Effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize (Zea mays) and barley (Hordeum vulgare)

Summary The addition of sugars or amino acids to the soil gave rise to the development of different groups of microorganisms. The increase in the number of different groups of microorganisms in the soil had an influence on the microbiota in the rhizoplane and endorhizosphere of maize and barley grown in that soil. Furthermore, growth of maize and barley decreased with increasing microbial activity and density in soil. This effect could be counteracted effectively by the rhizopseudomonad strain 7NSK2. The beneficial effect of the strain 7NSK2 correlated inversely with the microbial activity, as measured by soil respiration, in the bulk-pretreated soil.The effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize and barley was evaluated. The strain 7NSK2 was capable of colonizing the rhizoplane and endorhizosphere of the maize cultivar Beaupré and barley cultivar Than very effectively and of considerably altering their composition. The number of total bacteria, fungi, pseudomonads and coliform bacteria in the rhizoplane and endorhizosphere of both plants was strongly reduced by inoculating the seeds with the strain 7NSK2.     

Susceptibility and effectiveness of vesicular-arbuscular mycorrhizae in wheat cultivars under different growing conditions

Summary Wheat cultivars assumed to be non-susceptible to vesicular-arbuscular (VA) mycorrhizae became colonized, and this effect persisted under different growth conditions. Colonization of all cultivars was similar regardless of the amount of inoculum and the time interval of inoculation. Different plant growth temperatures and the support given by the culture media, inoculation with different endophytes, and inoculation with sterilized and unsterilized spores affected VA colonization levels, although the level of colonization reached in cv. Champlein was similar to that reached in cv. 7-Cerros under each condition. VA mycorrhizal colonization was also affected by different plant growth conditions. After VA reinoculation, the plant dry weight of Castan and 7-Cerros increased, but not Negrillo and Champlein cultivars. VA mycorrhizae increased the shoot dry weight of 7-Cerros only, but not of Champlein, when grown at 35/24°C, and had no effect on the dry weight of either cultivar grown at 18/12°C and 42/24°C. Inoculation with Glomus mosseae increased the dry weight of the cultivars more than inoculation with G. fasciculatum or G. agregatum. The effect on the plant dry weight was greater in plants grown in soil than in sand/vermiculite pots. Inoculation with sterilized and unsterilized spores of G. mosseae, either in soil pots or in sand/vermiculite tubes, did not increase the plant dry weight. Our results indicate that there was no close relationship between the level of root colonization and the effect on plant growth. The effects of accompanying microorganisms in the VA inoculum on VA mycorrhizal symbiosis are discussed.     

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.     

The mycorrhizal fungus Glomus intraradices and rock phosphate amendment influence plant growth and microbial activity in the rhizosphere of Acacia holosericea

Plants inoculated with arbuscular mycorrhizal (AM) fungi utilize more soluble phosphorus from soil mineral phosphate than non-inoculated plants. However, there is no information on the response of soil microflora to mineral phosphate weathering by AM fungi and, in particular, on the catabolic diversity of soil microbial communities.The AM fungus, Glomus intraradices was examined for (i) its effect on the growth of Acacia holosericea, (ii) plant-available phosphate and (iii) soil microbial activity with and without added rock phosphate.After 4-months culture, AM fungal inoculation significantly increased the plant biomasses (by 1.78× and 2.23× for shoot and root biomasses, respectively), while mineral phosphate amendment had no effect in a sterilized soil. After 12-months culture, the biomasses of A. holosericea plants growing in a non-sterilized soil amended with mineral phosphate were significantly higher than those recorded in the control treatment (by 2.5× and 5× for shoot and root biomasses, respectively). The fungal inoculation also significantly stimulated plant growth, which was significantly higher than that measured in the mineral phosphate treatment. When G. intraradices and mineral phosphate were added together to the soil, shoot growth were significantly stimulated over the single treatments (inoculation or amendment) (1.45×). The P leaf mineral content was also higher in the G. intraradices+mineral phosphate treatment than in G. intraradices or rock phosphate amendment. Moreover, the number of fluorescent pseudomonads has been significantly increased when G. intraradices and/or mineral phosphate were added to the soil. By using a specific type of multivariate analysis (co-inertia analysis), it has been shown that plant growth was positively correlated to the metabolization of ketoglutaric acid, and negatively linked to the metabolisation of phenylalanine and other substrates, which shows that microbial activity is also affected.G. intraradices inoculation is highly beneficial to the growth of A. holosericea plants in controlled conditions. This AM symbiosis optimises the P solubilization from the mineral phosphate and affects microbial activity in the hyphosphere of A. holosericea plants.     

