae improves N2 fixation by field-grown soybeans

Summary A field study carried out in a sandy, relatively acid Senegalese soil with a low soluble P content (7 ppm) and low vesicular-arbuscular mycorrhizal (VAM) populations showed that soybean responded toGlomus mosseae inoculation when the soluble P level in the soil had been raised by the addition of 22 kg P ha^–1. In P-fertilized plots, N₂ fixation of soybean, assessed by the A value method, was 109 kg N₂ fixed hat when plants were inoculated withRhizobium alone and it reached 139 kg N₂ fixed ha^–1 when plants were dually inoculated withRhizobium andGlomus mosseae using an alginate bead inoculum. In addition to this N₂ fixation increase (+28%),Glomus mosseae inoculation significantly improved grain yield (+13%) and total N content of grains (+16%). This success was attributed mainly to the low infection potential of the native VAM populations in the experimental site. In treatments without solubleP or with rock phosphate, no effect of VAM inoculation was observed.     

Effects of mes [2(n‐morpholino)‐ethanesulfonic acid] and ph on mineral nutrient uptake by mycor‐rhizal and nonmycorrhizal maize

Mycorrhizal (+VAM) and nonmycorrhizal (‐VAM) maize (Zea mays L.) plants were grown in sand culture in a greenhouse to determine effects of MES [2(N‐morpholino)‐ethanesulfonic acid] (2.0 mM) and pH (4.0, 5.0, 6.0, and 7.0) on mineral nutrient uptake. Plants were inoculated with the vesicular‐arbuscular mycorrhizal (VAM) isolate Glomus intraradices UT143. Shoot and root dry matter yields were lower in plants grown with MES (+MES) than without MES (‐MES), and decreased as pH increased. Shoot concentrations of N, Ca, Mg, Mn, and Zn were generally higher in +MES than in ‐MES plants, and nutrient contents of most nutrients were generally higher in + MES than in ‐MES plants. Concentrations of N, Ca, Mg, and Mn increased and P, S, and Fe decreased, while contents of all measured nutrients except Mn and Zn decreased as pH increased. Concentrations of Mn, Fe, Zn, and Cu were higher in +VAM than in ‐VAM plants, and contents of P and Ca were higher in ‐VAM than in +VAM plants and Zn content was higher in +VAM than in ‐VAM plants. MES had marked effects on mineral nutrient uptake which should be considered when MES is used to control pH of nutrient solutions for growth of maize.     

Effects of excess manganese on mineral uptake in mycorrhizal sorghum

Associations between vesicular‐arbuscular mycorrhizal (VAM) fungi and manganese (Mn) nutrition/toxicity are not clear. This study was conducted to determine the effects of excess levels of Mn on mineral nutrient uptake in shoots and roots of mycorrhizal (+VAM) and non‐mycorrhizal (‐VAM) sorghum [Sorghum bicolor (L) Moench, cv. NB9040]. Plants colonized with and without two VAM isolates [Glomus intraradices UT143–2 (UT1 43) and Gl. etunicatum UT316A‐2 (UT316)] were grown in sand irrigated with nutrient solution at pH 4.8 containing 0, 270, 540, and 1080 μM of added Mn (as manganese chloride) above the basal solution (18 μM). Shoot and root dry matter followed the sequence of UT316 > UT143 > ‐VAM, and shoots had greater differences than roots. Shoot and root concentrations and contents of Mn, phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and copper (Cu were determined. The +VAM plants generally had higher mineral nutrient concentrations and contents than ‐VAM plants, although ‐VAM plants had higher concentrations and contents of some minerals than +VAM plants at some Mn levels. Plants colonized with UT143 had higher concentrations of shoot P, Ca, Zn, and Cu and higher root Mg, Zn, and Cu than UT316 colonized plants, while UT316 colonized plants had higher shoot and root K concentrations than UT143 colonized plants. These results showed that VAM isolates differ in enhancement of mineral nutrient uptake by sorghum.     

Effect of VA Mycorrhiza on Dry Weight and Phosphorus Content in Shoots of Cereal Crops Fertilized with Rock Phosphates at Different Soil pH and Temperature Levels

The influence of the VAM fungi Glomus macrocarpum and G. manihotis on shoot dry weight and P contents in the shoots of various graminaceous species was studied in pot culture experiments. The treatments included fertilization with different rock phosphates, four soil pH levels (pH 4.5, 5.5, 6.5, 7.5) and four soil temperatures (20, 25, 30, 35°C). The rock phosphate treatments were compared with soluble phosphate (mono calcium phosphate, MCP) and with a check (no P fertilizer, OP). Increases of shoot dry weight up to 143% could be found with mycorrhizal Triticum aestivum using Kodjari rock phosphate as P source. In the presence of VAM, Sorghum bicolor and T. aestivum fertilized with any of the rock phosphates, except Kola, produced yields comparable with those of plants fertilized with MCP, at soil pH 5.5 to 7.5 and at 25°C soil temperature. As the soil pH increased from 5.5 to 7.5 dry weight declined. Likewise, yields decreased with increasing soil temperature and at 35°C VAM showed no effect in all treatments.     

