Selection of mixed inoculants exhibiting growth-promoting activity in rice plants from undefined consortia obtained by continuous enrichment

Aims

The main objective of this study was to test the hypothesis that isolating and characterizing bacterial suspensions (undefined consortia) from the root/rhizosphere of rice will contribute to the selection of mixtures of rhizobacteria with better growth-promoting activity of rice plants.

Methods

Bacterial consortia were obtained from roots/rhizosphere soil samples of rice plants grown under upland and irrigated production systems. Those undefined consortia were subjected to five consecutive passes every 7 days in NFb (N-free broth) semisolid medium. Thereafter, strains of each growth-promoting consortia were isolated by plating on three different culture media. Then, undefined consortia, as well as mix and single bacterial strains, were characterized in terms of indoleacetic acid production, nitrogen fixation capacity, and growth promotion of rice plants.

Results

Of the 72 consortia analyzed, 41.7 % and 50.0 % increased nitrogenase activity and the production of indolic compounds, respectively, after 5 continuous passes in NFB medium. Three undefined consortia, 11 single strains and 5 strain mixtures, exhibited plant growth promotion in rice plants under greenhouse conditions.

Conclusions

Continuous enrichment in Nfb medium of undefined consortia from root/rhizosphere soil is a good strategy for the selection of plant growth-promoting bacteria for rice plants.     

Selection of phosphate-solubilizing diazotrophic Herbaspirillum and Burkholderia strains and their effect on rice crop yield and nutrient uptake

Background and Aims

Plant growth-promoting bacteria, mainly diazotrophs and phosphate solubilizers, can reduce the use of chemical fertilizers for rice crops. Here, diazotrophic bacteria isolated from rice were screened for their ability to solubilize inorganic P (P_i) in vitro and in association with rice plants cultivated in pots.

Methods

Forty-nine isolates were tested for the ability to solubilize P_i on NBRIP and GL agar plate media and seven selected strains were further evaluated in NBRIP liquid medium. Three of these strains were inoculated in rice plants grown in soil pots containing ¹⁵N-labeled fertilizer and two sources of P: tricalcium phosphate (TCP) or simple superphosphate (SSP). The dry matter, yield, N, P, and the ¹⁵N content accumulated in plant tissues were measured at 135 days after planting.

Results

Seven strains belonging to the genera Herbaspirillum and Burkholderia formed a halo of solubilized P_i on agar plates. The Burkholderia strains showed peak soluble P (around 200 mg P L^?1) on the fifth day when grown in NBRIP liquid medium for 14 days. Inoculation of Herbaspirillum strains (H18, ZA15) and a Burkholderia vietaminensis strain (AR114) increased rice grain yield from 33 to 47 % with TCP and 18 to 44 % with TSS, respectively. The bacterial inoculation led to enhanced N-use efficiency of the ¹⁵N-labeled fertilizer.

Conclusion

These results suggest that the selection and use of P-solubilizing diazotrophic bacteria are a good strategy to promote P solubilization and/or N use efficiency in rice plants.     

Physiological and genetic characterization of rice nitrogen fixer PGPR isolated from rhizosphere soils of different crops

Aims

We aimed to identify plant growth-promoting rhizobacteria that could be used to develop a biofertilizer for rice.

Methods

To obtain plant growth-promoting rhizobacteria, rhizosphere soils from different crops (rice, wheat, oats, crabgrass, maize, ryegrass, and sweet potato) were inoculated to rice plants. In total, 166 different bacteria were isolated and their plant growth-promoting traits were evaluated in terms of colony morphology, indole-3-acetic acid production, acetylene reduction activity, and phosphate solubilization activity. Moreover, genetic analysis was carried out to evaluate their phylogenetic relationships based on 16S rRNA sequence data.

Results

Strains of Bacillus altitudinis, Pseudomonas monteilii, and Pseudomonas mandelii formed associations with rice plants and fixed nitrogen. A strain of Rhizobium daejeonense showed nitrogen fixation activity in an in vitro assay and in vivo. Strains of B. altitudinis and R. daejeonense derived from rice rhizosphere soil, strains of P. monteilii and Enterobacter cloacae derived from wheat rhizosphere soil, and a strain of Bacillus pumilus derived from maize rhizosphere soil significantly promoted rice plant growth.

