Effect of arbuscular mycorrhizal fungi on rhizosphere organic acid content and microbial activity of trifoliate orange under different low P conditions

ABSTRACT

Arbuscular mycorrhizal (AM) fungi can improve plant phosphorus (P) uptake; however, information about how AM fungi affect rhizosphere organic acid and microbial activity to alleviate citrus low P stress is limited. Here, a pot experiment was conducted to evaluate the effect of AM fungi (Rhizophagus intraradices, Ri) inoculation on rhizosphere organic acid content, microbial biomass (MB) and enzyme activity of trifoliate orange (Poncirus trifoliata L. Raf.) seedlings grown under three low P conditions. The results showed that mycorrhizal seedlings all recorded higher P concentrations, plant biomass and better root morphology with more lateral and fine roots, but lower root mass ratios, irrespective of P conditions. Mycorrhizal P absorption contribution did not differ significantly among three P conditions. Mycorrhizal seedling rhizosphere soil exhibited lower organic acid content, soil organic P content and ratio of MB-carbon (C)/MB-P, but higher MB and enzyme activity. Additionally, the main organic acids showed a negative relationship with mycorrhizal colonization rate and hyphal length; however, phosphatase and phytase activity had a significantly positive relationship with MB. Therefore, the results suggest that AM fungi inoculation may help citrus to efficiently utilize organic P source by improving microbial activity under low available P conditions.     

Interactions between phosphorus availability and an AM fungus (Glomus intraradices) and their effects on soil microbial respiration, biomass and enzyme activities in a calcareous soil

The interactions between soil P availability and mycorrhizal fungi could potentially impact the activity of soil microorganisms and enzymes involved in nutrient turnover and cycling, and subsequent plant growth. However, much remains to be known of the possible interactions among phosphorus availability and mycorrhizal fungi in the rhizosphere of berseem clover (Trifolium alexandrinum L.) grown in calcareous soils deficient in available P. The primary purpose of this study was to look at the interaction between P availability and an arbuscular mycorrhizal (AM) fungus (Glomus intraradices) on the growth of berseem clover and on soil microbial activity associated with plant growth. Berseem clover was grown in P unfertilized soil (−P) and P fertilized soil (+P), inoculated (+M) and non-inoculated (−M) with the mycorrhizal fungus for 70 days under greenhouse conditions. We found an increased biomass production of shoot and root for AM fungus-inoculated berseem relative to uninoculated berseem grown at low P levels. AM fungus inoculation led to an improvement of P and N uptake. Soil respiration (SR) responded positively to P addition, but negatively to AM fungus inoculation, suggesting that P limitation may be responsible for stimulating effects on microbial activity by P fertilization. Results showed decreases in microbial respiration and biomass C in mycorrhizal treatments, implying that reduced availability of C may account for the suppressive effects of AM fungus inoculation on microbial activity. However, both AM fungus inoculation and P fertilization affected neither substrate-induced respiration (SIR) nor microbial metabolic quotients (qCO₂). So, both P and C availability may concurrently limit the microbial activity in these calcareous P-fixing soils. On the contrary, the activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) enzymes responded negatively to P addition, but positively to AM fungus inoculation, indicating that AM fungus may only contribute to plant P nutrition without a significant contribution from the total microbial activity in the rhizosphere. Therefore, the contrasting effects of P and AM fungus on the soil microbial activity and biomass C and enzymes may have a positive or negative feedback to C dynamics and decomposition, and subsequently to nutrient cycling in these calcareous soils. In conclusion, soil microbial activity depended on the addition of P and/or the presence of AM fungus, which could affect either P or C availability.     