Rate variables associated with P uptake,utilization and growth of mycorrhizal and nonmycorrhizal Leucaena leucocephala 1

A sequential harvest experiment was conducted in the greenhouse to determine relative growth rate (RGR), specific absorption rate (SAR) of P, P utilization rate (PUR) and P utilization efficiency (PUE) of vesicular‐arbuscular mycorrhizal (VAM) and nonmycorrhizal Leucaena leucocephala. Total P content, root length and total dry‐matter yield of mycorrhizal plants were significantly higher than those of nonmycorrhizal plants beginning on 15, 25 and 25 days after planting, respectively. The length of root colonized by Glomus aggregatum increased exponentially with time and leveled off 30 days after planting. In mycorrhizal plants, RGR of roots (based on total root length) was lower than those of RGR of infected roots till 30 days after planting, after which time the trend was reversed. Although, RGR based on dry‐matter yield was higher in mycorrhizal plants than in nonmycorrhizal plants, the differences observed were not statistically significant. SAR of P was higher in mycorrhizal plants than in nonmycorrhizal ones till 30 days after planting. Even though, total P contents and concentrations in mycorrhizal plants were higher than nonmycorrhizal plants, PUR and PUE were higher in nonmycorrhizal plants. These results indicate that, although VAM plants were very efficient in P absorption and accumulation, they were not superior to non‐VAM plants in P utilization. However, plant species forming effective symbiosis with VAM fungi are likely to be successful competitors in nutrient‐poor environments than plants not infected with the fungi.     

Influence of bacteria on growth and phosphorus nutrition of mycorrhizal corn

Com plants were grown in a non‐sterile soil in a greenhouse or in hydroponic culture in a growth chamber. We studied the influence of chitinolytic, pectinolytic, P‐solubilizing bacterial isolates, and a collection of bacterial strains on the development of native vesicular‐arbuscular mycorrhizal (VAM) populations, colonization of roots by the VAM fungus Glomus fasciculatum and their influence on the phosphorus (P) nutrition and growth of plants. As compared with VAM native control, the most potent stimulants for root colonization of soil‐grown plants by the VAM native population was a strain of Agrobacterium radiobacter and isolate H30. All bacteria used significantly supressed shoot fresh weight of mycorrhizal plants (‐13% up to ‐37%), with the exception of Agrobacterium. Under hydroponic conditions, the P‐solubilizing isolate F27 significantly stimulated the intensity of mycorrhiza, the number of arbuscules in roots, and increased both the P concentration and P content in corn shoots (+30% and +35%), than did the VAM fungus alone. Isolate F27 significantly increased shoot dry weight as compared with the mycorrhizal control. The other bacteria did not influence biomass production of corn.     

Influence of inoculation with bradyrhizobium japonicum and glomus claroideum on seed yield of soybean under greenhouse and field conditions

Soybean plants [Glycine max (L.) Men., cv. Polanka], inoculated with the VAM fungus Glomus claroideum Schenck and Smith and Bradyrhizobium japonicum strain D344, were grown in pots and in the field. The VAM fungus positively influenced N2 fixation, nodulation and N, P, K, and Mg concentrations in the leaves. In pots, (at green pods formation) VAM inoculated plants produced a 24% greater biomass as compared with non‐inoculated plants colonized by native VAM populations. Under field conditions characterized by a high level of P and N, the seed yield of VAM inoculated plants increased in comparison with non‐ and only rhizobia‐inoculated soybean (+28% and 17%, respectively). Glomus claroideum was capable of competing with the native VAM populations both in the greenhouse and in the field experiment.     

