Effect of peat on mycorrhizal colonization and effectiveness of the arbuscular mycorrhizal fungus Gigaspora margarita

Abstract

The influence of the addition of Chinese peat and Canadian peat on arbuscular mycorrhizal colonization, mycorrhizal effectiveness and host-plant growth was investigated in a pot experiment. Chinese peat or Canadian peat was mixed with Masa soil (weathered granite soil) at different levels (0, 25, 50, 100, 150 or 200 g kg^?1) into which an arbuscular mycorrhizal fungus (AMF) Gigaspora margarita Becker & Hall was inoculated, and seedlings of Miscanthus sinensis Anderess were planted. There was a significant increase in plant growth with increasing amounts of Chinese peat. The growth-promoting effect of the AMF on the host was enhanced when the addition of Chinese peat was increased from 25 to 100 g kg^?1. Root colonization and the number of spores proliferating increased with increases at low levels of Chinese peat (from 25 to 100 g kg^?1), and decreased gradually with higher Chinese peat increments. Although plant growth and root colonization with the addition of Canadian peat increased slightly, Canadian peat suppressed mycorrhizal effectiveness. In contrast to Canadian peat, the addition of Chinese peat improved considerably the physical and chemical properties of the soil, which might result in the promotion of AM formation and mycorrhizal effectiveness.     

Variable inhibition of iron uptake by oat phytosiderophore in five soybean cultivars

Abstract

Greenhouse experiment was conducted to evaluate the effect of arbuscular mycorrhizal fungi (AMF) on plant growth, and nutrient uptake in saline soils with different salt and phosphorus (P) levels. The following treatments were included in this experiment: (i) Soil A, with salt level of 16.6 dS m^?1 and P level of 8.4 mg kg^?1; (ii) Soil B, with salt level of 6.2 dS m^?1 and P level of 17.5 mg kg^?1; and (iii) Soil C, with salt level of 2.4 dS m^?1 and P level of 6.5 mg kg^?1. Soils received no (control) or 25 mg P kg^?1 soil as triple super phosphate and were either not inoculated (control) or inoculated with a mixture of AM (AM1) and/or with Glomus intraradices (AM2). All pots were amended with 125 mg N kg^?1 soil as ammonium sulfate. Barley (Hordeum vulgar L., cv. “ACSAD 6”) was grown for five weeks. Plants grown on highly saline soils were severely affected where the dry weight was significantly lower than plants growing on moderately and low saline soils. The tiller number and the plant height were also lower under highly saline condition. The reduced plant growth under highly saline soils is mainly attributed to the negative effect of the high osmotic potential of the soil solution of the highly saline soils which tend to reduce the nutrient and water uptake as well as reduce the plant root growth. Both the application of P fertilizers and the soil inoculation with either inoculum mixture or G. intraradices increased the dry weight and the height of the plants but not the tiller number. The positive effect of P application on plant growth was similar to the effect of AM inoculation. Phosphorus concentration in the plants was higher in the mycorrhizal plant compared to the non mycorrhizal ones when P was not added. On the other hand, the addition of P increased the P concentration in the plants of the non mycorrhizal plants to as high as that of the mycorrhizal plants. Iron (Fe) and zinc (Zn) uptake increased with AM inoculation. The addition of P had a positive effect on micronutrient uptake in soil with low level of soil P, but had a negative effect in soil with high level of soil P. Micronutrient uptake decreases with increasing soil salinity level. Inoculation with AMF decreases sodium (Na) concentration in plants grown in soil of the highest salinity level but had no effect when plants were grown in soil with moderate or low salinity level. The potassium (K) concentration was not affected by any treatment while the K/Na ratio was increased by AM inoculation only when plant were grown in soil of the highest salinity level.     