Depletion of organic phosphorus from Oxisols in relation to phosphatase activities in the rhizosphere

Phosphorus (P) deficiency is a major limitation to agricultural production in many parts of the world. It is therefore desirable to identify plants with enhanced abilities to utilize P more efficiently. Exudation of phosphatase from roots may improve P availability, yet there is little direct evidence for this. Here we report the dynamics of organic P in the rhizosphere of plants that have enhanced rhizosphere phosphatase activity. Agroforestry species and transgenic subterranean clover (engineered to produce phytase) were compared with crop and wild‐type plant controls, respectively. Depletion of organic P was measured in pools defined by chemical extraction, solution ³¹P NMR spectroscopy, and microbial immobilization of radio‐isotopic P. Plants that had greater extracellular phosphatase activity depleted more organic P from P‐deficient Oxisols than control plants. Depleted organic P forms were primarily phosphate monoesters. Plants with enhanced extracellular phosphatase activity also had access to a pool of soil P that was less isotopically exchangeable. Transgenic subterranean clover that expresses a microbial phytase gene appeared to have greater access to recently immobilized P, whereas plants expressing endogenous phosphatases utilized the unlabelled portion of soil organic P to a greater extent. Collectively, these results indicate that the enhancement of phosphatase activity in the rhizosphere of plants is implicated in the depletion of organic P forms from soils, most notably orthophosphate monoesters, whilst also suggesting that there is some exclusivity to the pools of organic P utilized by plants and microorganisms.     

Contribution of Pseudomonas mendocina and Glomus intraradices to aggregate stabilization and promotion of biological fertility in rhizosphere soil of lettuce plants under field conditions

A field‐plot experiment was undertaken to compare the effect of inorganic fertilizer with that of inoculation with an arbuscular mycorrhizal fungus, Glomus intraradices, or with a plant‐growth‐promoting rhizobacterium, Pseudomonas mendocina, alone or in combination with inorganic fertilizer, on plant growth and nutrient uptake by lettuce. The influence of the microbial inoculation treatments on soil physical, biochemical and biological properties was also assessed. Two months after planting, fertilizer and inoculation with G. intraradices or P. mendocina had significantly increased shoot and root biomass and foliar nutrient contents (P, Fe). The inoculation with G. intraradices or P. mendocina both increased the soil water‐soluble carbohydrates and the percentage of stable aggregates. In this study, we provide the first evidence of the beneficial effect of a plant‐growth‐promoting rhizobacterium on soil aggregate stabilization under field conditions. Only inoculation with P. mendocina had a significant effect on the dehydrogenase and phosphatase activities, 21 and 89%, respectively, compared with the control. Inorganic fertilization alone did not increase aggregate stability or enzyme activities in soil, even though this treatment produced the largest increases in mass of lettuce.     

Soil–Phosphorus Mobilization Potential of Phytate Mineralizing Fungi

Four most efficient phytase and phosphatase producing fungi belonging to genera Aspergillus, Trichoderma, and Penicillium were isolated from the rhizosphere soil of leguminous, cereal, and vegetable crops. Efficacy order of fungi in terms of phytate hydrolysis under laboratory conditions was Aspergillus > Penicillium > Trichoderma. The test fungi released more of extracellular (E) phytase than intracellular (I) phytase (E: I- 3.44 - 6.03:1) and produced acid phosphatase activity ranging from 367- 830 μmol pNP ml^?1 h^?1. Aspergillus niger possessed the twin ability of phosphate mineralization and solubilization. The incubation studies in compost-amended soil exhibited the higher competence of Penicillium chrysogenum to improve the soil available P and increase the level of extractable organic P under alkaline soil to benefit P nutrition. Developing microbial inoculant using P. chrysogenum strain and its subsequent application to soil may help the marginal farmer to replenish soil P more economically compared to chemical fertilizer.     

Dual inoculation of peanut with Glomus sp. and Bradyrhizobium sp. enhanced the symbiotic nitrogen fixation as assessed by 15N-Technique

Abstract

The response of peanut (Arachis hypogaea L.) to inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus etunicatum) and Bradyrhizobiurn sp. was studied in pots by the acetylene reduction activity (ARA) and ‘A-value’ methods. The soil used was a Light-coloured Andosol and the treatments consisted of the inoculation of VAM fungi only, inoculation of Bradyrhizobium only, dual inoculation of VAM fungi and Bradyrhizobium and control, under non-sterilized and sterilized soil conditions.