Conclusions

These methods are effective to identify candidate species that could be developed as biofertilizers for target crops.     

Soil nitrogen balance resulting from N fixation and rhizodeposition by the symbiotic association Anthyllis vulneraria/Mesorhizobium metallidurans grown in highly polluted Zn,Pb and Cd mine tailings

Background and aims

The association of the legume Anthyllis vulneraria and the grass Festuca arvernensis, was found to be very efficient for the phytostabilisation of highly multi-metal contaminated mine tailings. Our objective was to quantify the contribution of Anthyllis inoculated with its symbiotic bacteria Mesorhizobium metallidurans to the soil N pool and to test whether a starter nitrogen fertilization may improve symbiotic nitrogen fixation and the growth of Festuca.

Methods

Plants of Festuca and of Anthyllis inoculated with M. metallidurans were grown separately during eight months in pots filled with mine contaminated soil. Estimation of the N fluxes was realized using ¹⁵?N isotopic methods.

Results

Starter N fertilization (28 kg N ha^?1) improved symbiotic N₂ fixation and the growth of both species. Belowground N balance (N rhizodeposition – soil N uptake) of the non-fertilized Anthyllis at maturity was negative (?30.6 kg N ha^?1). However, the amount of N derived from fixation, including above- and belowground parts, was 78.6 kg N ha^?1, demonstrating the ability of this symbiotic association to improve soil N content after senescence.

Conclusions

i) soil N enrichment by the N₂-fixing symbiotic association occurs after plant senescence, when decaying leaves and shoots are incorporated into the soil; ii) application of a starter fertilization is an efficient solution to improve phytostabilisation of highly contaminated sites.     

Fine-root dynamics in sugi (Cryptomeria japonica) under manipulated soil nitrogen conditions

Aims

Nitrogen deposition affect fine-root dynamics, a key factor in forest carbon and nutrient dynamics. This study aimed to elucidate the effects of increased soil inorganic nitrogen (N) levels on the fine-root dynamics of Cryptomeria japonica, which is tolerant to excess N load.

Methods

An ammonium nitrate solution (28 kg ha^?1 month^?1) was applied for 3 years to plots (1 m?×?2 m) in a C. japonica plantation. The elongation and disappearance of the fine roots were examined using the minirhizotron technique.

Results

The N fertilization increased soil inorganic N content and lowered the soil pH. Fine-root elongation rates increased with fertilization, whereas patterns of their seasonal changes were not affected. The ratio of cumulative disappearance to cumulative elongation of fine roots was lower in the N-fertilized plots than in the control plots. The mean diameter of the fine roots was not affected by N fertilization.

Conclusions

Our results suggest that C. japonica can respond to increased levels of soil inorganic N by increasing both the production and residence time of the fine roots. However, the effects of the changing soil N content are less evident for the phenology and morphology of the fine roots in C. japonica.     

Liebig’s law of the minimum applied to a greenhouse gas: alleviation of P-limitation reduces soil N2O emission

Background and aims

Emission of the greenhouse gas (GHG) nitrous oxide (N₂O) are strongly affected by nitrogen (N) fertilizer application rates. However, the role of other nutrients through stoichiometric relations with N has hardly been studied. We tested whether phosphorus (P) availability affects N₂O emission. We hypothesized that alleviation of plant P-limitation reduces N₂O emission through lowering soil mineral N concentrations.

Methods

We tested our hypothesis in a pot experiment with maize (Zea mays L.) growing on a P-limiting soil/sand mixture. Treatment factors included P and N fertilization and inoculation with Arbuscular Mycorrhizal Fungi (AMF; which can increase P uptake).

Results

Both N and P fertilization, as well as their interaction significantly (P?<?0.01) affected N₂O emission. Highest N₂O emissions (2.38 kg N₂O-N ha^?1) were measured at highest N application rates without P fertilization or AMF. At the highest N application rate, N₂O fluxes were lowest (0.71 kg N₂O-N ha^?1) with both P fertilization and AMF. The N₂O emission factors decreased with 50 % when P fertilization was applied.

