Biomass Of Maize Plants Research Articles

CONTENT AND EXPORT OF N, P, K AND SI WITH MAIZE BIOMASS DEPENDING ON THE FERTILIZATION ON ALLUVIAL-MEADOW SOIL

The aim of the study in a pot experiment on Alluvial-meadow soil (Fluvisol, FAO) was to evaluate the effect of different rates and combinations of nitrogen, phosphorus, potassium and silicon fertilizers on the growth of maize (Zea mays L.) an early hybrid Р-8834 from group 310 FAO “Syngenta”. The experiment included 16 variants of fertilization in 3 replications. Data were obtained on the yield of fresh and absolutely dry biomass of maize plants and the content of N, P, K and Si in the dry biomass was assessed. It was found that the concentrations and the export of the studied macroelements with the biomass were significantly influenced by the fertilization applied. Nitrogen export was the highest in the N200, N300 and N400 rate treatments, and in comparison with the export of the other investigated elements. The export of N, P, K, and Si with maize dry biomass corresponded to a significant extent the contents of the macroelements in it. With increasing fertilization rates, not only the content, but also the export of nitrogen, phosphorus, and silicon increased. Regarding the potassium, this tendency was expressed to a less extent.

Enhancing nitrogen use efficiency and yield of maize (Zea mays L.) through Ammonia volatilization mitigation and nitrogen management approaches

Management of nitrogen (N) fertilizer is a critical factor that can improve maize (Zea mays L.) production. On the other hand, high volatilization losses of N also pollute the air. A field experiment was established using a silt clay soil to examine the effect of sulfur-coated urea and sulfur from gypsum on ammonia (NH3) emission, N use efficiency (NUE), and the productivity of maize crop under alkaline calcareous soil. The experimental design was a randomized complete block (RCBD) with seven treatments in three replicates: control with no N, urea150 alone (150 kg N ha−1), urea200 alone (200 kg N ha−1), urea150 + S (60 kg ha−1 S from gypsum), urea200 + S, SCU150 (sulfur-coated urea) and SCU200. The results showed that the urea150 + S and urea200 + S significantly reduced the total NH3 by (58 and 42%) as compared with the sole application urea200. The NH3 emission reduced further in the treatment with SCU150 and SCU200 by 74 and 65%, respectively, compared to the treatment with urea200. The maize plant biomass, grain yield, and total N uptake enhanced by 5–14%, 4–17%, and 7–13, respectively, in the treatments with urea150 + s and urea200 + S, relative to the treatment with urea200 alone. Biomass, grain yield, and total N uptake further increased significantly by 22–30%, 25–28%, and 26–31%, respectively, in the treatments with SCU150 and SCU200, relative to the treatment with urea200 alone. The applications of SCU150 enhanced the nitrogen use efficiency (NUE) by (72%) and SCU200 by (62%) respectively, compared with the sole application of urea200 alone. In conclusion, applying S-coated urea at a lower rate of 150 kg N ha−1 compared with a higher rate of 200 kg N ha−1 may be an effective way to reduce N fertilizer application rate and mitigate NH3 emission, improve NUE, and increase maize yield. More investigations are suggested under different soil textures and climatic conditions to declare S-coated urea at 150 kg N ha−1 as the best application rate for maize to enhance maize growth and yield.

EXPLORING THE PROSPECTS OF UAV-REMOTELY SENSED DATA IN ESTIMATING PRODUCTIVITY OF MAIZE CROPS IN TYPICAL SMALLHOLDER FARMS OF SOUTHERN AFRICA

Abstract. This study estimated maize grain biomass, and grain biomass as a proportion of the absolute maize plant biomass using UAV-derived multispectral data. Results showed that UAV-derived data could accurately predict yield with R2 ranging from 0.80 – 0.95, RMSE ranging from 0.03 – 0.94 kg/m2 and RRMSE ranging from 2.21% – 39.91% based on the spectral datasets combined. Results of this study further revealed that the VT-R1 (56–63 days after emergence) vegetative growth stage was the most optimal stage for the early prediction of maize grain yield (R2 = 0.85, RMSE = 0.1, RRMSE = 5.08%) and proportional yield (R2 = 0.92, RMSE = 0.06, RRMSE = 17.56%), with the Normalized Difference Vegetation Index (NDVI), Enhanced Normalized Difference Vegetation Index (ENDVI), Soil Adjusted Vegetation Index (SAVI) and the red edge band being the most optimal prediction variables. The grain yield models produced more accurate results in estimating maize yield when compared to the biomass and proportional yield models. The results demonstrate the value of UAV-derived data in predicting maize yield on smallholder farms – a previously challenging task with coarse spatial resolution satellite sensors.