Boron fertilization,vesicular‐arbuscular mycorrhizal colonization and growth of citrus jambhiri lush

The role of boron (B) fertilization in the vesicular‐arbuscular mycorrhizal (VAM) colonization and growth of container‐grown Citrus seedlings was evaluated. Citrus jambhiri Lush, seedlings inoculated with Glomus fasciculatum, Glomus etunicatum or non‐inoculated were grown in a sandy loam soil for sixteen weeks. Seedlings were fertilized with 25 ug/ml B applied to the foliage as a mist, to the soil as a solution, or to both the foliage and the soil. Boron applied to the foliage or to the soil significantly increased root exudation of reducing sugars and amino acids two weeks after seedling germination. Subsequently, foliar fertilization with B significantly increased VAH colonization of seedlings relative to the controls. Plants inoculated with G. fasciculatum were larger and had greater VAM development than those inoculated with G. etunicatum. The growth of the noninoculated seedlings was not enhanced by B fertilization. The superior VAH colonization and growth of inoculated seedlings fertilized with B suggests that B stimulates the efficacy of plant fungi symbiosis.     

Growth response of field-grown Siratro (Macroptilium atropurpureum Urb.) and Aeschynomene american L. to inoculation with selected vesicular-arbuscular mycorrhizal fungi

Summary The effect of inoculation with a selected isolate of Glomus etunicatum Becker and Gerdemann and one of G. intraradices Schenck and Smith on the growth and nutrient content of Macroptilium atropurpureum Urb. cv. Siratro and Aeschynomene americana L., at applied P levels of 10, 30, 60, and 120 kg ha^-1, was studied under field conditions. At all P levels and for all harvests, the shoot dry mass of Siratro and A. americana were greater for the plants inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungi than the control plants. Differences between the VAM fungus-inoculated and the control plants were most marked between 30 and 90 kg ha^-1 of applied P and diminished at 120 kg ha^-1. At the first harvest of Siratro, the plants inoculated with G. etunicatum had a greater shoot dry mass than those inoculated with G. intraradices, for all levels of applied P. However, for subsequent harvest of Siratro and for the one harvest of A. americana the response of shoot dry mass to the two VAM fungi was equivocal. Fungal inoculation gave at least a 30% saving in the amount of P fertilizer required (40 kg ha^-1) for the maximum yield. The plants inoculated with VAM fungi had a greater tissue concentration and total content of P and N than the control plants at low and intermediate levels of applied P. The percentage of root colonized by VAM fungi for the inoculated plants of the two legumes increased linearly with P additions up to 60 kg ha^-1. The conclusion is that under amended (limed and fertilized) soil conditions, inoculation with selected VAM fungi can improve the establishement and growth of forage legumes in fields that contain ineffective populations of native VAM fungi.     

Effect of triple superphosphate and biowaste compost on mycorrhizal colonization and enzymatic P mobilization under maize in a long‐term field experiment

Phosphorus (P) fertilizers and mycorrhiza formation can both significantly improve the P supply of plants, but P fertilizers might inhibit mycorrhiza formation and change the microbial P cycling. To test the dimension and consequences of P fertilizer impacts under maize (Zea mays L.), three fertilizer treatments (1) triple superphosphate (TSP, 21–30 kg P ha^?1 annually), biowaste compost (ORG, 30 Mg ha^?1 wet weight every third year) and a combination of both (OMI) were compared to a non‐P‐fertilized control (C) in 2015 and 2016. The test site was a long‐term field experiment on a Stagnic Cambisol in Rostock (NE Germany). Soil microbial biomass P (P_mic) and soil enzyme activities involved in P mobilization (phosphatases and ß‐glucosidase), plant‐available P content (double lactate‐extract; P_DL), mycorrhizal colonization, shoot biomass, and shoot P concentrations were determined. P deficiency led to decreased P immobilization in microbial biomass, but the maize growth was not affected. TSP application alone promoted the P uptake by the microbial biomass but reduced the mycorrhizal colonization of maize compared to the control by more than one third. Biowaste compost increased soil enzyme activities in the P cycling, increased P_mic and slightly decreased the mycorrhizal colonization of maize. Addition of TSP to biowaste compost increased the content of P_DL in soil to the level of optimal plant supply. Single TSP supply decreased the ratio of P_DL:P_mic to 1:1 from about 4:1 in the control. Decreased plant‐benefits from mycorrhizal symbiosis were assumed from decreased mycorrhizal colonization of maize with TSP supply. The undesirable side effects of TSP supply on the microbial P cycling can be alleviated by the use of compost. Thus, it can be concluded that the plant‐availability of P from soil amendments is controlled by the amendment‐specific microbial P cycling and, likely, P transfer to 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.     