In the non-sterilized soil the ARA and nitrogen fixation determined by the ‘A-value’ method increased significantly only by dual inoculation of VAM fungi and Bradyrhizobium at 100 days after planting (DAP), but no significant difference was observed at 70 DAP. In the case of dual inoculation, 75% of the nitrogen of the plant was derived from fixation whereas the plants inoculated only with Bradyrhizobium derived 68% of their nitrogen from fixation and the control plants, 64%. Amount of P in plant increased significantly only by dual inoculation with VAM fungi and Bradyrhizobium.

In the sterilized soil a highly significant increase in the ARA was observed of the dual inoculation at all the sampling times. Nitrogen fixation determined by the A-value technique and N and P contents in plant also increased significantly by dual inoculation. Results obtained by the A-value method showed that plants with dual inoculation derived 68% of their nitrogen from fixation while the plants inoculated only with Bradyrhizobium, 38%.

From our this study we conclude that nitrogen fixation as well as N and P contents in peanut increased significantly only by dual inoculation with VAM fungi and Bradyrhizobium.     

Yield promotion and phosphorus solubilization by plant growth–promoting rhizobacteria in extensive wheat production in Turkey

Plant growth–promoting rhizobacteria (PGPR) have been reported to stimulate the growth and yield of grain crops, particularly when nutrient supply is poor. However, the mechanisms underlying stimulation of plant growth may vary depending not only on growth conditions and crop management but also on plant and bacterial species. The present study assessed the effect of an inoculation with single or multiple PGPR strains on phosphorus (P)‐solubilization processes in the soil and on grain yield in wheat. Single inoculation with Bacillus subtilis OSU‐142, Bacillus megaterium M3, or Azospirillum brasilense Sp245 increased grain yield by 24%, 19%, and 19%, respectively, while a mixed inoculation with OSU‐142, M3, and Sp245 increased grain yield by 33% relative to noninoculated plants. Single inoculations with Paenibacillus polymyxa RC05 or Bacillus megaterium RC07 were less effective. Single or mixed treatments with OSU‐142, M3, and Sp245 increased the concentrations of the labile and moderately labile P fractions in rhizosphere soil. The growth‐stimulating effect of OSU‐142, M3, and Sp245 was also reflected by higher P concentrations in most plant organs. Among all inocula tested, the highest plant P acquisition was obtained in the presence of M3 and accompanied by the highest microbial P levels and the highest phosphatase activities in the rhizosphere soil. In conclusion, seed inoculation with mixed PGPR strains may effectively substitute for a part of P‐fertilizer application in extensive wheat production, and in particular M3 appears to improve the solubilization of inorganic soil P.     

Mycorrhizal inoculation enhances growth and nutrition of cotton plant

Arbuscular Mycorrhizae Fungi (AMF) inoculations may improve growth and nutrient uptake of cotton (Gossypium hirsutum L.) plant. Although the importance of mycorrhizal symbioses for growth and nutrient acquisition of cotton plant is known, less is known about mycorrhizal dependency on P and Zn nutrition under low Zn fertile soil conditions. A greenhouse experiment was conducted to investigate the effect of different of P and Zn fertilizer addition on cotton plant growth as well as Zn and P uptake. Sterilized and non-sterilized low Zn fertile Konya series soil was treated with different levels of P and Zn. Soils were inoculated with two mycorrhizae species like Funneliformis mosseae and Claroideoglomus etunicatum after sterilization. Results showed that mycorrhizal inoculation on plant growth and nutrient uptake has significant effect when soil was sterilized. Cl. etunicatum mycorrhizae species has greater effect than Fu. mosseae mycorrhizae species. Root colonization increased 23–65% due to mycorrhizal amendment. The shoot: root ratio increased by 13 and 22% for non-sterile and sterile condition respectively in mycorrhiza amended soil. Mycorrhizal dependency varies 1–55% and 3–64% for non-sterile and sterile soil respectively on mycorrhizae, P and Zn amended soil. Mycorrhizal dependency analysis showed that cotton plant in both sterile and non-sterile soil conditions depends on mycorrhizae species, P nutrition, however is less depend on Zn nutrition. This study concluded that the inoculation of cotton plant with selected mycorrhizae is necessary under both sterile and non-sterile soil conditions.     