Contribution of Roots and Mycorrhizal Hyphae on Phosphorus Efficiency of Maize (Zea mays,L.) Genotypes Grown on Calcareous Soil—A Mechanistic Modeling Approach

ABSTRACT

This work was conducted to study phosphorus (P) efficiency of two maize genotypes (Zea mays, L.) in calcareous soil grown in potted soil with two levels of P in soil by adding 40 and 270 mg P/kg soil. Half of the pots were inoculated with arbuscular mycorrhizal fungi (AMF) (Rhizoglomus irregulare). The maize genotypes were harvested two times at 35 and 50 days after transplanting. The plant dry matter, root length and Plant P uptake of maize genotype Hagen 1 without mycorrhizal fungi (AMF) increased significantly compared with Hagen 9 at a low P level. In contrast, there was no significant difference between two maize genotypes inoculated with AMF under the same P level. The predicted value increased rapidly with increasing P levels from about 70% up to 97% in both maize genotypes with and without mycorrhizal fungi. At a low P level, the mycorrhizae hyphae contributed by about 31.6% and 30.2% of the predicted total P uptake in maize genotype Hagen 1 and Hagen 9, respectively. The results of this study suggested that the P-inefficient genotype Hagen 9 improved with inoculation with mycorrhizal fungi under a low P level at the same conditions of this experiment. Also, root growth system and mycorrhizal hyphae length would be a suitable plant parameter for studying P efficient maize genotypes, especially under limited P supply. The current study clearly pointed out that the mechanistic simulation model (NST 3.0) provides useful tools for studying the role of AMF in P uptake of plant.     

Subcritical soil hydrophobicity in the presence of native and exotic arbuscular mycorrhizal species at different soil salinity levels

Soil salinity and arbuscular mycorrhizal fungi (AMF) influence the soil hydrophobicity. An experiment was performed to determine the effects of soil salinity and AMF species on soil water repellency (SWR) under wheat (Triticum aestivum L.) crop. Six AMF treatments, including four exotic species (Rhizophagus irregularis, Funneliformis mosseae and Claroideoglomus claroideum, a mix of three species), one mix native AMF species treatment and an AMF-free soil in combination with four salinity levels (1, 5, 10, and 15 dS m^?1) were used. The soil repellency index (RI) increased with salinity increment ranging from 2.4 to 10.5. The mix of three exotic and native AMF treatments enhanced the RI significantly compared to AMF-free soil in all salinity levels with one exception for native treatment at 1 dS m^?1. Among individual AMF species, the C. claroideum treatment at 10 dS m^?1 increased the RI by 67% compared to AMF-free soil. The native AMF treatment was more efficient in root colonization, glomalin production and SWR development at 10 and 15 dS m^?1, compared to exotic species. In addition to the net positive effect of salinity on SWR, the AMF influences on the RI were greatly dependent on salinity levels.     

Stimulation in the movement and uptake of phosphorus in response to magnetic P solution and arbuscular mycorrhizal fungi in Ocimum basilicum

A greenhouse experiment was conducted to assess the effects of magnetic field, arbuscular mycorrhizal fungi (AMF), and phosphorus (P) concentration in the nutrient solution (0, 5, 10, 20, or 40 mg L^?1) on the mobility and accumulation of P in soil and plant tissues of basil (Ocimum basilicum L.). The experiment was designed as a factorial combination and treatments were arranged in a completely randomized design with four replicates. Magnetic field increased water-soluble P in the soil and P concentration in plant shoot by 30.0% and 13.0%, respectively, in comparison to the control. The application of magnetic field and inoculation of AMF at 10 mg P L^?1 increased the P translocation efficiency by 23.3% and 17.8%, respectively. Overall, our results demonstrated that the use of magnetic field and AMF could be an effective tool for enhancing of uptake and movement efficiency of P even at low concentrations.     