Silicon mitigates K deficiency in maize by modifying C, N, and P stoichiometry and nutritional efficiency

Potassium (K) deficiency in maize plants damages the nutritional functions of K. However, few studies have investigated the influence of K on C:N:P stoichiometry, the nutritional efficiency of these nutrients, and whether the mitigating effect of Si in plants under stress could act on these nutritional mechanisms involved with C, N, and P to mitigate K deficiency. Therefore, this study aimed to evaluate the impact of K deficiency in the absence and presence of Si on N and P uptake, C:N:P stoichiometric homeostasis, nutritional efficiency, photosynthetic rate, and dry matter production of maize plants. The experiment was conducted under controlled conditions using a 2 × 2 factorial scheme comprising two K concentrations: potassium deficiency (7.82 mg L−1) and potassium sufficiency (234.59 mg L−1). These concentrations were combined with the absence (0.0 mg L−1) and presence of Si (56.17 mg L−1), arranged in randomized blocks with five replicates. Potassium deficiency decreased stoichiometric ratios (C:N and C:P) and the plant’s C, N, and P accumulation. Furthermore, it decreased the use efficiency of these nutrients, net photosynthesis, and biomass of maize plants. The results showed that Si supply stood out in K-deficient maize plants by increasing the C, N, and P accumulation. Moreover, it decreased stoichiometric ratios (C:N, C:P, N:P, C:Si, N:Si, and P:Si) and increased the efficiencies of uptake, translocation, and use of nutrients, net photosynthesis, and dry matter production of maize plants. Therefore, the low nutritional efficiency of C, N, and P caused by K deficiency in maize plants can be alleviated with the supply of 56.17 mg L−1 of Si in the nutrient solution. It changes C:N:P stoichiometry and favors the use efficiency of these nutrients, which enhances the photosynthesis and sustainability of maize.

Modeling and optimization of trivalent arsenic removal from wastewater using activated carbon produced from maize plant biomass: a multivariate experimental design approach

Modeling and optimization of trivalent arsenic removal from wastewater using activated carbon produced from maize plant biomass: a multivariate experimental design approach

Zinc-solubilizing Pseudomonas strains improve zinc nutrition of maize plants grown in sand amended with tire waste powder

The present study was conducted to investigate the potential of Zn-solubilizing Pseudomonas strains to release Zn from tire waste powder (TWP) in a liquid medium and soil. A pot experiment was also conducted to investigate the effects of TWP (as a Zn source) at four rates of 0, 9, 18 and 27 g TWP kg−1 soil and Pseudomonas strains (Ctrl: without bacterial inoculation, or inoculated with B1: A5, B2: K5, B3: A2, B4: A11 or B5: D12 strain) on growth and Zn nutrition of maize. Fourteen bacterial strains were grown in liquid Pikovskayas (PVK) medium supplemented with TWP, and ten superior Pseudomonas strains with high Zn solubilization activities were selected for the subsequent Zn kinetics study. In the TWP-treated soil, the concentrations of DTPA-extractable Zn were significantly higher in inoculated treatments than those in the control treatment in all incubation times. Individual application of Pseudomonas strains or TWP treatments significantly increased the shoot biomass of maize plants. Furthermore, the combined application of Pseudomonas strains and TWP led to higher shoot Zn concentration of plants as compared to the individual applications. The highest shoot Zn concentration was observed with the use of 18 g TWP kg−1 soil in treatment inoculated with B4 strain, which was 16.5-fold higher than that in the control. These findings indicate that co-application of effective Pseudomonas strains with TWP in soils can lead to higher Zn bioavailability for plants, i.e. indicating the potential of TWP as a slow-release Zn fertilizer for crops.

AMF Inoculation Alleviates Molybdenum Toxicity to Maize by Protecting Leaf Performance.