Effect of Rhizobium inoculation on growth,modulation, and nitrogenase activity of some legume tree species

An experiment was conducted to study the effect of inoculation of Rhizobium suspension in Albizia procera (Roxb.) Benth, Albizia lebbeck (L.) Benth, and Leucaena leucocephala (Lam.) De Wit. seedlings grown in sterilized and non‐sterilized soil media. Control treatments were maintained by non‐inoculation. Inoculation response was observed strong in sterilized and modest in non‐sterilized soil when compared to respective control treatments. Increase in height was found 105.07%, 63.42%, and 109% higher in sterilized soil and 52.1%, 68.6%, and 95.8% in non‐sterilized soil for Albizia procera, Albizia lebbeck, and Leucaena leucocephala, respectively, after a period of 4 months. Nodule number increased up to 10.27 and 3.51 times in Albizia procera, 11.47 and 4.3 times in Albizia lebbeck, and 7.22 and 2.9 times in Leucaena leucocephala due to inoculation in sterilized and non‐sterilized soil media respectively. Significant increase in nodule dry weight and nitrogenase activity was also recorded in both sterilized and non‐sterilized soil for all the species tested. Nitrogenase activity per plant per hour was recorded 68.75,11.58, and 13 times higher in sterilized and 6.7,5.53, and 3.38 times higher in non‐sterilized soil over control for the species respectively after 4 months. In the tree species tested the inoculation of Rhizobium showed higher productivity, modulation and nitrogenase activity than control suggesting the idea that application of Rhizobium suspension greatly enhances plant growth, modulation, and nitrogenase activity.     

Microbial phytase activity and their role in organic P mineralization

Plants respond to their external environment to optimize their nutrition and production potential to minimize the food security issues and support sustainable agriculture system. Phosphorus (P) is an important nutrient for plants and is involved in plant metabolic processes. It is mostly available as orthophosphate and has a tendency to form complexes with cations. It has low mobility in soil, thus becoming unavailable for plant uptake that causes a reduction in plant growth and yield. Besides free P, phytate is the major form of organic P in soil and plant tissues. Phytases obtained from different sources, that is, plants, animals, and microorganisms, catalyze the hydrolysis of phytate and release available forms of inorganic P. The knowledge of mechanisms involved in catalytic activity of phytase obtained from microorganisms in soil is limited. This review summarizes the role of microbial phytase in releasing organic P by hydrolysis of phytate and factors affecting its activity in the soil.     

Effect of indigenous and introduced vesicular-arbuscular mycorrhizal fungi on growth and phosphorus uptake of Trifolium pratense and on inorganic phosphorus fractions in a cambisol

Summary Five selected vesicular-arbuscular mycorrhizal (VAM) fungi and the native population of a cambisol were tested in sterilized soil conditions, with Trifolium pratense as host plant. Indigenous fungi were the most effective in enhancing plant growth and P uptake, which were correlated with a higher root colonization. Selected fungi did not spread further in the root after 4 months from sowing, occupying less than 10% at the end of the experiment; inoculation with Glomus fasciculatum E3 yielded a higher dry-matter production than any other VAM species, but did not significantly increase shoot P concentration above that of the non-mycorrhizal control. Interactions between indigenous and introduced VAM fungi were studied in unsterilized soil. Results from fresh and dry weights of shoots and the percentage of fungal infection showed that the native endophytes competed more efficiently in colonizing the root. Inoculation with selected VAM species did not improve plant growth. Sterilization altered the inorganic P fractions of the soil, particularly those extracted with NH₄F and NaOH. Sterilized soil contained less inorganic P than unsterilized soil, but more soluble P. By the end of the experiment in sterilized soil, P extracted with NH₄Cl, NH₄F and NaOH and total inorganic P were significantly different among inoculation treatments, suggesting that VAM fungi may differ in their ability to take up P.     