Conclusions

Our results illustrate the importance of the judicious use of all nutrients to minimize N₂O emission, and thereby further underline the intimate link between sound agronomic practice and prudent soil GHG management.     

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

Background and Aims

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.

Methods

Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg^?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.

Results

Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg^?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.

Conclusions

The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.     

Oxidation and reduction of sulfite contribute to susceptibility and detoxification of SO2 in Populus × canescens leaves

Key Message

The critical level for SO ₂ susceptibility of Populus × canescens is approximately 1.2 μL L ^?1 SO ₂ . Both sulfite oxidation and sulfite reduction and assimilation contribute to SO ₂ detoxification.

Abstract

In the present study, uptake, susceptibility and metabolism of SO₂ were analyzed in the deciduous tree species poplar (Populus × canescens). A particular focus was on the significance of sulfite oxidase (SO) for sulfite detoxification, as SO has been characterized as a safety valve for SO₂ detoxification in herbaceous plants. For this purpose, poplar plants were exposed to different levels of SO₂ (0.65, 0.8, 1.0, 1.2 μL L^?1) and were characterized by visible injuries and at the physiological level. Gas exchange parameters (stomatal conductance for water vapor, CO₂ assimilation, SO₂ uptake) of the shoots were compared with metabolite levels (sulfate, thiols) and enzyme activities [SO, adenosine 5′-phosphosulfate reductase (APR)] in expanding leaves (80–90 % expanded). The critical dosage of SO₂ that confers injury to the leaves was 1.2 μL L^?1 SO₂. The observed increase in sulfur containing compounds (sulfate and thiols) in the expanding leaves strongly correlated with total SO₂ uptake of the plant shoot, whereas SO₂ uptake rate was strongly correlated with stomatal conductance for water vapor. Furthermore, exposure to high concentration of SO₂ revealed channeling of sulfite through assimilatory sulfate reduction that contributes in addition to SO-mediated sulfite oxidation to sulfite detoxification in expanding leaves of this woody plant species.     

Interaction between root growth allocation and mycorrhizal fungi in soil with patchy P distribution

Aims and Background

Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.

Methods

Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot^?1), (c) low heterogeneous P (9.3 mg pot^?1), and (d) high heterogeneous P (28 mg pot^?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.

Results

Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.

Conclusion

Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions.     

Alfalfa plant-derived biostimulant stimulate short-term growth of salt stressed Zea mays L. plants

Background & Aims

The effects of an alfalfa plant (Medicago sativa L.) hydrolysate-based biostimulant (EM) containing triacontanol (TRIA) and indole-3-acetic acid (IAA) were tested in salt-stressed maize plants.

Methods

Plants were grown for 2 weeks in the absence of NaCl or in the presence (25, 75 and 150 mM). On the 12th day, plants were supplied for 48 h with 1.0 mg L^?1 EM or 11.2 μM TRIA.

Results

EM and TRIA stimulated the growth and nitrogen assimilation of control plants to a similar degree, while NaCl reduced plant growth, SPAD index and protein content. EM or TRIA increased plant biomass under salinity conditions. Furthermore, EM induced the activity of enzymes functioning in nitrogen metabolism. The activity of antioxidant enzymes and the synthesis of phenolics were induced by salinity, but decreased after EM treatment. The enhancement of phenylalanine ammonia-lyase (PAL) activity and gene expression by EM was consistent with the increase of flavonoids.

Conclusion

The present study proves that the EM increases plant biomass even when plants are grown under salinity conditions. This was likely because EM stimulated plant nitrogen metabolism and antioxidant systems. Therefore, EM may be proposed as bioactive product in agriculture to help plants overcome stress situations.     

Heterologous expression of Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) enhanced chilling tolerance in transgenic eggplant (Solanum melongena L.)

Key message

Our study shows that the expression of AtCBF3 and AtCOR15A improved the chilling tolerance in transgenic eggplant.