Influence of a plant growth-promoting pseudomonad and vesicular-arbuscular mycorrhizal fungus on alfalfa and birdsfoot trefoil growth and nodulation

Summary In a growth chamber study we examined the influence of a plant growth-promoting rhizobacterium, Pseudomonas putida R-20, and an acid-tolerant vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus intraradices 25, on Medicago sativa L. and Lotus corniculatus L. growth and nodule development. Seedlings were planted in an acidic (pH 5.5), P-deficient soil containing re-established native microflora (minus VAM) and appropriate rhizobia, and inoculated with the rhizobacterium, the VAM fungus, or both. The plants were assayed at three intervals for up to 10–11 weeks. The growth-promoting rhizobacteria alone increased alfalfa shoot mass by 23% compared to all other treatments, but only at 8 weeks of growth, apparently by promoting nodulation and N₂ fixation (acetylene reduction activity). The presence of VAM, either alone or in combination with the rhizobacteria, generally decreased root length but only at 8 weeks also. As a group, the inoculation treatments increased all nodular measurements by 10 weeks of growth. Few treatment effects were found at 7 and 9 weeks for birdsfoot trefoil; neither plant nor nodular measurements differed among treatments. By 11 weeks, shoot mass was increased by the rhizobacteria alone by 36% compared to the control. As a group, the inoculation treatments all showed increased nodular responses by this time. The rhizobacteria stimulated mycorrhizal development on both plant species, but only at the initial samplings. No synergistic effects between the plant growth-promoting rhizobacterium and VAM inoculation were found. Although these results lend credence to the concept of managing microorganisms in the rhizosphere to improve plant growth, they emphasize the necessity for a more thorough understanding of microbial interactions as plants mature.     

Soil inoculation with the biocontrol agent Clonostachys rosea and the mycorrhizal fungus Glomus intraradices results in mutual inhibition, plant growth promotion and alteration of soil microbial communities

Interactions between the biocontrol fungus Clonostachys rosea IK 726 and a tomato/Glomus intraradices BEG87 symbiosis were examined with and without wheat bran, which served as a food base for C. rosea. In soil without wheat bran amendment, inoculation with C. rosea increased plant growth and altered shoot nutrient content resulting in an increase and decrease in P and N content, respectively. Inoculation with G. intraradices had no effect on plant growth, but increased the shoot P content. Dual inoculation with G. intraradices and C. rosea followed the pattern of C. rosea in terms of plant growth and nutrient content. Wheat bran amendment resulted in marked plant growth depressions, which were counteracted by both inoculants and dual inoculation increased plant growth synergistically. Amendment with wheat bran increased the population density of C. rosea and reduced mycorrhizal fungus colonisation of roots. The inoculants were mutually inhibitory, which was shown by a reduction in root colonisation with G. intraradices in treatments with C. rosea and a reduction in colony-forming units (cfu) of C. rosea in treatments with G. intraradices, irrespective of wheat bran amendment. Moreover, both inoculants markedly influenced soil microbial communities examined with biomarker fatty acids. Inoculation with G. intraradices increased most groups of microorganisms irrespective of wheat bran amendment, whereas the influence of C. rosea on other soil microorganisms was affected by wheat bran amendment. Overall, inoculation with C. rosea increased and decreased most groups of microorganisms without and with wheat bran amendment, respectively. In conclusion, despite mutual inhibition between the two inoculants this interaction did not impair their observed plant growth promotion. Both inoculants also markedly influenced other soil microorganisms, which should be further studied in relation to their plant growth-promoting features.     