The use of arbuscular mycorrhizal fungi (AMF) is a vital strategy for enhancing the phytoremediation of heavy metals. However, the role of AMF under molybdenum (Mo) stress is elusive. A pot culture experiment was conducted to explore the effects of AMF (Claroideoglomus etunicatum and Rhizophagus intraradices) inoculation on the uptake and transport of Mo and the physiological growth of maize plants under different levels of Mo addition (0, 100, 1000, and 2000 mg/kg). AMF inoculation significantly increased the biomass of maize plants, and the mycorrhizal dependency reached 222% at the Mo addition level of 1000 mg/kg. Additionally, AMF inoculation could induce different growth allocation strategies in response to Mo stress. Inoculation significantly reduced Mo transport, and the active accumulation of Mo in the roots reached 80% after inoculation at the high Mo concentration of 2000 mg/kg. In addition to enhancing the net photosynthetic and pigment content, inoculation also increased the biomass by enhancing the uptake of nutrients, including P, K, Zn, and Cu, to resist Mo stress. In conclusion, C. etunicatum and R. intraradices were tolerant to the Mo stress and could alleviate the Mo-induced phytotoxicity by regulating the allocation of Mo in plants and improving photosynthetic leaf pigment contents and the uptake of nutrition. Compared with C. etunicatum, R. intraradices showed a stronger tolerance to Mo, which was manifested by a stronger inhibition of Mo transport and a higher uptake of nutrient elements. Accordingly, AMF show potential for the bioremediation of Mo-polluted soil.

Effects of concentration-dependent graphene on maize seedling development and soil nutrients

The long-term use of chemical fertilizers to maintain agricultural production has had various harmful effects on farmland and has greatly impacted agriculture's sustainable expansion. Graphene, a unique and effective nanomaterial, is used in plant-soil applications to improve plant nutrient uptake, reduce chemical fertilizer pollution by relieving inadequate soil nutrient conditions and enhance soil absorption of nutrient components. We investigated the effects of graphene amendment on nutrient content, maize growth, and soil physicochemical parameters. In each treatment, 5 graphene concentration gradients (0, 25, 50, 100, and 150 g kg−1) were applied in 2 different types (single-layer and few-layers, SL and FL). Soil aggregates, soil accessible nutrients, soil enzyme activity, plant nutrients, plant height, stem diameter, dry weight, and fresh weight were all measured throughout the maize growth to the V3 stage. Compared to the control (0 g kg−1), we found that graphene increased the percentage of large agglomerates (0.25–10 mm) in the soil and significantly increased the geometric mean diameter (GMD) and mean weight diameter (MWD) values of > 0.25 mm water-stable agglomerates as the increase of concentration. Soil available nutrient content (AN, AP, and AK) increased, peaking at 150 g kg−1. Graphene boosted nutrient absorption by maize plants, and aboveground total nitrogen (TN), total phosphorus (TP), and total potassium (TK) contents rose with the increasing application, which raised aboveground fresh weight, dry weight, plant height, and stalk thickness. The findings above confirmed our prediction that adding graphene to the soil may improve maize plant biomass by enhancing soil fertility and improving the soil environment. Given the higher manufacturing cost of single-layer graphene and the greater effect of few-layer graphene on soil and maize plants at the same concentration, single-layer graphene and few-layer graphene at a concentration of 50 g kg−1 were the optimal application rates.

Influence of biochar and microorganism co-application on stabilization of cadmium (Cd) and improved maize growth in Cd-contaminated soil.

Cadmium (Cd) is one the leading environmental contaminants. The Cd toxicity and its potential stabilization strategies have been investigated in the recent years. However, the combined effects of biochar and microorganisms on the adsorption of Cd and maize plant physiology, still remained unclear. Therefore, this experiment was conducted to evaluate the combined effects of biochar (BC) pyrolyzed from (maize-straw, cow-manure, and poultry-manure, and microorganisms [Trichoderma harzianum (fungus) and Bacillus subtilis (bacteria)], on plant nutrient uptake under various Cd-stress levels (0, 10, and 30 ppm). The highest level of Cd stress (30 ppm) caused the highest reduction in maize plant biomass, intercellular CO2, transpiration rate, water use efficiency, stomatal conductance, and photosynthesis rate as compared to control Cd0 (0 ppm). The sole application of BC and microorganisms significantly improved plant growth, intercellular CO2, transpiration rate, water use efficiency, stomatal conductance, and photosynthesis rate and caused a significant reduction in root and shoot Cd. However, the co-application of BC and microorganisms was more effective than the sole applications. In this regard, the highest improvement in plant growth and carbon assimilation, and highest reduction in root and shoot Cd was recorded from co-application of cow-manure and combined inoculation of Trichoderma harzianum (fungus) + Bacillus subtilis (bacteria) under Cd stress. However, due to the aging factor and biochar leaching alkalinity, the effectiveness of biochar in removing Cd may diminish over time, necessitating long-term experiments to improve understanding of biochar and microbial efficiency for specific bioremediation aims.