Organic-acid-producing,phytate-mineralizing rhizobacteria and their effect on growth of pigeon pea (Cajanus cajan)

Phytates represent a significant pool of organic phosphorus (Po) that is largely unavailable to plants. This study deals with phytate-mineralizing (PM), organic-acid-producing (OAP) rhizobacterial isolates, their characterization and their effect on plant growth. Their genetic diversity was assessed by 16S rRNA amplified ribosomal DNA restriction analysis (ARDRA) and selected isolates were identified by partial sequencing of 16S rRNA gene. Na-phytate and Po rich poultry farm manure (PFM) used as sources of phosphorus in semi-solid-agar (SSA) medium and soil respectively, for plant inoculation studies, where Cajanus cajan (pigeon pea) used as plant. Of thirty-nine rhizobacterial isolates, nineteen were proficient at releasing phosphate (Pi) (up to 85 μg/ml) from sparingly soluble calcium (Ca)-phytate and concomitantly decreasing the pH of minimal medium with 100 mM glucose from 8.0 to below 5. When the medium contained glycerol in place of glucose, Ca-phytate remained undissolved with no significant Pi released and no decline in pH. Genetic diversity of phytate-mineralizing (PM) rhizobacterial isolates suggests that the isolates mainly fall in two populations: acid-producing (AP) population (mainly represented by members of Enterobacteriaceae) and non-AP population. OAP-PM rhizobacterial isolates were identified as Citrobacter, Pantoea, Klebsiella and Enterobacter species. Organic acids (OAs) secreted by PM isolates were detected by HPLC, showed secretion of gluconic and acetic acids. Importance of OAs in Ca-phytate dephosphorylation was demonstrated in vitro using A. ficuum phytase. Gluconate and acetate additions enhanced phytase catalyzed dephosphorylation of Ca-phytate in vitro. Sonicated cell lysates of isolates showed significant Pi release from Ca-phytate compared to whole cells, indicating inaccessibility of Ca-phytate due to poor solubility. Selected isolates showed that they possess cell-associated acid phytase and modulators of phytase activity suggested that the enzymes are histidine acid phosphatase (HAP) type of phytase. OAP-PM isolates PP1 and DHRSS showed significant increase in dry shoot/root ratio and P content of shoot in Na-phytate containing semi-solid agar (SSA) medium, but isolate DHRSS did not increase dry shoot/root ratio in soil experiments containing poultry farm manure as source of P, although it significantly increased shoot P content of plants. The inoculation of isolates enhanced the shoot P content and dry shoot/root ratio, but did not increase the dry weight in SSA medium. It may be concluded that some OAP-PM rhizobacterial isolates that release P from Ca-phytate show increase in shoot P content in phytate containing SSA medium and in soils.     

接种丛枝菌根真菌和巨大芽孢杆菌的红三叶草对难溶磷的利用

A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic andorganic sources of phosphorus (P) by red clover (Trghlium pmtense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate hada synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activityin the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.     

Phosphatase activity in the rhizosphere and its relation to the depletion of soil organic phosphorus

Summary The distribution of phosphatase activity and of phosphate fractions of the soil in the proximity of roots was studied in order to evaluate the significance of phosphatases in P nutrition of various plants (Brassica oleracea, Allium cepa, Triticum aestivum, Trifolium alexandrinum). A considerable increase in both acid and alkaline phosphatase activity in all the four soil-root interfaces was observed. Maximum distances from the root surface at which activity increases were observed ranged from 2.0 mm to 3.1 mm for acid phosphatase and from 1.2 mm to 1.6 mm for alkaline phosphatase. The increase in phosphatase activity depended upon plant age, plant species and soil type. A significant correlation was noticed between the depletion of organic P and phosphatase activity in the rhizosphere soil of wheat (r = 0.99^**) and clover (r = 0.97^**). The maximum organic P depletion was 65% in clover and 86% in wheat, which was observed within a distance from the root of 0.8 mm in clover and 1.5 mm in wheat. Both the phosphatases in combination appear to be responsible for the depletion of organic P.     