Mycorrhizae,biocides, and biocontrol. 4. Response of a mixed culture of arbuscular mycorrhizal fungi and host plant to three fungicides

The effects of three commonly used fungicides on the colonization and sporulation by a mixture of three arbuscular mycorrhizal (AM) fungi consisting of Glomus etunicatum (Becker & Gerd.), Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, and Gigaspora rosea (Nicol. & Schenck) in symbiosis with pea plants and the resulting response of the host-plant were examined. Benomyl, PCNB, and captan were applied as soil drenches at a rate of 20 mg active ingredient kg^-1 soil 2 weeks after transplanting pea seedlings in a silty clay-loam soil containing the mixed inocula of AM fungi (AM plants). Effects of fungicides were compared to untreated plants that were inoculated with fungi (AM control). The effect of mycorrhizal inoculation on plant growth was also examined by including nonmycorrhizal, non-fungicide-treated plants (non-AM control). Fungicides or inoculation with AM fungi had only a small effect on the final shoot weights of pea plants, but had greater effects on root length and seed yield. AM control plants had higher seed yields and lower root lengths than the corresponding non-AM plants, and the fungicide-treated AM plants had intermediate yields and root lengths. Seed N and P contents were likewise highest in AM control plants, lowest in non-AM plants, and intermediate in fungicide-treated AM plants. All three fungicides depressed the proportion (%) of root length colonized by AM fungi, but these differences did not translate to reductions in the total root length that was colonized, since roots were longer in the fungicide-treated AM plants. Pea plants apparently compensated for the reduction in AM-fungal metabolism due to fungicides by increasing root growth. Fungicides affected the population of the three fungi as determined by sporulation at the final harvest. Captan significantly reduced the number, relative abundance, and relative volume of G. rosea spores in the final population relative to the controls. The relative volume of G. etunicatum spores was greater in all the fungicide-treated soils, while G. mosseae relative volumes were only greater in the captan-treated soil. These findings show that fungicides can alter the species composition of an AM-fungal community. The results also show that AM fungi can increase seed yield without enhancing the vegetative shoot growth of host plants.     

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

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

Soil sterilisation and plant growth-promoting rhizobacteria promote root respiration and growth of sweet cherry rootstocks

Soil microorganisms play important roles in the plant-soil ecosystem, and plant growth-promoting rhizobacterium (PGPR) promotes plant growth through several mechanisms. To investigate the benefits of PGPR for root functions such as respiration, we used the plant model Cerasus sachalinensis Kom., in which root respiration provides a sensitive functional indicator to demonstrate the effect of soil sterilisation (SS) and inoculation with the PGPR Staphylococcus sciuri ss sciuri after SS on seedling root respiration and growth. Root respiration increased in the presence of PGPR inoculation alone, whereas Embden–Meyerhof–Parnas pathway activity decreased due to reduced phosphofructokinase and pyruvate kinase activities. Although cytochrome c oxidase activity decreased and alternative oxidase activity increased, only slight changes were observed in growth indicators such as seedling height. However, SS and PGPR inoculation after sterilisation reduced soil microbial biomass carbon and reduced root respiration. Pyruvate kinase activity as well as plant height and leaf number increased, thus promoting plant growth. Thus, we conclude that SS and PGPR inoculation altered enzymes activities, root respiration and plant growth of cherry rootstocks. The effects of microbial inoculation were altered by SS.     

Occurrence and nature of mixed infections in nodules of field-grown soybeans (Glycine max)

Summary Mixed infections of Bradyrhizobium japonicum strains in early and late nodules of four soybean cultivars were studied in a field soil. Nodule occupants were identified by immunofluorescence using serogroup specific antibodies prepared against B. japonicum strains USDA 110, USDA 123, and USDA 138. Double infection was determined directly by combined examination of the same microscopic field by fluorescence and phase contrast microscopy. Double strain occupancy was observed consistently, and its occurrence did not differ substantially in pouch, soil pot, and field experiments, ranging in incidence from 12% to 32%. No significant differences in the incidence or nature of double infection could be attributed to cultivar, seed inoculation, or plant maturity. Strains reactive to strain USDA 123-fluorescent antibody were dominant in both singly and doubly infected nodules irrespective of cultivar, plant age, or seed inoculation with strain USDA 110.Paper no. 15092 in the Scientific Journal Series of the Minnesota Agricultural Experiment Station, St. Paul     