Impact of Pseudomonads and Ethylene on the Cadmium and Nickel Rhizofiltration of Sunflower,Squash, and Indian Mustard

Three hydroponic experiments were set up to study the rhizofiltration of cadmium (Cd) or nickel (Ni) from artificially contaminated nutrient solution with sunflower, squash, or Indian mustard. After 48 h of exposure with 2 mg L^?1 Cd‐contaminated water, 460, 415, or 1092 µg Cd g^?1 (dry weight) was detected in roots of 33‐day‐old sunflower and squash or in 50‐day‐old Indian mustard, respectively. As calculated, 1 g of root dry matter of the tested crop species removed 5.7–12.4% of total Cd content present in the nutrient solution. It was supposed that pseudomonads (soil rhizoplane bacteria) and the plant growth hormone ethylene can enhance the specific surface of roots and hence roots' metal adsorption capacity. As a trend, pretreatment of Indian mustard with Pseudomonas fluorescens bacteria enhanced slightly the Cd (from 1793 to 2346 µg g^?1) or Ni (from 1088 to 1192 µg g^?1) concentration of roots. Cadmium concentration in roots was also enhanced from 2694 to 3273 µg g^?1 when the roots of Indian mustard were pretreated with Cd‐tolerant rather than Cd‐sensitive Pseudomonas cepacia. In spite of the occurrence of new root hairs, the pretreatment of roots with ethylene proved to be ineffective in enhancement of the Cd rhizofiltration capacity of Indian mustard.     

Host–pathogen interaction of maize (Zea mays L.) and Aspergillus niger as influenced by arbuscular mycorrhizal fungi (Glomus deserticola)

This study was carried out to investigate the interaction of maize and Aspergillus niger as influenced by arbuscular mycorrhizal fungi (AMF). Three quality protein maize (QPM) genotypes (ILE1-OB, ART-98-SW5-OB and ART-98-SW6-OB) and two market accessions (Ilishan and Shagamu) were evaluated in a pot experiment conducted under natural environment conditions at the Research and Teaching Farm of Babcock University, Ogun State, Nigeria. AMF (Glomus deserticola) in mixtures of soil and root fragments was inoculated at the rate of 15 g per plant, while maize was artificially infected with A. niger (15 cfu ml^?1) in each designated pots. The coefficient of emergence (COV), percentage emergence (% E) and disease severity were determined using standard methods. Generally, plants treated with AMF only produced the highest cumulative cob yield (18 g), followed by plants treated with AMF and A. niger (15 g) and then control (12 g), while the least was recorded for only A. niger-treated plants (4 g).     

DO MAIZE AND PEPPER PLANTS DEPEND ON MYCORRHIZAE IN TERMS OF PHOSPHORUS AND ZINC UPTAKE?

Nutrient deficiency, especially zinc (Zn) and phosphorus (P), is a common nutritional problem for the production of some crops in Turkey. This problem results in the application of increasing amounts of several fertilizers. Mycorrhizal inoculation or the indigenous potential of mycorrhizae in the soil is a critical factor in crop production under low supply of Zn and P. The effects of selected mycorrhizal inoculation on growth and Zn and P uptake of maize and green pepper were investigated in Zn- and P-deficient calcareous soils from Central Anatolia. Soils were sterilized by autoclaving and plants were grown for 7 weeks in pots under greenhouse conditions with inoculation of two selected arbuscular mycorrhizal (AM) species (Glommus moseea and G. etunicatum) at three rates of P (0, 25, 125 mg P kg^?1 soil) and two rates of Zn (0 and 5 mg Zn kg^?1soil). Without mycorrhizal inoculation, shoot and root dry matter production were severely affected by P and Zn deficiencies, and supply of adequate amounts of P and Zn significantly enhanced plant growth. When the soil was inoculated with mycorrhizal inoculation, the increasing effects of P and Zn fertilization on plant growth remained less pronounced. In accordance with growth data, mycorrhizae inoculation enhanced P and Zn concentration of plants, especially under low supply of P and Zn. The results obtained indicate that maize and green pepper are highly mycorrizal–dependent (MD) plant species under both low P and Zn supply and mycorrhizae play an essential role in P and Zn nutrition of plants in P and Zn-deficient soils. Although addition of P and Zn increased plant growth and plants are mycorrhizal dependent on P and Zn nutrition however dependence is much more dependent on P nutrition.     