Arbuscular Mycorrhizal Association for Growth and Nutrients Assimilation of Pharagmites japonica and Polygonum cuspidatum Plants Growing on River Bank Soil

Effects of arbuscular mycorrhizal fungi (AMF) on the growth, nutrient absorption, and inoculation effectiveness of AMF on pioneer plants Pharagmites japonica (C4) and Polygonum cuspidatum (C3) were evaluated by performing a pot experiment in a greenhouse at Saitama University, Japan. AMF spores were collected from the commercial product, Serakinkon. The average colonization levels of P. japonica and P. cuspidatum were 24–33% and 0.2–0.5% respectively and no colonization was found in sterilized soil treatment. AMF colonization increased the plant dry mass, phosphorus (P), and nitrogen (N) concentrations of P. japonica’s roots, stems, and leaves when AMF applied with natural and sterilized soil compared with only sterilized and natural soil. This was a significant effect for N-loss minimization from soil. Maximum value showed when P. japonica was grown with natural soil in combination with AMF whereas P. cuspidatum showed very less or a negative response to AMF colonization in all cases.     

Effects of plant species on microbial biomass phosphorus and phosphatase activity in a range of grassland soils

Soil P transformations are primarily mediated by plant root and soil microbial activity. A short-term (40 weeks) glasshouse experiment with 15 grassland soils collected from around New Zealand was conducted to examine the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil microbial properties and microbiological processes involved in P dynamics. Results showed that the effect of plant species on soil microbial parameters varied greatly with soil type. Concentrations of microbial biomass C and soil respiration were significantly greater in six out of 15 soils under radiata pine compared with ryegrass, while there were no significant effects of plant species on these parameters in the remaining soils. However, microbial biomass P (MBP) was significantly lower in six soils under radiata pine, while there were no significant effects of plant species on MBP in the remaining soils. The latter indicated that P was released from the microbial biomass in response to greater P demand by radiata pine. Levels of water soluble organic C were significantly greater in most soils under radiata pine, compared with ryegrass, which suggested that greater root exudation might have occurred under radiata pine. Activities of acid and alkaline phosphatase and phosphodiesterase were generally lower in most soils under radiata pine, compared with ryegrass. The findings of this study indicate that root exudation plays an important role in increased soil microbial activities, solubility of organic P and mineralization of organic P in soils under radiata pine.     

Effect of plant growth-promoting bacteria and soil compaction on barley seedling growth, nutrient uptake, soil properties and rhizosphere microflora

Inoculants are of great importance in sustainable and/or organic agriculture. In the present study, plant growth of barley (Hordeum vulgare) has been studied in sterile soil inoculated with four plant growth-promoting bacteria and mineral fertilizers at three different soil bulk densities and in three harvests of plants. Three bacterial species were isolated from the rhizosphere of barley and wheat. These bacteria fixed N₂, dissolved P and significantly increased growth of barley seedlings. Available phosphate in soil was significantly increased by seed inoculation of Bacillus M-13 and Bacillus RC01. Total culturable bacteria, fungi and P-solubilizing bacteria count increased with time. Data suggest that seed inoculation of barley with Bacillus RC01, Bacillus RC02, Bacillus RC03 and Bacillus M-13 increased root weight by 16.7, 12.5, 8.9 and 12.5% as compared to the control (without bacteria inoculation and mineral fertilizers) and shoot weight by 34.7, 34.7, 28.6 and 32.7%, respectively. Bacterial inoculation gave increases of 20.3–25.7% over the control as compared with 18.9 and 35.1% total biomass weight increases by P and NP application. The concentration of N and P in soil was decreased by increasing soil compaction. In contrast to macronutrients, the concentration of Fe, Cu and Mn was lower in plants grown in the loosest soil. Soil compaction induced a limitation in root and shoot growth that was reflected by a decrease in the microbial population and activity. Our results show that bacterial population was stimulated by the decrease in soil bulk density. The results suggest that the N₂-fixing and P-solubilizing bacterial strains tested have a potential on plant growth activity of barley.     