紫茎泽兰和黄顶菊入侵对土壤微生物群落结构和旱稻生长的影响

为比较入侵植物与本地植物对土壤微生态影响的差异, 探索外来植物入侵的土壤微生物学机制, 本研究通过同质园试验, 比较分析了2种入侵菊科植物(紫茎泽兰、黄顶菊)和2种本地植物(马唐、猪毛菜)对土壤肥力和微生物群落的影响, 并通过盆栽反馈试验验证入侵植物改变后的土壤微生物对本地植物旱稻生长的反馈作用。同质园试验结果表明: 2种入侵植物和2种本地植物分别对土壤微生态产生了不同的影响, 尤其是紫茎泽兰显著提高了土壤有效氮、有效磷和有效钾含量,紫茎泽兰根际土壤中有效氮含量为39.80 mg·kg^-1,有效磷含量为48.52 mg·kg^-1。磷脂脂肪酸指纹图谱结果表明, 2种入侵植物与2种本地植物相比, 较显著增加了土壤中放线菌数量, 而紫茎泽兰比其他3种植物显著增加了细菌和真菌数量。盆栽结果表明: 黄顶菊生长过的土壤灭菌后比灭菌前旱稻株高增加113%, 紫茎泽兰也使旱稻的株高增加17%。由以上结果可知, 紫茎泽兰和黄顶菊可能通过改变入侵地土壤的微环境, 形成利于其自身生长扩散的微生态环境从而实现其成功入侵。     

Effect of soil pH on plant growth and nodulation of cowpea

Abstract

A study was conducted to evaluate the effect of soil pH on rhizobium inoculation, plant growth and nodulation of cowpea (Vigna unguiculata). Both inoculated and non‐inoculated seeds of the cultivar ‘California Blackeye No. 5’ were grown in the greenhouse in plastic pots with growth medium being a Norfolk sandy loam (Fine, loamy siliceous, thermic, Typic Palendult) soil under different pH levels. Both soil pH and rhizobium inoculation significantly affected root length, plant height, nodule and pod number per plant. Within the pH range of 6.6 to 7.6, these growth parameters generally were at their maximum, decreasing above or below this pH range. Non‐inoculated plants produced some nodules, indicating failure of the methyl bromide to totally destroy all residual soil rhizobta before inoculation treatment.

The inoculated plants produced more seeds and the increased number of nodules of treated plants was directly related to increased seed weight. Since nodule number was highest at the approximate pH range of 6.6 to 7.6, this range was considered optimum for nodulation of cowpea by this strain of rhizobium under greenhouse conditions. At pH 7.5 and above, roots tended to be more fibrous and nodules were generally smaller in size.     

Effect of inoculation with Azotobacter chroococcum on nitrogenase activity of Zea mays roots grown in agricultural soils under aseptic and non-sterile conditions

Summary Inoculated and non-inoculated seedlings of Zea mays were grown in agricultural soils under aseptic and non-sterile conditions. Acetylene reduction activity and microbial counts were determined after 7 and 30 days of growth. Irrespective of the soil type Azotobacter spp. were commonly isolated under maize cultivation. Inoculation of agricultural soils with a suspension of A. chroococcum led to an increase in Azotobacter numbers, although this effect diminished with time. Nitrogenase activity was detected on maize roots and increased in response to the inoculation with A. chroococcum, showing that this associative growth could be of primary importance for the plant. The results of assays for acetylene reduction activity indicated that the nitrogenase activity was associated only with the root systems.     

Effect of manganese-reducing rhizosphere bacteria on the growth of Gaeumannomyces graminis var. tritici and on manganese uptake by wheat (Triticum aestivum L.)