Earthworm (Aporrectodea trapezoides)–mycorrhiza (Glomus intraradices) interaction and nitrogen and phosphorus uptake by maize

The interactive impacts of arbuscular mycorrhizal fungi (AMF, Glomus intraradices) and earthworms (Aporrectodea trapezoides) on maize (Zea mays L.) growth and nutrient uptake were studied under near natural conditions with pots buried in the soil of a maize field. Treatments included maize plants inoculated vs. not inoculated with AMF, treated or not treated with earthworms, at low (25 mg kg⁻¹) or high (175 mg kg⁻¹) P fertilization rate. Wheat straw was added as feed for earthworms. Root colonization, mycorrhiza structure, plant biomass and N and P contents of shoots and roots, soil available P and NO₃⁻–N concentrations, and soil microbial biomass C and N were measured at harvest. Results indicated that mycorrhizal colonization increased markedly in maize inoculated with AMF especially at low P rate, which was further enhanced by the addition of earthworms. AMF and earthworms interactively increased maize shoot and root biomass as well as N and P uptake but decreased soil NO₃⁻–N and available P concentrations at harvest. Earthworm and AMF interaction also increased soil microbial biomass C, which probably improved root N and P contents and indirectly increased the shoot N and P uptake. At low P rate, soil N mobilization by earthworms might have reduced potential N competition by arbuscular mycorrhizal hyphae, resulting in greater plant shoot and root biomass. Earthworms and AMF interactively enhanced soil N and P availability, leading to greater nutrient uptake and plant growth.     

Yield and phosphorus uptake of a processing tomato crop grown at different phosphorus levels in a calcareous soil as affected by mycorrhizal inoculation under field conditions

We have evaluated the effectiveness of arbuscular mycorrhizal fungi (AMF) inoculation (+M and ?M) at 0, 60, and 120 kg ?ha^?1 of P fertilizer on crop growth (IE_g), plant P nutrition and yield (IE_y), and on mycorrhization occurrence in a processing tomato crop. Two experiments were carried out in calcareous soil under field conditions. Phosphorus fertilization had no effect on crop growth and yield. At harvests, +M plants showed higher aerial dry weight, fruit fresh weight, and P concentration. Inoculated plants produced larger inflorescences, higher flower number, and total and marketable fruit number compared with ?M plants. At P₀ and P₆₀, plants associated with exogenous AMF were able to enhance P recovery, nevertheless factors other than the P uptake improvement concurred to make the inoculation effective. In both years, P fertilization enhanced IE_g and IE_y, and the application of 60 kg ?ha^?1 of P in inoculated soil was enough to reach high production level (134 Mg ?ha^?1). In the first trial, due to earlier root mycorrhization in inoculated and P fertilized soil, higher IE_g and IE_y were obtained compared with the second experiment. In the latter, during the initial phase, plant growth was more affected by P fertilization than by soil arbuscular mycorrhizal (AM) inoculation. Root mycorrhization by native AM fungi indicates that the intensive management of the investigated agro-system did not depress fungi infectivity; however, it caused the selection of less effective AMF. The application of selected AMF as a biofertilizer may represent an innovative ecosustainable practice for improving the crop profitability for growers while reducing the need for P fertilization.     