Abstract

In an attempt to improve chilling tolerance of eggplant (Solanum melongena L) plants, Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) genes both driven by an Arabidopsis RESPONSIVE TO DESSICATION 29A promoter (AtRD29A) were transferred into the plants of eggplant cultivar Sanyueqie. Two independent homozygous transgenic lines were tested for their cold tolerance. The leaves of the transgenic plants in both lines withered much slower and slighter than the wild-type plants after exposure to cold stress treatment at 2 ± 1 °C. The gene expression of AtCBF3 and AtCOR15A was significantly increased as well as the proline content and the levels of catalase and peroxidase activities, while the relative electrical conductivity and the malondialdehyde content were remarkably decreased in the transgenic plants compared with the wild type at 4 ± 0.5 °C. The results showed that the expression of the exogenous AtCBF3 and AtCOR15A could promote the cold adaptation process to protect eggplant plants from chilling stress.     

Utilizing pyrene-degrading endophytic bacteria to reduce the risk of plant pyrene contamination

Aims

Endophytic bacteria are ubiquitous in plants, but little information is available on the influence of endophytic bacteria on the uptake and metabolism of PAH by plants. Thus, we seek to investigate whether the colonization of a target plant by a PAH-degrading endophytic bacterium would improve the PAH metabolism of the plant and reduce the risk of plant PAH contamination.

Methods

A pyrene-degrading endophyte was isolated from PAH-contaminated plants using enrichment culture. After root inoculation with the isolated bacterium, greenhouse container experiments were conducted. Pyrene residues in soil and plant samples were analyzed by HPLC.

Results

A pyrene-degrading endophytic bacterium, Staphylococcus sp. BJ06, was isolated from Alopecurus aequalis and could degrade 56.0 % of pyrene (50 mg?·?L^?1) within 15 days. BJ06 grew and degraded pyrene efficiently under environmental conditions. The bacterium significantly promoted ryegrass growth and pyrene removal from contaminated soil in container experiments. The pyrene concentrations in ryegrass roots and shoots in endophyte-inoculated planted soil were reduced by 31.01 % and 44.22 %, respectively, compared with endophyte-free planted soil.

Conclusions

We have provided new perspectives on the regulation and control of plant uptake of organic contaminants with endophytic bacteria. The results of this study will be valuable to risk assessments of plant PAH contamination.     

Zinc accumulation patterns in four Anthyllis vulneraria subspecies supplemented with mineral nitrogen or grown in the presence of their symbiotic bacteria

Aims

This work examines Zn accumulation in four Anthyllis vulneraria subspecies supplemented with mineral nitrogen or grown in the presence of their symbiotic bacteria.

Methods

Anthyllis vulneraria subspecies were grown hydroponically in the presence of high levels of ZnSO₄. The plants were either grown in symbiosis with one of two non-metallicolous or metallicolous Mesorhizobium inoculants or in the presence of KNO₃.

Results

When exposed to 1,000 μM Zn, shoot and root biomass of three out of our four Anthyllis subspecies cultivated with NO₃ dropped significantly by about 24–28 %; carpatica, the fourth subspecies, was not affected. Subspecies carpatica Zn tolerance was confirmed when in symbiosis with the metallicolous strain. In the presence of 1,000 μM Zn, the different Anthyllis subspecies concentrated more Zn in their roots than in their shoots and only subsp. carpatica accumulated a significant amount of Zn in its shoots. The most remarkable feature was the drastic decrease in Zn concentration in both roots (up to 2.5–3 fold) and shoots (2.6-fold) of subsp. carpatica exposed to 1,000 μM Zn and nodulated whatever the Mesorhizobium strain used, compared to the N-grown plants.

Conclusions

Our results bring new perspectives as regards phytostabilization, with the potential use of a rhizobium-inoculated leguminous subspecies displaying unusual Zn tolerance.     

The effect of plant growth-promoting rhizobacteria on the growth of rice (Oryza sativa L.) cropped in southern Brazilian fields

Background and Aims

Several strains of rhizobacteria may be found in the rhizospheric soil, on the root surface or in association with rice plants. These bacteria are able to colonize plant root systems and promote plant growth and crop yield through a variety of mechanisms. The objectives of this study were to isolate, identify, and characterize putative plant growth-promoting rhizobacteria (PGPR) associated with rice cropped in different areas of southern Brazil.