Summary Five bacterial strains capable of Mn reduction were isolated from the rhizosphere of plants growing in different South Australian soils. They differed in their Mn-reducing capacity. The antagonism of these strains compared to the imported strain 2–79 (from the United States) against Gaeumannomyces graminis var. tritici was tested in agar and in a soil sandwich experiment at different Mn²⁺ concentrations in the soil. In addition, wheat seeds were coated with the different strains and with MnSO₄ or with MnSO₄ only in order to investigate their effect on plant growth and Mn uptake. With one exception, all strains inhibited the growth of G. graminis in agar, but to different degrees. In contrast, only two strains significantly inhibited the growth of the fungus in the soil. The hyphal density was decreased more than the hyphal length. The Mn²⁺ concentration in the soil also had a marked effect on fungal growth; low Mn concentrations slightly increased while high Mn concentrations strongly decreased the fungal growth. Seed treatment with MnSO₄ only (+Mn) increased Mn uptake above that of the control (no seed treatment). Only the weakest Mn reducer on agar significantly increased plant growth and Mn uptake from soil in comparison with the Mn treatment. One strain was tested as seed coating without adding MnSO₄; it increased the plant growth to an extent similar to the Mn treatment. Increasing the Mn uptake by plants may be one of the growth-promoting effects exerted by rhizosphere bacteria.     

Antioxidant activities and metal acquisition in mycorrhizal plants growing in a heavy-metal multicontaminated soil amended with treated lignocellulosic agrowaste

The plant growth, nutrient acquisition, metal translocation and antioxidant activities [ascorbate peroxidase (APX), glutatione reductase (GR), superoxide dismutase (SOD) and catalase (CAT)] were measured in plants growing in a heavy-metal (HM) multicontaminated soil inoculated with selected autochthonous microorganisms [arbuscular mycorrhizal (AM) fungus and/or plant growth promoting bacteria (PGPB)] and/or amended with an Aspergillus niger-treated agrowaste. The treated agrowaste on its own increased root growth by 296% and shoot growth by 504% compared with non-treated control plants. Both chemical and biological treatments, particularly when combined, enhanced plant shoot and root development. The stimulation effect on plant biomass was concomitant with increased AM colonization, P and K assimilation, and reduced metal translocation from soil to plant shoot. The treated residue, particularly through interactions with AM inoculation, produced the expected bioremediation effect, leading to enhanced plant development and successful rehabilitation of contaminated soil. The enhancement of CAT, APX and GR activities caused by AM inoculation suggests that AM colonization helped plants to limit oxidative damage to biomolecules in response to metal stress. The response of the plant's antioxidant activities to the amendment appears to be related to enhanced plant biomass production. The application of amendments and/or microbial inoculations to enhance plant growth and reduce metal translocation in multicontaminated soil could be a promising strategy for remediating HM pollution.     

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。     

Single and double inoculation with Azospirillum/Trichoderma: the effects on dry bean and wheat

A plant growth-promoting rhizobacterium (Azospirillum brasilense Sp7) and a bio-control fungus, which can solubilize insoluble phosphorus (Trichoderma harzianum Rifai 1295-22), were evaluated for their single and combined effects on dry bean (Phaseolus vulgaris) and wheat (Triticum aestivum L.) grown in soil. A pot experiment with bean and a field experiment with both bean and wheat were established. In contrast to single inoculation of Trichoderma, the single inoculation of Azospirillum and the double inoculation did not significantly (P >0.05) increase nodule numbers and nodule mass at 45 days after planting in pot grown beans. However, the Azospirillum inoculation with supplementary phosphorus significantly (P <0.05) increased nodule mass. There were no significant (P >0.05) differences among the inoculation treatments for plant dry weight, total plant nitrogen, and total plant phosphorus at 45 days after planting in both pot and field experiments with bean. However, the combined inoculation and rock phosphate application at 1 Mg ha^–1 significantly (P <0.05) increased bean seed yield, total seed nitrogen and phosphorus in the bean field trial. This treatment more than doubled the mentioned properties compared to the control. The microbial inoculations, with the exception of the combined inoculation, significantly (P <0.05) increased total seed nitrogen, but never affected seed yield in the wheat field trial (P >0.05). The combined inoculation improves many plant and yield parameters and, therefore, has some advantages over single inoculation provided that rock phosphate was supplied at an amount not exceeding 1 Mg ha^–1. Higher rock phosphate application rates decreased many plant and yield parameters in our study.This work was carried out at Gaziosmanpaa University, Tokat, Turkey.     