Phosphorus uptake and growth of barley as affected by soil temperature and mycorrhizal infection

A glasshouse study was conducted to investigate the effects of soil temperatures of 20, 15 and 10°C on growth and phosphorus (P) uptake of barley (Hordeum vulgare L. cv. Galleon) inoculated with Glomus intraradices Schenck & Smith. Vesicular‐arbuscular (VA) mycorrhiza formation was significantly reduced as the soil temperature decreased. Plant growth depression due to temperature stress was more pronounced in mycorrhizal plants than in non‐mycorrhizal plants. The lower the soil temperature, the higher was the root‐shoot ratio. The ratio was also higher in non‐mycorrhizal plants than in mycorrhizal plants. Concentration of P in roots was influenced by mycorrhiza. Significant interaction between mycorrhiza and soil temperature was observed for root dry matter and specific P uptake (P uptake per unit weight of root). Compared to non‐mycorrhizal plants, specific P uptake in mycorrhizal plants was higher.     

Influence of vesicular-arbuscular mycorrhizae on phosphate fertilizer efficiency in two tropical acid soils planted with micropropagated oil palm (Elaeis guineensis jacq.)

Summary The influence of vesicular-arbuscular mycorrhizae on the efficiency of triple superphosphate and rock phosphate fertilizers was compared in two tropical, acid, P-fixing soils (Ivory Coast) in which the available P was labelled with ³²PO _inf4 ^sup3- . Both soils were planted with micropropagated oil palms. The growth reponses to the fertilizer applications were low unless accompanied by VAM inoculation, but both fertilizers were equally available to plants. Isotopic-dilution kinetics analyses indicated that the rock phosphate was solubilized in both soils and there was an enrichment of the labile pool of plant-available P, similar to that with superphosphate. The specific activity and the fraction of P derived from either fertilizer was similar in both mycorrhizal and non-mycorrhizal plants, showing that both absorbed P from the same labile pool of P in the fertilized soils. However, VAM inoculation increased the fertilizer utilization coefficient of plants 2.7- to 5.6-fold, depending on the soil and fertilizer. We conclude that VAM inoculation increases fertilizer efficiency, as much of rock phosphate as of superphosphate, for plants growing in acid, P-fixing soils, and the processes involved are not different for the two fertilizers.     

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.     

Uptake and metabolism of nitrate in mycorrhizal plants as affected by water availability and N concentration in soil

We compare the effect of arbuscular mycorrhizal (AM) colonization and PO₄^?3 fertilization on nitrate assimilation, plant growth and proline content in lettuce plants growing under well‐watered (?0.04 MPa) or drought (?0.17 MPa) conditions. We also tested how AM‐colonization and PO₄^?3 fertilization influenced N uptake (¹⁵N) and the percentage of N derived from the fertilizer (% NdfF) by plants under a concentration gradient of N in soil. Growth of mycorrhizal plants was comparable with that of P‐fertilized plants only under well‐watered conditions. Shoot nitrogen content, proline and nitrate reductase activity were greater in AM than in P‐fertilized plants under drought. The addition of 100 μg g^?1 P to the soil did not replace the AM effect under drought. Under well‐watered conditions, AM plants showed similar (at 3 mmol N), greater (at 6 mmol N) or lesser (at 9 mmol N) %NdfF than P‐fertilized plants. Comparing a control (without AM inoculation) to AM plants, differences in % NdfF ranged from 138% (3 mmol N) to 22.6% (6 mmol N) whereas no differences were found at 9 mmol N. In comparison with P fertilization, mycorrhizal effects on %NdfF were only evident at the lowest N levels, which indicated a regulatory mechanism for N uptake in AM plants affected by N availability in the soil. At the highest N level, P‐fertilized plants showed the greatest %NdfF. In conclusion, AM symbiosis is important for N acquisition and N fertilizer utilization but this beneficial mycorrhizal effect on N nutrition is reduced under large quantities of N fertilizer.     

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.     

Effects of vesicular‐arbuscular mycorrhizas and phosphorus on water status and growth of apple

Apple (Malus hupehensis Rehd) seedlings were grown in sterilized and non‐sterilized soil with or without phosphorus (P) added and inoculated by VA mycorrhizal (VAM) fungi (Glomus versifome Daniels et Tappe and Glomus macrocarpum Tul et Tul). In sterilized soil, the VAM infection increased the transpiration rate (Tr.) of the leaves, reduced the stomatal resistance (Sr.) and the permanent wilting percentage (PWP) and enhanced the rate of recovery of the plant from the water stress and the plant growth (e.g. leaf number, stem diameter and dry weight). It also increased absorption of most minerals, especially Zn and Cu by the roots and weakened the P‐Cu and P‐Zn interactions. Phosphorus fertilization had some positive effects on the water status, P nutrition and growth, but it reduced the Cu concentration. VAM improved the water status and enhanced drought tolerance of the trees by enhancing absorption and translocation of water by the external hyphae. The efficiency of inoculation in nonsterile soil was not obvious.