Methods

Bacterial strains were selectively isolated based on their growth on three selective semi-solid nitrogen-free media. Bacteria were identified at the genus level by PCR-RFLP 16S rRNA gene analysis and partial sequencing methodologies. Bacterial isolates were evaluated for their ability to produce indolic compounds and siderophores and to solubilize phosphate. In vitro biological nitrogen fixation and the ability to produce 1-aminocyclopropane-1-carboxylate deaminase were evaluated for each bacterial isolate used in the inoculation experiments.

Results

In total, 336 bacterial strains were isolated representing 31 different bacterial genera. Strains belonging to the genera Agrobacterium, Burkholderia, Enterobacter, and Pseudomonas were the most prominent isolates. Siderophore and indolic compounds producers were widely found among isolates, but 101 isolates were able to solubilize phosphate. Under gnotobiotic conditions, eight isolates were able to stimulate the growth of rice plants. Five of these eight isolates were also field tested in rice plants subjected to different nitrogen fertilization rates.

Conclusions

The results showed that the condition of half-fertilization plus separate inoculation with the isolates AC32 (Herbaspirillum sp.), AG15 (Burkholderia sp.), CA21 (Pseudacidovorax sp.), and UR51 (Azospirillum sp.) achieved rice growth similar to those achieved by full-fertilization without inoculation, thus highlighting the potential of these strains for formulating new bioinoculants for rice crops.     

Enhanced nodulation and symbiotic effectiveness of Medicago truncatula when co-inoculated with Pseudomonas fluorescens WSM3457 and Ensifer (Sinorhizobium) medicae WSM419

Aims

Low numbers of rhizobia in soil or inoculants delay nodulation and decrease symbiotic legume productivity. This study investigated the effect of co-inoculation with a helper bacterium, Pseudomonas fluorescens WSM3457 on the Medicago truncatula - Ensifer (Sinorhizobium) medicae WSM419 symbiosis challenged by a low inoculum dose.

Methods

In a glasshouse experiment the effect of co-inoculation with WSM3457 on the kinetics of nodule initiation and development was assessed 5, 7, 10, 14, 17, 21, and 42 days after inoculation of M. truncatula cv. Caliph with 10³ cells/plant of E. medicae WSM419.

Results

Co-inoculated plants had enhanced rate of nodule initiation and development, greater numbers of larger crown nodules, and by day 42 accumulated more N than plants inoculated with E. medicae WSM419 alone. Nodule development was altered by co-inoculation. Approximately 25% of nodule initials on co-inoculated plants formed in closely associated pairs, young nodules were larger with multiple meristems and developed into cluster-like multi-lobed nodules compared to those on WSM419 inoculated plants. Molecular typing showed WSM3457 occupied a significant proportion of root nodules on co-inoculated plants.

Conclusion

Co-inoculation with P. fluorescens WSM3457 enhanced symbiotic effectiveness of M. truncatula when inoculated with a low inoculum dose of E. medicae WSM419.     

Effects of experimental warming and nitrogen fertilization on soil microbial communities and processes of two subalpine coniferous species in Eastern Tibetan Plateau,China

Aim

This study aimed at predicting how sub-alpine coniferous ecosystems respond to global changes in the Eastern Tibetan Plateau by understanding soil microbial communities and activities, as well as variation in the quality and quantity of soil organic matter.

Methods

An experiment was conducted to examine soil microbial communities and their related soil processes in rhizospheric soil of two coniferous species that were exposed to two levels of temperature (unwarmed and infrared heater warming) and two levels of nitrogen (unfertilized and 25 g N m^?2 a^?1) from April 2007.

Results

Four-year night warming alone slightly affected the phospholipid fatty acid contents of the microbial community. However, the combination of nitrogen addition and soil warming significantly affected soil microbial composition while reducing the biomass of major microbial groups and the activities of most enzymes, especially in Abies faxoniana plots. The combination of warming and nitrogen addition increased soil labile C and N pools in Picea asperata plots and was beneficial for soil recalcitrant C, as well as for labile and total C and N pools in A. faxoniana plots.

Conclusion

Results indicated that future warming will slightly affect soil microbial communities and their related soil processes. However, warming combined with high nitrogen deposition will significantly constrain soil microbial biomass and enzyme activities, consequently increasing soil C and N pools in sub-alpine coniferous forests of this region.     