Use of Trichoderma spp. and arbuscular mycorrhizal fungi to increase soil beneficial population of bacteria in a nectarine commercial orchard: Effect on root growth,nutrient acquisition and replanting disease

The aim of the present experiment was to evaluate the effect of commercial Trichoderma and arbuscular mycorrhizal fungi (AMF)-based bio-fertilizers on nectarine root growth, nutrient acquisition and replanting disease. The experiment was performed from 2008 to 2012 in an A. mellea-infected nectarine orchard subjected to the following treatments: 1) untreated control; 2) AMF-biofertilizer applied at planting (120 kg ha^?1) and every year in spring and autumn at the rate of 6 kg ha^?1; 3) Trichoderma spp applied at planting (5 g plant^?1) and every year (in April, May and September) at 2.5 kg ha^?1. AMF bio-fertilizers decreased root diameter and increased root survivorship. Leaf phosphorus concentration increased in AMF bio-fertilizers plots, while no significant treatments effects were observed on other leaf nutrient concentration. Although biofertilizer application did not affect soil microbial population, at the end of the trial (2012) the application of Trichoderma alone increased the population of the fungus.     

Fulvic acid in foliar spray is more effective than humic acid via soil in improving coffee seedlings growth

ABSTRACT

Humic (HA) and fulvic (FA) acids improve the nutrient availability and uptake by plants but some aspects of their agronomic use still need to be clarified. The effects of HA soil application and FA foliar application on the growth, Zn and B uptake by coffee seedlings were evaluated. HA was added to an Oxisol at concentrations 0, 10, 25, 50, 75 and 100 mg kg^?1 (C-HA), in both limed (pH 6.2) and overlimed (pH 7.2) conditions. FA (0, 0.2, 0.5 and 1 g L^?1 C-FA) was applied to coffee leaves in three different application modes (M): with 0.3% Zn and 0.6% B supplied via foliar (M₁), 0.6% B and 1.2% Zn supplied via foliar (M₂) and 1.2 mg kg^?1 B and 6 mg kg^?1 Zn supplied via soil (M₃). HA addition in soil significantly (p < 0.05) reduced leaf B and Zn accumulation and coffee growth in both pH conditions. In the M₁ and M₂, FA application significantly (p < 0.05) increased the shoot growth at 0.59 and 0.45 g L^?1 and B accumulation at 0.96 and 0.45 g L^?1 C-FA. Foliar application of C-FA, instead soil application of C-HA, is a suitable practice to improve coffee seedlings growth and nutrition on Oxisol.     

AMF和PGPR修复甲胺磷污染土壤的效应

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)和根围促生细菌(plant growthpromoting rhizobacteria,PGPR)能降解有毒有机物,但分解土壤中残留甲胺磷农药尚未见报道。本试验旨在测定AMF和PGPR矿化甲胺磷的效应。试验设甲胺磷0、50、100和150μg g-1下,对番茄(Lycospersicon esculentum,品种金冠)接种AMF Glomus mosseae(Gm)、Glomus etunicatum(Ge)、PGPR Bacillus subtilis(Bs)、Bacillus sp.B697(Bsp)、Pseudomonas fluorescens(Pf)、Gm+Bs、Gm+Bsp、Gm+Pf、Ge+Bs、Ge+Bsp、Ge+Pf和不接种对照,共48个处理。结果表明,接种Gm显著增加了根区土壤和根内PGPR定殖数量,而Pf处理显著提高了AMF侵染率,表明Gm与Pf能够相互促进。甲胺磷100μg g-1水平下,Gm+Pf处理的番茄株高显著高于其他处理,地上部干重显著高于其他处理(Ge+Pf除外),根系干重显著高于对照、PGPR各处理和Ge处理;而根内甲胺磷浓度则显著低于其他处理,茎叶中的则显著低于其他处理(Gm+Bs、Gm+Bsp和Ge+Pf除外)。AMF、PGPR或AMF+PGPR处理均显著降低番茄体内甲胺磷浓度。甲胺磷50~100μg g-1水平下,Gm+Pf显著降低根区土壤中甲胺磷残留量,矿化率达52%~60.6%。AMF和PGPR显著提高了根区土壤中甲胺脱氢酶活性,其中以Gm+Pf组合处理的酶活性最高。表明AMF和PGPR均能促进土壤中残留甲胺磷的降解,Gm+Pf是本试验条件下的最佳组合。     