The Interactions between Arbuscular Mycorrhizal Fungi and Trichoderma longibrachiatum Enhance Maize Growth and Modulate Root Metabolome under Increasing Soil Salinity.

Trichoderma longibrachiatum sp. are free-living filamentous fungi which are common in agro-ecosystems. However, few studies thus far have examined the interaction between Trichoderma longibrachiatum and arbuscular mycorrhizal (AM) fungi in saline soil and their potential for improving plant stress tolerance. Here, single, dual-inoculated (T. longibrachiatum MF, AM fungal community or Glomus sp.), and non-inoculated maize (Zea may L.) were subjected to different salinity levels (0, 75, 150, and 225 mM NaCl) to test the synergistic effects of dual inoculants on maize plants in different salt stress conditions. Plant performance and metabolic profiles were compared to find the molecular mechanisms underlying plant protection against salt stress. The first experiment revealed that dual inoculation of an AM fungal community and T. longibrachiatum MF improved the biomass and K+/Na+ ratio in maize under non-saline conditions, and generally enhanced AM fungal growth in root and soil under all but the 225 mM NaCl conditions. However, MF inoculant did not influence the structure of AM fungal communities in maize roots. In the second experiment, dual inoculation of Glomus sp. and T. longibrachiatum MF increased maize plant biomass, K+/Na+ ratio, and AM fungal growth in root and soil significantly at both 0 and 75 mM NaCl conditions. We identified metabolic compounds differentially accumulated in dual-inoculated maize that may underline their enhanced maize plant tolerance to increasing soil salinity. Our data suggested that the combination of Glomus sp. and T. longibrachiatum leads to interactions, which may play a potential role in alleviating the stress and improve crop productivity in salt-affected soils.

Enhancing agronomic efficiency and maize grain yield with Azospirillum brasilense inoculation under Brazilian savannah conditions

In view of ecological and economic costs of nitrogen (N) fertilization, measures are needed to enhance the sustainability of cereal production in tropical savannah regions. In this context, we investigated the combined effects of N application levels and inoculation with Azospirillum brasilense on maize plant biomass, grain yield, agronomic efficiency (AE), and N content in plants, focusing on the economic feasibility of maize production systems. The field trial involved four N application levels (control, low, average and high, i.e., 0, 50, 100 and 200 kg ha−1, respectively, applied as sidedress) either with seed inoculation with A. brasilense or without inoculation. Inoculation with A. brasilense enhanced AE and N uptake in maize plants with increased shoot, root and grain N accumulation, augmenting grain yield by 7%. The increase in total N accumulation was mainly the result of improved N-NH4+ accumulation in plant roots and shoots. Our results showed that it is possible to reduce the N fertilization level by 50% while increasing the operating profit by 11% with A. brasilense inoculation. Additionally, when inoculation was performed in the presence of a high N level, the operating profit was 11% higher than that for the same N level in the absence of inoculation. Therefore, in view of the low economic cost, ease of application, and high probability of a positive response by maize crops, even in the presence of different N application levels, inoculation with A. brasilense has the potential to be a key technology for improving plant-soil N management, leading to more sustainable maize production under tropical conditions.