胶质芽孢杆菌与苜蓿根瘤菌双接种对排土场紫花苜蓿生长和土壤性质的影响

为了明确胶质芽孢杆菌和苜蓿根瘤菌在矿区排土场复垦中的协同作用,以矿区排土场土壤作为基质进行盆栽试验,设置两菌单接种处理、双接种处理及对照,其中胶质芽孢杆菌和苜蓿根瘤菌用量分别为1.50%和0.25%,测定紫花苜蓿产量指标、叶片生理指标、土壤速效养分含量和土壤微生物指标。结果表明,接种胶质芽孢杆菌和苜蓿根瘤菌的各处理均能显著提高紫花苜蓿的产量指标,其中以双接种处理效果最优,将生物量和结瘤量分别比对照显著提高110.27%和124.32%;在生理指标方面,双接种处理效果低于单接种处理,未表现出协同作用;在土壤养分和微生物性质方面,单接种胶质芽孢杆菌仅显著提高土壤速效钾含量,单接种苜蓿根瘤菌对大部分指标均有显著效果,而双接种处理效果最佳,土壤碱解氮、速效钾含量比对照分别显著提高94.14%和84.55%,土壤微生物指标MBC含量、呼吸强度、蔗糖酶、脲酶、磷酸酶、过氧化氢酶活性比对照分别显著提高204.02%,65.86%,212.32%,91.87%,30.57%,51.87%。双接种处理对紫花苜蓿产量指标、养分和微生物指标表现出显著的协同作用。因此,1.50%用量胶质芽孢杆菌和0.25%用量苜蓿根瘤菌双接种能够有效提高排土场土壤的复垦效果,具有协同作用,可以作为矿区排土场复垦的高效方法。     

Response of Different Crops to Arbuscular Mycorrhiza Fungal Inoculation in Phosphorus-Deficient Soil

Arbuscular mycorrhizal fungi (AMF) have the capability to improve crop yields by increasing plant nutrient supply. A pot experiment was conducted under natural conditions to determine the response of AMF inoculation on the growth of maize (Zea mays L.), sorghum (Sorghum bicolor L.), millet (Pennisetum glaucum L.), mash bean (Vigna mungo L.), and mung bean (Vigna radiata. L.) crops during 2008. The experiment was conducted as a completely randomized design in three replications using phosphorus (P)–deficient soil. Three plants were grown in 10 kg soil up to the stage of maximum growth for 70 days. Spores of AMF were isolated from rhizosphere of freshly growing wheat and berseem crops and mixed with sterilized soil with fine particles. Crops were inoculated in the presence of indigenous mycorrhiza with the inoculum containing 20 g sterilized soil mixed with 40–50 AMF spores. Inoculation with AMF improved yield and nutrient uptake by different crops significantly over uninoculated crops. Inoculated millet crop showed 20% increase in shoot dry matter and 21% in root dry matter when compared with other inoculated crops. Increases of 67% in plant nitrogen (N) and iron (Fe) were observed in millet, 166% in plant P uptake was observed in mash beans, 186% in zinc (Zn) was measured in maize, and 208% in copper (Cu) and 48% in manganese (Mn) were noted in sorghum crops. Maximum root infection intensity of 35% by AMF and their soil spore density were observed in millet crop followed by 32% in mash beans. Results suggest that inoculation of AMF may play a role in improving crop production and the varied response of different crops to fungi signifies the importance of evaluating the compatibility of the fungi and plant host species.     

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.