Ecosystem partitioning of N-glycine after long-term climate and nutrient manipulations, plant clipping and addition of labile carbon in a subarctic heath tundra

Low temperatures and high soil moisture restrict cycling of organic matter in arctic soils, but also substrate quality, i.e. labile carbon (C) availability, exerts control on microbial activity. Plant exudation of labile C may facilitate microbial growth and enhance microbial immobilization of nitrogen (N). Here, we studied ¹⁵N label incorporation into microbes, plants and soil N pools after both long-term (12 years) climate manipulation and nutrient addition, plant clipping and a pulse-addition of labile C to the soil, in order to gain information on interactions among soil N and C pools, microorganisms and plants. There were few effects of long-term warming and fertilization on soil and plant pools. However, fertilization increased soil and plant N pools and increased pool dilution of the added ¹⁵N label. In all treatments, microbes immobilized a major part of the added ¹⁵N shortly after label addition. However, plants exerted control on the soil inorganic N concentrations and recovery of total dissolved ¹⁵N (TD¹⁵N), and likewise the microbes reduced these soil pools, but only when fed with labile C. Soil microbes in clipped plots were primarily C limited, and the findings of reduced N availability, both in the presence of plants and with the combined treatment of plant clipping and addition of sugar, suggest that the plant control of soil N pools was not solely due to plant uptake of soil N, but also partially caused by plants feeding labile C to the soil microbes, which enhanced their immobilization power. Hence, the cycling of N in subarctic heath tundra is strongly influenced by alternating release and immobilization by microorganisms, which on the other hand seems to be less affected by long-term warming than by addition or removal of sources of labile C.     

Effect of soil physical properties on soybean nodulation and N2 fixation at the early growth stage in heavy soil field in Hachirougata Polder,Japan

We studied the effect of the soil physical properties on soybean nodulation and N₂ fixation in the heavy soil of an upland field (UF) and an upland field converted from a paddy field (UCPF) in the Hachirougata polder, Japan. Seeds of the soybean cultivar Ryuho were sown in each field with or without inoculation of Bradyrhizobium japonicum A1017. The soybean plants were sampled at 35 (V3) and 65 (Rl) d after sowing (DAS), and then nodulation and the percentage of N derived from N₂ fixation in the xylem sap were determined. The soil physical properties were different between UF and UCPF, especially the air permeability and soil water regime. Nodule growth was restricted in UCPF irrespective of rhizobial inoculation, though rhizobial infection was not inhibited by the unfavorable soil physical conditions. Soybean plant growth was closely related to the nodule mass and N₂ fixation activity, and the inoculation of a superior rhizobium strain was effective only at 35 DAS. These results indicate that soybean nodulation and N₂ fixation was considerably affected by the physical properties of heavy soil, and that it is important to maintain the N₂ fixation activity and inoculate the soybean plants with a superior rhizobium strain at a later growth stage in order to increase soybean production in heavy soil fields.     

Penicillium bilaii effects on maize growth and P uptake from soil and localized sewage sludge in a rhizobox experiment

With P being a non-renewable resource, the use of microbial inoculants and waste products for more efficient and sustainable P use in plant production has been proposed. We investigated the ability of Penicillium bilaii to mobilize P in a low-fertility soil with or without amendment of sewage sludge as additional P source. Maize was grown for 27 days in rhizoboxes enabling studies of root growth in addition to plant and soil parameters. P. bilaii was inoculated either at the seed or the sewage sludge patch. At early growth stages, P. bilaii inoculation of seeds increased maize shoot length. However, at the end of experiment, the effect had ceased. Root growth was increased by seed P. bilaii inoculation alone and in combination with sewage sludge, whereas patch inoculation was less effective. Colonization studies performed at harvest showed that P. bilaii could not be detected in the maize rhizosphere but stayed at the place of inoculation. In sewage sludge patches, the growth of Penicillium strains other than P. bilaii was stimulated; hence, using sewage sludge for combined P resource and carrier of microbial inoculants is discussed. Unexpectedly, the greater root development of seed-inoculated plants did not result in increased plant P uptake and neither did inoculation at the sewage sludge patch. This study raises the question if the soil P status can be too low for a beneficial effect of additional early root growth and thus a beneficial effect of seed inoculation of P. bilaii.