Effects of the nitrification inhibitor nitrapyrin and the plant growth regulator gibberellic acid on yield-scale nitrous oxide emission in maize fields under hot climatic conditions

Nitrification inhibitors are widely used in agriculture to mitigate nitrous oxide (N2O) emission and increase crop yield. However, no concrete information on their mitigation of N2O emission is available under soil and environmental conditions as in Pakistan. A field experiment was established using a silt clay loam soil from Peshawar, Pakistan, to study the effect of urea applied in combination with a nitrification inhibitor, nitrapyrin (2-chloro-6-tri-chloromethyl pyridine), and/or a plant growth regulator, gibberellic acid (GA3), on N2O emission and the nitrogen (N) uptake efficiency of maize. The experimental design was a randomized complete block with five treatments in four replicates: control with no N (CK), urea (200 kg N ha–1) alone, urea in combination with nitrapyrin (700 g ha–1), urea in combination with GA3 (60 g ha–1), and urea in combination with nitrapyrin and GA3. The N2O emission, yield, N response efficiency, and total N uptake were measured during the experimental period. The treatment with urea and nitrapyrin reduced total N2O emission by 39%–43% and decreased yield-scaled N2O emission by 47%–52%, relative to the treatment with urea alone. The maize plant biomass, grain yield, and total N uptake increased significantly by 23%, 17%, and 15%, respectively, in the treatment with urea and nitrapyrin, relative to the treatment with urea alone, which was possibly due to N saving, lower N loss, and increased N uptake in the form of ammonium; they were further enhanced in the treatment with urea, nitrapyrin, and GA3 by 27%, 36%, and 25%, respectively, probably because of the stimulating effect of GA3 on plant growth and development and the reduction in biotic and abiotic stresses. These results suggest that applying urea in combination with nitrapyrin and GA3 has the potential to mitigate N2O emission, improve N response efficiency, and increase maize yield.

Application of non-linear partial least squares analysis on prediction of biomass of maize plants using hyperspectral images

With the application of hyperspectral imaging systems on high-throughput plant phenotyping, multivariable spectral data modelling methods have been proposed to predict plant physiological features such as biomass. However, most presented modelling methods are linear models such as the regression model between projected leaf area and plant biomass, which cannot accurately reflect some non-linear relationships between hyperspectral imaging information and the phenomes to be predicted. Therefore, it is important to develop a prediction model for plant physiological features that fully utilises the information in plant hyperspectral images. In this paper, a non-linear modelling method known as kernel partial least squares (KPLS) was investigated to improve the prediction performance of maize (US corn) biomass. The main idea of KPLS is mapping the original input features into higher dimensional feature spaces before obtaining the principle components for a standard PLS model. In the new mapping spaces, the original, nonlinear inputs may exhibit linear patterns with different kernel functions. This method was tested in a greenhouse assay containing 102 maize plants, which were subjected to a combination of three water treatments and two nitrogen treatments at three different growth stages. KPLS methods were successfully applied on the collected hyperspectral images. The results showed that compared with conventional linear models, statistics including R 2 of KPLS with radial basis function (RBF) kernel had improved accuracy (R 2 = 0.924). We expect that besides plant biomass, this new non-linear KPLS model could improve the quality of estimation of other plant features as well. • Proposed KPLS model with RBF kernel more accurately predicts maize fresh weight. • Kernel functions map original features into higher dimensional feature spaces. • Hyperspectral image provides image-derived features for biomass prediction. • Performances of projected leaf area, linear PLS and KPLS models are investigated. • We conduct a greenhouse phenotyping assay to explore maize biomass prediction models.

Soil Compaction and Soil Amendments on the Growth and Biomass Yield of Maize (Zea mays L.) and Soybean (Glycine max L.)

Two factorial pot experiments arranged in a Completely Randomised Design (CRD) with three replications were carried out to assess the impact of different levels of soil compaction and fertilizer amendments on root growth and biomass yield of maize (Zea mays L.) and soybean (Glycine max L.) plants. The treatments were different rates of bulk densities – 1.3, 1.5 and 1.7 Mg m-3 and fertilizer amendments comprising 100% poultry manure (applied at 15 g/plant), 100% 15:15:15 NPK fertilizer (applied at 2.89 g/plant) and 50% rate each of poultry manure and NPK fertilizer (applied at 7.5 g poultry manure + 1.45 g NPK/plant), and control (no fertilizer amendments). Soil compaction reduced the heights of maize and soybean plants. Increasing soil compaction resulted in the accumulation of most of the root biomass in the uncompacted soil above the compacted layer. Application of soil amendments increased the relative root biomass of maize plants in the uncompacted soil, while that in the compacted soil was reduced. In the case of soybean plants, although the relative root biomass in the uncompacted soil was relatively greater than that of maize plants, application of soil amendments tended to slightly decrease the relative root biomass to that of the control. The shoot biomass of both crops decreased with increasing soil bulk density. All the applied soil amendments significantly increased the shoot biomass of maize and soybean plants over the control. The magnitude of response of the crops to the soil amendments was greater in soybean than in maize plants. Soil compaction and amendments significantly influenced root/shoot ratio of both crops. The root/shoot ratio decreased with increasing compaction from 1.3 to 1.5 Mg m-3, however, at 1.7 Mg m-3, the root/shoot ratio increased. The fertilizer amendments significantly influenced the root/shoot ratio of maize but not soybean plants. The fertilizer amendments increased the biomass of both roots and shoots, being higher in the former than in the latter. The fertilizer amendments x compaction interactions showed that the root/shoot ratio was influenced by the type of crop, and the confounding effects of factor interactions on the relative increases/decreases in shoot and root growth. Overall, soil compaction accounted for 52 to 100% of the variations in the magnitude of the measured parameters of maize plants, and 62 to 98% for soybean plants. The ideal bulk density for shoot biomass production of both crops should, therefore, be within the range of 1.3 – 1.5 Mg m-3. At soil bulk density of 1.5 Mg m-3 and above, soil amendment should be added to ameliorate the negative impact of soil compaction.