Nitrogen response efficiency of a managed and phytodiverse temperate grassland

Aims

Our goal was to assess how management and sward functional diversity affect nitrogen response efficiency (NRE), the ratio of plant biomass production to supply of available nitrogen (N) in temperate grassland.

Methods

A three-factorial design was employed: three sward compositions, two mowing frequencies, and two fertilization treatments.

Results

NRE was largely influenced by fertilization followed by mowing frequency and sward composition. NRE was larger in unfertilized than fertilized plots, in plots cut thrice than plots cut once per year, and in control swards than in monocot- or dicot-enhanced swards. Fertilization decreased NRE through decreases in both N uptake efficiency (plant N uptake per supply of available N) and N use efficiency (NUE, biomass produced per plant N uptake) whereas mowing frequency and sward composition affected NRE through N uptake efficiency rather than NUE. The largest NRE in the control sward with 70 % monocots and 30 % dicots attests that these proportions of functional groups were best adapted in this grassland ecosystem.

Conclusions

Optimum NRE may not be a target of most farmers, but it is an appropriate tool to evaluate the consequences of grassland management practices, which farmers may employ to maximize profit, on environmental quality.     

A multi-environmental study of recent breeding progress on nitrogen use efficiency in wheat (Triticum aestivum L.)

Key message

By comparing 195 varieties in eight trials, this study assesses nitrogen use efficiency improvement in high and low nitrogen conditions in European winter wheat over the last 25 years.

Abstract

In a context where European agriculture practices have to deal with environmental concerns and nitrogen (N) fertiliser cost, nitrogen use efficiency (NUE) has to be improved. This study assessed genetic progress in winter wheat (Triticum aestivum L.) NUE. Two hundred and twenty-five European elite varieties were tested in four environments under two levels of N. Global genetic progress was assessed on additive genetic values and on genotype × N interaction, covering 25 years of European breeding. To avoid sampling bias, quality, precocity and plant height were added as covariates in the analyses when needed. Genotype × environment interactions were highly significant for all the traits studied to such an extent that no additive genetic effect was detected on N uptake. Genotype × N interactions were significant for yield, grain protein content (GPC), N concentration in straw, N utilisation, and NUE. Grain yield improvement (+0.45 % year^?1) was independent of the N treatment. GPC was stable, thus grain nitrogen yield was improved (+0.39 % year^?1). Genetic progress on N harvest index (+0.12 % year^?1) and on N concentration in straw (?0.52 % year^?1) possibly revealed improvement in N remobilisation. There has been an improvement of NUE additive genetic value (+0.33 % year^?1) linked to better N utilisation (+0.20 % year^?1). Improved yield stability was detected as a significant improvement of NUE in low compared to high N conditions. The application of these results to breeding programs is discussed.     

Impact of plant growth-promoting bacteria on grain yield,protein content,and urea-<Superscript>15</Superscript> N recovery by maize in a Cerrado Oxisol

Background and aims

The inoculation of cereal crops with plant growth-promoting bacteria (PGPB) is a potential strategy to improve fertilizer-N acquisition by crops in soils with low capacity to supply N. A study was conducted to assess the impact of three inoculants on grain yield, protein content, and urea-¹⁵ N recovery in maize (Zea mays L.) under Cerrado soil and climate conditions.

Methods

The main treatments included inoculants containing (i) Azospirillum brasilense strain Sp245, (ii) A. brasilense strains AbV5 + AbV6, (iii) Herbaspirillum seropedicae strain ZAE94, and (iv) a non-inoculated control. The subtreatments were (i) urea-N fertilization (100 kg N ha^?1) at 30 days after sowing and (ii) no N addition at the stage. To determine fertilizer-N recovery, ¹⁵N–labelled urea was applied in microplots.

Results

Inoculants carrying A. brasilense improved urea-¹⁵ N acquisition efficiency in maize and also improved grain yield compared to the non-inoculated control, while urea-N fertilization enhanced grain quality by providing higher protein content.

Conclusion

Our results suggest that the inoculation of maize grains with PGPB represents a strategy to improve fertilizer-N recovery and maize yield in Cerrado soil with a low capacity to supply N.