Responses of directly seeded wetland rice to arbuscular mycorrhizal fungi inoculation

The mycorrhizal enhancement of plant growth is generally attributed to increased nutrients uptake. A greenhouse experiment was conducted to investigate the effect of arbuscular mycorrhizal fungi (AMF) inoculation on the growth and nutrient uptake of directly seeded wetland rice. Seeds were germinated and inoculated with arbuscular mycorrhizal fungi or left uninoculated. The plants were grown at 60% of ‐0.03 MPa to establish the mycorrhizas. After 5 weeks, half of the pots were harvested and the rest were flooded with deionized water to maintain 3–5 cm of standing water until harvesting (122 days after sowing). Mycorrhizal fungal colonization of rice roots was 36.2% at harvest. Mycorrhizal fungi inoculated rice seedlings grew better compared to uninoculated seedlings and had increased grain yield (10%) at the harvesting stage. Shoot and root growth were effectively increased by AMF inoculation at the harvesting stage. The nitrogen (N) and phosphorus (P) acquisition of direct seeding wetland rice were significantly increased by AMF inoculation. The AMF enhanced N and P translocation through the hyphae from soils to roots/shoots to grains effectively.     

Effects of arbuscular mycorrhizal fungus Rhizoglomus intraradices on active and passive pools of carbon in long-term soil fertility gradients of maize based cropping system

A potculture study was conducted in soils collected from long-term fertilizer experiment (LTFE) being kept up as far the past 40 years to determine whether arbuscular mycorrhizal fungus (AMF) Rhizoglomus intraradices colonization changes the active and passive pools of carbon in a maize (Zea mays) – finger millet (Eleusine crocana)- cowpea (Vigna sinensis) cropping sequence in the Experimental Farm of the Tamil Nadu Agricultural University, Coimbatore, India. Soil samples were processed, sterilized and maize plants were grown in various fertility gradients in the absence (M-) or presence (M+) of AMF (Rhizoglomus intraradices) inoculation. The data have clearly shown that M+ soils had consistently higher active pools such as water soluble carbon, hot water soluble carbon and biomass carbon (M- 189; M + 305 mg kg^?1), and passive pools such as soil organic carbon (M- 4.17; M + 4.31 mg g^?1) and total glomalin. Among the fertility gradients, 100% NPK + Farm Yard Manure (FYM) with or without mycorrhizal fungal inoculation registered higher values for both active and passive pools of C but the response was more pronounced in the presence AMF inoculation. Overall, the data suggest that mycorrhizal fungal inoculation assists in effective carbon sequestration in an intensive cereal-legume cropping system.Abbreviations: AMF: Arbuscular mycorrhizal fungi; DAS: Days After Sowing; LTFE: Long-Term Fertilizer Experiment; WSC: Water soluble organic carbon; HA: Humic acid; FA: Fulvic acid; HWSC: Hot water soluble carbon     

Impact of Mycorrhizae Formation on the Phosphorus and Heavy-Metal Uptake of Alfalfa

Three pot experiments were set up to determine how efficiently mycorrhizal fungi affect the uptake, translocation, and distribution of labeled phosphorus (³²P), phosphorus (P), and heavy metals in alfalfa (Medicago sativa L.). In experiments 1 and 2, the efficiencies of different arbuscular mycorrhizal fungi (AMF) species including Glomus mosseae, G. etunicatum, G. intraradices and a mixed strain (G. mosseae, Gigaspora hartiga, and G. fasciculatum) on uptake, translocation, and distribution of ³²P and P in alfalfa were investigated, respectively. In a third experiment, the efficiency of G. mosseae on uptake and distribution of heavy metals [cadmium (Cd), cobalt (Co), lead (Pb), and combinations] was tested. Results of experiments 1 and 2 suggest that G. mosseae was the most effective at increasing the uptake of ³²P and P. Experiment 3 result showed that in the triple-metal-contaminated soil, inoculated plants had greater Co (32.56 mg kg^?1) and Pb (289.50 mg kg^?1) concentration and G. mosseae enhanced the translocation of heavy metals to shoot. Hence, mycorrhizal alfalfa in symbiosis with G. mosseae can be used for remediation of heavy metals polluted soils with high efficiency.     