Estimating the upper and lower limits of kernel weight under different water regimes in hybrid maize seed production

In hybrid maize (Zea mays L.) seed production, both the kernel quality and the germination rate, which are positively related to kernel weight (KW), are very important. Water deficit can change the source–sink ratio (SSR) and thus affects KW. To create a water-saving irrigation program that facilitates the production of high-quality seed, it is necessary to properly model the KW–water relationship. Irrigation experiments were conducted in 2014 and 2015 in an arid region of Northwest China to investigate the effects of deficit irrigation on maize plant biomass and yield; and pollination experiments were conducted in 2016 to obtain a wide range of SSR and KW data. Analysis of the results showed that water deficit at the vegetative or flowering stages reduced post-flowering biomass gain (PBG) and kernel number (KN), thus significantly affecting SSR. At the grain-filling stage it reduced PBG but had no significant effect on KN, thus reducing SSR. Only the treatment of no irrigation in the grain-filling stage in 2015 significantly reduced KW. The Jensen model can accurately simulate the relationship between PBG and relative evapotranspiration at each growth stage. The water sensitivity index of PBG in the vegetative, flowering, grain-filling and ripening stages were respectively 0.48, 0.48, 0.97, and 0.16. Based on the experimental data of 2016, the hyperbolic upper (UpKW) and lower (LowKW) limit equations were created for KW as a function of SSR using boundary analysis. UpKW and LowKW increased as SSR increased, but the difference between UpKW and LowKW first increased and then decreased as SSR increased. When SSR was 0, UpKW was 178.39 mg and LowKW was 155.56 mg. When SSR is not less than 867.23 mg kernel−1, UpKW and LowKW are both 326.97 mg, which is the potential KW. Combined with the KN–water model, the models developed in this study can be used to develop a water-saving and irrigation program that produces high-quality seed.

Ammonium excretion, auxin production and effects of maize inoculation with ethylenediamine-resistant mutants of Pseudomonas sp.

ABSTRACT Plant growth-promoting bacteria (PGPB) comprise part of plant microbiome of biotechnological interest due to their potential to decrease the use of agrochemicals in agriculture. Among the commonly found PGPB species, the Pseudomonas genus is known for high competitiveness and efficiency in expressing growth-promotion traits. To increase the contribution of diazotrophic Pseudomonas sp. to the plant nitrogen nutrition, the strain AZM-01 was chemically mutagenized with methyl methanesulfonate (MMS), following the selection for resistance to ethylenediamine (EDA). From the 13 EDA-resistant mutant strains selected, four showed increased the ammonium excretion, with the highest value reaching up to 284% increase as compared to the wild strain, and six strains were found to produce significantly more auxins than the wild strain. Two independent inoculation trials with the wild and EDA-resistant Pseudomonas were performed on maize, with the objective to study the influence of bacteria on seed germination and its potential to promote maize growth under N-limiting condition. In general, Pseudomonas inoculation modified the root architecture of germinating seeds, and increased biomass of maize plants grown under N-limiting conditions. Shoot dry weight of maize was increased by inoculation with several EDA-resistant mutants as compared to the strain AZM-01, with emphasis on the EDA-5 strain which supports biomass accumulation at equivalent amount of plants grown under full N supply. Significant correlations between in vitro and in vivo parameters were found although low coefficient values predominate. The strategy of random mutagenesis was found suitable to develop PGPB strains with higher potential to supply maize plants with nitrogen.