Vegetative Growth,Yield and Leaf Mineral Composition in Strawberry (Fragaria × Ananassa DUCH. CV. Pajaro) as Influenced using Nickel Sulfate and Urea Sprays

In this study, interactions of nickel sulfate and urea sprays on vegetative growth, yield and leaf mineral contents in strawberry were investigated. Rooted Pajaro strawberry plants were potted in 3 liter pots filled with soil, leaf mold and sand (1:1:1, v/v/v). Established plants were foliar sprayed with nickel sulfate at 0, 150, 300 and 450 mg L^?1 and urea 0 and 2 g L^?1 concentrations. Results indicated that nickel (Ni; 300 mg L^?1) plus urea (2 g L^?1) significantly increased the yield and runner numbers. Nickel sulfate at the rate of 300 and 150 mg L^?1and urea (2 g L^?1) significantly increased the crown numbers. The greatest root fresh and dry weights were obtained from untreated plants. Urea at 2 g L^?1 without nickel significantly increased shoot fresh and dry weights. Nickel at 450 mg L^?1 without urea significantly increased Ni concentration in leaves. Overall, nickel sulfate at 150 and 300 mg L^?1 along with urea at 2 g L^?1 were the best treatments.     

Occurrence and Geochemistry of Arsenic in Groundwater of Punjab,Northwest India

Abstract

Arsenic (As) is a deadly poison at high concentrations. It is mysterious in the sense that people are exposed to it most of the time through drinking groundwater, fortunately at much lower concentrations than the deadly levels, and usually without knowing it. Arsenic content in alluvial aquifers of Punjab varied from 3.5 to 688 µg L^?1. Arsenic status of groundwater is classified into low (<10 µg L^?1), moderate (≥10 to <25 µg L^?1), high (≥25 to <50 µg L^?1), and very high (>50 µg L^?1). In zone I, the concentration of As in groundwater varied from 3.5 to 42 µg L^?1 with a mean value of 23.4 µg L^?1. On the basis of these limits, only 8% of samples were low, whereas 51 and 41% of the total samples collected from this region fall in the moderate and high As categories. The concentration of As in groundwater of zone II varied from 9.8 to 42.5 µg L^?1 with a mean value of 24.1 µg L^?1. Arsenic concentration in the alluvial aquifers of the central plain of zone II is 2 and 52% in the low and moderate limits. In this region, 46% of groundwater sites contain high As concentrations. Arsenic concentrations in the aridic southwestern parts are significantly different from other two provinces. The As concentration ranged from 11.4 to 688 µg L^?1 with average value of 76.8 µg L^?1. Eleven percent of the aquifers of the southwestern region of zone III are in the moderate category, 54% in the high, and 35% in the very high. According to safe As limits (<10 µg L^?1), only 3 and 1% of the groundwater samples collected from zones I and II were fit for dinking purposes with respect to As content. In the aridic southwest, zone III, all water samples contained As concentrations greater than the safe limits and thus are not suitable for drinking purposes. The presence of elevated As concentrations in groundwater are generally due to the results of natural occurrences of As in the aquifer materials. The concentration of other competitive oxyanions in waters such as phosphate, sulfate, and borate also depressed the adsorption of As on the sorption sites of aquifer materials and thereby eventually elevate the As concentration in groundwaters. In groundwater of alluvial aquifers of Punjab, released from sulfide oxidation and oxyhydroxide of iron, elevated (>10 µg L^?1) concentrations of As were widespread because of high pH (>8.0) and higher concentrations of phosphate, borate, sulfate, and hydroxyl anions. It is conclusively evident that geochemical conditions, such as pH, oxidation–reduction, associated or competing ions, and evaporative environments have significant effects on As concentration in groundwater. These conditions influence how much As is dissolved or precipitated into the water and how much is bound to the aquifer materials or the solid particles in water.     

Response of a wild-type and modern cowpea cultivars to arbuscular mycorrhizal inoculation in sterilized and non-sterilized soil

Cowpea is an important crop that serves as a legume and vegetable source to many smallholder farmers in sub-Saharan Africa. Soil fertility is a significant limitation to its production thus; inoculation with beneficial soil biota such as arbuscular mycorrhizal fungi (AMF) could improve its performance. However, plant–AMF interaction could vary based on crop cultivar hence affecting overall crop production. The present study aimed at determining the effect of AMF inoculation and soil sterilization on root colonization and growth of a wild-type and three modern cowpea cultivars grown by smallholder farmers in Kenya. Potted cowpea plants were inoculated with a commercial AMF inoculum comprising of Rhizophagus irregularis, Funneliformis mosseae, Glomus aggregatum and Glomus etunicatum and maintained in a greenhouse for 40 days. After harvesting, mycorrhizal colonization, nodule number and dry weight, root and shoot dry weights, nitrogen (N,) phosphorus (P) and potassium (K) content were determined. Interestingly, the modern cultivars showed significantly (p < 0.001) higher root colonization, nodulation, shoot P and N compared to the wild-type cultivar. Moreover, a strong positive correlation between AMF root colonization and shoot P (r² = 0.73, 0.90, p < 0.001), AMF root colonization and shoot N (r² = 0.78; 0.89, p < 0.001) was observed in both sterilized and non-sterilized soil, respectively. Soil sterilization affected root colonization and growth parameters with plants grown in non-sterilized soil performing better than those grown in sterilized soil. This study provides major evidence that modern cowpea cultivars are still responsive to mycorrhizal inoculation suggesting that modern breeding programs are not deleterious AMF symbiosis.     

Effects of early mycorrhization and colonized root length on low‐soil‐phosphorus resistance of West African pearl millet

Phosphorus (P) deficiency at early seedling stages is a critical determinant for survival and final yield of pearl millet in multi‐stress Sahelian environments. Longer roots and colonization with arbuscular mycorrhizal fungi (AMF) enhance P uptake and crop performance of millet. Assessing the genotypic variation of early mycorrhization and its effect on plant growth is necessary to better understand mechanisms of resistance to low soil P and to use them in breeding strategies for low P. Therefore, in this study, eight pearl millet varieties contrasting in low‐P resistance were grown in pots under low P (no additional P supply) and high P (+ 0.4 g P pot^?1) conditions, and harvested 2, 4, 6, and 8 weeks after sowing (WAS). Root length was calculated 2 WAS by scanning of dissected roots and evaluation with WinRhizo software. AM infection (%) and P uptake (shoot P concentration multiplied per shoot dry matter) were measured at each harvest. Across harvests under low P (3.3 mg Bray P kg^?1), resistant genotypes had greater total root length infected with AMF (837 m), higher percentage of AMF colonization (11.6%), and increased P uptake (69.4 mg P plant^?1) than sensitive genotypes (177 m, 7.1% colonization and 46.4 mg P plant^?1, respectively). Two WAS, resistant genotypes were infected almost twice as much as sensitive ones (4.1% and 2.1%) and the individual resistant genotypes differed in the percentage of AMF infection. AMF colonization was positively related to final dry matter production in pots, which corresponded to field performance. Early mycorrhization enhanced P uptake in pearl millet grown under P‐deficient conditions, with the genotypic variation for this parameter allowing selection for better performance under field conditions.