Effects of soil sterilization and metal spiking in plant growth promoting rhizobacteria selection for phytotechnology purposes

The contamination of the soil with heavy metals (e.g. Zn) is a serious and crosscutting issue worldwide. Phytotechnologies can minimize the negative impact of this problem using plants and microorganisms in soil rehabilitation. However, the efficiency of proper plant-microbe combinations is usually assessed using spiked and/or sterilized soils, which do not mimic the conditions in situ, and therefore can lead to outcomes that will not be observed under field situations.This study aimed to quantify the effect of soil origin and sterilization on the performance of the two plant growth promoting rhizobacteria (PGPR), Ralstonia eutropha 1C2 and Chryseobacterium humi ECP37, for promoting the growth and metal accumulation of maize plants. A two-experiment approach was applied: the PGPR were inoculated in maize plants growing in (i) sterilized soils spiked with Zn (0, 100, 500 and 1000 mg Zn kg−1); and in (ii) a field-contaminated soil, under sterilized and non-sterilized conditions (599 mg Zn kg−1). Biomass and Zn accumulation in the root and shoot, and Zn bioavailability in soils were determined. Additionally, lipid peroxidation, activity of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were assessed in the shoots of plants grown in the field-contaminated soil, as well as the composition of the rhizospheric bacterial community.Zn in the soils negatively affected maize growth, and its effect was strongest in the field-contaminated soil. Overall, PGPR attenuated the negative effects of Zn by improving plant growth, although less pronounced in non-sterilized soils. Sterilization significantly reduced soil Zn availability and affected its' accumulation in plant tissues. Bioinoculants performance was also different in sterilized soil, i.e., bacteria had no effect in the accumulation of Zn but tended to increase the biomass of maize plants. Despite the higher Zn accumulation in shoot tissues, lipid peroxidation was lower whereas antioxidant enzymes were enhanced in non-sterilized soils, suggesting that plant antioxidant system functioned properly. PGPR tended to decrease the diversity of the rhizospheric community.This study highlights that while inoculation with PGPR is effective in increasing Zn bioavailability in soil, accumulation in the plant and maize growth in Zn-contaminated soils, the extent of their effect can be different depending on whether the soil is field-contaminated or metal spiked, and on whether is sterilized prior contaminated. Consequently, the effect of bacterial inoculants assessed exclusively in metal spiked soil and/or sterilized soil may be overestimated, and potentially not transferable to field conditions.

Genetic diversity of plant growth promoting rhizobacteria and their effects on the growth of maize plants under greenhouse conditions

Engineering of plant rhizosphere with beneficial plant growth promoting (PGP) bacteria offers a great promise for sustainable crop productivity. In this context, 49 rhizospheric/endophytic bacterial isolates were purified using N-free medium, screened in vitro for PGP characteristics and evaluated for their beneficial effects on the early growth of maize (Zea mays L.). The biodiversity of isolated bacteria was analyzed by amplified ribosomal DNA restriction analysis (ARDRA) using four restriction enzymes. Out of the 49 isolates, 7 produced high levels (32.1–82.8 μg mL−1) of indole-3-acetic acid (IAA); 11 had potential phosphate solubilizing abilities (101–163 μg mL−1), while significant acetylene reduction activities (100–1800 nmole C2H4 mg−1 protein h−1) were observed in 12 isolates. Five ribogroups (A-E) were identified using ARDRA. The 16S rRNA-sequence analysis of bacterial representatives from different ribogroups revealed that, 89% of isolates belonged to phylum Proteobacteria, while 11% of them were assigned into phylum Bacteroidetes. Phylum Proteobacteria included Achromobacter, Agrobacterium, Bordetella, Cupriavidus, Ochrobactrum, Pseudoxanthomonas and Stenotrophomonas genera. While, phylum Bacteroidetes was represented by Chryseobacterium and Flavobacterium genera. Under greenhouse conditions, all the selected isolates significantly increased shoot and root fresh and dry biomass of maize plants, compared to the non-inoculated control. Inoculation with Chryseobacterium sp. NGB-29 and Flavobacterium sp. NGB-31 showed the highest beneficial effects on plant growth parameters that were tentatively associated with the high efficiency of these isolates to fix nitrogen and produce high amounts of IAA. The study indicates the potential use of these isolates for production of maize biofertilizers under field conditions.

Nitrogen fertilizer fate after introducing maize and upland-rice into continuous paddy rice cropping systems

Water scarcity and economic incentives favor the introduction of upland crops into permanent paddy rice systems during dry seasons. However, introducing upland crops into permanently flooded cropping systems temporarily changes soil conditions from anaerobic to aerobic, affecting nitrogen (N) dynamics profoundly. We hypothesized that under maize and dry rice, total fertilizer 15N recovery in soil as well as the immobilization of fertilizer 15N in microbial residues is reduced compared with continuous paddy rice cropping. Furthermore, we expected enhanced emissions of fertilizer 15N in form of nitrous oxide (N2O) under maize and dry rice. To test these hypotheses, we traced the fate of a 15N-urea pulse in a field experiment in the Philippines with three different crop rotations: continuous paddy rice, paddy rice – dry rice, and paddy rice – maize for two years. Indeed, the 15N recovery in the first 5 cm of bulk soil was lowest in the paddy rice – maize rotation (arithmetic mean with standard error: 19.2 ± 1.8% of applied 15N), while twice as much was recovered in the first 5 cm of bulk soil of the continuous paddy rice cropping systems (37.8 ± 2.2% of applied 15N) during the first dry season. The 15N recovery in the plant biomass (shoots and roots) in the continuous paddy rice cropping was 13% larger than in the dry rice plant biomass and 5% larger than in the maize plant biomass during the first dry season. Fertilizer 15N remained longest in paddy rice – maize (mean residence time = 90 ± 25 days) and in continuous paddy rice (mean residence time = 77 ± 30 days), compared with dry rice – paddy rice rotation (mean residence time = 16 ± 5 days). After 2 years, 10% (paddy rice – dry rice, paddy rice – maize) to 23% (continuous paddy rice) of the applied fertilizer 15N were still stored in soil. The largest fraction of this 15N was immobilized by soil microbes, which stored 3–4% of applied 15N in the form of amino sugars as specific cell wall constituents, in all cropping systems. Nevertheless, introducing upland crops into continuous paddy rice systems likely increased N leaching losses and resulted in initial losses of urea- 15N to N2O, which thus has to be considered in climate smart mitigation strategies.

Experimental warming enhances the carbon gain but does not affect the yield of maize (Zea mays L.) in the North China Plain

Temperature response and sensitivity of photosynthesis and respiration are critical for projection of changes in the carbon exchange and net primary production of terrestrial ecosystems under global warming. Understanding the mechanisms and processes of photosynthetic and respiratory acclimation in response to warming may shed further lights on the change of crop yield in agricultural ecosystems in a warmer climate regime. We examined the temperature responses and sensitivity of net photosynthetic rate (An) and dark respiration (Rd) for exploring the mechanisms of thermal acclimation associated with physiological and biochemical processes affecting maize yield in the North China Plain with a field manipulative warming experiment. We found that warming substantially enhanced the carbon gain of maize plants through facilitating CO2 diffusion from ambient air to chloroplasts by altering stomatal structure and spatial distribution pattern, and benefitting CO2 assimilation efficiency with smaller vascular bundles and bigger chloroplasts. Moreover, we also found that acclimation of An to temperature (T), evidenced by the upward shift of An–T, was determined by the maximum velocity of Rubisco carboxylation (Vcmax), the maximum rate of electron transport (Jmax), and the stomatal-regulated CO2 diffusion process, whereas the balance between respiration and gross photosynthetic rate (Rd/Ag), and/or regeneration of RuBP and the Rubisco carboxylation (Jmax/Vcmax) made little contribution to the thermal acclimation of An in maize plants. In addition, temperature response and sensitivity of Rd was closely associated with the changes in foliar N concentration induced by warming. As a result, experimental warming barely affected the yield and biomass of maize plants. These results suggest that the impacts of future climate warming on maize production may be mitigated or even offset by the leaf-level thermal acclimation of photosynthesis and respiration. Our findings may have important implications for improving the accuracy of process-based ecosystem models and advancing the understanding on the interactions between ecosystem functions and climate warming.